[edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Yao, Jiewen]

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Hi, All
We plan to do a design review for TDVF in OVMF package.


The TDVF Design slides for TinaoCore Design Review Meeting (Jun 11) is now available in blow link: https://edk2.groups.io/g/devel/files/Designs/2021/0611.

The Bugzilla is https://bugzilla.tianocore.org/show_bug.cgi?id=3429



You can have an offline review first. You comments will be warmly welcomed and we will continuously update the slides based on the feedbacks.



Thank you

Yao Jiewen






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Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Laszlo Ersek]

On 06/03/21 15:51, Yao, Jiewen wrote:
> Hi, All
> We plan to do a design review for TDVF in OVMF package.
>
>
> The TDVF Design slides for TinaoCore Design Review Meeting (Jun 11) is
> now available in blow link:
> https://edk2.groups.io/g/devel/files/Designs/2021/0611.
>
> The Bugzilla is https://bugzilla.tianocore.org/show_bug.cgi?id=3429
>
>
>
> You can have an offline review first. You comments will be warmly
> welcomed and we will continuously update the slides based on the
> feedbacks.

Resending my earlier comments in this mailing list thread, with the
feedback inserted at the proper spots that has been given in the
off-list thread since then:


*** Slides 4, 6, 7: the "one binary requirement".

(1) The presentation refers to "OvmfPkgX64.dsc" as "the one" on slide#4,
but then the explanation for the requirement, given on slide 7, speaks
about "common attestation interface".

I think we have a misunderstanding here. The "OvmfPkgX64.dsc" platform
indeed contains SEV, SEV-ES, and (in the future, will contain) SEV-SNP
support. In that sense, adding TDX support to the same platform should
be (hopefully) possible, at the cost of ugly gymnastics in the reset
vector.

But "OvmfPkgX64.dsc" is *already* different from the remotely attested
OVMF platform, namely "OvmfPkg/AmdSev/AmdSevX64.dsc".

The latter has some additional modules (secret PEIM and DXE driver), it
has the Grub binary built in, and -- probably most importantly -- it
trusts host-originated information less than "OvmfPkgX64.dsc".

For example, "OvmfPkg/AmdSev/AmdSevX64.dsc" has a dedicated
PlatformBootManagerLib instance, one that ignores the non-volatile UEFI
variables Boot#### and BootOrder, and ignores (thus far) the fw_cfg
originated kernel/initrd/cmdline as well.

It remains an "area of research" to see what else should be removed from
the traditional host-guest integration (which integration is usually
desirable for management and convenience), in the remotely-attested boot
scenario. See e.g.
<https://bugzilla.tianocore.org/show_bug.cgi?id=3180>.

My point is that the "one binary" that the slide deck refers to (i.e.,
OvmfPkgX64.dsc) might prove OK for utilizing the Intel TDX *technology*
in itself. Simply enabling OVMF + a guest OS to boot in a TDX domain.

But "OvmfPkgX64.dsc" is *not* the "one binary" that is suitable for
remote attestation, which has a much broader scope, involving multiple
computers, networking, deployment, guest-owner/host-owner separation,
whatever. For the latter, we needed a separate platform anyway, even
with only SEV in mind; that's why "OvmfPkg/AmdSev/AmdSevX64.dsc" exists.


*** Slides 8-9: general boot flow -- TDVF; TDVF Flow

I'm likely missing a big bunch of background here, so just a few
questions:

(2) Not sure what RTMR is, but it's associated with "Enable TrustedBoot"
-- so is a virtual TPM a hard requirement?

... Back from slide 10: "TCG measurement and event log framework w/o
TPM" -- that's curious.

[response from Dave Gilbert:]
> My reading of this is that the RTMR (and another set of similar
> registers) are a TDX thing that is like the PCRs from a TPM but
> without the rest of the TPM features;  so you can do the one-way
> measurement into the RTMRs just like you do into a TPM PCR, and the
> measurements pop out somewhere in the TDX quote.  Just like a TPM you
> need the event log to make any sense of how the final hashed value
> supposedly got to where it did.

[response from Erdem Aktas:]
> +1 to David on this. TDX provides 2 kinds of measurement registers:
> MRTDs and RTMRs
> (https://software.intel.com/content/dam/develop/external/us/en/documents/tdx-module-1eas-v0.85.039.pdf
> section 10.1.2) . MRTDs are build-time measurement registers which are
> updated when TDX is being created. Once TDX is finalized (before the
> first run), the MRTDs are finalized and cannot be updated anymore. On
> the other hand, while the TD is running, TD can extend RTMRs through
> TDCALLs which will provide TPM PCR kind of capabilities.

... Back from slide 43: feel free to skip this now; I will comment in
more detail below.

(3) Prepare AcpiTable -- OVMF fetches ACPI tables from QEMU; is this a
new (firmware originated) table that is installed in addition, or does
it replace QEMU's tables?

... Ignore for now, will comment on the MADT stuff later.

(4) Does DMA management mean a different IOMMU protocol? That is going
to conflict with the SEV IOMMU protocol. Depexes in OVMF expect one or
zero IOMMU protocols to be present.

... Back from slide 40: feel free to skip this now; I'll comment on this
separately, below.

(5) Enumerate VirtIO -- virtio enumeration is PCI based on x86. But I
see no mention of PCI. If you mean VirtioMmioDeviceLib, that's no good,
because it does not support virtio-1.0, only virtio-0.9.5.

... Back from slide 42: I got my answer to this on slide 42, so don't
worry about this point.

(6) The PEI phase is skipped as a whole. I don't see how that can be
reasonably brought together with either "OvmfPkgX64.dsc" or
"OvmfPkg/AmdSev/AmdSevX64.dsc". I guess you can always modify SEC to
jump into DXE directly, but then why keep the PEI core and a bunch of
PEIMs in the firmware binary?

Also touched on by slide 9, TDVF Flow -- PEI is eliminated but SEC
becomes more heavy-weight.

Wouldn't this deserve a dedicated, separate platform DSC? The
8-bit/32-bit branching at the front of the reset vector is a smaller
complication in comparison.

Slide 6 references the mailing list archive:

  https://edk2.groups.io/g/devel/topic/81969494#74319

and in that message, I wrote:

    I'm doubtful that this is a unique problem ("just fix the reset
    vector") the likes of which will supposedly never return during the
    integration of SEV and TDX

See also:

  https://listman.redhat.com/archives/edk2-devel-archive/2021-April/msg00784.html

where I said:

    It's not lost on me that we're talking about ~3 instructions.

    Let's keep a close eye on further "polymorphisms" that would require
    hacks.

The first 9 slides in the presentation introduce much-much more
intrusive problems than the "polymorphism" of the reset vector. Would I
be correct to say that my concern in the above messages was right? I
think I was only given a fraction of the necessary information when I
was asked "do you agree 'one binary' is viable".

[response from Erdem Aktas:]
> Let's not worry about this for now. We want the one binary solution
> for practical reasons and also for simplicity.  In the end, we want to
> do what is right and good for everyone.
> Those are legit concerns and I think what Intel is trying to do (sorry
> for mind reading) is to discuss all those concerns and questions to
> make the right decision. I really appreciate their effort on preparing
> those slides and bringing it to the community to review.
>
> I will also read your comments more carefully and provide my thoughts
> on them.
> Sorry for being a little slow on this.


*** Slide 10 -- Key impact to firmware

(7) "CPUs are left running in long mode after exiting firmware" -- what
kind of "pen" are we talking about? Does a HLT loop still work?

(8) "I/O, MMIO, MSR accesses are different" -- those are implemented by
low-level libraries in edk2; how can they be configured dynamically?

... Back from slide 53: I'll comment on slide 53 separately; ignore
this.


*** Slide 11 -- TDVF Image (1)

(9) CFV -- Configuration Firmware Volume (VarStore.fdf.inc),
containing SB keys -- how is this firmware volume populated (at build
time)? Is this a hexdump?

... Back from slide 16: it seems like CFV is a raw hexdump indeed; how
is that managed when keys change (at build time)?

(10) This slide (slide 11) basically describes an intrusive
reorganization of "OvmfPkgX64.fdf". I don't think I can agree to that.
While confidential computing is important, it is not relevant for many
users. Even if we don't cause outright regressions for existent setups,
the maintenance cost of the traditional OVMF platform will skyrocket.

The big bunch of areas that SEV-ES introduced to MEMFD is already a big
complication. I'd feel much better if we could isolate all that to a
dedicated "remote attested boot" firmware platform, and not risk the
functionality and maintenance of the traditional platform. I think this
ties in with my comment (1).

For example, seeing a configuration firmware volume (CFV) with secure
boot keys embedded, in the "usual" FDF, will confuse lots of people, me
included. In the traditional OVMF use case, we use a different method:
namely OvmfPkg/EnrollDefaultKeys, for "priming" a variable store
template, in the build environment.

Edk2 (and PI and UEFI) are definitely flexible enough for accommodating
TDX, but the existent, traditional OVMF platforms are a bad fit. In my
opinion.


*** Slide 12: TDVF Image (2)

(11) "Page table should support both 4-level and 5-level page table"

As a general development strategy, I would suggest building TDX support
in small, well-isolated layers. 5-level paging is not enabled (has never
been tested, to my knowledge) with OVMF on QEMU/KVM, regardless of
confidential computing, for starters. If 5-level paging is a strict
requirement for TDX, then it arguably needs to be implemented
independently of TDX, at first. So that the common edk2 architecture be
at least testable on QEMU/KVM with 5-level paging enabled.


*** Slide 13:

(12) My comment is that the GUID-ed structure chain already starts at a
fixed GPA (the "AMD SEV option"). Ordering between GUID-ed structures is
irrelevant, so any TDX-specific structures should be eligible for
appending to, prepending to, or intermixing with, other (possibly
SEV-specific) structures. There need not be a separate entry point, just
different GUIDS.

(13) Regarding "4G-0x20[0x10] is OVMF AP reset vector (used in OVMF
implementation)" -- I think this is a typo: this "AP reset vector" is
*not* used in OVMF. To my knowledge, it is a vestige from the UefiCpuPkg
reset vector. In OVMF, APs are booted via MpInitLib (in multiple
firmware phases), using INIT-SIPI-SIPI, and the reset vector for the
APs, posited through those IPIs, is prepared in low RAM.


*** Slides 14 through 16:

I consider these TDVF firmware image internals, implementation details
-- do whatever you need to do, just don't interfere with existing
platforms / use cases. See my comment (10) above.


*** Slides 17-21:

(14) Again, a very big difference from traditional OVMF: APs never enter
SEC in traditional OVMF. I assume this new functionality is part of
TdxStartupLib (from slide 18) -- will there be a Null instance of that?

Last week I posted a 43-part patch series to edk2-devel, for separating
out the dynamic Xen enlightenments from the IA32, IA32X64, X64
platforms, in favor of the dedicated OvmfXen platform. TDX seems to
bring in incomparably more complications than Xen, and the OvmfPkg
maintainers have found even the Xen complications troublesome in the
long term.

If I had had access to all this information when we first discussed "one
binary" on the mailing list, I'd have never agreed to "one binary". I'm
OK with attempting one firmware binary for "confidential computing", but
that "one platform" cannot be "OvmfPkgX64.dsc".

Even if I make a comparison with just the "technology" (not the
remotely-attested deployment) of SEV and SEV-ES, as it is included in
"OvmfPkgX64.dsc", TDX is hugely more complicated and intrusive than
that. SEV proved possible to integrate into existing modules, into the
existing boot flow, maybe through the addition of some new drivers (such
as a new IOMMU protocol implementation, and some "clever" depexes). But
we never had to restructure the FD layout, eliminate whole firmware
phases, or think about multiprocessing in the reset vector or the SEC
phase.

In order to bring an example from the ARM world, please note that
platforms that use a PEI phase, and platforms that don't, are distinct
platforms. In ArmVirtPkg, two examples are ArmVirtQemu and
ArmVirtQemuKernel. The latter does not include the PEI Core.


*** Slides 22 through 34:

(15) All these extra tasks and complications are perfectly fine, as long
as they exist peacefully *separately* from the traditional ("legacy")
OVMF platforms.

Honestly, in the virtual world, picking your firmware binary is easy.
The approach here reminds me of a physical firmware binary that includes
everything possible from "edk2-platforms/Features/Intel", just so it can
be deployed to any physical board imaginable. That's not how Intel
builds physical firmware, right? We have "edk2-platforms/Platform/Intel"
and "edk2-platforms/Silicon/Intel" with many-many separate DSC files.


*** Slide 35-36: DXE phase

(16) "Some DXE Drivers not allowed to load/start in Td guest -- Network
stack, RNG, ..."

Same comment as (several times) above. The Linuxboot project is a good
example for eliminating cruft from DXEFV (in fact, for eliminating most
of the DXE phase). In a TDX environment, why include drivers in the
firmware binary that are never used? Meanwhile, DXEFV in OVMF grows by a
MB every 1.5 years or so. Again, remove these drivers from the DSC/FDF
then, and it needs to be a separate platform.

(17) "Other DXE Phase drivers -- [...] AcpiPlatformDxe"

I'm not sure what this section is supposed to mean. Other DXE phase
drivers included, or excluded? Without AcpiPlatformDxe, the guest OS
will not see QEMU's ACPI content, and will almost certainly malfunction.

... Back from slide 48: ignore this for now, I'll comment in more detail
later.


*** Slide 37: DXE Core

(18) says "SMM is not supported in Td guest" -- how is the variable
store protected from direct hardware (pflash) access from the guest OS?
Without SMM, the guest OS need not go through gRT->SetVariable() to
update authenticated non-volatile UEFI variables, and that undermines
Secure Boot.

Note that, while SEV-ES has the same limitation wrt. SMM, the
"OvmfPkg/AmdSev/AmdSevX64.dsc" platform doesn't even include the Secure
Boot firmware feature. For another example, the OVMF firmware binary in
RHEL that's going to support SEV-ES is such a build of "OvmfPkgX64.dsc"
that does not include the Secure Boot feature either.

But in this TDX slide deck, Secure Boot certificates are embedded in the
CFV (configuration firmware volume) -- see slide 11 and slide 16 --,
which suggests that this platform does want secure boot.

... Back from slide 48: I'm going to make *additional* comments on this,
when I'm at slide 48, too.

The rest of this slide (slide 37) looks reasonable (generic DXE Core
changes -- possibly PI spec changes too).


*** Slides 38 through 39:

These seem reasonable (TdxDxe assumes some responsibilities of
OvmfPkg/PlatformPei)


*** Slides 40 through 42:

*If* you really can implement TDX support for the IOMMU driver *this*
surgically, then I'm OK with it. The general logic in the IOMMU driver
was truly difficult to write, and I'd be seriously concerned if those
parts would have to be modified. Customizing just the page
encryption/decryption primitives for TDX vs. SEV is OK.


*** Slides 43 through 47:

(19) Slide 46 and slide 47 are almost identical. Please consolidate them
into a single slide.

(20) the TPM2 infrastructure in edk2 is baroque (over-engineered), in my
opinion. It has so many layers that I can never keep them in mind. When
we added TPM support to OVMF, I required commit messages that would help
us recall the layering. In particular, please refer to commit
0c0a50d6b3ff ("OvmfPkg: include Tcg2Dxe module", 2018-03-09). Here's an
excerpt:

           TPM 2 consumer driver
                    |
                    v
      Tpm2DeviceLib class: Tpm2DeviceLibTcg2 instance
                    |
                    v
             TCG2 protocol interface
                    |
                    v
      TCG2 protocol provider: Tcg2Dxe.inf driver
                    |
                    v
      Tpm2DeviceLib class: Tpm2DeviceLibRouter instance
                    |
                    v
         NULL class: Tpm2InstanceLibDTpm instance
            (via earlier registration)
                    |
                    v
           TPM2 chip (actual hardware)

The slide deck says that EFI_TD_PROTOCOL is supposed to reuse the
EFI_TCG2_PROTOCOL definition. If that's the case, then why don't we push
the TDX specifics (more or less: the replacement of PCRs with RTMR) down
to the lowest possible level?

Can we have "Tpm2InstanceLibTdxRtmr", plugged into the same Tcg2Dxe.inf
driver?

If not, can we have a new TdTcg2Dxe.inf driver, but make it so that it
install the same protocol as before (EFI_TCG2_PROTOCOL -- same old
protocol GUID)? Then DxeTpmMeasurementLib doesn't have to change.

As long as there is *at most* one EFI_TCG2_PROTOCOL instance published
in the protocol database, DxeTpmMeasurementLib should be fine. In SEV*
guests, the standard Tcg2Dxe driver provides that protocol. In TDX
guests, TdTcg2Dxe.inf should provide the protocol. Arbitration between
the two can be implemented with the pattern seen in the following
commits:

 1  05db0948cc60 EmbeddedPkg: introduce EDKII Platform Has ACPI GUID
 2  786f476323a6 EmbeddedPkg: introduce PlatformHasAcpiLib
 3  65a69b214840 EmbeddedPkg: introduce EDKII Platform Has Device Tree
                 GUID
 4  2558bfe3e907 ArmVirtPkg: add PlatformHasAcpiDtDxe

The basic idea is that Tcg2Dxe can have a depex on a new "running in
SEV" protocol GUID, and TdTcg2Dxe can have a depex on a new "running in
TDX" protocol GUID. A separate platform driver can install the proper
GUID -- possibly *neither* of those GUIDs.

And, we don't have to change the depex section of
"SecurityPkg/Tcg/Tcg2Dxe/Tcg2Dxe.inf" for this; we can implement a
library instance with an empty constructor, but a non-empty depex, and
then hook this lib instance into Tcg2Dxe.inf via module scope NULL lib
class override in the DSC file. Basically we could forcibly restrict
Tcg2Dxe's DEPEX by making it inherit the new DEPEX from the library.


*** Slide 48: DXE Phase -- Other Modules

Regarding IncompatiblePciDeviceSupportDxe: the proposed update sounds
plausible and simple enough.

(21) "AcpiPlatformDxe: Support for MADT/ACPI addition to report Td
Mailbox entry"

Firmware-owned tables must not be installed from this driver.

Please refer to my "Xen removal" patch set again, for
<https://bugzilla.tianocore.org/show_bug.cgi?id=2122>, which I mention
above in point (14). As part of the Xen removal, the AcpiPlatformDxe
driver in OvmfPkg is significantly trimmed: all unused (dead) cruft is
removed, including any ACPI table templates that are built into the
firmware.

OvmfPkg/AcpiPlatformDxe is responsible *solely* for implementing the
client side of the QEMU ACPI linker/loader.

If you need to prepare & install different ACPI tables, please do it
elsewhere, in another DXE driver. A bunch of other firmware modules do
that (NFIT, IBFT, BGRT, ...).

For example, the OvmfPkg/TdxDxe DXE_DRIVER is supposed to be launched
early in the DXE phase, via APRIORI section -- please consider
registering a protocol notify in that driver, for
EFI_ACPI_TABLE_PROTOCOL, and when it becomes available, install whatever
*extra* tables you need.

Note that if you need to *customize* an ACPI table that QEMU already
provides, then you will have to modify the ACPI generator on the QEMU
side. It is a design tenet between QEMU and OVMF that OVMF include no
business logic for either parsing or fixing up ACPI tables that QEMU
provides. AcpiPlatformDxe contains the minimum (which is already a whole
lot, unfortunately) that's necessary for implementing the QEMU ACPI
linker/loader client in the UEFI environment.

The slide deck mentions MADT, which is also known as the "APIC" table --
and indeed, QEMU does provide that. (See acpi_build_madt()
[hw/i386/acpi-common.c].) So if TDX needs MADT customizations, that
should go into QEMU.

(22) EmuVariableFvbRuntimeDxe

Ouch, this is an unpleasant surprise.

First, if you know for a fact that pflash is not part of the *board* in
any TDX setup, then pulling

  OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf

into the firmware platform is useless, as it is mutually exclusive with

  OvmfPkg/EmuVariableFvbRuntimeDxe/Fvb.inf

(via dynamic means -- a dynamic PCD).

Note that the FDF file places QemuFlashFvbServicesRuntimeDxe in APRIORI
DXE when SMM_REQUIRE is FALSE. This driver checks for pflash presence,
and lets EmuVariableFvbRuntimeDxe perform its in-RAM flash emulation
only in case pflash is not found.

So this is again in favor of a separate platform -- if we know pflash is
never part of the board, then QemuFlashFvbServicesRuntimeDxe is never
needed, but you cannot remove it from the traditional DSC/FDF files.

Second, EmuVariableFvbRuntimeDxe consumes the PlatformFvbLib class, for
the PlatformFvbDataWritten() API (among other things). This lib class is
implemented by two instances in OvmfPkg, PlatformFvbLibNull and
EmuVariableFvbLib. The latter instance allows Platform BDS to hook an
event (for signaling) via "PcdEmuVariableEvent" into the
EmuVariableFvbRuntimeDxe driver.

In old (very old) QEMU board configurations, namely those without
pflash, this (mis)feature is used by OVMF's PlatformBootManagerLib to
write out all variables to the EFI system partition in a regular file
called \NvVars, with the help of NvVarsFileLib, whenever
EmuVariableFvbRuntimeDxe writes out an emulated "flash" block. For this
purpose, the traditional OVMF DSC files link EmuVariableFvbLib into
EmuVariableFvbRuntimeDxe.

But it counts as an absolute disaster nowadays, and should not be
revived in any platform. If you don't have pflash in TDX guests, just
accept that you won't have non-volatile variables. And link
PlatformFvbLibNull into EmuVariableFvbRuntimeDxe. You're going to need a
separate PlatformBootManagerLib instance anyway.

(We should have removed EmuVariableFvbRuntimeDxe a long time ago from
the traditional OVMF platforms, i.e. made pflash a hard requirement,
even when SMM is not built into the platform -- but whenever I tried
that, Jordan always shot me down.)

My point is: using EmuVariableFvbRuntimeDxe in the TDX platform may be
defensible per se, but we must be very clear that it will never provide
a standards-conformant service for non-volatile UEFI variables, and we
must keep as much of the \NvVars mess out of EmuVariableFvbRuntimeDxe as
possible. This will require a separate PlatformBootManagerLib instance
for TDX anyway (or maybe share PlatformBootManagerLibGrub with
"OvmfPkg/AmdSev/AmdSevX64.dsc").

Apart from the volatility aspect, let's assume we have this in-RAM
emulated "flash device", storing authenticated UEFI variables for Secure
Boot purposes. And we don't have SMM.

What protects this in-RAM variable store from tampering by the guest OS?
It's all guest RAM only, after all. What provides the privilege barrier
between the guest firmware and the guest OS?


*** Slide 50: Library

(23) Should we introduce Null instances for all (or most) new lib
classes here? Code size is a concern (static linking). If we extend a
common OvmfPkg module with new hook points, it's one thing to return
from that hook point early *dynamically*, but it's even better (given
separate platforms) to allow the traditional platform firmware to use a
Null lib instance, to cut out all the dead code statically.


*** Slides 51 through 52

Seems OK.


*** Slide 53:

(24) It might be worth noting that BaseIoLibIntrinsic already has some
SEV enlightenment, as the FIFO IO port operations (which normally use
the REP prefix) are not handled on SEV. I don't have an immediate idea
why this might matter, we should just minimize code duplication if
possible.


*** Slides 54-56:

No  comments, this stuff seems reasonable.


*** Slide 57: MpInitLib

I don't know enough to give a summary judgement.


All in all, I see the controversial / messy parts in the platform
bringup, and how all that differs from the traditional ("legacy") OVMF
platforms. I admit I *may* be biased in favor of SEV, possibly because
SEV landed first -- if you find signs of such a bias in my comments,
please don't hesitate to debunk those points. Yet my general impression
is that the early bringup stuff is significantly different from
everything before, and because of this, a separate platform is
justified.

Definitely separate from the traditional OVMF IA32, IA32X64, and X64
platforms, and *possibly* separate from the "remote attestation"
AmdSevX64.dsc platform. I would approach the TDX feature-set in complete
isolation (exactly how Intel commenced the work, if I understand
correctly), modulo obviously shareable / reusable parts, and then slowly
& gradually work on extracting / refactoring commonalities.

(But, given my stance on Xen for example, I could disagree even with the
latter, retroactive kind of unification -- it all boils down to shared
developer and user base. Component sharing should reflect the community
structure, otherwise maintenance will be a nightmare.)

Thanks
Laszlo

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Yao, Jiewen]

Hi Laszlo.

To clarify your "one binary" feedback below, do you mean you suggest A) create a separate DSC (for example OvmfPkg/ConfidentialComputing.dsc) for a full solution including AMD SEC + Intel TDX + NonConfidentialComputing?
Or B) to create a standalone DSC for Intel TDX (for example, create a OvmfPkg/IntelTdx/IntelTdxXS64.dsc) ?

To me, A) does not change too much, we just create another DSC file - that is it.
Then the original OvmfPkgX64.dsc will only be used for POC/Testing purpose. It does not provide any security guarantee.
(The threat model is: we don't trust VMM. Without attestation, you don't know if VMM modified the OVMF.)

I don't know how "simply" it means. To enable TDX to make it work is not a simple work.
Some architecture changes are mandatory, such as reset vector, IO/MMIO access, #VE handler, IOMMU based shared memory access, etc. I think AMD SEV already did those.

===================
My point is that the "one binary" that the slide deck refers to (i.e.,
OvmfPkgX64.dsc) might prove OK for utilizing the Intel TDX *technology*
in itself. Simply enabling OVMF + a guest OS to boot in a TDX domain.

But "OvmfPkgX64.dsc" is *not* the "one binary" that is suitable for
remote attestation, which has a much broader scope, involving multiple
computers, networking, deployment, guest-owner/host-owner separation,
whatever. For the latter, we needed a separate platform anyway, even
with only SEV in mind; that's why "OvmfPkg/AmdSev/AmdSevX64.dsc" exists.
===================

Thank you
Yao Jiewen

> -----Original Message-----
> From: rfc@edk2.groups.io <rfc@edk2.groups.io> On Behalf Of Laszlo Ersek
> Sent: Friday, June 4, 2021 12:12 AM
> To: Yao, Jiewen <jiewen.yao@intel.com>; rfc@edk2.groups.io;
> devel@edk2.groups.io
> Cc: jejb@linux.ibm.com; Brijesh Singh <brijesh.singh@amd.com>; Tom
> Lendacky <thomas.lendacky@amd.com>; erdemaktas@google.com;
> cho@microsoft.com; bret.barkelew@microsoft.com; Jon Lange
> <jlange@microsoft.com>; Karen Noel <knoel@redhat.com>; Paolo Bonzini
> <pbonzini@redhat.com>; Nathaniel McCallum <npmccallum@redhat.com>;
> Dr. David Alan Gilbert <dgilbert@redhat.com>; Ademar de Souza Reis Jr.
> <areis@redhat.com>
> Subject: Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF
> 
> On 06/03/21 15:51, Yao, Jiewen wrote:
> > Hi, All
> > We plan to do a design review for TDVF in OVMF package.
> >
> >
> > The TDVF Design slides for TinaoCore Design Review Meeting (Jun 11) is
> > now available in blow link:
> > https://edk2.groups.io/g/devel/files/Designs/2021/0611.
> >
> > The Bugzilla is https://bugzilla.tianocore.org/show_bug.cgi?id=3429
> >
> >
> >
> > You can have an offline review first. You comments will be warmly
> > welcomed and we will continuously update the slides based on the
> > feedbacks.
> 
> Resending my earlier comments in this mailing list thread, with the
> feedback inserted at the proper spots that has been given in the
> off-list thread since then:
> 
> 
> *** Slides 4, 6, 7: the "one binary requirement".
> 
> (1) The presentation refers to "OvmfPkgX64.dsc" as "the one" on slide#4,
> but then the explanation for the requirement, given on slide 7, speaks
> about "common attestation interface".
> 
> I think we have a misunderstanding here. The "OvmfPkgX64.dsc" platform
> indeed contains SEV, SEV-ES, and (in the future, will contain) SEV-SNP
> support. In that sense, adding TDX support to the same platform should
> be (hopefully) possible, at the cost of ugly gymnastics in the reset
> vector.
> 
> But "OvmfPkgX64.dsc" is *already* different from the remotely attested
> OVMF platform, namely "OvmfPkg/AmdSev/AmdSevX64.dsc".
> 
> The latter has some additional modules (secret PEIM and DXE driver), it
> has the Grub binary built in, and -- probably most importantly -- it
> trusts host-originated information less than "OvmfPkgX64.dsc".
> 
> For example, "OvmfPkg/AmdSev/AmdSevX64.dsc" has a dedicated
> PlatformBootManagerLib instance, one that ignores the non-volatile UEFI
> variables Boot#### and BootOrder, and ignores (thus far) the fw_cfg
> originated kernel/initrd/cmdline as well.
> 
> It remains an "area of research" to see what else should be removed from
> the traditional host-guest integration (which integration is usually
> desirable for management and convenience), in the remotely-attested boot
> scenario. See e.g.
> <https://bugzilla.tianocore.org/show_bug.cgi?id=3180>.
> 
> My point is that the "one binary" that the slide deck refers to (i.e.,
> OvmfPkgX64.dsc) might prove OK for utilizing the Intel TDX *technology*
> in itself. Simply enabling OVMF + a guest OS to boot in a TDX domain.
> 
> But "OvmfPkgX64.dsc" is *not* the "one binary" that is suitable for
> remote attestation, which has a much broader scope, involving multiple
> computers, networking, deployment, guest-owner/host-owner separation,
> whatever. For the latter, we needed a separate platform anyway, even
> with only SEV in mind; that's why "OvmfPkg/AmdSev/AmdSevX64.dsc"
> exists.
> 
> 
> *** Slides 8-9: general boot flow -- TDVF; TDVF Flow
> 
> I'm likely missing a big bunch of background here, so just a few
> questions:
> 
> (2) Not sure what RTMR is, but it's associated with "Enable TrustedBoot"
> -- so is a virtual TPM a hard requirement?
> 
> ... Back from slide 10: "TCG measurement and event log framework w/o
> TPM" -- that's curious.
> 
> [response from Dave Gilbert:]
> > My reading of this is that the RTMR (and another set of similar
> > registers) are a TDX thing that is like the PCRs from a TPM but
> > without the rest of the TPM features;  so you can do the one-way
> > measurement into the RTMRs just like you do into a TPM PCR, and the
> > measurements pop out somewhere in the TDX quote.  Just like a TPM you
> > need the event log to make any sense of how the final hashed value
> > supposedly got to where it did.
> 
> [response from Erdem Aktas:]
> > +1 to David on this. TDX provides 2 kinds of measurement registers:
> > MRTDs and RTMRs
> >
> (https://software.intel.com/content/dam/develop/external/us/en/docume
> nts/tdx-module-1eas-v0.85.039.pdf
> > section 10.1.2) . MRTDs are build-time measurement registers which are
> > updated when TDX is being created. Once TDX is finalized (before the
> > first run), the MRTDs are finalized and cannot be updated anymore. On
> > the other hand, while the TD is running, TD can extend RTMRs through
> > TDCALLs which will provide TPM PCR kind of capabilities.
> 
> ... Back from slide 43: feel free to skip this now; I will comment in
> more detail below.
> 
> (3) Prepare AcpiTable -- OVMF fetches ACPI tables from QEMU; is this a
> new (firmware originated) table that is installed in addition, or does
> it replace QEMU's tables?
> 
> ... Ignore for now, will comment on the MADT stuff later.
> 
> (4) Does DMA management mean a different IOMMU protocol? That is
> going
> to conflict with the SEV IOMMU protocol. Depexes in OVMF expect one or
> zero IOMMU protocols to be present.
> 
> ... Back from slide 40: feel free to skip this now; I'll comment on this
> separately, below.
> 
> (5) Enumerate VirtIO -- virtio enumeration is PCI based on x86. But I
> see no mention of PCI. If you mean VirtioMmioDeviceLib, that's no good,
> because it does not support virtio-1.0, only virtio-0.9.5.
> 
> ... Back from slide 42: I got my answer to this on slide 42, so don't
> worry about this point.
> 
> (6) The PEI phase is skipped as a whole. I don't see how that can be
> reasonably brought together with either "OvmfPkgX64.dsc" or
> "OvmfPkg/AmdSev/AmdSevX64.dsc". I guess you can always modify SEC to
> jump into DXE directly, but then why keep the PEI core and a bunch of
> PEIMs in the firmware binary?
> 
> Also touched on by slide 9, TDVF Flow -- PEI is eliminated but SEC
> becomes more heavy-weight.
> 
> Wouldn't this deserve a dedicated, separate platform DSC? The
> 8-bit/32-bit branching at the front of the reset vector is a smaller
> complication in comparison.
> 
> Slide 6 references the mailing list archive:
> 
>   https://edk2.groups.io/g/devel/topic/81969494#74319
> 
> and in that message, I wrote:
> 
>     I'm doubtful that this is a unique problem ("just fix the reset
>     vector") the likes of which will supposedly never return during the
>     integration of SEV and TDX
> 
> See also:
> 
>   https://listman.redhat.com/archives/edk2-devel-archive/2021-
> April/msg00784.html
> 
> where I said:
> 
>     It's not lost on me that we're talking about ~3 instructions.
> 
>     Let's keep a close eye on further "polymorphisms" that would require
>     hacks.
> 
> The first 9 slides in the presentation introduce much-much more
> intrusive problems than the "polymorphism" of the reset vector. Would I
> be correct to say that my concern in the above messages was right? I
> think I was only given a fraction of the necessary information when I
> was asked "do you agree 'one binary' is viable".
> 
> [response from Erdem Aktas:]
> > Let's not worry about this for now. We want the one binary solution
> > for practical reasons and also for simplicity.  In the end, we want to
> > do what is right and good for everyone.
> > Those are legit concerns and I think what Intel is trying to do (sorry
> > for mind reading) is to discuss all those concerns and questions to
> > make the right decision. I really appreciate their effort on preparing
> > those slides and bringing it to the community to review.
> >
> > I will also read your comments more carefully and provide my thoughts
> > on them.
> > Sorry for being a little slow on this.
> 
> 
> *** Slide 10 -- Key impact to firmware
> 
> (7) "CPUs are left running in long mode after exiting firmware" -- what
> kind of "pen" are we talking about? Does a HLT loop still work?
> 
> (8) "I/O, MMIO, MSR accesses are different" -- those are implemented by
> low-level libraries in edk2; how can they be configured dynamically?
> 
> ... Back from slide 53: I'll comment on slide 53 separately; ignore
> this.
> 
> 
> *** Slide 11 -- TDVF Image (1)
> 
> (9) CFV -- Configuration Firmware Volume (VarStore.fdf.inc),
> containing SB keys -- how is this firmware volume populated (at build
> time)? Is this a hexdump?
> 
> ... Back from slide 16: it seems like CFV is a raw hexdump indeed; how
> is that managed when keys change (at build time)?
> 
> (10) This slide (slide 11) basically describes an intrusive
> reorganization of "OvmfPkgX64.fdf". I don't think I can agree to that.
> While confidential computing is important, it is not relevant for many
> users. Even if we don't cause outright regressions for existent setups,
> the maintenance cost of the traditional OVMF platform will skyrocket.
> 
> The big bunch of areas that SEV-ES introduced to MEMFD is already a big
> complication. I'd feel much better if we could isolate all that to a
> dedicated "remote attested boot" firmware platform, and not risk the
> functionality and maintenance of the traditional platform. I think this
> ties in with my comment (1).
> 
> For example, seeing a configuration firmware volume (CFV) with secure
> boot keys embedded, in the "usual" FDF, will confuse lots of people, me
> included. In the traditional OVMF use case, we use a different method:
> namely OvmfPkg/EnrollDefaultKeys, for "priming" a variable store
> template, in the build environment.
> 
> Edk2 (and PI and UEFI) are definitely flexible enough for accommodating
> TDX, but the existent, traditional OVMF platforms are a bad fit. In my
> opinion.
> 
> 
> *** Slide 12: TDVF Image (2)
> 
> (11) "Page table should support both 4-level and 5-level page table"
> 
> As a general development strategy, I would suggest building TDX support
> in small, well-isolated layers. 5-level paging is not enabled (has never
> been tested, to my knowledge) with OVMF on QEMU/KVM, regardless of
> confidential computing, for starters. If 5-level paging is a strict
> requirement for TDX, then it arguably needs to be implemented
> independently of TDX, at first. So that the common edk2 architecture be
> at least testable on QEMU/KVM with 5-level paging enabled.
> 
> 
> *** Slide 13:
> 
> (12) My comment is that the GUID-ed structure chain already starts at a
> fixed GPA (the "AMD SEV option"). Ordering between GUID-ed structures is
> irrelevant, so any TDX-specific structures should be eligible for
> appending to, prepending to, or intermixing with, other (possibly
> SEV-specific) structures. There need not be a separate entry point, just
> different GUIDS.
> 
> (13) Regarding "4G-0x20[0x10] is OVMF AP reset vector (used in OVMF
> implementation)" -- I think this is a typo: this "AP reset vector" is
> *not* used in OVMF. To my knowledge, it is a vestige from the UefiCpuPkg
> reset vector. In OVMF, APs are booted via MpInitLib (in multiple
> firmware phases), using INIT-SIPI-SIPI, and the reset vector for the
> APs, posited through those IPIs, is prepared in low RAM.
> 
> 
> *** Slides 14 through 16:
> 
> I consider these TDVF firmware image internals, implementation details
> -- do whatever you need to do, just don't interfere with existing
> platforms / use cases. See my comment (10) above.
> 
> 
> *** Slides 17-21:
> 
> (14) Again, a very big difference from traditional OVMF: APs never enter
> SEC in traditional OVMF. I assume this new functionality is part of
> TdxStartupLib (from slide 18) -- will there be a Null instance of that?
> 
> Last week I posted a 43-part patch series to edk2-devel, for separating
> out the dynamic Xen enlightenments from the IA32, IA32X64, X64
> platforms, in favor of the dedicated OvmfXen platform. TDX seems to
> bring in incomparably more complications than Xen, and the OvmfPkg
> maintainers have found even the Xen complications troublesome in the
> long term.
> 
> If I had had access to all this information when we first discussed "one
> binary" on the mailing list, I'd have never agreed to "one binary". I'm
> OK with attempting one firmware binary for "confidential computing", but
> that "one platform" cannot be "OvmfPkgX64.dsc".
> 
> Even if I make a comparison with just the "technology" (not the
> remotely-attested deployment) of SEV and SEV-ES, as it is included in
> "OvmfPkgX64.dsc", TDX is hugely more complicated and intrusive than
> that. SEV proved possible to integrate into existing modules, into the
> existing boot flow, maybe through the addition of some new drivers (such
> as a new IOMMU protocol implementation, and some "clever" depexes).
> But
> we never had to restructure the FD layout, eliminate whole firmware
> phases, or think about multiprocessing in the reset vector or the SEC
> phase.
> 
> In order to bring an example from the ARM world, please note that
> platforms that use a PEI phase, and platforms that don't, are distinct
> platforms. In ArmVirtPkg, two examples are ArmVirtQemu and
> ArmVirtQemuKernel. The latter does not include the PEI Core.
> 
> 
> *** Slides 22 through 34:
> 
> (15) All these extra tasks and complications are perfectly fine, as long
> as they exist peacefully *separately* from the traditional ("legacy")
> OVMF platforms.
> 
> Honestly, in the virtual world, picking your firmware binary is easy.
> The approach here reminds me of a physical firmware binary that includes
> everything possible from "edk2-platforms/Features/Intel", just so it can
> be deployed to any physical board imaginable. That's not how Intel
> builds physical firmware, right? We have "edk2-platforms/Platform/Intel"
> and "edk2-platforms/Silicon/Intel" with many-many separate DSC files.
> 
> 
> *** Slide 35-36: DXE phase
> 
> (16) "Some DXE Drivers not allowed to load/start in Td guest -- Network
> stack, RNG, ..."
> 
> Same comment as (several times) above. The Linuxboot project is a good
> example for eliminating cruft from DXEFV (in fact, for eliminating most
> of the DXE phase). In a TDX environment, why include drivers in the
> firmware binary that are never used? Meanwhile, DXEFV in OVMF grows by
> a
> MB every 1.5 years or so. Again, remove these drivers from the DSC/FDF
> then, and it needs to be a separate platform.
> 
> (17) "Other DXE Phase drivers -- [...] AcpiPlatformDxe"
> 
> I'm not sure what this section is supposed to mean. Other DXE phase
> drivers included, or excluded? Without AcpiPlatformDxe, the guest OS
> will not see QEMU's ACPI content, and will almost certainly malfunction.
> 
> ... Back from slide 48: ignore this for now, I'll comment in more detail
> later.
> 
> 
> *** Slide 37: DXE Core
> 
> (18) says "SMM is not supported in Td guest" -- how is the variable
> store protected from direct hardware (pflash) access from the guest OS?
> Without SMM, the guest OS need not go through gRT->SetVariable() to
> update authenticated non-volatile UEFI variables, and that undermines
> Secure Boot.
> 
> Note that, while SEV-ES has the same limitation wrt. SMM, the
> "OvmfPkg/AmdSev/AmdSevX64.dsc" platform doesn't even include the
> Secure
> Boot firmware feature. For another example, the OVMF firmware binary in
> RHEL that's going to support SEV-ES is such a build of "OvmfPkgX64.dsc"
> that does not include the Secure Boot feature either.
> 
> But in this TDX slide deck, Secure Boot certificates are embedded in the
> CFV (configuration firmware volume) -- see slide 11 and slide 16 --,
> which suggests that this platform does want secure boot.
> 
> ... Back from slide 48: I'm going to make *additional* comments on this,
> when I'm at slide 48, too.
> 
> The rest of this slide (slide 37) looks reasonable (generic DXE Core
> changes -- possibly PI spec changes too).
> 
> 
> *** Slides 38 through 39:
> 
> These seem reasonable (TdxDxe assumes some responsibilities of
> OvmfPkg/PlatformPei)
> 
> 
> *** Slides 40 through 42:
> 
> *If* you really can implement TDX support for the IOMMU driver *this*
> surgically, then I'm OK with it. The general logic in the IOMMU driver
> was truly difficult to write, and I'd be seriously concerned if those
> parts would have to be modified. Customizing just the page
> encryption/decryption primitives for TDX vs. SEV is OK.
> 
> 
> *** Slides 43 through 47:
> 
> (19) Slide 46 and slide 47 are almost identical. Please consolidate them
> into a single slide.
> 
> (20) the TPM2 infrastructure in edk2 is baroque (over-engineered), in my
> opinion. It has so many layers that I can never keep them in mind. When
> we added TPM support to OVMF, I required commit messages that would
> help
> us recall the layering. In particular, please refer to commit
> 0c0a50d6b3ff ("OvmfPkg: include Tcg2Dxe module", 2018-03-09). Here's an
> excerpt:
> 
>            TPM 2 consumer driver
>                     |
>                     v
>       Tpm2DeviceLib class: Tpm2DeviceLibTcg2 instance
>                     |
>                     v
>              TCG2 protocol interface
>                     |
>                     v
>       TCG2 protocol provider: Tcg2Dxe.inf driver
>                     |
>                     v
>       Tpm2DeviceLib class: Tpm2DeviceLibRouter instance
>                     |
>                     v
>          NULL class: Tpm2InstanceLibDTpm instance
>             (via earlier registration)
>                     |
>                     v
>            TPM2 chip (actual hardware)
> 
> The slide deck says that EFI_TD_PROTOCOL is supposed to reuse the
> EFI_TCG2_PROTOCOL definition. If that's the case, then why don't we push
> the TDX specifics (more or less: the replacement of PCRs with RTMR) down
> to the lowest possible level?
> 
> Can we have "Tpm2InstanceLibTdxRtmr", plugged into the same Tcg2Dxe.inf
> driver?
> 
> If not, can we have a new TdTcg2Dxe.inf driver, but make it so that it
> install the same protocol as before (EFI_TCG2_PROTOCOL -- same old
> protocol GUID)? Then DxeTpmMeasurementLib doesn't have to change.
> 
> As long as there is *at most* one EFI_TCG2_PROTOCOL instance published
> in the protocol database, DxeTpmMeasurementLib should be fine. In SEV*
> guests, the standard Tcg2Dxe driver provides that protocol. In TDX
> guests, TdTcg2Dxe.inf should provide the protocol. Arbitration between
> the two can be implemented with the pattern seen in the following
> commits:
> 
>  1  05db0948cc60 EmbeddedPkg: introduce EDKII Platform Has ACPI GUID
>  2  786f476323a6 EmbeddedPkg: introduce PlatformHasAcpiLib
>  3  65a69b214840 EmbeddedPkg: introduce EDKII Platform Has Device Tree
>                  GUID
>  4  2558bfe3e907 ArmVirtPkg: add PlatformHasAcpiDtDxe
> 
> The basic idea is that Tcg2Dxe can have a depex on a new "running in
> SEV" protocol GUID, and TdTcg2Dxe can have a depex on a new "running in
> TDX" protocol GUID. A separate platform driver can install the proper
> GUID -- possibly *neither* of those GUIDs.
> 
> And, we don't have to change the depex section of
> "SecurityPkg/Tcg/Tcg2Dxe/Tcg2Dxe.inf" for this; we can implement a
> library instance with an empty constructor, but a non-empty depex, and
> then hook this lib instance into Tcg2Dxe.inf via module scope NULL lib
> class override in the DSC file. Basically we could forcibly restrict
> Tcg2Dxe's DEPEX by making it inherit the new DEPEX from the library.
> 
> 
> *** Slide 48: DXE Phase -- Other Modules
> 
> Regarding IncompatiblePciDeviceSupportDxe: the proposed update sounds
> plausible and simple enough.
> 
> (21) "AcpiPlatformDxe: Support for MADT/ACPI addition to report Td
> Mailbox entry"
> 
> Firmware-owned tables must not be installed from this driver.
> 
> Please refer to my "Xen removal" patch set again, for
> <https://bugzilla.tianocore.org/show_bug.cgi?id=2122>, which I mention
> above in point (14). As part of the Xen removal, the AcpiPlatformDxe
> driver in OvmfPkg is significantly trimmed: all unused (dead) cruft is
> removed, including any ACPI table templates that are built into the
> firmware.
> 
> OvmfPkg/AcpiPlatformDxe is responsible *solely* for implementing the
> client side of the QEMU ACPI linker/loader.
> 
> If you need to prepare & install different ACPI tables, please do it
> elsewhere, in another DXE driver. A bunch of other firmware modules do
> that (NFIT, IBFT, BGRT, ...).
> 
> For example, the OvmfPkg/TdxDxe DXE_DRIVER is supposed to be launched
> early in the DXE phase, via APRIORI section -- please consider
> registering a protocol notify in that driver, for
> EFI_ACPI_TABLE_PROTOCOL, and when it becomes available, install
> whatever
> *extra* tables you need.
> 
> Note that if you need to *customize* an ACPI table that QEMU already
> provides, then you will have to modify the ACPI generator on the QEMU
> side. It is a design tenet between QEMU and OVMF that OVMF include no
> business logic for either parsing or fixing up ACPI tables that QEMU
> provides. AcpiPlatformDxe contains the minimum (which is already a whole
> lot, unfortunately) that's necessary for implementing the QEMU ACPI
> linker/loader client in the UEFI environment.
> 
> The slide deck mentions MADT, which is also known as the "APIC" table --
> and indeed, QEMU does provide that. (See acpi_build_madt()
> [hw/i386/acpi-common.c].) So if TDX needs MADT customizations, that
> should go into QEMU.
> 
> (22) EmuVariableFvbRuntimeDxe
> 
> Ouch, this is an unpleasant surprise.
> 
> First, if you know for a fact that pflash is not part of the *board* in
> any TDX setup, then pulling
> 
>   OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf
> 
> into the firmware platform is useless, as it is mutually exclusive with
> 
>   OvmfPkg/EmuVariableFvbRuntimeDxe/Fvb.inf
> 
> (via dynamic means -- a dynamic PCD).
> 
> Note that the FDF file places QemuFlashFvbServicesRuntimeDxe in APRIORI
> DXE when SMM_REQUIRE is FALSE. This driver checks for pflash presence,
> and lets EmuVariableFvbRuntimeDxe perform its in-RAM flash emulation
> only in case pflash is not found.
> 
> So this is again in favor of a separate platform -- if we know pflash is
> never part of the board, then QemuFlashFvbServicesRuntimeDxe is never
> needed, but you cannot remove it from the traditional DSC/FDF files.
> 
> Second, EmuVariableFvbRuntimeDxe consumes the PlatformFvbLib class,
> for
> the PlatformFvbDataWritten() API (among other things). This lib class is
> implemented by two instances in OvmfPkg, PlatformFvbLibNull and
> EmuVariableFvbLib. The latter instance allows Platform BDS to hook an
> event (for signaling) via "PcdEmuVariableEvent" into the
> EmuVariableFvbRuntimeDxe driver.
> 
> In old (very old) QEMU board configurations, namely those without
> pflash, this (mis)feature is used by OVMF's PlatformBootManagerLib to
> write out all variables to the EFI system partition in a regular file
> called \NvVars, with the help of NvVarsFileLib, whenever
> EmuVariableFvbRuntimeDxe writes out an emulated "flash" block. For this
> purpose, the traditional OVMF DSC files link EmuVariableFvbLib into
> EmuVariableFvbRuntimeDxe.
> 
> But it counts as an absolute disaster nowadays, and should not be
> revived in any platform. If you don't have pflash in TDX guests, just
> accept that you won't have non-volatile variables. And link
> PlatformFvbLibNull into EmuVariableFvbRuntimeDxe. You're going to need
> a
> separate PlatformBootManagerLib instance anyway.
> 
> (We should have removed EmuVariableFvbRuntimeDxe a long time ago
> from
> the traditional OVMF platforms, i.e. made pflash a hard requirement,
> even when SMM is not built into the platform -- but whenever I tried
> that, Jordan always shot me down.)
> 
> My point is: using EmuVariableFvbRuntimeDxe in the TDX platform may be
> defensible per se, but we must be very clear that it will never provide
> a standards-conformant service for non-volatile UEFI variables, and we
> must keep as much of the \NvVars mess out of EmuVariableFvbRuntimeDxe
> as
> possible. This will require a separate PlatformBootManagerLib instance
> for TDX anyway (or maybe share PlatformBootManagerLibGrub with
> "OvmfPkg/AmdSev/AmdSevX64.dsc").
> 
> Apart from the volatility aspect, let's assume we have this in-RAM
> emulated "flash device", storing authenticated UEFI variables for Secure
> Boot purposes. And we don't have SMM.
> 
> What protects this in-RAM variable store from tampering by the guest OS?
> It's all guest RAM only, after all. What provides the privilege barrier
> between the guest firmware and the guest OS?
> 
> 
> *** Slide 50: Library
> 
> (23) Should we introduce Null instances for all (or most) new lib
> classes here? Code size is a concern (static linking). If we extend a
> common OvmfPkg module with new hook points, it's one thing to return
> from that hook point early *dynamically*, but it's even better (given
> separate platforms) to allow the traditional platform firmware to use a
> Null lib instance, to cut out all the dead code statically.
> 
> 
> *** Slides 51 through 52
> 
> Seems OK.
> 
> 
> *** Slide 53:
> 
> (24) It might be worth noting that BaseIoLibIntrinsic already has some
> SEV enlightenment, as the FIFO IO port operations (which normally use
> the REP prefix) are not handled on SEV. I don't have an immediate idea
> why this might matter, we should just minimize code duplication if
> possible.
> 
> 
> *** Slides 54-56:
> 
> No  comments, this stuff seems reasonable.
> 
> 
> *** Slide 57: MpInitLib
> 
> I don't know enough to give a summary judgement.
> 
> 
> All in all, I see the controversial / messy parts in the platform
> bringup, and how all that differs from the traditional ("legacy") OVMF
> platforms. I admit I *may* be biased in favor of SEV, possibly because
> SEV landed first -- if you find signs of such a bias in my comments,
> please don't hesitate to debunk those points. Yet my general impression
> is that the early bringup stuff is significantly different from
> everything before, and because of this, a separate platform is
> justified.
> 
> Definitely separate from the traditional OVMF IA32, IA32X64, and X64
> platforms, and *possibly* separate from the "remote attestation"
> AmdSevX64.dsc platform. I would approach the TDX feature-set in complete
> isolation (exactly how Intel commenced the work, if I understand
> correctly), modulo obviously shareable / reusable parts, and then slowly
> & gradually work on extracting / refactoring commonalities.
> 
> (But, given my stance on Xen for example, I could disagree even with the
> latter, retroactive kind of unification -- it all boils down to shared
> developer and user base. Component sharing should reflect the community
> structure, otherwise maintenance will be a nightmare.)
> 
> Thanks
> Laszlo
> 
> 
> 
> 
> 

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Laszlo Ersek]

On 06/04/21 01:19, Yao, Jiewen wrote:
> Hi Laszlo.
> 
> To clarify your "one binary" feedback below, do you mean you suggest A) create a separate DSC (for example OvmfPkg/ConfidentialComputing.dsc) for a full solution including AMD SEC + Intel TDX + NonConfidentialComputing?
> Or B) to create a standalone DSC for Intel TDX (for example, create a OvmfPkg/IntelTdx/IntelTdxXS64.dsc) ?
> 
> To me, A) does not change too much, we just create another DSC file - that is it.
> Then the original OvmfPkgX64.dsc will only be used for POC/Testing purpose. It does not provide any security guarantee.
> (The threat model is: we don't trust VMM. Without attestation, you don't know if VMM modified the OVMF.)
> 
> I don't know how "simply" it means. To enable TDX to make it work is not a simple work.
> Some architecture changes are mandatory, such as reset vector, IO/MMIO access, #VE handler, IOMMU based shared memory access, etc. I think AMD SEV already did those.

I mean option (B). Create a completely separate DSC+FDF for Intel TDX.

In my mind, there are two (very high level) stages for developing the
"Confidential Computing with TDX" feature in edk2.

Stage 1: allow a guest to run in a TDX domain. "Guest owner" and "Cloud
owner" are *not* separate concepts in this stage.

Stage 2: enable such a guest to be deployed remotely to an untrusted
cloud, and ensure its integrity via remote attestation.


Stage 1 is *hugely different* between AMD SEV* technologies and Intel
TDX. That's why we need, in my opinion, a separate DSC+FDF for Intel TDX
right from the start. This does not necessarily mean that we need to
duplicate every single module (library, PEIM, DXE driver, etc) for Intel
TDX. Wherever it makes sense, and the changes are not very intrusive or
wasteful (considering binary code that becomes "dead" on in a TDX
guest), we can modify (extend) existent modules in-place.

Stage 1 is complete for AMD SEV and AMD SEV-ES. AMD SEV-SNP is in
progress. These AMD SEV* technologies have been possible to integrate
(thus far) into the existing "OvmfPkg/OvmfPkgX64.dsc" platform. But
Intel TDX is very different from that, even in Stage 1.


Stage 2 is far out in the future, for Intel TDX. I have no idea about
it, but whatever it's going to look like, it will be based on Stage 1.

The "OvmfPkg/AmdSev/AmdSevX64.dsc" platform is *one approach* for
implementing Stage 2. And this platform utilizes AMD SEV* technologies
only (thus far). *If* and *how much* the approach of
"OvmfPkg/AmdSev/AmdSevX64.dsc" will apply to Intel TDX -- once Stage 1
of Intel TDX is complete --, I cannot predict.


The underlying physical hardware features are completely different
between AMD SEV* and Intel TDX, as much as I can tell. It makes zero
sense to me to start from a unified perspective, and shoehorn everything
possible (and impossible) into a common blob and framework. That
approach has never *ever* worked for me, not even when I started working
on the virtio drivers for OVMF 9 years ago. I extracted VirtioLib only
when I worked on the second virtio driver -- that is, when I was about
to have *working code* for two *distinct* virtio devices, and it was
possible to identify commonalities between the drivers, and to extract
those commonalities. The fact that I knew, in advance, that my "end
goal" was the same with these devices, namely to "boot from them", made
no difference whatsoever. I still I had to start implementing them in
separate sandboxes. Soon enough, VirtioLib emerged, and later
VIRTIO_DEVICE_PROTOCOL emerged even.

I'm 100% incapable of dealing with a top-down approach here. Only
bottom-up works for me.


Most importantly, the OvmfPkgIa32, OvmfPkgIa32X64, OvmfPkgX64 platforms
must be kept regression-free, and preferably their complexity should be
kept manageable for maintenance too. These platforms are *entirely
irrelevant* for Stage 2 (regardless of underlying security technology).
They *happen* to be relevant for Stage 1 of AMD SEV*, purely because SEV
proved possible to integrate into them, in very small, well isolated,
surgical advances, without upsetting everything. But I can tell upfront
that Intel TDX is way more intrusive than anything I've seen thus far in
AMD SEV*. So I want Intel TDX to exist in a brand new platform, even as
Stage 1. And, to reiterate, just because Confidential Computing is the
new hot thing, the use cases for OvmfPkgIa32, OvmfPkgIa32X64, OvmfPkgX64
do not disappear. Regressing them, or making them unmaintainable due to
skyrocketing complexity, is not acceptable.

Thanks
Laszlo

> 
> ===================
> My point is that the "one binary" that the slide deck refers to (i.e.,
> OvmfPkgX64.dsc) might prove OK for utilizing the Intel TDX *technology*
> in itself. Simply enabling OVMF + a guest OS to boot in a TDX domain.
> 
> But "OvmfPkgX64.dsc" is *not* the "one binary" that is suitable for
> remote attestation, which has a much broader scope, involving multiple
> computers, networking, deployment, guest-owner/host-owner separation,
> whatever. For the latter, we needed a separate platform anyway, even
> with only SEV in mind; that's why "OvmfPkg/AmdSev/AmdSevX64.dsc" exists.
> ===================
> 
> Thank you
> Yao Jiewen
> 
>> -----Original Message-----
>> From: rfc@edk2.groups.io <rfc@edk2.groups.io> On Behalf Of Laszlo Ersek
>> Sent: Friday, June 4, 2021 12:12 AM
>> To: Yao, Jiewen <jiewen.yao@intel.com>; rfc@edk2.groups.io;
>> devel@edk2.groups.io
>> Cc: jejb@linux.ibm.com; Brijesh Singh <brijesh.singh@amd.com>; Tom
>> Lendacky <thomas.lendacky@amd.com>; erdemaktas@google.com;
>> cho@microsoft.com; bret.barkelew@microsoft.com; Jon Lange
>> <jlange@microsoft.com>; Karen Noel <knoel@redhat.com>; Paolo Bonzini
>> <pbonzini@redhat.com>; Nathaniel McCallum <npmccallum@redhat.com>;
>> Dr. David Alan Gilbert <dgilbert@redhat.com>; Ademar de Souza Reis Jr.
>> <areis@redhat.com>
>> Subject: Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF
>>
>> On 06/03/21 15:51, Yao, Jiewen wrote:
>>> Hi, All
>>> We plan to do a design review for TDVF in OVMF package.
>>>
>>>
>>> The TDVF Design slides for TinaoCore Design Review Meeting (Jun 11) is
>>> now available in blow link:
>>> https://edk2.groups.io/g/devel/files/Designs/2021/0611.
>>>
>>> The Bugzilla is https://bugzilla.tianocore.org/show_bug.cgi?id=3429
>>>
>>>
>>>
>>> You can have an offline review first. You comments will be warmly
>>> welcomed and we will continuously update the slides based on the
>>> feedbacks.
>>
>> Resending my earlier comments in this mailing list thread, with the
>> feedback inserted at the proper spots that has been given in the
>> off-list thread since then:
>>
>>
>> *** Slides 4, 6, 7: the "one binary requirement".
>>
>> (1) The presentation refers to "OvmfPkgX64.dsc" as "the one" on slide#4,
>> but then the explanation for the requirement, given on slide 7, speaks
>> about "common attestation interface".
>>
>> I think we have a misunderstanding here. The "OvmfPkgX64.dsc" platform
>> indeed contains SEV, SEV-ES, and (in the future, will contain) SEV-SNP
>> support. In that sense, adding TDX support to the same platform should
>> be (hopefully) possible, at the cost of ugly gymnastics in the reset
>> vector.
>>
>> But "OvmfPkgX64.dsc" is *already* different from the remotely attested
>> OVMF platform, namely "OvmfPkg/AmdSev/AmdSevX64.dsc".
>>
>> The latter has some additional modules (secret PEIM and DXE driver), it
>> has the Grub binary built in, and -- probably most importantly -- it
>> trusts host-originated information less than "OvmfPkgX64.dsc".
>>
>> For example, "OvmfPkg/AmdSev/AmdSevX64.dsc" has a dedicated
>> PlatformBootManagerLib instance, one that ignores the non-volatile UEFI
>> variables Boot#### and BootOrder, and ignores (thus far) the fw_cfg
>> originated kernel/initrd/cmdline as well.
>>
>> It remains an "area of research" to see what else should be removed from
>> the traditional host-guest integration (which integration is usually
>> desirable for management and convenience), in the remotely-attested boot
>> scenario. See e.g.
>> <https://bugzilla.tianocore.org/show_bug.cgi?id=3180>.
>>
>> My point is that the "one binary" that the slide deck refers to (i.e.,
>> OvmfPkgX64.dsc) might prove OK for utilizing the Intel TDX *technology*
>> in itself. Simply enabling OVMF + a guest OS to boot in a TDX domain.
>>
>> But "OvmfPkgX64.dsc" is *not* the "one binary" that is suitable for
>> remote attestation, which has a much broader scope, involving multiple
>> computers, networking, deployment, guest-owner/host-owner separation,
>> whatever. For the latter, we needed a separate platform anyway, even
>> with only SEV in mind; that's why "OvmfPkg/AmdSev/AmdSevX64.dsc"
>> exists.
>>
>>
>> *** Slides 8-9: general boot flow -- TDVF; TDVF Flow
>>
>> I'm likely missing a big bunch of background here, so just a few
>> questions:
>>
>> (2) Not sure what RTMR is, but it's associated with "Enable TrustedBoot"
>> -- so is a virtual TPM a hard requirement?
>>
>> ... Back from slide 10: "TCG measurement and event log framework w/o
>> TPM" -- that's curious.
>>
>> [response from Dave Gilbert:]
>>> My reading of this is that the RTMR (and another set of similar
>>> registers) are a TDX thing that is like the PCRs from a TPM but
>>> without the rest of the TPM features;  so you can do the one-way
>>> measurement into the RTMRs just like you do into a TPM PCR, and the
>>> measurements pop out somewhere in the TDX quote.  Just like a TPM you
>>> need the event log to make any sense of how the final hashed value
>>> supposedly got to where it did.
>>
>> [response from Erdem Aktas:]
>>> +1 to David on this. TDX provides 2 kinds of measurement registers:
>>> MRTDs and RTMRs
>>>
>> (https://software.intel.com/content/dam/develop/external/us/en/docume
>> nts/tdx-module-1eas-v0.85.039.pdf
>>> section 10.1.2) . MRTDs are build-time measurement registers which are
>>> updated when TDX is being created. Once TDX is finalized (before the
>>> first run), the MRTDs are finalized and cannot be updated anymore. On
>>> the other hand, while the TD is running, TD can extend RTMRs through
>>> TDCALLs which will provide TPM PCR kind of capabilities.
>>
>> ... Back from slide 43: feel free to skip this now; I will comment in
>> more detail below.
>>
>> (3) Prepare AcpiTable -- OVMF fetches ACPI tables from QEMU; is this a
>> new (firmware originated) table that is installed in addition, or does
>> it replace QEMU's tables?
>>
>> ... Ignore for now, will comment on the MADT stuff later.
>>
>> (4) Does DMA management mean a different IOMMU protocol? That is
>> going
>> to conflict with the SEV IOMMU protocol. Depexes in OVMF expect one or
>> zero IOMMU protocols to be present.
>>
>> ... Back from slide 40: feel free to skip this now; I'll comment on this
>> separately, below.
>>
>> (5) Enumerate VirtIO -- virtio enumeration is PCI based on x86. But I
>> see no mention of PCI. If you mean VirtioMmioDeviceLib, that's no good,
>> because it does not support virtio-1.0, only virtio-0.9.5.
>>
>> ... Back from slide 42: I got my answer to this on slide 42, so don't
>> worry about this point.
>>
>> (6) The PEI phase is skipped as a whole. I don't see how that can be
>> reasonably brought together with either "OvmfPkgX64.dsc" or
>> "OvmfPkg/AmdSev/AmdSevX64.dsc". I guess you can always modify SEC to
>> jump into DXE directly, but then why keep the PEI core and a bunch of
>> PEIMs in the firmware binary?
>>
>> Also touched on by slide 9, TDVF Flow -- PEI is eliminated but SEC
>> becomes more heavy-weight.
>>
>> Wouldn't this deserve a dedicated, separate platform DSC? The
>> 8-bit/32-bit branching at the front of the reset vector is a smaller
>> complication in comparison.
>>
>> Slide 6 references the mailing list archive:
>>
>>   https://edk2.groups.io/g/devel/topic/81969494#74319
>>
>> and in that message, I wrote:
>>
>>     I'm doubtful that this is a unique problem ("just fix the reset
>>     vector") the likes of which will supposedly never return during the
>>     integration of SEV and TDX
>>
>> See also:
>>
>>   https://listman.redhat.com/archives/edk2-devel-archive/2021-
>> April/msg00784.html
>>
>> where I said:
>>
>>     It's not lost on me that we're talking about ~3 instructions.
>>
>>     Let's keep a close eye on further "polymorphisms" that would require
>>     hacks.
>>
>> The first 9 slides in the presentation introduce much-much more
>> intrusive problems than the "polymorphism" of the reset vector. Would I
>> be correct to say that my concern in the above messages was right? I
>> think I was only given a fraction of the necessary information when I
>> was asked "do you agree 'one binary' is viable".
>>
>> [response from Erdem Aktas:]
>>> Let's not worry about this for now. We want the one binary solution
>>> for practical reasons and also for simplicity.  In the end, we want to
>>> do what is right and good for everyone.
>>> Those are legit concerns and I think what Intel is trying to do (sorry
>>> for mind reading) is to discuss all those concerns and questions to
>>> make the right decision. I really appreciate their effort on preparing
>>> those slides and bringing it to the community to review.
>>>
>>> I will also read your comments more carefully and provide my thoughts
>>> on them.
>>> Sorry for being a little slow on this.
>>
>>
>> *** Slide 10 -- Key impact to firmware
>>
>> (7) "CPUs are left running in long mode after exiting firmware" -- what
>> kind of "pen" are we talking about? Does a HLT loop still work?
>>
>> (8) "I/O, MMIO, MSR accesses are different" -- those are implemented by
>> low-level libraries in edk2; how can they be configured dynamically?
>>
>> ... Back from slide 53: I'll comment on slide 53 separately; ignore
>> this.
>>
>>
>> *** Slide 11 -- TDVF Image (1)
>>
>> (9) CFV -- Configuration Firmware Volume (VarStore.fdf.inc),
>> containing SB keys -- how is this firmware volume populated (at build
>> time)? Is this a hexdump?
>>
>> ... Back from slide 16: it seems like CFV is a raw hexdump indeed; how
>> is that managed when keys change (at build time)?
>>
>> (10) This slide (slide 11) basically describes an intrusive
>> reorganization of "OvmfPkgX64.fdf". I don't think I can agree to that.
>> While confidential computing is important, it is not relevant for many
>> users. Even if we don't cause outright regressions for existent setups,
>> the maintenance cost of the traditional OVMF platform will skyrocket.
>>
>> The big bunch of areas that SEV-ES introduced to MEMFD is already a big
>> complication. I'd feel much better if we could isolate all that to a
>> dedicated "remote attested boot" firmware platform, and not risk the
>> functionality and maintenance of the traditional platform. I think this
>> ties in with my comment (1).
>>
>> For example, seeing a configuration firmware volume (CFV) with secure
>> boot keys embedded, in the "usual" FDF, will confuse lots of people, me
>> included. In the traditional OVMF use case, we use a different method:
>> namely OvmfPkg/EnrollDefaultKeys, for "priming" a variable store
>> template, in the build environment.
>>
>> Edk2 (and PI and UEFI) are definitely flexible enough for accommodating
>> TDX, but the existent, traditional OVMF platforms are a bad fit. In my
>> opinion.
>>
>>
>> *** Slide 12: TDVF Image (2)
>>
>> (11) "Page table should support both 4-level and 5-level page table"
>>
>> As a general development strategy, I would suggest building TDX support
>> in small, well-isolated layers. 5-level paging is not enabled (has never
>> been tested, to my knowledge) with OVMF on QEMU/KVM, regardless of
>> confidential computing, for starters. If 5-level paging is a strict
>> requirement for TDX, then it arguably needs to be implemented
>> independently of TDX, at first. So that the common edk2 architecture be
>> at least testable on QEMU/KVM with 5-level paging enabled.
>>
>>
>> *** Slide 13:
>>
>> (12) My comment is that the GUID-ed structure chain already starts at a
>> fixed GPA (the "AMD SEV option"). Ordering between GUID-ed structures is
>> irrelevant, so any TDX-specific structures should be eligible for
>> appending to, prepending to, or intermixing with, other (possibly
>> SEV-specific) structures. There need not be a separate entry point, just
>> different GUIDS.
>>
>> (13) Regarding "4G-0x20[0x10] is OVMF AP reset vector (used in OVMF
>> implementation)" -- I think this is a typo: this "AP reset vector" is
>> *not* used in OVMF. To my knowledge, it is a vestige from the UefiCpuPkg
>> reset vector. In OVMF, APs are booted via MpInitLib (in multiple
>> firmware phases), using INIT-SIPI-SIPI, and the reset vector for the
>> APs, posited through those IPIs, is prepared in low RAM.
>>
>>
>> *** Slides 14 through 16:
>>
>> I consider these TDVF firmware image internals, implementation details
>> -- do whatever you need to do, just don't interfere with existing
>> platforms / use cases. See my comment (10) above.
>>
>>
>> *** Slides 17-21:
>>
>> (14) Again, a very big difference from traditional OVMF: APs never enter
>> SEC in traditional OVMF. I assume this new functionality is part of
>> TdxStartupLib (from slide 18) -- will there be a Null instance of that?
>>
>> Last week I posted a 43-part patch series to edk2-devel, for separating
>> out the dynamic Xen enlightenments from the IA32, IA32X64, X64
>> platforms, in favor of the dedicated OvmfXen platform. TDX seems to
>> bring in incomparably more complications than Xen, and the OvmfPkg
>> maintainers have found even the Xen complications troublesome in the
>> long term.
>>
>> If I had had access to all this information when we first discussed "one
>> binary" on the mailing list, I'd have never agreed to "one binary". I'm
>> OK with attempting one firmware binary for "confidential computing", but
>> that "one platform" cannot be "OvmfPkgX64.dsc".
>>
>> Even if I make a comparison with just the "technology" (not the
>> remotely-attested deployment) of SEV and SEV-ES, as it is included in
>> "OvmfPkgX64.dsc", TDX is hugely more complicated and intrusive than
>> that. SEV proved possible to integrate into existing modules, into the
>> existing boot flow, maybe through the addition of some new drivers (such
>> as a new IOMMU protocol implementation, and some "clever" depexes).
>> But
>> we never had to restructure the FD layout, eliminate whole firmware
>> phases, or think about multiprocessing in the reset vector or the SEC
>> phase.
>>
>> In order to bring an example from the ARM world, please note that
>> platforms that use a PEI phase, and platforms that don't, are distinct
>> platforms. In ArmVirtPkg, two examples are ArmVirtQemu and
>> ArmVirtQemuKernel. The latter does not include the PEI Core.
>>
>>
>> *** Slides 22 through 34:
>>
>> (15) All these extra tasks and complications are perfectly fine, as long
>> as they exist peacefully *separately* from the traditional ("legacy")
>> OVMF platforms.
>>
>> Honestly, in the virtual world, picking your firmware binary is easy.
>> The approach here reminds me of a physical firmware binary that includes
>> everything possible from "edk2-platforms/Features/Intel", just so it can
>> be deployed to any physical board imaginable. That's not how Intel
>> builds physical firmware, right? We have "edk2-platforms/Platform/Intel"
>> and "edk2-platforms/Silicon/Intel" with many-many separate DSC files.
>>
>>
>> *** Slide 35-36: DXE phase
>>
>> (16) "Some DXE Drivers not allowed to load/start in Td guest -- Network
>> stack, RNG, ..."
>>
>> Same comment as (several times) above. The Linuxboot project is a good
>> example for eliminating cruft from DXEFV (in fact, for eliminating most
>> of the DXE phase). In a TDX environment, why include drivers in the
>> firmware binary that are never used? Meanwhile, DXEFV in OVMF grows by
>> a
>> MB every 1.5 years or so. Again, remove these drivers from the DSC/FDF
>> then, and it needs to be a separate platform.
>>
>> (17) "Other DXE Phase drivers -- [...] AcpiPlatformDxe"
>>
>> I'm not sure what this section is supposed to mean. Other DXE phase
>> drivers included, or excluded? Without AcpiPlatformDxe, the guest OS
>> will not see QEMU's ACPI content, and will almost certainly malfunction.
>>
>> ... Back from slide 48: ignore this for now, I'll comment in more detail
>> later.
>>
>>
>> *** Slide 37: DXE Core
>>
>> (18) says "SMM is not supported in Td guest" -- how is the variable
>> store protected from direct hardware (pflash) access from the guest OS?
>> Without SMM, the guest OS need not go through gRT->SetVariable() to
>> update authenticated non-volatile UEFI variables, and that undermines
>> Secure Boot.
>>
>> Note that, while SEV-ES has the same limitation wrt. SMM, the
>> "OvmfPkg/AmdSev/AmdSevX64.dsc" platform doesn't even include the
>> Secure
>> Boot firmware feature. For another example, the OVMF firmware binary in
>> RHEL that's going to support SEV-ES is such a build of "OvmfPkgX64.dsc"
>> that does not include the Secure Boot feature either.
>>
>> But in this TDX slide deck, Secure Boot certificates are embedded in the
>> CFV (configuration firmware volume) -- see slide 11 and slide 16 --,
>> which suggests that this platform does want secure boot.
>>
>> ... Back from slide 48: I'm going to make *additional* comments on this,
>> when I'm at slide 48, too.
>>
>> The rest of this slide (slide 37) looks reasonable (generic DXE Core
>> changes -- possibly PI spec changes too).
>>
>>
>> *** Slides 38 through 39:
>>
>> These seem reasonable (TdxDxe assumes some responsibilities of
>> OvmfPkg/PlatformPei)
>>
>>
>> *** Slides 40 through 42:
>>
>> *If* you really can implement TDX support for the IOMMU driver *this*
>> surgically, then I'm OK with it. The general logic in the IOMMU driver
>> was truly difficult to write, and I'd be seriously concerned if those
>> parts would have to be modified. Customizing just the page
>> encryption/decryption primitives for TDX vs. SEV is OK.
>>
>>
>> *** Slides 43 through 47:
>>
>> (19) Slide 46 and slide 47 are almost identical. Please consolidate them
>> into a single slide.
>>
>> (20) the TPM2 infrastructure in edk2 is baroque (over-engineered), in my
>> opinion. It has so many layers that I can never keep them in mind. When
>> we added TPM support to OVMF, I required commit messages that would
>> help
>> us recall the layering. In particular, please refer to commit
>> 0c0a50d6b3ff ("OvmfPkg: include Tcg2Dxe module", 2018-03-09). Here's an
>> excerpt:
>>
>>            TPM 2 consumer driver
>>                     |
>>                     v
>>       Tpm2DeviceLib class: Tpm2DeviceLibTcg2 instance
>>                     |
>>                     v
>>              TCG2 protocol interface
>>                     |
>>                     v
>>       TCG2 protocol provider: Tcg2Dxe.inf driver
>>                     |
>>                     v
>>       Tpm2DeviceLib class: Tpm2DeviceLibRouter instance
>>                     |
>>                     v
>>          NULL class: Tpm2InstanceLibDTpm instance
>>             (via earlier registration)
>>                     |
>>                     v
>>            TPM2 chip (actual hardware)
>>
>> The slide deck says that EFI_TD_PROTOCOL is supposed to reuse the
>> EFI_TCG2_PROTOCOL definition. If that's the case, then why don't we push
>> the TDX specifics (more or less: the replacement of PCRs with RTMR) down
>> to the lowest possible level?
>>
>> Can we have "Tpm2InstanceLibTdxRtmr", plugged into the same Tcg2Dxe.inf
>> driver?
>>
>> If not, can we have a new TdTcg2Dxe.inf driver, but make it so that it
>> install the same protocol as before (EFI_TCG2_PROTOCOL -- same old
>> protocol GUID)? Then DxeTpmMeasurementLib doesn't have to change.
>>
>> As long as there is *at most* one EFI_TCG2_PROTOCOL instance published
>> in the protocol database, DxeTpmMeasurementLib should be fine. In SEV*
>> guests, the standard Tcg2Dxe driver provides that protocol. In TDX
>> guests, TdTcg2Dxe.inf should provide the protocol. Arbitration between
>> the two can be implemented with the pattern seen in the following
>> commits:
>>
>>  1  05db0948cc60 EmbeddedPkg: introduce EDKII Platform Has ACPI GUID
>>  2  786f476323a6 EmbeddedPkg: introduce PlatformHasAcpiLib
>>  3  65a69b214840 EmbeddedPkg: introduce EDKII Platform Has Device Tree
>>                  GUID
>>  4  2558bfe3e907 ArmVirtPkg: add PlatformHasAcpiDtDxe
>>
>> The basic idea is that Tcg2Dxe can have a depex on a new "running in
>> SEV" protocol GUID, and TdTcg2Dxe can have a depex on a new "running in
>> TDX" protocol GUID. A separate platform driver can install the proper
>> GUID -- possibly *neither* of those GUIDs.
>>
>> And, we don't have to change the depex section of
>> "SecurityPkg/Tcg/Tcg2Dxe/Tcg2Dxe.inf" for this; we can implement a
>> library instance with an empty constructor, but a non-empty depex, and
>> then hook this lib instance into Tcg2Dxe.inf via module scope NULL lib
>> class override in the DSC file. Basically we could forcibly restrict
>> Tcg2Dxe's DEPEX by making it inherit the new DEPEX from the library.
>>
>>
>> *** Slide 48: DXE Phase -- Other Modules
>>
>> Regarding IncompatiblePciDeviceSupportDxe: the proposed update sounds
>> plausible and simple enough.
>>
>> (21) "AcpiPlatformDxe: Support for MADT/ACPI addition to report Td
>> Mailbox entry"
>>
>> Firmware-owned tables must not be installed from this driver.
>>
>> Please refer to my "Xen removal" patch set again, for
>> <https://bugzilla.tianocore.org/show_bug.cgi?id=2122>, which I mention
>> above in point (14). As part of the Xen removal, the AcpiPlatformDxe
>> driver in OvmfPkg is significantly trimmed: all unused (dead) cruft is
>> removed, including any ACPI table templates that are built into the
>> firmware.
>>
>> OvmfPkg/AcpiPlatformDxe is responsible *solely* for implementing the
>> client side of the QEMU ACPI linker/loader.
>>
>> If you need to prepare & install different ACPI tables, please do it
>> elsewhere, in another DXE driver. A bunch of other firmware modules do
>> that (NFIT, IBFT, BGRT, ...).
>>
>> For example, the OvmfPkg/TdxDxe DXE_DRIVER is supposed to be launched
>> early in the DXE phase, via APRIORI section -- please consider
>> registering a protocol notify in that driver, for
>> EFI_ACPI_TABLE_PROTOCOL, and when it becomes available, install
>> whatever
>> *extra* tables you need.
>>
>> Note that if you need to *customize* an ACPI table that QEMU already
>> provides, then you will have to modify the ACPI generator on the QEMU
>> side. It is a design tenet between QEMU and OVMF that OVMF include no
>> business logic for either parsing or fixing up ACPI tables that QEMU
>> provides. AcpiPlatformDxe contains the minimum (which is already a whole
>> lot, unfortunately) that's necessary for implementing the QEMU ACPI
>> linker/loader client in the UEFI environment.
>>
>> The slide deck mentions MADT, which is also known as the "APIC" table --
>> and indeed, QEMU does provide that. (See acpi_build_madt()
>> [hw/i386/acpi-common.c].) So if TDX needs MADT customizations, that
>> should go into QEMU.
>>
>> (22) EmuVariableFvbRuntimeDxe
>>
>> Ouch, this is an unpleasant surprise.
>>
>> First, if you know for a fact that pflash is not part of the *board* in
>> any TDX setup, then pulling
>>
>>   OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf
>>
>> into the firmware platform is useless, as it is mutually exclusive with
>>
>>   OvmfPkg/EmuVariableFvbRuntimeDxe/Fvb.inf
>>
>> (via dynamic means -- a dynamic PCD).
>>
>> Note that the FDF file places QemuFlashFvbServicesRuntimeDxe in APRIORI
>> DXE when SMM_REQUIRE is FALSE. This driver checks for pflash presence,
>> and lets EmuVariableFvbRuntimeDxe perform its in-RAM flash emulation
>> only in case pflash is not found.
>>
>> So this is again in favor of a separate platform -- if we know pflash is
>> never part of the board, then QemuFlashFvbServicesRuntimeDxe is never
>> needed, but you cannot remove it from the traditional DSC/FDF files.
>>
>> Second, EmuVariableFvbRuntimeDxe consumes the PlatformFvbLib class,
>> for
>> the PlatformFvbDataWritten() API (among other things). This lib class is
>> implemented by two instances in OvmfPkg, PlatformFvbLibNull and
>> EmuVariableFvbLib. The latter instance allows Platform BDS to hook an
>> event (for signaling) via "PcdEmuVariableEvent" into the
>> EmuVariableFvbRuntimeDxe driver.
>>
>> In old (very old) QEMU board configurations, namely those without
>> pflash, this (mis)feature is used by OVMF's PlatformBootManagerLib to
>> write out all variables to the EFI system partition in a regular file
>> called \NvVars, with the help of NvVarsFileLib, whenever
>> EmuVariableFvbRuntimeDxe writes out an emulated "flash" block. For this
>> purpose, the traditional OVMF DSC files link EmuVariableFvbLib into
>> EmuVariableFvbRuntimeDxe.
>>
>> But it counts as an absolute disaster nowadays, and should not be
>> revived in any platform. If you don't have pflash in TDX guests, just
>> accept that you won't have non-volatile variables. And link
>> PlatformFvbLibNull into EmuVariableFvbRuntimeDxe. You're going to need
>> a
>> separate PlatformBootManagerLib instance anyway.
>>
>> (We should have removed EmuVariableFvbRuntimeDxe a long time ago
>> from
>> the traditional OVMF platforms, i.e. made pflash a hard requirement,
>> even when SMM is not built into the platform -- but whenever I tried
>> that, Jordan always shot me down.)
>>
>> My point is: using EmuVariableFvbRuntimeDxe in the TDX platform may be
>> defensible per se, but we must be very clear that it will never provide
>> a standards-conformant service for non-volatile UEFI variables, and we
>> must keep as much of the \NvVars mess out of EmuVariableFvbRuntimeDxe
>> as
>> possible. This will require a separate PlatformBootManagerLib instance
>> for TDX anyway (or maybe share PlatformBootManagerLibGrub with
>> "OvmfPkg/AmdSev/AmdSevX64.dsc").
>>
>> Apart from the volatility aspect, let's assume we have this in-RAM
>> emulated "flash device", storing authenticated UEFI variables for Secure
>> Boot purposes. And we don't have SMM.
>>
>> What protects this in-RAM variable store from tampering by the guest OS?
>> It's all guest RAM only, after all. What provides the privilege barrier
>> between the guest firmware and the guest OS?
>>
>>
>> *** Slide 50: Library
>>
>> (23) Should we introduce Null instances for all (or most) new lib
>> classes here? Code size is a concern (static linking). If we extend a
>> common OvmfPkg module with new hook points, it's one thing to return
>> from that hook point early *dynamically*, but it's even better (given
>> separate platforms) to allow the traditional platform firmware to use a
>> Null lib instance, to cut out all the dead code statically.
>>
>>
>> *** Slides 51 through 52
>>
>> Seems OK.
>>
>>
>> *** Slide 53:
>>
>> (24) It might be worth noting that BaseIoLibIntrinsic already has some
>> SEV enlightenment, as the FIFO IO port operations (which normally use
>> the REP prefix) are not handled on SEV. I don't have an immediate idea
>> why this might matter, we should just minimize code duplication if
>> possible.
>>
>>
>> *** Slides 54-56:
>>
>> No  comments, this stuff seems reasonable.
>>
>>
>> *** Slide 57: MpInitLib
>>
>> I don't know enough to give a summary judgement.
>>
>>
>> All in all, I see the controversial / messy parts in the platform
>> bringup, and how all that differs from the traditional ("legacy") OVMF
>> platforms. I admit I *may* be biased in favor of SEV, possibly because
>> SEV landed first -- if you find signs of such a bias in my comments,
>> please don't hesitate to debunk those points. Yet my general impression
>> is that the early bringup stuff is significantly different from
>> everything before, and because of this, a separate platform is
>> justified.
>>
>> Definitely separate from the traditional OVMF IA32, IA32X64, and X64
>> platforms, and *possibly* separate from the "remote attestation"
>> AmdSevX64.dsc platform. I would approach the TDX feature-set in complete
>> isolation (exactly how Intel commenced the work, if I understand
>> correctly), modulo obviously shareable / reusable parts, and then slowly
>> & gradually work on extracting / refactoring commonalities.
>>
>> (But, given my stance on Xen for example, I could disagree even with the
>> latter, retroactive kind of unification -- it all boils down to shared
>> developer and user base. Component sharing should reflect the community
>> structure, otherwise maintenance will be a nightmare.)
>>
>> Thanks
>> Laszlo
>>
>>
>>
>> 
>>
> 

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Yao, Jiewen]

thank you Laszlo. Your feedback is received.
I am waiting for comment from other people. 

thank you!
Yao, Jiewen


> 在 2021年6月4日，下午6:11，Laszlo Ersek <lersek@redhat.com> 写道：
> 
> On 06/04/21 01:19, Yao, Jiewen wrote:
>> Hi Laszlo.
>> 
>> To clarify your "one binary" feedback below, do you mean you suggest A) create a separate DSC (for example OvmfPkg/ConfidentialComputing.dsc) for a full solution including AMD SEC + Intel TDX + NonConfidentialComputing?
>> Or B) to create a standalone DSC for Intel TDX (for example, create a OvmfPkg/IntelTdx/IntelTdxXS64.dsc) ?
>> 
>> To me, A) does not change too much, we just create another DSC file - that is it.
>> Then the original OvmfPkgX64.dsc will only be used for POC/Testing purpose. It does not provide any security guarantee.
>> (The threat model is: we don't trust VMM. Without attestation, you don't know if VMM modified the OVMF.)
>> 
>> I don't know how "simply" it means. To enable TDX to make it work is not a simple work.
>> Some architecture changes are mandatory, such as reset vector, IO/MMIO access, #VE handler, IOMMU based shared memory access, etc. I think AMD SEV already did those.
> 
> I mean option (B). Create a completely separate DSC+FDF for Intel TDX.
> 
> In my mind, there are two (very high level) stages for developing the
> "Confidential Computing with TDX" feature in edk2.
> 
> Stage 1: allow a guest to run in a TDX domain. "Guest owner" and "Cloud
> owner" are *not* separate concepts in this stage.
> 
> Stage 2: enable such a guest to be deployed remotely to an untrusted
> cloud, and ensure its integrity via remote attestation.
> 
> 
> Stage 1 is *hugely different* between AMD SEV* technologies and Intel
> TDX. That's why we need, in my opinion, a separate DSC+FDF for Intel TDX
> right from the start. This does not necessarily mean that we need to
> duplicate every single module (library, PEIM, DXE driver, etc) for Intel
> TDX. Wherever it makes sense, and the changes are not very intrusive or
> wasteful (considering binary code that becomes "dead" on in a TDX
> guest), we can modify (extend) existent modules in-place.
> 
> Stage 1 is complete for AMD SEV and AMD SEV-ES. AMD SEV-SNP is in
> progress. These AMD SEV* technologies have been possible to integrate
> (thus far) into the existing "OvmfPkg/OvmfPkgX64.dsc" platform. But
> Intel TDX is very different from that, even in Stage 1.
> 
> 
> Stage 2 is far out in the future, for Intel TDX. I have no idea about
> it, but whatever it's going to look like, it will be based on Stage 1.
> 
> The "OvmfPkg/AmdSev/AmdSevX64.dsc" platform is *one approach* for
> implementing Stage 2. And this platform utilizes AMD SEV* technologies
> only (thus far). *If* and *how much* the approach of
> "OvmfPkg/AmdSev/AmdSevX64.dsc" will apply to Intel TDX -- once Stage 1
> of Intel TDX is complete --, I cannot predict.
> 
> 
> The underlying physical hardware features are completely different
> between AMD SEV* and Intel TDX, as much as I can tell. It makes zero
> sense to me to start from a unified perspective, and shoehorn everything
> possible (and impossible) into a common blob and framework. That
> approach has never *ever* worked for me, not even when I started working
> on the virtio drivers for OVMF 9 years ago. I extracted VirtioLib only
> when I worked on the second virtio driver -- that is, when I was about
> to have *working code* for two *distinct* virtio devices, and it was
> possible to identify commonalities between the drivers, and to extract
> those commonalities. The fact that I knew, in advance, that my "end
> goal" was the same with these devices, namely to "boot from them", made
> no difference whatsoever. I still I had to start implementing them in
> separate sandboxes. Soon enough, VirtioLib emerged, and later
> VIRTIO_DEVICE_PROTOCOL emerged even.
> 
> I'm 100% incapable of dealing with a top-down approach here. Only
> bottom-up works for me.
> 
> 
> Most importantly, the OvmfPkgIa32, OvmfPkgIa32X64, OvmfPkgX64 platforms
> must be kept regression-free, and preferably their complexity should be
> kept manageable for maintenance too. These platforms are *entirely
> irrelevant* for Stage 2 (regardless of underlying security technology).
> They *happen* to be relevant for Stage 1 of AMD SEV*, purely because SEV
> proved possible to integrate into them, in very small, well isolated,
> surgical advances, without upsetting everything. But I can tell upfront
> that Intel TDX is way more intrusive than anything I've seen thus far in
> AMD SEV*. So I want Intel TDX to exist in a brand new platform, even as
> Stage 1. And, to reiterate, just because Confidential Computing is the
> new hot thing, the use cases for OvmfPkgIa32, OvmfPkgIa32X64, OvmfPkgX64
> do not disappear. Regressing them, or making them unmaintainable due to
> skyrocketing complexity, is not acceptable.
> 
> Thanks
> Laszlo
> 
>> 
>> ===================
>> My point is that the "one binary" that the slide deck refers to (i.e.,
>> OvmfPkgX64.dsc) might prove OK for utilizing the Intel TDX *technology*
>> in itself. Simply enabling OVMF + a guest OS to boot in a TDX domain.
>> 
>> But "OvmfPkgX64.dsc" is *not* the "one binary" that is suitable for
>> remote attestation, which has a much broader scope, involving multiple
>> computers, networking, deployment, guest-owner/host-owner separation,
>> whatever. For the latter, we needed a separate platform anyway, even
>> with only SEV in mind; that's why "OvmfPkg/AmdSev/AmdSevX64.dsc" exists.
>> ===================
>> 
>> Thank you
>> Yao Jiewen
>> 
>>> -----Original Message-----
>>> From: rfc@edk2.groups.io <rfc@edk2.groups.io> On Behalf Of Laszlo Ersek
>>> Sent: Friday, June 4, 2021 12:12 AM
>>> To: Yao, Jiewen <jiewen.yao@intel.com>; rfc@edk2.groups.io;
>>> devel@edk2.groups.io
>>> Cc: jejb@linux.ibm.com; Brijesh Singh <brijesh.singh@amd.com>; Tom
>>> Lendacky <thomas.lendacky@amd.com>; erdemaktas@google.com;
>>> cho@microsoft.com; bret.barkelew@microsoft.com; Jon Lange
>>> <jlange@microsoft.com>; Karen Noel <knoel@redhat.com>; Paolo Bonzini
>>> <pbonzini@redhat.com>; Nathaniel McCallum <npmccallum@redhat.com>;
>>> Dr. David Alan Gilbert <dgilbert@redhat.com>; Ademar de Souza Reis Jr.
>>> <areis@redhat.com>
>>> Subject: Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF
>>> 
>>>> On 06/03/21 15:51, Yao, Jiewen wrote:
>>>>> Hi, All
>>>>> We plan to do a design review for TDVF in OVMF package.
>>>>> 
>>>>> 
>>>>> The TDVF Design slides for TinaoCore Design Review Meeting (Jun 11) is
>>>>> now available in blow link:
>>>>> https://edk2.groups.io/g/devel/files/Designs/2021/0611.
>>>>> 
>>>>> The Bugzilla is https://bugzilla.tianocore.org/show_bug.cgi?id=3429
>>>>> 
>>>>> 
>>>>> 
>>>>> You can have an offline review first. You comments will be warmly
>>>>> welcomed and we will continuously update the slides based on the
>>>>> feedbacks.
>>> 
>>> Resending my earlier comments in this mailing list thread, with the
>>> feedback inserted at the proper spots that has been given in the
>>> off-list thread since then:
>>> 
>>> 
>>> *** Slides 4, 6, 7: the "one binary requirement".
>>> 
>>> (1) The presentation refers to "OvmfPkgX64.dsc" as "the one" on slide#4,
>>> but then the explanation for the requirement, given on slide 7, speaks
>>> about "common attestation interface".
>>> 
>>> I think we have a misunderstanding here. The "OvmfPkgX64.dsc" platform
>>> indeed contains SEV, SEV-ES, and (in the future, will contain) SEV-SNP
>>> support. In that sense, adding TDX support to the same platform should
>>> be (hopefully) possible, at the cost of ugly gymnastics in the reset
>>> vector.
>>> 
>>> But "OvmfPkgX64.dsc" is *already* different from the remotely attested
>>> OVMF platform, namely "OvmfPkg/AmdSev/AmdSevX64.dsc".
>>> 
>>> The latter has some additional modules (secret PEIM and DXE driver), it
>>> has the Grub binary built in, and -- probably most importantly -- it
>>> trusts host-originated information less than "OvmfPkgX64.dsc".
>>> 
>>> For example, "OvmfPkg/AmdSev/AmdSevX64.dsc" has a dedicated
>>> PlatformBootManagerLib instance, one that ignores the non-volatile UEFI
>>> variables Boot#### and BootOrder, and ignores (thus far) the fw_cfg
>>> originated kernel/initrd/cmdline as well.
>>> 
>>> It remains an "area of research" to see what else should be removed from
>>> the traditional host-guest integration (which integration is usually
>>> desirable for management and convenience), in the remotely-attested boot
>>> scenario. See e.g.
>>> <https://bugzilla.tianocore.org/show_bug.cgi?id=3180>.
>>> 
>>> My point is that the "one binary" that the slide deck refers to (i.e.,
>>> OvmfPkgX64.dsc) might prove OK for utilizing the Intel TDX *technology*
>>> in itself. Simply enabling OVMF + a guest OS to boot in a TDX domain.
>>> 
>>> But "OvmfPkgX64.dsc" is *not* the "one binary" that is suitable for
>>> remote attestation, which has a much broader scope, involving multiple
>>> computers, networking, deployment, guest-owner/host-owner separation,
>>> whatever. For the latter, we needed a separate platform anyway, even
>>> with only SEV in mind; that's why "OvmfPkg/AmdSev/AmdSevX64.dsc"
>>> exists.
>>> 
>>> 
>>> *** Slides 8-9: general boot flow -- TDVF; TDVF Flow
>>> 
>>> I'm likely missing a big bunch of background here, so just a few
>>> questions:
>>> 
>>> (2) Not sure what RTMR is, but it's associated with "Enable TrustedBoot"
>>> -- so is a virtual TPM a hard requirement?
>>> 
>>> ... Back from slide 10: "TCG measurement and event log framework w/o
>>> TPM" -- that's curious.
>>> 
>>> [response from Dave Gilbert:]
>>>> My reading of this is that the RTMR (and another set of similar
>>>> registers) are a TDX thing that is like the PCRs from a TPM but
>>>> without the rest of the TPM features;  so you can do the one-way
>>>> measurement into the RTMRs just like you do into a TPM PCR, and the
>>>> measurements pop out somewhere in the TDX quote.  Just like a TPM you
>>>> need the event log to make any sense of how the final hashed value
>>>> supposedly got to where it did.
>>> 
>>> [response from Erdem Aktas:]
>>>> +1 to David on this. TDX provides 2 kinds of measurement registers:
>>>> MRTDs and RTMRs
>>>> 
>>> (https://software.intel.com/content/dam/develop/external/us/en/docume
>>> nts/tdx-module-1eas-v0.85.039.pdf
>>>> section 10.1.2) . MRTDs are build-time measurement registers which are
>>>> updated when TDX is being created. Once TDX is finalized (before the
>>>> first run), the MRTDs are finalized and cannot be updated anymore. On
>>>> the other hand, while the TD is running, TD can extend RTMRs through
>>>> TDCALLs which will provide TPM PCR kind of capabilities.
>>> 
>>> ... Back from slide 43: feel free to skip this now; I will comment in
>>> more detail below.
>>> 
>>> (3) Prepare AcpiTable -- OVMF fetches ACPI tables from QEMU; is this a
>>> new (firmware originated) table that is installed in addition, or does
>>> it replace QEMU's tables?
>>> 
>>> ... Ignore for now, will comment on the MADT stuff later.
>>> 
>>> (4) Does DMA management mean a different IOMMU protocol? That is
>>> going
>>> to conflict with the SEV IOMMU protocol. Depexes in OVMF expect one or
>>> zero IOMMU protocols to be present.
>>> 
>>> ... Back from slide 40: feel free to skip this now; I'll comment on this
>>> separately, below.
>>> 
>>> (5) Enumerate VirtIO -- virtio enumeration is PCI based on x86. But I
>>> see no mention of PCI. If you mean VirtioMmioDeviceLib, that's no good,
>>> because it does not support virtio-1.0, only virtio-0.9.5.
>>> 
>>> ... Back from slide 42: I got my answer to this on slide 42, so don't
>>> worry about this point.
>>> 
>>> (6) The PEI phase is skipped as a whole. I don't see how that can be
>>> reasonably brought together with either "OvmfPkgX64.dsc" or
>>> "OvmfPkg/AmdSev/AmdSevX64.dsc". I guess you can always modify SEC to
>>> jump into DXE directly, but then why keep the PEI core and a bunch of
>>> PEIMs in the firmware binary?
>>> 
>>> Also touched on by slide 9, TDVF Flow -- PEI is eliminated but SEC
>>> becomes more heavy-weight.
>>> 
>>> Wouldn't this deserve a dedicated, separate platform DSC? The
>>> 8-bit/32-bit branching at the front of the reset vector is a smaller
>>> complication in comparison.
>>> 
>>> Slide 6 references the mailing list archive:
>>> 
>>>  https://edk2.groups.io/g/devel/topic/81969494#74319
>>> 
>>> and in that message, I wrote:
>>> 
>>>    I'm doubtful that this is a unique problem ("just fix the reset
>>>    vector") the likes of which will supposedly never return during the
>>>    integration of SEV and TDX
>>> 
>>> See also:
>>> 
>>>  https://listman.redhat.com/archives/edk2-devel-archive/2021-
>>> April/msg00784.html
>>> 
>>> where I said:
>>> 
>>>    It's not lost on me that we're talking about ~3 instructions.
>>> 
>>>    Let's keep a close eye on further "polymorphisms" that would require
>>>    hacks.
>>> 
>>> The first 9 slides in the presentation introduce much-much more
>>> intrusive problems than the "polymorphism" of the reset vector. Would I
>>> be correct to say that my concern in the above messages was right? I
>>> think I was only given a fraction of the necessary information when I
>>> was asked "do you agree 'one binary' is viable".
>>> 
>>> [response from Erdem Aktas:]
>>>> Let's not worry about this for now. We want the one binary solution
>>>> for practical reasons and also for simplicity.  In the end, we want to
>>>> do what is right and good for everyone.
>>>> Those are legit concerns and I think what Intel is trying to do (sorry
>>>> for mind reading) is to discuss all those concerns and questions to
>>>> make the right decision. I really appreciate their effort on preparing
>>>> those slides and bringing it to the community to review.
>>>> 
>>>> I will also read your comments more carefully and provide my thoughts
>>>> on them.
>>>> Sorry for being a little slow on this.
>>> 
>>> 
>>> *** Slide 10 -- Key impact to firmware
>>> 
>>> (7) "CPUs are left running in long mode after exiting firmware" -- what
>>> kind of "pen" are we talking about? Does a HLT loop still work?
>>> 
>>> (8) "I/O, MMIO, MSR accesses are different" -- those are implemented by
>>> low-level libraries in edk2; how can they be configured dynamically?
>>> 
>>> ... Back from slide 53: I'll comment on slide 53 separately; ignore
>>> this.
>>> 
>>> 
>>> *** Slide 11 -- TDVF Image (1)
>>> 
>>> (9) CFV -- Configuration Firmware Volume (VarStore.fdf.inc),
>>> containing SB keys -- how is this firmware volume populated (at build
>>> time)? Is this a hexdump?
>>> 
>>> ... Back from slide 16: it seems like CFV is a raw hexdump indeed; how
>>> is that managed when keys change (at build time)?
>>> 
>>> (10) This slide (slide 11) basically describes an intrusive
>>> reorganization of "OvmfPkgX64.fdf". I don't think I can agree to that.
>>> While confidential computing is important, it is not relevant for many
>>> users. Even if we don't cause outright regressions for existent setups,
>>> the maintenance cost of the traditional OVMF platform will skyrocket.
>>> 
>>> The big bunch of areas that SEV-ES introduced to MEMFD is already a big
>>> complication. I'd feel much better if we could isolate all that to a
>>> dedicated "remote attested boot" firmware platform, and not risk the
>>> functionality and maintenance of the traditional platform. I think this
>>> ties in with my comment (1).
>>> 
>>> For example, seeing a configuration firmware volume (CFV) with secure
>>> boot keys embedded, in the "usual" FDF, will confuse lots of people, me
>>> included. In the traditional OVMF use case, we use a different method:
>>> namely OvmfPkg/EnrollDefaultKeys, for "priming" a variable store
>>> template, in the build environment.
>>> 
>>> Edk2 (and PI and UEFI) are definitely flexible enough for accommodating
>>> TDX, but the existent, traditional OVMF platforms are a bad fit. In my
>>> opinion.
>>> 
>>> 
>>> *** Slide 12: TDVF Image (2)
>>> 
>>> (11) "Page table should support both 4-level and 5-level page table"
>>> 
>>> As a general development strategy, I would suggest building TDX support
>>> in small, well-isolated layers. 5-level paging is not enabled (has never
>>> been tested, to my knowledge) with OVMF on QEMU/KVM, regardless of
>>> confidential computing, for starters. If 5-level paging is a strict
>>> requirement for TDX, then it arguably needs to be implemented
>>> independently of TDX, at first. So that the common edk2 architecture be
>>> at least testable on QEMU/KVM with 5-level paging enabled.
>>> 
>>> 
>>> *** Slide 13:
>>> 
>>> (12) My comment is that the GUID-ed structure chain already starts at a
>>> fixed GPA (the "AMD SEV option"). Ordering between GUID-ed structures is
>>> irrelevant, so any TDX-specific structures should be eligible for
>>> appending to, prepending to, or intermixing with, other (possibly
>>> SEV-specific) structures. There need not be a separate entry point, just
>>> different GUIDS.
>>> 
>>> (13) Regarding "4G-0x20[0x10] is OVMF AP reset vector (used in OVMF
>>> implementation)" -- I think this is a typo: this "AP reset vector" is
>>> *not* used in OVMF. To my knowledge, it is a vestige from the UefiCpuPkg
>>> reset vector. In OVMF, APs are booted via MpInitLib (in multiple
>>> firmware phases), using INIT-SIPI-SIPI, and the reset vector for the
>>> APs, posited through those IPIs, is prepared in low RAM.
>>> 
>>> 
>>> *** Slides 14 through 16:
>>> 
>>> I consider these TDVF firmware image internals, implementation details
>>> -- do whatever you need to do, just don't interfere with existing
>>> platforms / use cases. See my comment (10) above.
>>> 
>>> 
>>> *** Slides 17-21:
>>> 
>>> (14) Again, a very big difference from traditional OVMF: APs never enter
>>> SEC in traditional OVMF. I assume this new functionality is part of
>>> TdxStartupLib (from slide 18) -- will there be a Null instance of that?
>>> 
>>> Last week I posted a 43-part patch series to edk2-devel, for separating
>>> out the dynamic Xen enlightenments from the IA32, IA32X64, X64
>>> platforms, in favor of the dedicated OvmfXen platform. TDX seems to
>>> bring in incomparably more complications than Xen, and the OvmfPkg
>>> maintainers have found even the Xen complications troublesome in the
>>> long term.
>>> 
>>> If I had had access to all this information when we first discussed "one
>>> binary" on the mailing list, I'd have never agreed to "one binary". I'm
>>> OK with attempting one firmware binary for "confidential computing", but
>>> that "one platform" cannot be "OvmfPkgX64.dsc".
>>> 
>>> Even if I make a comparison with just the "technology" (not the
>>> remotely-attested deployment) of SEV and SEV-ES, as it is included in
>>> "OvmfPkgX64.dsc", TDX is hugely more complicated and intrusive than
>>> that. SEV proved possible to integrate into existing modules, into the
>>> existing boot flow, maybe through the addition of some new drivers (such
>>> as a new IOMMU protocol implementation, and some "clever" depexes).
>>> But
>>> we never had to restructure the FD layout, eliminate whole firmware
>>> phases, or think about multiprocessing in the reset vector or the SEC
>>> phase.
>>> 
>>> In order to bring an example from the ARM world, please note that
>>> platforms that use a PEI phase, and platforms that don't, are distinct
>>> platforms. In ArmVirtPkg, two examples are ArmVirtQemu and
>>> ArmVirtQemuKernel. The latter does not include the PEI Core.
>>> 
>>> 
>>> *** Slides 22 through 34:
>>> 
>>> (15) All these extra tasks and complications are perfectly fine, as long
>>> as they exist peacefully *separately* from the traditional ("legacy")
>>> OVMF platforms.
>>> 
>>> Honestly, in the virtual world, picking your firmware binary is easy.
>>> The approach here reminds me of a physical firmware binary that includes
>>> everything possible from "edk2-platforms/Features/Intel", just so it can
>>> be deployed to any physical board imaginable. That's not how Intel
>>> builds physical firmware, right? We have "edk2-platforms/Platform/Intel"
>>> and "edk2-platforms/Silicon/Intel" with many-many separate DSC files.
>>> 
>>> 
>>> *** Slide 35-36: DXE phase
>>> 
>>> (16) "Some DXE Drivers not allowed to load/start in Td guest -- Network
>>> stack, RNG, ..."
>>> 
>>> Same comment as (several times) above. The Linuxboot project is a good
>>> example for eliminating cruft from DXEFV (in fact, for eliminating most
>>> of the DXE phase). In a TDX environment, why include drivers in the
>>> firmware binary that are never used? Meanwhile, DXEFV in OVMF grows by
>>> a
>>> MB every 1.5 years or so. Again, remove these drivers from the DSC/FDF
>>> then, and it needs to be a separate platform.
>>> 
>>> (17) "Other DXE Phase drivers -- [...] AcpiPlatformDxe"
>>> 
>>> I'm not sure what this section is supposed to mean. Other DXE phase
>>> drivers included, or excluded? Without AcpiPlatformDxe, the guest OS
>>> will not see QEMU's ACPI content, and will almost certainly malfunction.
>>> 
>>> ... Back from slide 48: ignore this for now, I'll comment in more detail
>>> later.
>>> 
>>> 
>>> *** Slide 37: DXE Core
>>> 
>>> (18) says "SMM is not supported in Td guest" -- how is the variable
>>> store protected from direct hardware (pflash) access from the guest OS?
>>> Without SMM, the guest OS need not go through gRT->SetVariable() to
>>> update authenticated non-volatile UEFI variables, and that undermines
>>> Secure Boot.
>>> 
>>> Note that, while SEV-ES has the same limitation wrt. SMM, the
>>> "OvmfPkg/AmdSev/AmdSevX64.dsc" platform doesn't even include the
>>> Secure
>>> Boot firmware feature. For another example, the OVMF firmware binary in
>>> RHEL that's going to support SEV-ES is such a build of "OvmfPkgX64.dsc"
>>> that does not include the Secure Boot feature either.
>>> 
>>> But in this TDX slide deck, Secure Boot certificates are embedded in the
>>> CFV (configuration firmware volume) -- see slide 11 and slide 16 --,
>>> which suggests that this platform does want secure boot.
>>> 
>>> ... Back from slide 48: I'm going to make *additional* comments on this,
>>> when I'm at slide 48, too.
>>> 
>>> The rest of this slide (slide 37) looks reasonable (generic DXE Core
>>> changes -- possibly PI spec changes too).
>>> 
>>> 
>>> *** Slides 38 through 39:
>>> 
>>> These seem reasonable (TdxDxe assumes some responsibilities of
>>> OvmfPkg/PlatformPei)
>>> 
>>> 
>>> *** Slides 40 through 42:
>>> 
>>> *If* you really can implement TDX support for the IOMMU driver *this*
>>> surgically, then I'm OK with it. The general logic in the IOMMU driver
>>> was truly difficult to write, and I'd be seriously concerned if those
>>> parts would have to be modified. Customizing just the page
>>> encryption/decryption primitives for TDX vs. SEV is OK.
>>> 
>>> 
>>> *** Slides 43 through 47:
>>> 
>>> (19) Slide 46 and slide 47 are almost identical. Please consolidate them
>>> into a single slide.
>>> 
>>> (20) the TPM2 infrastructure in edk2 is baroque (over-engineered), in my
>>> opinion. It has so many layers that I can never keep them in mind. When
>>> we added TPM support to OVMF, I required commit messages that would
>>> help
>>> us recall the layering. In particular, please refer to commit
>>> 0c0a50d6b3ff ("OvmfPkg: include Tcg2Dxe module", 2018-03-09). Here's an
>>> excerpt:
>>> 
>>>           TPM 2 consumer driver
>>>                    |
>>>                    v
>>>      Tpm2DeviceLib class: Tpm2DeviceLibTcg2 instance
>>>                    |
>>>                    v
>>>             TCG2 protocol interface
>>>                    |
>>>                    v
>>>      TCG2 protocol provider: Tcg2Dxe.inf driver
>>>                    |
>>>                    v
>>>      Tpm2DeviceLib class: Tpm2DeviceLibRouter instance
>>>                    |
>>>                    v
>>>         NULL class: Tpm2InstanceLibDTpm instance
>>>            (via earlier registration)
>>>                    |
>>>                    v
>>>           TPM2 chip (actual hardware)
>>> 
>>> The slide deck says that EFI_TD_PROTOCOL is supposed to reuse the
>>> EFI_TCG2_PROTOCOL definition. If that's the case, then why don't we push
>>> the TDX specifics (more or less: the replacement of PCRs with RTMR) down
>>> to the lowest possible level?
>>> 
>>> Can we have "Tpm2InstanceLibTdxRtmr", plugged into the same Tcg2Dxe.inf
>>> driver?
>>> 
>>> If not, can we have a new TdTcg2Dxe.inf driver, but make it so that it
>>> install the same protocol as before (EFI_TCG2_PROTOCOL -- same old
>>> protocol GUID)? Then DxeTpmMeasurementLib doesn't have to change.
>>> 
>>> As long as there is *at most* one EFI_TCG2_PROTOCOL instance published
>>> in the protocol database, DxeTpmMeasurementLib should be fine. In SEV*
>>> guests, the standard Tcg2Dxe driver provides that protocol. In TDX
>>> guests, TdTcg2Dxe.inf should provide the protocol. Arbitration between
>>> the two can be implemented with the pattern seen in the following
>>> commits:
>>> 
>>> 1  05db0948cc60 EmbeddedPkg: introduce EDKII Platform Has ACPI GUID
>>> 2  786f476323a6 EmbeddedPkg: introduce PlatformHasAcpiLib
>>> 3  65a69b214840 EmbeddedPkg: introduce EDKII Platform Has Device Tree
>>>                 GUID
>>> 4  2558bfe3e907 ArmVirtPkg: add PlatformHasAcpiDtDxe
>>> 
>>> The basic idea is that Tcg2Dxe can have a depex on a new "running in
>>> SEV" protocol GUID, and TdTcg2Dxe can have a depex on a new "running in
>>> TDX" protocol GUID. A separate platform driver can install the proper
>>> GUID -- possibly *neither* of those GUIDs.
>>> 
>>> And, we don't have to change the depex section of
>>> "SecurityPkg/Tcg/Tcg2Dxe/Tcg2Dxe.inf" for this; we can implement a
>>> library instance with an empty constructor, but a non-empty depex, and
>>> then hook this lib instance into Tcg2Dxe.inf via module scope NULL lib
>>> class override in the DSC file. Basically we could forcibly restrict
>>> Tcg2Dxe's DEPEX by making it inherit the new DEPEX from the library.
>>> 
>>> 
>>> *** Slide 48: DXE Phase -- Other Modules
>>> 
>>> Regarding IncompatiblePciDeviceSupportDxe: the proposed update sounds
>>> plausible and simple enough.
>>> 
>>> (21) "AcpiPlatformDxe: Support for MADT/ACPI addition to report Td
>>> Mailbox entry"
>>> 
>>> Firmware-owned tables must not be installed from this driver.
>>> 
>>> Please refer to my "Xen removal" patch set again, for
>>> <https://bugzilla.tianocore.org/show_bug.cgi?id=2122>, which I mention
>>> above in point (14). As part of the Xen removal, the AcpiPlatformDxe
>>> driver in OvmfPkg is significantly trimmed: all unused (dead) cruft is
>>> removed, including any ACPI table templates that are built into the
>>> firmware.
>>> 
>>> OvmfPkg/AcpiPlatformDxe is responsible *solely* for implementing the
>>> client side of the QEMU ACPI linker/loader.
>>> 
>>> If you need to prepare & install different ACPI tables, please do it
>>> elsewhere, in another DXE driver. A bunch of other firmware modules do
>>> that (NFIT, IBFT, BGRT, ...).
>>> 
>>> For example, the OvmfPkg/TdxDxe DXE_DRIVER is supposed to be launched
>>> early in the DXE phase, via APRIORI section -- please consider
>>> registering a protocol notify in that driver, for
>>> EFI_ACPI_TABLE_PROTOCOL, and when it becomes available, install
>>> whatever
>>> *extra* tables you need.
>>> 
>>> Note that if you need to *customize* an ACPI table that QEMU already
>>> provides, then you will have to modify the ACPI generator on the QEMU
>>> side. It is a design tenet between QEMU and OVMF that OVMF include no
>>> business logic for either parsing or fixing up ACPI tables that QEMU
>>> provides. AcpiPlatformDxe contains the minimum (which is already a whole
>>> lot, unfortunately) that's necessary for implementing the QEMU ACPI
>>> linker/loader client in the UEFI environment.
>>> 
>>> The slide deck mentions MADT, which is also known as the "APIC" table --
>>> and indeed, QEMU does provide that. (See acpi_build_madt()
>>> [hw/i386/acpi-common.c].) So if TDX needs MADT customizations, that
>>> should go into QEMU.
>>> 
>>> (22) EmuVariableFvbRuntimeDxe
>>> 
>>> Ouch, this is an unpleasant surprise.
>>> 
>>> First, if you know for a fact that pflash is not part of the *board* in
>>> any TDX setup, then pulling
>>> 
>>>  OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf
>>> 
>>> into the firmware platform is useless, as it is mutually exclusive with
>>> 
>>>  OvmfPkg/EmuVariableFvbRuntimeDxe/Fvb.inf
>>> 
>>> (via dynamic means -- a dynamic PCD).
>>> 
>>> Note that the FDF file places QemuFlashFvbServicesRuntimeDxe in APRIORI
>>> DXE when SMM_REQUIRE is FALSE. This driver checks for pflash presence,
>>> and lets EmuVariableFvbRuntimeDxe perform its in-RAM flash emulation
>>> only in case pflash is not found.
>>> 
>>> So this is again in favor of a separate platform -- if we know pflash is
>>> never part of the board, then QemuFlashFvbServicesRuntimeDxe is never
>>> needed, but you cannot remove it from the traditional DSC/FDF files.
>>> 
>>> Second, EmuVariableFvbRuntimeDxe consumes the PlatformFvbLib class,
>>> for
>>> the PlatformFvbDataWritten() API (among other things). This lib class is
>>> implemented by two instances in OvmfPkg, PlatformFvbLibNull and
>>> EmuVariableFvbLib. The latter instance allows Platform BDS to hook an
>>> event (for signaling) via "PcdEmuVariableEvent" into the
>>> EmuVariableFvbRuntimeDxe driver.
>>> 
>>> In old (very old) QEMU board configurations, namely those without
>>> pflash, this (mis)feature is used by OVMF's PlatformBootManagerLib to
>>> write out all variables to the EFI system partition in a regular file
>>> called \NvVars, with the help of NvVarsFileLib, whenever
>>> EmuVariableFvbRuntimeDxe writes out an emulated "flash" block. For this
>>> purpose, the traditional OVMF DSC files link EmuVariableFvbLib into
>>> EmuVariableFvbRuntimeDxe.
>>> 
>>> But it counts as an absolute disaster nowadays, and should not be
>>> revived in any platform. If you don't have pflash in TDX guests, just
>>> accept that you won't have non-volatile variables. And link
>>> PlatformFvbLibNull into EmuVariableFvbRuntimeDxe. You're going to need
>>> a
>>> separate PlatformBootManagerLib instance anyway.
>>> 
>>> (We should have removed EmuVariableFvbRuntimeDxe a long time ago
>>> from
>>> the traditional OVMF platforms, i.e. made pflash a hard requirement,
>>> even when SMM is not built into the platform -- but whenever I tried
>>> that, Jordan always shot me down.)
>>> 
>>> My point is: using EmuVariableFvbRuntimeDxe in the TDX platform may be
>>> defensible per se, but we must be very clear that it will never provide
>>> a standards-conformant service for non-volatile UEFI variables, and we
>>> must keep as much of the \NvVars mess out of EmuVariableFvbRuntimeDxe
>>> as
>>> possible. This will require a separate PlatformBootManagerLib instance
>>> for TDX anyway (or maybe share PlatformBootManagerLibGrub with
>>> "OvmfPkg/AmdSev/AmdSevX64.dsc").
>>> 
>>> Apart from the volatility aspect, let's assume we have this in-RAM
>>> emulated "flash device", storing authenticated UEFI variables for Secure
>>> Boot purposes. And we don't have SMM.
>>> 
>>> What protects this in-RAM variable store from tampering by the guest OS?
>>> It's all guest RAM only, after all. What provides the privilege barrier
>>> between the guest firmware and the guest OS?
>>> 
>>> 
>>> *** Slide 50: Library
>>> 
>>> (23) Should we introduce Null instances for all (or most) new lib
>>> classes here? Code size is a concern (static linking). If we extend a
>>> common OvmfPkg module with new hook points, it's one thing to return
>>> from that hook point early *dynamically*, but it's even better (given
>>> separate platforms) to allow the traditional platform firmware to use a
>>> Null lib instance, to cut out all the dead code statically.
>>> 
>>> 
>>> *** Slides 51 through 52
>>> 
>>> Seems OK.
>>> 
>>> 
>>> *** Slide 53:
>>> 
>>> (24) It might be worth noting that BaseIoLibIntrinsic already has some
>>> SEV enlightenment, as the FIFO IO port operations (which normally use
>>> the REP prefix) are not handled on SEV. I don't have an immediate idea
>>> why this might matter, we should just minimize code duplication if
>>> possible.
>>> 
>>> 
>>> *** Slides 54-56:
>>> 
>>> No  comments, this stuff seems reasonable.
>>> 
>>> 
>>> *** Slide 57: MpInitLib
>>> 
>>> I don't know enough to give a summary judgement.
>>> 
>>> 
>>> All in all, I see the controversial / messy parts in the platform
>>> bringup, and how all that differs from the traditional ("legacy") OVMF
>>> platforms. I admit I *may* be biased in favor of SEV, possibly because
>>> SEV landed first -- if you find signs of such a bias in my comments,
>>> please don't hesitate to debunk those points. Yet my general impression
>>> is that the early bringup stuff is significantly different from
>>> everything before, and because of this, a separate platform is
>>> justified.
>>> 
>>> Definitely separate from the traditional OVMF IA32, IA32X64, and X64
>>> platforms, and *possibly* separate from the "remote attestation"
>>> AmdSevX64.dsc platform. I would approach the TDX feature-set in complete
>>> isolation (exactly how Intel commenced the work, if I understand
>>> correctly), modulo obviously shareable / reusable parts, and then slowly
>>> & gradually work on extracting / refactoring commonalities.
>>> 
>>> (But, given my stance on Xen for example, I could disagree even with the
>>> latter, retroactive kind of unification -- it all boils down to shared
>>> developer and user base. Component sharing should reflect the community
>>> structure, otherwise maintenance will be a nightmare.)
>>> 
>>> Thanks
>>> Laszlo
>>> 
>>> 
>>> 
>>> 
>>> 
>> 
> 
> 
> 
> 
> 
> 

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Michael Brown]

On 04/06/2021 11:11, Laszlo Ersek wrote:
> And, to reiterate, just because Confidential Computing is the
> new hot thing, the use cases for OvmfPkgIa32, OvmfPkgIa32X64, OvmfPkgX64
> do not disappear. Regressing them, or making them unmaintainable due to
> skyrocketing complexity, is not acceptable.

Totally agree with this.  Confidential Computing is a very niche use 
case, and there is no justification for exploding the complexity of the 
standard OVMF build.

If, several years from now, it ever reaches the point that the majority 
of real-world workloads are using TDX, then there would be an argument 
that the complexity cost has to be paid and that the standard OVMF build 
should include TDX features.  But that's several years away and may 
never happen.

Michael

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Michael Brown]

On 04/06/2021 11:43, Michael Brown wrote:
> On 04/06/2021 11:11, Laszlo Ersek wrote:
>> And, to reiterate, just because Confidential Computing is the
>> new hot thing, the use cases for OvmfPkgIa32, OvmfPkgIa32X64, OvmfPkgX64
>> do not disappear. Regressing them, or making them unmaintainable due to
>> skyrocketing complexity, is not acceptable.
> 
> Totally agree with this.  Confidential Computing is a very niche use 
> case, and there is no justification for exploding the complexity of the 
> standard OVMF build.
> 
> If, several years from now, it ever reaches the point that the majority 
> of real-world workloads are using TDX, then there would be an argument 
> that the complexity cost has to be paid and that the standard OVMF build 
> should include TDX features.  But that's several years away and may 
> never happen.

Out of interest: does Intel TDX provide any security benefits beyond the 
(much simpler) Intel SGX?

As far as I can tell from the various papers, the fundamental difference 
between TDX and SGX seems to be that TDX deliberately increases the 
attack surface from "just the application code" to "entire guest VM, 
including OS kernel, runtime libraries, etc".  Increasing the attack 
surface while adding complexity is a huge cost so I'm assuming that 
there must be some commensurate benefit, but nothing in the 
documentation I've seen seems to describe what this benefit actually is.

Thanks,

Michael

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[James Bottomley]

On Fri, 2021-06-04 at 15:52 +0100, Michael Brown wrote:
> On 04/06/2021 11:43, Michael Brown wrote:
> > On 04/06/2021 11:11, Laszlo Ersek wrote:
> > > And, to reiterate, just because Confidential Computing is the
> > > new hot thing, the use cases for OvmfPkgIa32, OvmfPkgIa32X64,
> > > OvmfPkgX64 do not disappear. Regressing them, or making them
> > > unmaintainable due to skyrocketing complexity, is not acceptable.
> > 
> > Totally agree with this.  Confidential Computing is a very niche
> > use case, and there is no justification for exploding the
> > complexity of the standard OVMF build.
> > 
> > If, several years from now, it ever reaches the point that the
> > majority of real-world workloads are using TDX, then there would be
> > an argument that the complexity cost has to be paid and that the
> > standard OVMF build should include TDX features.  But that's
> > several years away and may never happen.
> 
> Out of interest: does Intel TDX provide any security benefits beyond
> the (much simpler) Intel SGX?

The main benefit is ease of deployment for unmodified applications. 
While you might argue this isn't a "security" benefit, remember that
any security technology that is too complex for most people to deploy
doesn't have much impact, so ease of use is a significant consideration
in security technologies.

> As far as I can tell from the various papers, the fundamental
> difference between TDX and SGX seems to be that TDX deliberately
> increases the attack surface from "just the application code" to
> "entire guest VM, including OS kernel, runtime libraries,
> etc".  Increasing the attack surface while adding complexity is a
> huge cost so I'm assuming that there must be some commensurate
> benefit, but nothing in the documentation I've seen seems to describe
> what this benefit actually is.

The big problems of enclave technology like SGX is rewriting
applications into secure and insecure parts and controlling information
leak across the boundaries of the enclave ... even if you opt to run
the application entirely within the enclave, you still get leaks into
the kernel via syscalls and the machine owner still has a huge amount
of leeway to exfiltrate any secrets in the enclave.

The push towards VM based isolation is because all the handling of the
technology can be done inside an enlightened guest kernel (so any
application will run with no modification) and the guest to host
boundary is a far easier to analyse being a hardware emulation
vmexit/hypercall one rather than the huge and complex syscall
interface.

James

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Min Xu]

On 06/04/2021 12:12 AM, Laszlo wrote:
> On 06/03/21 15:51, Yao, Jiewen wrote:
> > Hi, All
> > We plan to do a design review for TDVF in OVMF package.
> >
> >
> > The TDVF Design slides for TinaoCore Design Review Meeting (Jun 11) is
> > now available in blow link:
> > https://edk2.groups.io/g/devel/files/Designs/2021/0611.
> >
> > The Bugzilla is https://bugzilla.tianocore.org/show_bug.cgi?id=3429
> >
> >
> >
> > You can have an offline review first. You comments will be warmly
> > welcomed and we will continuously update the slides based on the
> > feedbacks.
> 
> Resending my earlier comments in this mailing list thread, with the feedback
> inserted at the proper spots that has been given in the off-list thread since
> then:
> 
> 
> *** Slides 4, 6, 7: the "one binary requirement".
I would like to hear other reviewers' comments on the "one binary requirement".
> 
> (1) The presentation refers to "OvmfPkgX64.dsc" as "the one" on slide#4, but
> then the explanation for the requirement, given on slide 7, speaks about
> "common attestation interface".
> 
> I think we have a misunderstanding here. The "OvmfPkgX64.dsc" platform
> indeed contains SEV, SEV-ES, and (in the future, will contain) SEV-SNP
> support. In that sense, adding TDX support to the same platform should be
> (hopefully) possible, at the cost of ugly gymnastics in the reset vector.
> 
> But "OvmfPkgX64.dsc" is *already* different from the remotely attested
> OVMF platform, namely "OvmfPkg/AmdSev/AmdSevX64.dsc".
> 
> The latter has some additional modules (secret PEIM and DXE driver), it has
> the Grub binary built in, and -- probably most importantly -- it trusts host-
> originated information less than "OvmfPkgX64.dsc".
> 
> For example, "OvmfPkg/AmdSev/AmdSevX64.dsc" has a dedicated
> PlatformBootManagerLib instance, one that ignores the non-volatile UEFI
> variables Boot#### and BootOrder, and ignores (thus far) the fw_cfg
> originated kernel/initrd/cmdline as well.
> 
> It remains an "area of research" to see what else should be removed from
> the traditional host-guest integration (which integration is usually desirable
> for management and convenience), in the remotely-attested boot scenario.
> See e.g.
> <https://bugzilla.tianocore.org/show_bug.cgi?id=3180>.
> 
> My point is that the "one binary" that the slide deck refers to (i.e.,
> OvmfPkgX64.dsc) might prove OK for utilizing the Intel TDX *technology* in
> itself. Simply enabling OVMF + a guest OS to boot in a TDX domain.
> 
> But "OvmfPkgX64.dsc" is *not* the "one binary" that is suitable for remote
> attestation, which has a much broader scope, involving multiple computers,
> networking, deployment, guest-owner/host-owner separation, whatever.
> For the latter, we needed a separate platform anyway, even with only SEV in
> mind; that's why "OvmfPkg/AmdSev/AmdSevX64.dsc" exists.
> 
> 
> *** Slides 8-9: general boot flow -- TDVF; TDVF Flow
> 
> I'm likely missing a big bunch of background here, so just a few
> questions:
> 
> (2) Not sure what RTMR is, but it's associated with "Enable TrustedBoot"
> -- so is a virtual TPM a hard requirement?
> 
> ... Back from slide 10: "TCG measurement and event log framework w/o
> TPM" -- that's curious.
> 
Comments of Dave & Erdem are pretty good to explain what RTMR is. 
> [response from Dave Gilbert:]
> > My reading of this is that the RTMR (and another set of similar
> > registers) are a TDX thing that is like the PCRs from a TPM but
> > without the rest of the TPM features;  so you can do the one-way
> > measurement into the RTMRs just like you do into a TPM PCR, and the
> > measurements pop out somewhere in the TDX quote.  Just like a TPM you
> > need the event log to make any sense of how the final hashed value
> > supposedly got to where it did.
> 
> [response from Erdem Aktas:]
> > +1 to David on this. TDX provides 2 kinds of measurement registers:
> > MRTDs and RTMRs
> >
> (https://software.intel.com/content/dam/develop/external/us/en/documen
> > ts/tdx-module-1eas-v0.85.039.pdf section 10.1.2) . MRTDs are
> > build-time measurement registers which are updated when TDX is being
> > created. Once TDX is finalized (before the first run), the MRTDs are
> > finalized and cannot be updated anymore. On the other hand, while the
> > TD is running, TD can extend RTMRs through TDCALLs which will provide
> > TPM PCR kind of capabilities.
> 
> ... Back from slide 43: feel free to skip this now; I will comment in more detail
> below.
> 
> (3) Prepare AcpiTable -- OVMF fetches ACPI tables from QEMU; is this a new
> (firmware originated) table that is installed in addition, or does it replace
> QEMU's tables?
> 
> ... Ignore for now, will comment on the MADT stuff later.
> 
> (4) Does DMA management mean a different IOMMU protocol? That is going
> to conflict with the SEV IOMMU protocol. Depexes in OVMF expect one or
> zero IOMMU protocols to be present.
> 
There is only one IOMMU protocol. We will merge TDX features into the current SEV IOMMU implementation. Td or Non-Td will be probed in run-time, so that the corresponding APIs will be called to clear/set the memory encryption mask for SEV or the shared bit for TDX.
> ... Back from slide 40: feel free to skip this now; I'll comment on this
> separately, below.
> 
> (5) Enumerate VirtIO -- virtio enumeration is PCI based on x86. But I see no
> mention of PCI. If you mean VirtioMmioDeviceLib, that's no good, because it
> does not support virtio-1.0, only virtio-0.9.5.
> 
> ... Back from slide 42: I got my answer to this on slide 42, so don't worry
> about this point.
> 
I will comment it in my later response.
[...]
> (6) The PEI phase is skipped as a whole. I don't see how that can be
> reasonably brought together with either "OvmfPkgX64.dsc" or
> "OvmfPkg/AmdSev/AmdSevX64.dsc". I guess you can always modify SEC to
> jump into DXE directly, but then why keep the PEI core and a bunch of PEIMs
> in the firmware binary?
This is because of the *one binary*. In non-Td guest, Legacy OVMF still need PEI core and the PEIMs. 
> 
> Also touched on by slide 9, TDVF Flow -- PEI is eliminated but SEC becomes
> more heavy-weight.
I have to admit SEC is more heavy-weight in Td guest. TdxStartupLib wraps the whole stuff in SEC phase.
> 
> Wouldn't this deserve a dedicated, separate platform DSC? The 8-bit/32-bit
> branching at the front of the reset vector is a smaller complication in
> comparison.
> 
> Slide 6 references the mailing list archive:
> 
>   https://edk2.groups.io/g/devel/topic/81969494#74319
> 
> and in that message, I wrote:
> 
>     I'm doubtful that this is a unique problem ("just fix the reset
>     vector") the likes of which will supposedly never return during the
>     integration of SEV and TDX
> 
> See also:
> 
>   https://listman.redhat.com/archives/edk2-devel-archive/2021-
> April/msg00784.html
> 
> where I said:
> 
>     It's not lost on me that we're talking about ~3 instructions.
> 
>     Let's keep a close eye on further "polymorphisms" that would require
>     hacks.
> 
> The first 9 slides in the presentation introduce much-much more intrusive
> problems than the "polymorphism" of the reset vector. Would I be correct to
> say that my concern in the above messages was right? I think I was only given
> a fraction of the necessary information when I was asked "do you agree 'one
> binary' is viable".
> 
> [response from Erdem Aktas:]
> > Let's not worry about this for now. We want the one binary solution
> > for practical reasons and also for simplicity.  In the end, we want to
> > do what is right and good for everyone.
> > Those are legit concerns and I think what Intel is trying to do (sorry
> > for mind reading) is to discuss all those concerns and questions to
> > make the right decision. I really appreciate their effort on preparing
> > those slides and bringing it to the community to review.
> >
> > I will also read your comments more carefully and provide my thoughts
> > on them.
> > Sorry for being a little slow on this.
> 
> 
> *** Slide 10 -- Key impact to firmware
> 
> (7) "CPUs are left running in long mode after exiting firmware" -- what kind of
> "pen" are we talking about? Does a HLT loop still work?
> 
It is expected that TDX-VMM lauchs all CPUs to the ResetVector(0xfffffff0). After reset, all CPUs run the same initialization code (protected mode -> long mode) until Sec Entrypoint. (see slides 22)
After that APs spin at TdMailBox waiting for the commands (from BSP). Before jumping to DXE phase, TdMailBox will be relocated to a new address which is recorded in MADT table. APs then are waked up by BSP and spin at that new TdMailbox and wait for command. 
After exiting firmware, APs are spinning and waiting for OS to wake them up. OS send the wake up command to the TdMailbox by reading the MADT table.

> (8) "I/O, MMIO, MSR accesses are different" -- those are implemented by
> low-level libraries in edk2; how can they be configured dynamically?
I will add more description of the basic IoLib in next version design slides.
Simply say we probe Td or Non-Td in run-time and then call the corresponding IO operation. 
UINT8
EFIAPI
MmioRead8 (
  IN      UINTN                     Address
  )
{
  UINT8                             Value;

  if (IsTdGuest ()) {
    Value = TdMmioRead8 (Address);
    return Value;
  }

  MemoryFence ();
  Value = *(volatile UINT8*)Address;
  MemoryFence ();

  return Value;
}
> 
> ... Back from slide 53: I'll comment on slide 53 separately; ignore this.
> 
> 
> *** Slide 11 -- TDVF Image (1)
> 
> (9) CFV -- Configuration Firmware Volume (VarStore.fdf.inc), containing SB
> keys -- how is this firmware volume populated (at build time)? Is this a
> hexdump?
CFV is populated in post build. We can provide such python scripts to do the SB keys enrollment. 

I will continue my comments in my next mail.
[To be continued]
Thanks!

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Min Xu]

On June 4, 2021 12:12 AM, Laszlo wrote:
> On 06/03/21 15:51, Yao, Jiewen wrote:
> > Hi, All
> > We plan to do a design review for TDVF in OVMF package.
> >
> >
> > The TDVF Design slides for TinaoCore Design Review Meeting (Jun 11) is
> > now available in blow link:
> > https://edk2.groups.io/g/devel/files/Designs/2021/0611.
> >
> > The Bugzilla is https://bugzilla.tianocore.org/show_bug.cgi?id=3429
> >
> >
> >
> > You can have an offline review first. You comments will be warmly
> > welcomed and we will continuously update the slides based on the
> > feedbacks.
> 
> Resending my earlier comments in this mailing list thread, with the feedback
> inserted at the proper spots that has been given in the off-list thread since
> then:
> 

Continue my comments from here.

> 

> *** Slide 11 -- TDVF Image (1)
> 
> (9) CFV -- Configuration Firmware Volume (VarStore.fdf.inc), containing SB
> keys -- how is this firmware volume populated (at build time)? Is this a
> hexdump?
> 
CFV is populated in post build. We can provide such python scripts to do the
SB keys enrollment.

> ... Back from slide 16: it seems like CFV is a raw hexdump indeed; how is that
> managed when keys change (at build time)?
> 
As I mentioned above, SB keys are enrolled in post build phase. We can provide
a python scripts to add/delete/append the keys.

> (10) This slide (slide 11) basically describes an intrusive reorganization of
> "OvmfPkgX64.fdf". I don't think I can agree to that.
> While confidential computing is important, it is not relevant for many users.
> Even if we don't cause outright regressions for existent setups, the
> maintenance cost of the traditional OVMF platform will skyrocket.
> 
> The big bunch of areas that SEV-ES introduced to MEMFD is already a big
> complication. I'd feel much better if we could isolate all that to a dedicated
> "remote attested boot" firmware platform, and not risk the functionality and
> maintenance of the traditional platform. I think this ties in with my comment
> (1).
Actually in our first version of TDVF, it is a separated dsc/fdf. But when I try to
implement the *one binary*, I have to figure out some way to put our mailbox/tdhob.
I checked the OvmfPkgX64.fdf and mimics what SEV-ES does in MEMFD.
I would wait for a conclusion of the *one binary* and then figure out how to
handle the mailbox/tdhob.
> 
> For example, seeing a configuration firmware volume (CFV) with secure boot
> keys embedded, in the "usual" FDF, will confuse lots of people, me included.
> In the traditional OVMF use case, we use a different method:
> namely OvmfPkg/EnrollDefaultKeys, for "priming" a variable store template,
> in the build environment.

As I mentioned above, the SB keys are enrolled in post-build. The standard build
script:
  build -p OvmfPkg/OvmfPkgX64.dsc -a X64 -t GCC5
Its output is a standard OVMF image (with a clean CFV/VarStore)
If the customers want the SB feature configured, it's up to them to enroll the SB
keys. 
CFV is just a concept in TDVF. From the perspective of Standard OVMF, it is still
the VarStore.

> 
> Edk2 (and PI and UEFI) are definitely flexible enough for accommodating TDX,
> but the existent, traditional OVMF platforms are a bad fit. In my opinion.
> 
> 
> *** Slide 12: TDVF Image (2)
> 
> (11) "Page table should support both 4-level and 5-level page table"
> 
> As a general development strategy, I would suggest building TDX support in
> small, well-isolated layers. 5-level paging is not enabled (has never been
> tested, to my knowledge) with OVMF on QEMU/KVM, regardless of
> confidential computing, for starters. If 5-level paging is a strict requirement
> for TDX, then it arguably needs to be implemented independently of TDX, at
> first. So that the common edk2 architecture be at least testable on
> QEMU/KVM with 5-level paging enabled.
> 
Yes, 5-level paging is a strict requirement for TDX. 
I would wait for the conclusion of the *one binary*.
> 
> *** Slide 13:
> 
> (12) My comment is that the GUID-ed structure chain already starts at a fixed
> GPA (the "AMD SEV option"). Ordering between GUID-ed structures is
> irrelevant, so any TDX-specific structures should be eligible for appending to,
> prepending to, or intermixing with, other (possibly
> SEV-specific) structures. There need not be a separate entry point, just
> different GUIDS.
Yes, we prefer a TDX GUID in ResetVector. In that GUID there is a offset which
points to the actual TDX Metadata blob.
> 
> (13) Regarding "4G-0x20[0x10] is OVMF AP reset vector (used in OVMF
> implementation)" -- I think this is a typo: this "AP reset vector" is
> *not* used in OVMF. To my knowledge, it is a vestige from the UefiCpuPkg
> reset vector. In OVMF, APs are booted via MpInitLib (in multiple firmware
> phases), using INIT-SIPI-SIPI, and the reset vector for the APs, posited
> through those IPIs, is prepared in low RAM.
> 
Thanks Laszlo for explanation. 
> 
> *** Slides 14 through 16:
> 
> I consider these TDVF firmware image internals, implementation details
> -- do whatever you need to do, just don't interfere with existing platforms /
> use cases. See my comment (10) above.
> 
Sure. All the TDVF changes will not  interfere with existing platfomrs/use cases.
> 
> *** Slides 17-21:
> 
> (14) Again, a very big difference from traditional OVMF: APs never enter SEC
> in traditional OVMF. I assume this new functionality is part of TdxStartupLib
> (from slide 18) -- will there be a Null instance of that?

Yes, there is a NULL instance of TdxStartupLib.

> 
> Last week I posted a 43-part patch series to edk2-devel, for separating out
> the dynamic Xen enlightenments from the IA32, IA32X64, X64 platforms, in
> favor of the dedicated OvmfXen platform. TDX seems to bring in
> incomparably more complications than Xen, and the OvmfPkg maintainers
> have found even the Xen complications troublesome in the long term.
> 
> If I had had access to all this information when we first discussed "one
> binary" on the mailing list, I'd have never agreed to "one binary". I'm OK with
> attempting one firmware binary for "confidential computing", but that "one
> platform" cannot be "OvmfPkgX64.dsc".
> 
> Even if I make a comparison with just the "technology" (not the remotely-
> attested deployment) of SEV and SEV-ES, as it is included in
> "OvmfPkgX64.dsc", TDX is hugely more complicated and intrusive than that.
> SEV proved possible to integrate into existing modules, into the existing boot
> flow, maybe through the addition of some new drivers (such as a new
> IOMMU protocol implementation, and some "clever" depexes). But we never
> had to restructure the FD layout, eliminate whole firmware phases, or think
> about multiprocessing in the reset vector or the SEC phase.
> 
> In order to bring an example from the ARM world, please note that platforms
> that use a PEI phase, and platforms that don't, are distinct platforms. In
> ArmVirtPkg, two examples are ArmVirtQemu and ArmVirtQemuKernel. The
> latter does not include the PEI Core.
> 

Thanks Laszlo. I will check the example from the ARM world.

> 
> *** Slides 22 through 34:
> 
> (15) All these extra tasks and complications are perfectly fine, as long as they
> exist peacefully *separately* from the traditional ("legacy") OVMF platforms.
> 
> Honestly, in the virtual world, picking your firmware binary is easy.
> The approach here reminds me of a physical firmware binary that includes
> everything possible from "edk2-platforms/Features/Intel", just so it can be
> deployed to any physical board imaginable. That's not how Intel builds
> physical firmware, right? We have "edk2-platforms/Platform/Intel"
> and "edk2-platforms/Silicon/Intel" with many-many separate DSC files.
> 

I will continue my comments in my next mail. 

Thanks!
Min

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Michael Brown]

On 06/06/2021 03:03, Min Xu wrote:
>> (11) "Page table should support both 4-level and 5-level page 
>> table"
>> 
>> As a general development strategy, I would suggest building TDX 
>> support in small, well-isolated layers. 5-level paging is not 
>> enabled (has never been tested, to my knowledge) with OVMF on 
>> QEMU/KVM, regardless of confidential computing, for starters. If 
>> 5-level paging is a strict requirement for TDX, then it arguably 
>> needs to be implemented independently of TDX, at first. So that the
>> common edk2 architecture be at least testable on QEMU/KVM with 
>> 5-level paging enabled.
>> 
> Yes, 5-level paging is a strict requirement for TDX. I would wait for
> the conclusion of the *one binary*.

The "one binary" decision isn't relevant here, is it?  It would make
more sense to implement 5-level paging within the base EDK2
architecture.  This would allow that feature to be tested in isolation
from TDX (and consequently tested more widely), and would reduce the
distance between standard builds and TDX builds.

Michael

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Min Xu]

On June 6, 2021 7:30 PM, Michael Brown Wrote:
> On 06/06/2021 03:03, Min Xu wrote:
> >> (11) "Page table should support both 4-level and 5-level page table"
> >>
> >> As a general development strategy, I would suggest building TDX
> >> support in small, well-isolated layers. 5-level paging is not enabled
> >> (has never been tested, to my knowledge) with OVMF on QEMU/KVM,
> >> regardless of confidential computing, for starters. If 5-level paging
> >> is a strict requirement for TDX, then it arguably needs to be
> >> implemented independently of TDX, at first. So that the common edk2
> >> architecture be at least testable on QEMU/KVM with 5-level paging
> >> enabled.
> >>
> > Yes, 5-level paging is a strict requirement for TDX. I would wait for
> > the conclusion of the *one binary*.
> 
> The "one binary" decision isn't relevant here, is it?  It would make more
> sense to implement 5-level paging within the base EDK2 architecture.  This
> would allow that feature to be tested in isolation from TDX (and
> consequently tested more widely), and would reduce the distance between
> standard builds and TDX builds.
> 

In our first version of TDVF, a static 5-level page table is used. It is simple and
straight forward. But for *one binary* solution, we have to consider the compatibility
with the current 4-level page table. That's why I said "I would wait for the conclusion
of the *one binary*"

Thanks for the suggestion. We will discuss the it internally first.

> Michael

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Laszlo Ersek]

On 06/06/21 14:49, Xu, Min M wrote:
> On June 6, 2021 7:30 PM, Michael Brown Wrote:
>> On 06/06/2021 03:03, Min Xu wrote:
>>>> (11) "Page table should support both 4-level and 5-level page table"
>>>>
>>>> As a general development strategy, I would suggest building TDX
>>>> support in small, well-isolated layers. 5-level paging is not enabled
>>>> (has never been tested, to my knowledge) with OVMF on QEMU/KVM,
>>>> regardless of confidential computing, for starters. If 5-level paging
>>>> is a strict requirement for TDX, then it arguably needs to be
>>>> implemented independently of TDX, at first. So that the common edk2
>>>> architecture be at least testable on QEMU/KVM with 5-level paging
>>>> enabled.
>>>>
>>> Yes, 5-level paging is a strict requirement for TDX. I would wait for
>>> the conclusion of the *one binary*.
>>
>> The "one binary" decision isn't relevant here, is it?  It would make more
>> sense to implement 5-level paging within the base EDK2 architecture.  This
>> would allow that feature to be tested in isolation from TDX (and
>> consequently tested more widely), and would reduce the distance between
>> standard builds and TDX builds.
>>
> 
> In our first version of TDVF, a static 5-level page table is used. It is simple and
> straight forward. But for *one binary* solution, we have to consider the compatibility
> with the current 4-level page table. That's why I said "I would wait for the conclusion
> of the *one binary*"
> 
> Thanks for the suggestion. We will discuss the it internally first.

My primary concern with the 5-level paging is not that the core
infrastructure is absent from edk2 -- it is present alright. (Over time,
numerous issues have been found and fixed in it, but that's kind of
expected, with such a big feature.) I understand it has been in use
successfully on a number of physical platforms.

My problem is that, AFAICT, the 5-level paging infrastructure of edk2
has never been *tested* on QEMU/KVM, as a part of OVMF. I have
absolutely no idea what to expect.

The "one binary" decision is a little bit relevant:

- If 5-level paging blows up on QEMU/KVM, as a part of OVMF, then
restricting the breakage (possibly a regression even?) to the new TDX
platform is good.

- On the other hand, both 5-level paging and TDX are complex in their
own rights; developing feature sets in small isolated waves is always
best. There are going to be "bug hunts" in the TDX platform of course;
finding an *orthogonal* 5-level paging bug (anywhere in the virt stack,
for that matter) is not the greatest outcome for a supposed TDX bug hunt.

- I figure users might want 5-level paging for OVMF at some point
anyway, even without TDX.

The last two points (especially the middle point of the three) kind of
outweigh(s) the first point for me.

Thanks
Laszlo

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Min Xu]

On June 4, 2021 12:12 AM, Laszlo wrote:
> On 06/03/21 15:51, Yao, Jiewen wrote:
> > Hi, All
> > We plan to do a design review for TDVF in OVMF package.
> >
> >
> > The TDVF Design slides for TinaoCore Design Review Meeting (Jun 11) is
> > now available in blow link:
> > https://edk2.groups.io/g/devel/files/Designs/2021/0611.
> >
> > The Bugzilla is https://bugzilla.tianocore.org/show_bug.cgi?id=3429
> >
> >
> >
> > You can have an offline review first. You comments will be warmly
> > welcomed and we will continuously update the slides based on the
> > feedbacks.
> 
> Resending my earlier comments in this mailing list thread, with the feedback
> inserted at the proper spots that has been given in the off-list thread since
> then:
> 

Continue my comments from here.

> *** Slide 35-36: DXE phase
> 
> (16) "Some DXE Drivers not allowed to load/start in Td guest -- Network
> stack, RNG, ..."
> 
> Same comment as (several times) above. The Linuxboot project is a good
> example for eliminating cruft from DXEFV (in fact, for eliminating most of the
> DXE phase). In a TDX environment, why include drivers in the firmware binary
> that are never used? Meanwhile, DXEFV in OVMF grows by a MB every 1.5
> years or so. Again, remove these drivers from the DSC/FDF then, and it needs
> to be a separate platform.
> 
It is because of the *one binary* so that we have to include all the drivers in the
firmware binary. Some of the DXE drivers are not called in TDX, but they're dispatched
in Non-Tdx environment.
I will explain more about this topic in next version of design slides.
Also I would wait for the conclusion to the *one binary*.

> (17) "Other DXE Phase drivers -- [...] AcpiPlatformDxe"
> 
> I'm not sure what this section is supposed to mean. Other DXE phase drivers
> included, or excluded? Without AcpiPlatformDxe, the guest OS will not see
> QEMU's ACPI content, and will almost certainly malfunction.
> 
Sorry for the confusion about the title. This slides means Other DXE phase drivers
including AcpiPlatformDxe is included. I will update the slides to be more clear
and accurate.

> ... Back from slide 48: ignore this for now, I'll comment in more detail later.
> 
> 
> *** Slide 37: DXE Core
> 
> (18) says "SMM is not supported in Td guest" -- how is the variable store
> protected from direct hardware (pflash) access from the guest OS?
> Without SMM, the guest OS need not go through gRT->SetVariable() to
> update authenticated non-volatile UEFI variables, and that undermines
> Secure Boot.
> 
Let me explain the SMM and Secure boot in TDX like below:
1) TDX doesn't support virtual SMM in guest. Virtual SMI cannot be injected
     into TD guest.
2) SMI/SMM is used to manage variable update to avoid expose Flash direct.
    So SMM is not must-to-have for secure boot, but help to mitigate the security risk.
3) We don't trust VMM. That is why we need TDX. 
4) If you trust VMM to emulate SMM, then you don't need TDX.

> Note that, while SEV-ES has the same limitation wrt. SMM, the
> "OvmfPkg/AmdSev/AmdSevX64.dsc" platform doesn't even include the
> Secure Boot firmware feature. For another example, the OVMF firmware
> binary in RHEL that's going to support SEV-ES is such a build of
> "OvmfPkgX64.dsc"
> that does not include the Secure Boot feature either.
> 
> But in this TDX slide deck, Secure Boot certificates are embedded in the CFV
> (configuration firmware volume) -- see slide 11 and slide 16 --, which
> suggests that this platform does want secure boot.
> 
Yes, TDVF does support Secure Boot.

> ... Back from slide 48: I'm going to make *additional* comments on this,
> when I'm at slide 48, too.
> 
> The rest of this slide (slide 37) looks reasonable (generic DXE Core changes --
> possibly PI spec changes too).
Yes, there is new attribute (EFI_RESOURCE_ATTRIBUTE_ENCRYPTED) in PiHob.h

> 
> 
> *** Slides 38 through 39:
> 
> These seem reasonable (TdxDxe assumes some responsibilities of
> OvmfPkg/PlatformPei)
> 
> 
> *** Slides 40 through 42:
> 
> *If* you really can implement TDX support for the IOMMU driver *this*
> surgically, then I'm OK with it. The general logic in the IOMMU driver was
> truly difficult to write, and I'd be seriously concerned if those parts would
> have to be modified. Customizing just the page encryption/decryption
> primitives for TDX vs. SEV is OK.
Actually all the changes we do in IOMMU is to customize the page encryption 
/ decryption primitive for TDX and SEV. We will probe the Td or Non-Td in
run-time, then the corresponding APIs will be called.
 
> 
> 
> *** Slides 43 through 47:
> 
> (19) Slide 46 and slide 47 are almost identical. Please consolidate them into a
> single slide.
> 
Slide 46 is of Td measurement, like TpmMeasurement. 
    SecurityPkg/Library/DxeTpmMeasurementLib
Slide 47 is of Measure boot. 
    SecurityPkg/Library/DxeTpm2MeasureBootLib
I will refine the two slides to make it more clear. Thanks for reminder.

> (20) the TPM2 infrastructure in edk2 is baroque (over-engineered), in my
> opinion. It has so many layers that I can never keep them in mind. When we
> added TPM support to OVMF, I required commit messages that would help us
> recall the layering. In particular, please refer to commit 0c0a50d6b3ff
> ("OvmfPkg: include Tcg2Dxe module", 2018-03-09). Here's an
> excerpt:
> 
>            TPM 2 consumer driver
>                     |
>                     v
>       Tpm2DeviceLib class: Tpm2DeviceLibTcg2 instance
>                     |
>                     v
>              TCG2 protocol interface
>                     |
>                     v
>       TCG2 protocol provider: Tcg2Dxe.inf driver
>                     |
>                     v
>       Tpm2DeviceLib class: Tpm2DeviceLibRouter instance
>                     |
>                     v
>          NULL class: Tpm2InstanceLibDTpm instance
>             (via earlier registration)
>                     |
>                     v
>            TPM2 chip (actual hardware)
> 
> The slide deck says that EFI_TD_PROTOCOL is supposed to reuse the
> EFI_TCG2_PROTOCOL definition. If that's the case, then why don't we push
> the TDX specifics (more or less: the replacement of PCRs with RTMR) down
> to the lowest possible level?
> 
> Can we have "Tpm2InstanceLibTdxRtmr", plugged into the same Tcg2Dxe.inf
> driver?
> 
> If not, can we have a new TdTcg2Dxe.inf driver, but make it so that it install
> the same protocol as before (EFI_TCG2_PROTOCOL -- same old protocol
> GUID)? Then DxeTpmMeasurementLib doesn't have to change.
> 
> As long as there is *at most* one EFI_TCG2_PROTOCOL instance published in
> the protocol database, DxeTpmMeasurementLib should be fine. In SEV*
> guests, the standard Tcg2Dxe driver provides that protocol. In TDX guests,
> TdTcg2Dxe.inf should provide the protocol. Arbitration between the two can
> be implemented with the pattern seen in the following
> commits:
> 
>  1  05db0948cc60 EmbeddedPkg: introduce EDKII Platform Has ACPI GUID
>  2  786f476323a6 EmbeddedPkg: introduce PlatformHasAcpiLib
>  3  65a69b214840 EmbeddedPkg: introduce EDKII Platform Has Device Tree
>                  GUID
>  4  2558bfe3e907 ArmVirtPkg: add PlatformHasAcpiDtDxe
> 
> The basic idea is that Tcg2Dxe can have a depex on a new "running in SEV"
> protocol GUID, and TdTcg2Dxe can have a depex on a new "running in TDX"
> protocol GUID. A separate platform driver can install the proper GUID --
> possibly *neither* of those GUIDs.
> 
> And, we don't have to change the depex section of
> "SecurityPkg/Tcg/Tcg2Dxe/Tcg2Dxe.inf" for this; we can implement a library
> instance with an empty constructor, but a non-empty depex, and then hook
> this lib instance into Tcg2Dxe.inf via module scope NULL lib class override in
> the DSC file. Basically we could forcibly restrict Tcg2Dxe's DEPEX by making it
> inherit the new DEPEX from the library.
> 
This is a big topic. I need to discuss it internally first then give my comments.
Thanks for your patience.

> 
> *** Slide 48: DXE Phase -- Other Modules
> 
> Regarding IncompatiblePciDeviceSupportDxe: the proposed update sounds
> plausible and simple enough.
> 
> (21) "AcpiPlatformDxe: Support for MADT/ACPI addition to report Td Mailbox
> entry"
> 
> Firmware-owned tables must not be installed from this driver.
> 
> Please refer to my "Xen removal" patch set again, for
> <https://bugzilla.tianocore.org/show_bug.cgi?id=2122>, which I mention
> above in point (14). As part of the Xen removal, the AcpiPlatformDxe driver in
> OvmfPkg is significantly trimmed: all unused (dead) cruft is removed,
> including any ACPI table templates that are built into the firmware.
> 
> OvmfPkg/AcpiPlatformDxe is responsible *solely* for implementing the
> client side of the QEMU ACPI linker/loader.
> 
> If you need to prepare & install different ACPI tables, please do it elsewhere,
> in another DXE driver. A bunch of other firmware modules do that (NFIT, IBFT,
> BGRT, ...).
> 
> For example, the OvmfPkg/TdxDxe DXE_DRIVER is supposed to be launched
> early in the DXE phase, via APRIORI section -- please consider registering a
> protocol notify in that driver, for EFI_ACPI_TABLE_PROTOCOL, and when it
> becomes available, install whatever
> *extra* tables you need.
> 
> Note that if you need to *customize* an ACPI table that QEMU already
> provides, then you will have to modify the ACPI generator on the QEMU side.
> It is a design tenet between QEMU and OVMF that OVMF include no business
> logic for either parsing or fixing up ACPI tables that QEMU provides.
> AcpiPlatformDxe contains the minimum (which is already a whole lot,
> unfortunately) that's necessary for implementing the QEMU ACPI
> linker/loader client in the UEFI environment.
> 
> The slide deck mentions MADT, which is also known as the "APIC" table --
> and indeed, QEMU does provide that. (See acpi_build_madt()
> [hw/i386/acpi-common.c].) So if TDX needs MADT customizations, that
> should go into QEMU.
> 
Thanks for reminder. We will exam the implementation of MADT/ACPI carefully.

> (22) EmuVariableFvbRuntimeDxe
> 
> Ouch, this is an unpleasant surprise.
> 
> First, if you know for a fact that pflash is not part of the *board* in any TDX
> setup, then pulling
> 
>   OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf
> 
> into the firmware platform is useless, as it is mutually exclusive with
> 
>   OvmfPkg/EmuVariableFvbRuntimeDxe/Fvb.inf
> 
> (via dynamic means -- a dynamic PCD).
> 
> Note that the FDF file places QemuFlashFvbServicesRuntimeDxe in APRIORI
> DXE when SMM_REQUIRE is FALSE. This driver checks for pflash presence,
> and lets EmuVariableFvbRuntimeDxe perform its in-RAM flash emulation only
> in case pflash is not found.
> 
> So this is again in favor of a separate platform -- if we know pflash is never
> part of the board, then QemuFlashFvbServicesRuntimeDxe is never needed,
> but you cannot remove it from the traditional DSC/FDF files.
> 
> Second, EmuVariableFvbRuntimeDxe consumes the PlatformFvbLib class, for
> the PlatformFvbDataWritten() API (among other things). This lib class is
> implemented by two instances in OvmfPkg, PlatformFvbLibNull and
> EmuVariableFvbLib. The latter instance allows Platform BDS to hook an event
> (for signaling) via "PcdEmuVariableEvent" into the
> EmuVariableFvbRuntimeDxe driver.
> 
> In old (very old) QEMU board configurations, namely those without pflash,
> this (mis)feature is used by OVMF's PlatformBootManagerLib to write out all
> variables to the EFI system partition in a regular file called \NvVars, with the
> help of NvVarsFileLib, whenever EmuVariableFvbRuntimeDxe writes out an
> emulated "flash" block. For this purpose, the traditional OVMF DSC files link
> EmuVariableFvbLib into EmuVariableFvbRuntimeDxe.
> 
> But it counts as an absolute disaster nowadays, and should not be revived in
> any platform. If you don't have pflash in TDX guests, just accept that you
> won't have non-volatile variables. And link PlatformFvbLibNull into
> EmuVariableFvbRuntimeDxe. You're going to need a separate
> PlatformBootManagerLib instance anyway.
> 
> (We should have removed EmuVariableFvbRuntimeDxe a long time ago from
> the traditional OVMF platforms, i.e. made pflash a hard requirement, even
> when SMM is not built into the platform -- but whenever I tried that, Jordan
> always shot me down.)
> 
> My point is: using EmuVariableFvbRuntimeDxe in the TDX platform may be
> defensible per se, but we must be very clear that it will never provide a
> standards-conformant service for non-volatile UEFI variables, and we must
> keep as much of the \NvVars mess out of EmuVariableFvbRuntimeDxe as
> possible. This will require a separate PlatformBootManagerLib instance for
> TDX anyway (or maybe share PlatformBootManagerLibGrub with
> "OvmfPkg/AmdSev/AmdSevX64.dsc").
> 
> Apart from the volatility aspect, let's assume we have this in-RAM emulated
> "flash device", storing authenticated UEFI variables for Secure Boot purposes.
> And we don't have SMM.
> 
> What protects this in-RAM variable store from tampering by the guest OS?
> It's all guest RAM only, after all. What provides the privilege barrier between
> the guest firmware and the guest OS?
> 
Thanks Laszlo. I will carefully read your comments and discuss it internally first.

> 
> *** Slide 50: Library
> 
> (23) Should we introduce Null instances for all (or most) new lib classes here?
> Code size is a concern (static linking). If we extend a common OvmfPkg
> module with new hook points, it's one thing to return from that hook point
> early *dynamically*, but it's even better (given separate platforms) to allow
> the traditional platform firmware to use a Null lib instance, to cut out all the
> dead code statically.
>
Yes, agree. We will introduce the NULL instance for the new libs.
 
> 
> *** Slides 51 through 52
> 
> Seems OK.
> 
> 
> *** Slide 53:
> 
> (24) It might be worth noting that BaseIoLibIntrinsic already has some SEV
> enlightenment, as the FIFO IO port operations (which normally use the REP
> prefix) are not handled on SEV. I don't have an immediate idea why this
> might matter, we should just minimize code duplication if possible.
> 
Agree that we should minimize the code duplication if possible.

Before we start to enable IoLib for Tdx, we search out the EDK2 and find:
For BaseIoLibIntrinsicSev.inf, it is imported in OvmfPkg, such as
  - OvmfPkg/OvmfXen.dsc
  - OvmfPkg/Bhyve/BhyveX64.dsc
  - OvmfPkg/OvmfPkgIa32.dsc
  - OvmfPkg/OvmfPkgX64.dsc
  - OvmfPkg/OvmfPkgIa32X64.dsc
  - OvmfPkg/AmdSev/AmdSevX64.dsc

But for BaseIoLibIntrinsic.inf it seems it is not imported in any dsc in OvmfPkg.

BaseIoLibIntrinsic is the right IoLib base that we can enable TDX. But
it doesn't support SEV for the FIFO IO port operations. 
BaseIoLibIntrinsicSev handles the FIFO IO on SEV. But we have an open about
the name. 
Anyway we agree code duplication should be minimized.

> 
> *** Slides 54-56:
> 
> No  comments, this stuff seems reasonable.
> 
> 
> *** Slide 57: MpInitLib
> 
> I don't know enough to give a summary judgement.
> 
> 
> All in all, I see the controversial / messy parts in the platform bringup, and
> how all that differs from the traditional ("legacy") OVMF platforms. I admit I
> *may* be biased in favor of SEV, possibly because SEV landed first -- if you
> find signs of such a bias in my comments, please don't hesitate to debunk
> those points. Yet my general impression is that the early bringup stuff is
> significantly different from everything before, and because of this, a
> separate platform is justified.
> 
> Definitely separate from the traditional OVMF IA32, IA32X64, and X64
> platforms, and *possibly* separate from the "remote attestation"
> AmdSevX64.dsc platform. I would approach the TDX feature-set in complete
> isolation (exactly how Intel commenced the work, if I understand correctly),
> modulo obviously shareable / reusable parts, and then slowly & gradually
> work on extracting / refactoring commonalities.
> 
> (But, given my stance on Xen for example, I could disagree even with the
> latter, retroactive kind of unification -- it all boils down to shared developer
> and user base. Component sharing should reflect the community structure,
> otherwise maintenance will be a nightmare.)
> 
> Thanks
> Laszlo
> 

Some of the comments need be discussed internally in intel first. So I cannot answer
all your comments right now. 
Thanks again Laszlo for your valuable review comments!

Min

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Michael Brown]

On 06/06/2021 09:52, Min Xu wrote:
> On June 4, 2021 12:12 AM, Laszlo wrote:
>> (18) says "SMM is not supported in Td guest" -- how is the variable store
>> protected from direct hardware (pflash) access from the guest OS?
>> Without SMM, the guest OS need not go through gRT->SetVariable() to
>> update authenticated non-volatile UEFI variables, and that undermines
>> Secure Boot.
>>
> Let me explain the SMM and Secure boot in TDX like below:
> 1) TDX doesn't support virtual SMM in guest. Virtual SMI cannot be injected
>       into TD guest.
> 2) SMI/SMM is used to manage variable update to avoid expose Flash direct.
>      So SMM is not must-to-have for secure boot, but help to mitigate the security risk.
> 3) We don't trust VMM. That is why we need TDX.
> 4) If you trust VMM to emulate SMM, then you don't need TDX.

Secure Boot defines a security boundary between the firmware and the 
operating system: the operating system is not permitted to make 
arbitrary changes to firmware variables.

It sounds as though you have decided that the TDX security properties 
remove the need for the Secure Boot security properties.  That would be 
a viable conclusion: if the user is able to verify that the intended 
workload is running in the VM (and the VM is disposable anyway) then 
there is not much value added by also having Secure Boot.

However, it's not valid to pretend to also include Secure Boot, knowing 
that there is no way to actually provide the security properties of 
Secure Boot.

If TDX can't support SMM (or some equivalent way for the guest 
*firmware* to guarantee that the ring 0 guest OS cannot make arbitrary 
changes to UEFI variables), then TDX cannot support Secure Boot.

Thanks,

Michael

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Min Xu]

On 06/04/2021 12:12 AM, Laszlo wrote:

> (22) EmuVariableFvbRuntimeDxe
> 
> Ouch, this is an unpleasant surprise.
> 
> First, if you know for a fact that pflash is not part of the *board* in any TDX
> setup, then pulling
> 
>   OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FvbServicesRuntimeDxe.inf
> 
> into the firmware platform is useless, as it is mutually exclusive with
> 
>   OvmfPkg/EmuVariableFvbRuntimeDxe/Fvb.inf
> 
> (via dynamic means -- a dynamic PCD).
> 
> Note that the FDF file places QemuFlashFvbServicesRuntimeDxe in APRIORI
> DXE when SMM_REQUIRE is FALSE. This driver checks for pflash presence,
> and lets EmuVariableFvbRuntimeDxe perform its in-RAM flash emulation
> only in case pflash is not found.
> 
Right, pflash is not part of the *board* in any TDX setup.
This is a limitation from the Qemu (the tdx-qemu) side. TDVF is copied into
RAM. Generic loader is the one for it.
In this case (pflash is not found), FvbServiceRuntimeDxe.inf will return
EFI_WRITE_PROTECTED in its FvbInitialize().
EmuVariableFvbRuntimeDxe will then perform its in-RAM flash emulation.

> So this is again in favor of a separate platform -- if we know pflash is never
> part of the board, then QemuFlashFvbServicesRuntimeDxe is never needed,
> but you cannot remove it from the traditional DSC/FDF files.
> 
Yes, if TDVF is a separate DSD/FDF, QemuFlashFvbServicesRuntimeDxe will be
removed from the image.

> Second, EmuVariableFvbRuntimeDxe consumes the PlatformFvbLib class, for
> the PlatformFvbDataWritten() API (among other things). This lib class is
> implemented by two instances in OvmfPkg, PlatformFvbLibNull and
> EmuVariableFvbLib. The latter instance allows Platform BDS to hook an event
> (for signaling) via "PcdEmuVariableEvent" into the
> EmuVariableFvbRuntimeDxe driver.
> 
> In old (very old) QEMU board configurations, namely those without pflash,
> this (mis)feature is used by OVMF's PlatformBootManagerLib to write out all
> variables to the EFI system partition in a regular file called \NvVars, with the
> help of NvVarsFileLib, whenever EmuVariableFvbRuntimeDxe writes out an
> emulated "flash" block. For this purpose, the traditional OVMF DSC files link
> EmuVariableFvbLib into EmuVariableFvbRuntimeDxe.
> 
Thanks for the explanation. It's very helpful for me to understand the code.

> But it counts as an absolute disaster nowadays, and should not be revived in
> any platform. If you don't have pflash in TDX guests, just accept that you
> won't have non-volatile variables. And link PlatformFvbLibNull into
> EmuVariableFvbRuntimeDxe. You're going to need a separate
> PlatformBootManagerLib instance anyway.
>
I have a question here, that if PlatformFvbLibNull is linked into EmuVaiableFvRuntimeDxe,
Does it mean it cannot write to the in-RAM variable store?

> 
> (We should have removed EmuVariableFvbRuntimeDxe a long time ago from
> the traditional OVMF platforms, i.e. made pflash a hard requirement, even
> when SMM is not built into the platform -- but whenever I tried that, Jordan
> always shot me down.)
>
I am afraid in TDVF we have to use EmuVariableFvRuntimeDxe to emulate the
in-RAM, as I explained pflash is not part of the *board* in TDX setup.
In the traditional EmuVariableFvRuntimeDxe, the FV contents will be initialized.
But TDVF has its own requirement, that the SB keys in CFV need to be copied
into the FV contents. That's why EmuVariableFvRuntimeDxe is updated in
TDVF project.

> 
> My point is: using EmuVariableFvbRuntimeDxe in the TDX platform may be
> defensible per se, but we must be very clear that it will never provide a
> standards-conformant service for non-volatile UEFI variables, and we must
> keep as much of the \NvVars mess out of EmuVariableFvbRuntimeDxe as
> possible. This will require a separate PlatformBootManagerLib instance for
> TDX anyway (or maybe share PlatformBootManagerLibGrub with
> "OvmfPkg/AmdSev/AmdSevX64.dsc").
> 
> Apart from the volatility aspect, let's assume we have this in-RAM emulated
> "flash device", storing authenticated UEFI variables for Secure Boot purposes.
> And we don't have SMM.
> 
> What protects this in-RAM variable store from tampering by the guest OS?
> It's all guest RAM only, after all. What provides the privilege barrier between
> the guest firmware and the guest OS?
A good question and we will answer it a bit later. Thanks for your patience.

> Thanks
> Laszlo

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Laszlo Ersek]

On 06/08/21 14:27, Xu, Min M wrote:
> On 06/04/2021 12:12 AM, Laszlo wrote:

>> But it counts as an absolute disaster nowadays, and should not be revived in
>> any platform. If you don't have pflash in TDX guests, just accept that you
>> won't have non-volatile variables. And link PlatformFvbLibNull into
>> EmuVariableFvbRuntimeDxe. You're going to need a separate
>> PlatformBootManagerLib instance anyway.
>>
> I have a question here, that if PlatformFvbLibNull is linked into EmuVaiableFvRuntimeDxe,
> Does it mean it cannot write to the in-RAM variable store?

No, that's not the case; PlatformFvbLibNull only turns the hooks
(special callbacks) into no-ops; the normal operation of
EmuVariableFvbRuntimeDxe is not disrupted.

The APIs in the PlatformFvbLib class are PlatformFvbDataRead,
PlatformFvbDataWritten, PlatformFvbBlocksErased; they are called at the
ends of the functions FvbProtocolEraseBlocks(), FvbProtocolWrite(),
FvbProtocolRead(), in "OvmfPkg/EmuVariableFvbRuntimeDxe/Fvb.c". If the
PlatformFvb* APIs do nothing, that's not a problem for
EmuVariableFvbRuntimeDxe.

(In fact, even in the non-Null instance -- that is, in the
EmuVariableFvbLib instance --, the read and erase callbacks are empty;
and the write callback only signals an event, at best.)

>> (We should have removed EmuVariableFvbRuntimeDxe a long time ago from
>> the traditional OVMF platforms, i.e. made pflash a hard requirement, even
>> when SMM is not built into the platform -- but whenever I tried that, Jordan
>> always shot me down.)
>>
> I am afraid in TDVF we have to use EmuVariableFvRuntimeDxe to emulate the
> in-RAM, as I explained pflash is not part of the *board* in TDX setup.

Using EmuVariableFvbRuntimeDxe in the TDVF platform is fine (with the
Null hooks, see above), as long as we carefully document the expected /
resultant behavior of the UEFI variable services.

(This is not a comment on my part on the SB situation, which remains an
open question for TDVF, for the time being.)

Thanks
Laszlo

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[James Bottomley]

On Thu, 2021-06-03 at 13:51 +0000, Yao, Jiewen wrote:
> Hi, All
> We plan to do a design review for TDVF in OVMF package.
> 
> 
> The TDVF Design slides for TinaoCore Design Review Meeting (Jun 11)
> is now available in blow link: 
> https://edk2.groups.io/g/devel/files/Designs/2021/0611.
> 
> The Bugzilla is https://bugzilla.tianocore.org/show_bug.cgi?id=3429

It looks like I'll be travelling that day, but should be able to attend
at least the first 45 minutes of the design review from the airport
lounge.

> You can have an offline review first. You comments will be warmly
> welcomed and we will continuously update the slides based on the
> feedbacks.

On TdMailbox and TdHob, we already have two SEV pages in the MEMFD and
since TDX and SEV is an either/or, could we simply not rename both
pages and use them for either boot depending on what CPU type is
detected, so we only have two MEMFD pages, not four?

On your slide 13 Question: "Open: How will the QEMU find the metadata
location?" can't you just use the mechanism for SEV that's already
upstream in both QEMU and OVMF?

On slide 19, the mucking with the reset vector really worries me
because we don't have that much space to play with.  Given that you're
starting in 32 bit mode and can thus enter anywhere in the lower 4GB,
why not simply use a different and TDX specific entry point?

I'm not quite sure why you don't have a PEI phase, since TdxStartupLib
seems effectively to be PEI.

On all the Tcg2 changes: what about installing a vTPM driver that
simply translates to your MSRs?  That way we can use all the standard
TCG code as is?  Plus then we could do SEV-SNP measurement through an
actual vTPM running at higher VMPL or something.

Slide 41: IOMMU operation.  The implication is that you only transition
to unencrypted memory for DMA during the actual operation, so do I have
it correct that the guest writes DMA to encrypted memory, then the
iommu marks the region as unencrypted and transforms the memory to be
in the clear and then transforms it back after the DMA operation
completes?  Given that SEV operates quite happily with always in the
clear DMA buffers, this seems to have the potential to be a performance
problem, but what security does it gain?

James

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Laszlo Ersek]

(Min Xu got dropped from the CC list for some reason, at *some* point in
this sub-thread! Not sure when. Re-adding him.)

Commenting on excerpts:

On 06/08/21 18:01, James Bottomley wrote:

> On TdMailbox and TdHob, we already have two SEV pages in the MEMFD and
> since TDX and SEV is an either/or, could we simply not rename both
> pages and use them for either boot depending on what CPU type is
> detected, so we only have two MEMFD pages, not four?

Great idea, in my opinion.


> On your slide 13 Question: "Open: How will the QEMU find the metadata
> location?" can't you just use the mechanism for SEV that's already
> upstream in both QEMU and OVMF?

I think I made the same comment, in different words. (Point (12) at
<https://listman.redhat.com/archives/edk2-devel-archive/2021-June/msg00143.html>.)


> On slide 19, the mucking with the reset vector really worries me
> because we don't have that much space to play with.  Given that you're
> starting in 32 bit mode and can thus enter anywhere in the lower 4GB,
> why not simply use a different and TDX specific entry point?

What's more, we should use a dedicated ResetVector (through a DSC+FDF
dedicated solely to TDX).


> On all the Tcg2 changes: what about installing a vTPM driver that
> simply translates to your MSRs?  That way we can use all the standard
> TCG code as is?

I believe I made the same comment in point (20) (see URL above).


> Slide 41: IOMMU operation.

That's more like slides 40 and 42, no?


> The implication is that you only transition to unencrypted memory for
> DMA during the actual operation,

Yes, this is the idea behind EDKII_IOMMU_PROTOCOL, which
OvmfPkg/IoMmuDxe implements (for SEV only, currently).


> so do I have it correct that the guest writes DMA to encrypted memory,
> then the iommu marks the region as unencrypted and transforms the
> memory to be in the clear and then transforms it back after the DMA
> operation completes?

Effectively, yes. (Your summary corresponds to a BusMasterRead
operation.)


> Given that SEV operates quite happily with always in the clear DMA
> buffers,

I don't understand this comment -- is it a statement about SEV as a
technology, or about OvmfPkg/IoMmuDxe?

Specifically in the context of OvmfPkg/IoMmuDxe, there is no
"always-in-the-clear DMA".

EDKII_IOMMU_PROTOCOL was designed to fit cleanly into the Map(),
Unmap(), AllocateBuffer(), FreeBuffer() terminology of the UEFI standard
EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL and EFI_PCI_IO_PROTOCOL. As far as I can
tell, the original use case for EDKII_IOMMU_PROTOCOL was VT-d on bare
metal, but the protocol proved a good match for SEV too.

VIRTIO_DEVICE_PROTOCOL has similar member functions
(AllocateSharedPages, FreeSharedPages, MapSharedBuffer,
UnmapSharedBuffer).

As long as a PCI device driver (or virtio driver) uses these member
functions judiciously, only "BusMasterCommonBuffer" operations will be
backed by long-term plaintext (decrypted) pages. One-shot read and write
transactions will be backed by plaintext (decrypted) pages only as long
as necessary.

The transitions you outline already happen in any plain SEV guest that
uses PCI DMA or virtio.


> this seems to have the potential to be a performance problem, but what
> security does it gain?

We have not experienced performance problems due to this kind of IOMMU
protocol usage, when booting SEV guests.

The basic goal was to keep everything as tightly encrypted as possible
(as permitted by the individual PCI or Virtio driver, through its
conservative usage of BusMasterCommonBuffer operations).

I won't claim that it has zero performance impact, but we should
remember the purpose that firmware serves (namely, "booting an operating
system"). Really -- I don't recall any performance issues. This applies
to such virtio devices & drivers too that aren't "bootable", such as
virtio-gpu-pci (VirtioGpuDxe) and virtio-rng-pci (VirtioRngDxe).

(

  If you enable verbose logs, OvmfPkg/IoMmuDxe does produce an immense
  amount of messages (with the express purpose of a human reading
  through them, and matching up decryption and re-encryption actions --
  I've done it, likely with some ad-hoc scripts). *This* does slow down
  the boot considerably (if you actually enable the QEMU debug console),
  but for a different reason: producing debug logs through the QEMU
  debug console (IO Port) is very-very costly in a SEV guest. Not just
  because an IO port trap may be more expensive in a SEV guest, but
  because SEV does not support REP OUTSB, so every debug character
  written traps separately, as opposed to every line written. See
  the following commits:

  - b6d11d7c4678 ("MdePkg: BaseIoLibIntrinsic (IoLib class) library",
    2017-04-13),

  - 97353a9c914d ("OvmfPkg: Update dsc to use IoLib from
    BaseIoLibIntrinsicSev.inf", 2017-07-10),

  - 98a4d04e8fda ("MdePkg/BaseIoLibIntrinsic: fix SEV (=unrolled)
    variants of IoWriteFifoXX()", 2017-09-11),

  - c09d9571300a ("OvmfPkg: save on I/O port accesses when the debug
    port is not in use", 2017-11-17).

)

>From my perspective, I find the changes proposed for OvmfPkg/IoMmuDxe to
be among the least intrusive of the whole slide deck (after Min Xu
confirmed that the intent was really only to customize the page
decryption / encryption primitives in the driver, and to leave the
general logic untouched).

That's not to say that I'm unhappy about this topic being raised. To the
contrary!

Thanks
Laszlo

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Min Xu]

On 06/09/2021 3:33 AM, Laszlo wrote:
> (Min Xu got dropped from the CC list for some reason, at *some* point in this
> sub-thread! Not sure when. Re-adding him.)
> 
> Commenting on excerpts:
> 
> On 06/08/21 18:01, James Bottomley wrote:
> 
> > On TdMailbox and TdHob, we already have two SEV pages in the MEMFD and
> > since TDX and SEV is an either/or, could we simply not rename both
> > pages and use them for either boot depending on what CPU type is
> > detected, so we only have two MEMFD pages, not four?
> 
> Great idea, in my opinion.
> 
Agree, it's a good idea.
> 
> > On your slide 13 Question: "Open: How will the QEMU find the metadata
> > location?" can't you just use the mechanism for SEV that's already
> > upstream in both QEMU and OVMF?
> 
> I think I made the same comment, in different words. (Point (12) at
> <https://listman.redhat.com/archives/edk2-devel-archive/2021-
> June/msg00143.html>.)
> 
So my understanding to this solution is that: 
1) GUID-ed structure chain is started from a fixed GPA in ResetVector. 
2) Append a TDX-specific GUID-ed structure in the chain
3) Qemu search the GUID-ed chain from the fixed GPA and find the TDX-specific
    GUID-ed structure based on TDX-specific GUID.
Is the expected process for QEMU?

> 
> > On slide 19, the mucking with the reset vector really worries me
> > because we don't have that much space to play with.  Given that you're
> > starting in 32 bit mode and can thus enter anywhere in the lower 4GB,
> > why not simply use a different and TDX specific entry point?
>
> What's more, we should use a dedicated ResetVector (through a DSC+FDF
> dedicated solely to TDX).
> 
If TDVF has a separate DSC/FDF, then this is not a problem. Let's wait for a
conclusion to the *one binary* solution.
Thanks for your suggestion.
> 
> > On all the Tcg2 changes: what about installing a vTPM driver that
> > simply translates to your MSRs?  That way we can use all the standard
> > TCG code as is?
> 
> I believe I made the same comment in point (20) (see URL above).
> 
I will answer this comments in my later response. Thanks.
> 
> > Slide 41: IOMMU operation.
> 
> That's more like slides 40 and 42, no?
> 
> 
> > The implication is that you only transition to unencrypted memory for
> > DMA during the actual operation,
> 
> Yes, this is the idea behind EDKII_IOMMU_PROTOCOL, which
> OvmfPkg/IoMmuDxe implements (for SEV only, currently).
> 
> 
> > so do I have it correct that the guest writes DMA to encrypted memory,
> > then the iommu marks the region as unencrypted and transforms the
> > memory to be in the clear and then transforms it back after the DMA
> > operation completes?
> 
> Effectively, yes. (Your summary corresponds to a BusMasterRead
> operation.)
> 
In TDX there are the concepts of Private-Memory and Shared-Memory. 
By default the memory are private. Before the DMA operation, the private
memory should be converted to Shared-Memory by setting the S-Bit. Then
VMM and Guest can do the DMA operation.
(The difference is that in TDX even the Shared-Memory is encrypted with 
a shared-key between VMM and Guest. So we call it Shared-Memory)
So all the changes in IOMMU by TDX is just to customize the page 
decryption / encryption primitives in the driver , and the general logic will not
be touched.
> 
> > Given that SEV operates quite happily with always in the clear DMA
> > buffers,
> 
> I don't understand this comment -- is it a statement about SEV as a technology,
> or about OvmfPkg/IoMmuDxe?
> 
> Specifically in the context of OvmfPkg/IoMmuDxe, there is no "always-in-the-
> clear DMA".
> 
> EDKII_IOMMU_PROTOCOL was designed to fit cleanly into the Map(), Unmap(),
> AllocateBuffer(), FreeBuffer() terminology of the UEFI standard
> EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL and EFI_PCI_IO_PROTOCOL. As far as I
> can tell, the original use case for EDKII_IOMMU_PROTOCOL was VT-d on bare
> metal, but the protocol proved a good match for SEV too.
> 
> VIRTIO_DEVICE_PROTOCOL has similar member functions
> (AllocateSharedPages, FreeSharedPages, MapSharedBuffer,
> UnmapSharedBuffer).
> 
> As long as a PCI device driver (or virtio driver) uses these member functions
> judiciously, only "BusMasterCommonBuffer" operations will be backed by long-
> term plaintext (decrypted) pages. One-shot read and write transactions will be
> backed by plaintext (decrypted) pages only as long as necessary.
> 
> The transitions you outline already happen in any plain SEV guest that uses PCI
> DMA or virtio.
> 
> 
> > this seems to have the potential to be a performance problem, but what
> > security does it gain?
>
As I mentioned above, in TDX DMA operation even the Shared-Memory is encrypted
by a shared-key between VMM and Guest. It is not *plain-text* outside VMM&Guest.
>
> We have not experienced performance problems due to this kind of IOMMU
> protocol usage, when booting SEV guests.
> 
In our test, we don't see the performance problem when booting TDX guests.
We do have the performance issue in "Accept Pages". But we have several solutions
to resolve this performance. See below link.
https://software.intel.com/content/dam/develop/external/us/en/documents/tdx-virtual-firmware-design-guide-rev-1.pdf
Section 7.8 Optimization Consideration.
>
> The basic goal was to keep everything as tightly encrypted as possible (as
> permitted by the individual PCI or Virtio driver, through its conservative usage
> of BusMasterCommonBuffer operations).
> 
> I won't claim that it has zero performance impact, but we should remember
> the purpose that firmware serves (namely, "booting an operating system").
> Really -- I don't recall any performance issues. This applies to such virtio
> devices & drivers too that aren't "bootable", such as virtio-gpu-pci
> (VirtioGpuDxe) and virtio-rng-pci (VirtioRngDxe).
> 
> (
> 
>   If you enable verbose logs, OvmfPkg/IoMmuDxe does produce an immense
>   amount of messages (with the express purpose of a human reading
>   through them, and matching up decryption and re-encryption actions --
>   I've done it, likely with some ad-hoc scripts). *This* does slow down
>   the boot considerably (if you actually enable the QEMU debug console),
>   but for a different reason: producing debug logs through the QEMU
>   debug console (IO Port) is very-very costly in a SEV guest. Not just
>   because an IO port trap may be more expensive in a SEV guest, but
>   because SEV does not support REP OUTSB, so every debug character
>   written traps separately, as opposed to every line written. See
>   the following commits:
> 
>   - b6d11d7c4678 ("MdePkg: BaseIoLibIntrinsic (IoLib class) library",
>     2017-04-13),
> 
>   - 97353a9c914d ("OvmfPkg: Update dsc to use IoLib from
>     BaseIoLibIntrinsicSev.inf", 2017-07-10),
> 
>   - 98a4d04e8fda ("MdePkg/BaseIoLibIntrinsic: fix SEV (=unrolled)
>     variants of IoWriteFifoXX()", 2017-09-11),
> 
>   - c09d9571300a ("OvmfPkg: save on I/O port accesses when the debug
>     port is not in use", 2017-11-17).
> 
> )
> 
> From my perspective, I find the changes proposed for OvmfPkg/IoMmuDxe to
> be among the least intrusive of the whole slide deck (after Min Xu confirmed
> that the intent was really only to customize the page decryption / encryption
> primitives in the driver, and to leave the general logic untouched).
> 
> That's not to say that I'm unhappy about this topic being raised. To the
> contrary!
> 
> Thanks
> Laszlo
> 
Thanks
Min

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Laszlo Ersek]

On 06/09/21 02:58, Xu, Min M wrote:
> On 06/09/2021 3:33 AM, Laszlo wrote:
>> On 06/08/21 18:01, James Bottomley wrote:

>>> On your slide 13 Question: "Open: How will the QEMU find the metadata
>>> location?" can't you just use the mechanism for SEV that's already
>>> upstream in both QEMU and OVMF?
>>
>> I think I made the same comment, in different words. (Point (12) at
>> <https://listman.redhat.com/archives/edk2-devel-archive/2021-
>> June/msg00143.html>.)
>>
> So my understanding to this solution is that: 
> 1) GUID-ed structure chain is started from a fixed GPA in ResetVector. 
> 2) Append a TDX-specific GUID-ed structure in the chain
> 3) Qemu search the GUID-ed chain from the fixed GPA and find the TDX-specific
>     GUID-ed structure based on TDX-specific GUID.
> Is the expected process for QEMU?

This is my understanding, yes; James will know more details though.

[...]

Thanks,
Laszlo

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[James Bottomley]

On Wed, 2021-06-09 at 13:00 +0200, Laszlo Ersek wrote:
> On 06/09/21 02:58, Xu, Min M wrote:
> > On 06/09/2021 3:33 AM, Laszlo wrote:
> > > On 06/08/21 18:01, James Bottomley wrote:
> > > > On your slide 13 Question: "Open: How will the QEMU find the
> > > > metadata location?" can't you just use the mechanism for SEV
> > > > that's already upstream in both QEMU and OVMF?
> > > 
> > > I think I made the same comment, in different words. (Point (12)
> > > at
> > > <https://listman.redhat.com/archives/edk2-devel-archive/2021-
> > > June/msg00143.html>.)
> > > 
> > So my understanding to this solution is that: 
> > 1) GUID-ed structure chain is started from a fixed GPA in 
> >    ResetVector. 
> > 2) Append a TDX-specific GUID-ed structure in the chain
> > 3) Qemu search the GUID-ed chain from the fixed GPA and find the 
> >    TDX-specific GUID-ed structure based on TDX-specific GUID.
> > Is the expected process for QEMU?
> 
> This is my understanding, yes; James will know more details though.

Pretty much, yes.  The guided structure is designed as a backwards
table, so you can tell if it's present or not by looking for the table
guid (96b582de-1fb2-45f7-baea-a366c55a082d) at 0xffffffd0.  If you find
that, it gives you the size of the table as the u16 preceding the GUID.
All entries are of the form

<variable size data> <u16 tot len inc guid> <guid>

You can see how it works in

OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm

Beginning around line 35.

In QEMU you want the function pc_system_ovmf_table_find() which is in
hw/i386/pc_sysfw.c and finds entries by guid.

James

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Min Xu]

On 06/09/2021 12:01 AM, James Bottomley wrote:
> It looks like I'll be travelling that day, but should be able to attend at least the
> first 45 minutes of the design review from the airport lounge.
>
Thanks much James!
 
> On TdMailbox and TdHob, we already have two SEV pages in the MEMFD and
> since TDX and SEV is an either/or, could we simply not rename both pages and
> use them for either boot depending on what CPU type is detected, so we only
> have two MEMFD pages, not four?
>
Agree. A good idea.
> 
> On your slide 13 Question: "Open: How will the QEMU find the metadata
> location?" can't you just use the mechanism for SEV that's already upstream in
> both QEMU and OVMF?
>
I have answered this comments in my last answer to Laszlo.

>
> On slide 19, the mucking with the reset vector really worries me because we
> don't have that much space to play with.  Given that you're starting in 32 bit
> mode and can thus enter anywhere in the lower 4GB, why not simply use a
> different and TDX specific entry point?
>
If TDVF has a separate DSF/FDF, this is not a problem.

I once think about below solution, that different mode goes to its specific entry point.
For example:
    real-mode goes to 0xfffffff0, 
    protected-mode goes to 0xffffffe0, 
    long-mode goes to 0xffffffd0. 

Let's wait for a conclusion to the *one binary* solution.

> 
> I'm not quite sure why you don't have a PEI phase, since TdxStartupLib seems
> effectively to be PEI.
>
I will answer this comments in my next mail. Thanks
>
> On all the Tcg2 changes: what about installing a vTPM driver that simply
> translates to your MSRs?  That way we can use all the standard TCG code as is?
> Plus then we could do SEV-SNP measurement through an actual vTPM running
> at higher VMPL or something.
>
I don’t quite understand "installing a vTPM driver". Can you explain more about
the vTpm driver? Do you mean TDX specific RTMR extending is implemented in the
"vTpm driver" ?
 
>
> Slide 41: IOMMU operation.  The implication is that you only transition to
> unencrypted memory for DMA during the actual operation, so do I have it
> correct that the guest writes DMA to encrypted memory, then the iommu
> marks the region as unencrypted and transforms the memory to be in the clear
> and then transforms it back after the DMA operation completes?  Given that
> SEV operates quite happily with always in the clear DMA buffers, this seems to
> have the potential to be a performance problem, but what security does it gain?
> 
See my comments in my last answer to Laszlo.

Thanks!
Min

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[James Bottomley]

On Wed, 2021-06-09 at 02:01 +0000, Xu, Min M wrote:
> On 06/09/2021 12:01 AM, James Bottomley wrote:
[...]
> > On slide 19, the mucking with the reset vector really worries me
> > because we don't have that much space to play with.  Given that
> > you're starting in 32 bit mode and can thus enter anywhere in the
> > lower 4GB, why not simply use a different and TDX specific entry
> > point?
> > 
> If TDVF has a separate DSF/FDF, this is not a problem.
> 
> I once think about below solution, that different mode goes to its
> specific entry point.
> For example:
>     real-mode goes to 0xfffffff0, 
>     protected-mode goes to 0xffffffe0, 
>     long-mode goes to 0xffffffd0. 

That would cut across the ApEntrypoint and the guidedStructureEnd. 
However, nothing says anything in the reset vector guided structure has
to be data ... so it could equally well be code.  That means we can do
guid based entries that contain the 32 bit real and 64 bit entry
points.  This would also come with the added advantage that we can scan
the OVMF binary to see what entry points it supports.

James

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Paolo Bonzini]

On 09/06/21 16:28, James Bottomley wrote:
> That would cut across the ApEntrypoint and the guidedStructureEnd.
> However, nothing says anything in the reset vector guided structure has
> to be data ... so it could equally well be code.  That means we can do
> guid based entries that contain the 32 bit real and 64 bit entry
> points.  This would also come with the added advantage that we can scan
> the OVMF binary to see what entry points it supports.

Isn't the initial state included in the save area just like for SEV-ES? 
  So it's not even QEMU, but rather some external tool that builds the 
encrypted image, that needs to understand that GUIDed structure.

The GUIDed structure can either include the entry point code; or it 
could have room for a couple 8-byte pointers since any fixed-size area 
in the GUIDed structure would be just a jump anyway.

Paolo

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[James Bottomley]

On Wed, 2021-06-09 at 17:47 +0200, Paolo Bonzini wrote:
> On 09/06/21 16:28, James Bottomley wrote:
> > That would cut across the ApEntrypoint and the guidedStructureEnd.
> > However, nothing says anything in the reset vector guided structure
> > has to be data ... so it could equally well be code.  That means we
> > can do guid based entries that contain the 32 bit real and 64 bit
> > entry points.  This would also come with the added advantage that
> > we can scan the OVMF binary to see what entry points it supports.
> 
> Isn't the initial state included in the save area just like for SEV-
> ES?

Initial state of what?  We currently have two entries: one points to
the address and size of the secrets page and the other gives the
address of the ES work area page that's used for AP reset.

>    So it's not even QEMU, but rather some external tool that builds
> the encrypted image, that needs to understand that GUIDed structure.

Yes, it's really to make the configuration of the OVMF blob somewhat
introspectable.  The current consumer is QEMU, but I see no reason why
other tools might not use this mechanism as well.

> The GUIDed structure can either include the entry point code; or it 
> could have room for a couple 8-byte pointers since any fixed-size
> area in the GUIDed structure would be just a jump anyway.

Well, exactly ... depending on what the requirement is we can do pretty
much anything with the data contents with the only caveat that it's
currently constructed by an asm file, so we don't quite have the full
macro power of C available.  However, symbol resolution is definitely
possible and quite easy.

James

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Erdem Aktas]

Hi all,

Sorry for the late reply.  I like to add some clarification on "one
binary". I feel like the way everyone uses the term "one binary" in
the email threads is causing some confusion.

As I have tried to explain before, we are not looking for everything
in a single binary. As Laszlo has mentioned in a lot of places, some
additional features are TDX specific and not worth pushing into the
OvmfPkgX64.dsc.

What we are asking with "one binary" is: Simply enabling OVMF + a
guest OS to boot in a TDX domain without breaking any existing
functionality.  Intel should put everything else (specifically related
to remote attestation) in a separate platform configuration. This
aligns well with Laszlo's perspective and it is similar to what AMD is
doing as far as I can see.

Enabling a minimum functionality in OvmfPkgX64.dsc without breaking
existing functionality will allow a lot of flexibility for us for
integration/testing and productionization.
A separate platform  configuration file can be used to provide all the
security guarantees that TDX provides.

Based on the above clarification, Intel has updated their slides
accordingly - I really appreciate their hard work and community
collaboration spirit. I am hoping that this clears up the confusion.

On Thu, Jun 3, 2021 at 9:12 AM Laszlo Ersek <lersek@redhat.com> wrote:

> My point is that the "one binary" that the slide deck refers to (i.e.,
> OvmfPkgX64.dsc) might prove OK for utilizing the Intel TDX *technology*
> in itself. Simply enabling OVMF + a guest OS to boot in a TDX domain.

This is what we are asking as a single binary.

> But "OvmfPkgX64.dsc" is *not* the "one binary" that is suitable for
> remote attestation, which has a much broader scope, involving multiple
> computers, networking, deployment, guest-owner/host-owner separation,
> whatever. For the latter, we needed a separate platform anyway, even
> with only SEV in mind; that's why "OvmfPkg/AmdSev/AmdSevX64.dsc" exists.

This is okay for us.

> (10) This slide (slide 11) basically describes an intrusive
> reorganization of "OvmfPkgX64.fdf". I don't think I can agree to that.
> While confidential computing is important, it is not relevant for many
> users. Even if we don't cause outright regressions for existent setups,
> the maintenance cost of the traditional OVMF platform will skyrocket.
>
> The big bunch of areas that SEV-ES introduced to MEMFD is already a big
> complication. I'd feel much better if we could isolate all that to a
> dedicated "remote attested boot" firmware platform, and not risk the
> functionality and maintenance of the traditional platform. I think this
> ties in with my comment (1).
>
> For example, seeing a configuration firmware volume (CFV) with secure
> boot keys embedded, in the "usual" FDF, will confuse lots of people, me
> included. In the traditional OVMF use case, we use a different method:
> namely OvmfPkg/EnrollDefaultKeys, for "priming" a variable store
> template, in the build environment.

Embedding secure keys might be a good idea to remove the VMM from the
TCB but I agree with Laszlo, OvmfPkgX64 is not the best place to do
this.  The existing secure boot flow should not be changed. Any
additional improvement to reduce the TCB can go TDX specific platform
communication.

> (12) My comment is that the GUID-ed structure chain already starts at a
> fixed GPA (the "AMD SEV option"). Ordering between GUID-ed structures is
> irrelevant, so any TDX-specific structures should be eligible for
> appending to, prepending to, or intermixing with, other (possibly
> SEV-specific) structures. There need not be a separate entry point, just
> different GUIDS.

I think there is a confusion in slide #13. I agree that the GUIDed
table should solve this issue. And I do not think there is any
dependency on SEV patches. I am assuming anyone can easily add an
entry to the GUIDed table and based on other responses, this seems
like a trivial implementation.

> (13) Regarding "4G-0x20[0x10] is OVMF AP reset vector (used in OVMF
> implementation)" -- I think this is a typo: this "AP reset vector" is
> *not* used in OVMF. To my knowledge, it is a vestige from the UefiCpuPkg
> reset vector. In OVMF, APs are booted via MpInitLib (in multiple
> firmware phases), using INIT-SIPI-SIPI, and the reset vector for the
> APs, posited through those IPIs, is prepared in low RAM.
>

I am guessing what Intel refers to is "SEV-ES resetblock" which sets
the AP reset vector (jump address) address.

> (22) EmuVariableFvbRuntimeDxe
>
> Ouch, this is an unpleasant surprise.
>
> First, if you know for a fact that pflash is not part of the *board* in
> any TDX setup, then pulling

Copying configuration variables into configuration volume is "good"
to reduce the TCB but not necessary to boot a guest with TDX is
enabled. Again it goes under the topic of what is minimum and what is
secure and TDX specific platform configuration.
So I think it should not be part of OvmfPkgX64.dsc


On Thu, Jun 3, 2021 at 4:19 PM Yao, Jiewen <jiewen.yao@intel.com> wrote:
>
> Hi Laszlo.
>
> To clarify your "one binary" feedback below, do you mean you suggest A) create a separate DSC (for example OvmfPkg/ConfidentialComputing.dsc) for a full solution including AMD SEC + Intel TDX + NonConfidentialComputing?
> Or B) to create a standalone DSC for Intel TDX (for example, create a OvmfPkg/IntelTdx/IntelTdxXS64.dsc) ?
>
> To me, A) does not change too much, we just create another DSC file - that is it.
> Then the original OvmfPkgX64.dsc will only be used for POC/Testing purpose. It does not provide any security guarantee.
> (The threat model is: we don't trust VMM. Without attestation, you don't know if VMM modified the OVMF.)

I think we should separate what is minimum which should go to the
OvmfPkgX64.dsc to enable the TDX and what is required for removing the
VMM from the TCB. Anything improving security guarantees can go to TDX
specific configuration files.


On Sun, Jun 6, 2021 at 5:49 AM Xu, Min M <min.m.xu@intel.com> wrote:
>
> On June 6, 2021 7:30 PM, Michael Brown Wrote:
> > On 06/06/2021 03:03, Min Xu wrote:
> > >> (11) "Page table should support both 4-level and 5-level page table"
> > >>
> > >> As a general development strategy, I would suggest building TDX
> > >> support in small, well-isolated layers. 5-level paging is not enabled
> > >> (has never been tested, to my knowledge) with OVMF on QEMU/KVM,
> > >> regardless of confidential computing, for starters. If 5-level paging
> > >> is a strict requirement for TDX, then it arguably needs to be
> > >> implemented independently of TDX, at first. So that the common edk2
> > >> architecture be at least testable on QEMU/KVM with 5-level paging
> > >> enabled.
> > >>
> > > Yes, 5-level paging is a strict requirement for TDX. I would wait for
> > > the conclusion of the *one binary*.
> >
> > The "one binary" decision isn't relevant here, is it?  It would make more
> > sense to implement 5-level paging within the base EDK2 architecture.  This
> > would allow that feature to be tested in isolation from TDX (and
> > consequently tested more widely), and would reduce the distance between
> > standard builds and TDX builds.
> >
>
> In our first version of TDVF, a static 5-level page table is used. It is simple and
> straight forward. But for *one binary* solution, we have to consider the compatibility
> with the current 4-level page table. That's why I said "I would wait for the conclusion
> of the *one binary*"
>
> Thanks for the suggestion. We will discuss the it internally first.
>
> > Michael

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Min Xu]

[-- Attachment #1: Type: text/plain, Size: 1664 bytes --]

Hi, All
Thanks much for the valuable comments and discussion about the design.
We have updated the slides (v0.9) in below link. If some comments or concerns are not answered/addressed in the new slides, please don't hesitate to tell us. We do want to answer/address all the comments/concerns. But to be honest it is a rather complicated one and we appreciate your feedbacks.
https://edk2.groups.io/g/devel/files/Designs/2021/0611/TDVF_Design_Review%28v0.9%29.pptx

Thanks much!

Xu Min


From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Yao, Jiewen
Sent: Thursday, June 3, 2021 9:51 PM
To: rfc@edk2.groups.io; devel@edk2.groups.io
Cc: jejb@linux.ibm.com; Laszlo Ersek <lersek@redhat.com>; Brijesh Singh <brijesh.singh@amd.com>; Tom Lendacky <thomas.lendacky@amd.com>; erdemaktas@google.com; cho@microsoft.com; bret.barkelew@microsoft.com; Jon Lange <jlange@microsoft.com>; Karen Noel <knoel@redhat.com>; Paolo Bonzini <pbonzini@redhat.com>; Nathaniel McCallum <npmccallum@redhat.com>; Dr. David Alan Gilbert <dgilbert@redhat.com>; Ademar de Souza Reis Jr. <areis@redhat.com>
Subject: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

Hi, All
We plan to do a design review for TDVF in OVMF package.


The TDVF Design slides for TinaoCore Design Review Meeting (Jun 11) is now available in blow link: https://edk2.groups.io/g/devel/files/Designs/2021/0611.

The Bugzilla is https://bugzilla.tianocore.org/show_bug.cgi?id=3429



You can have an offline review first. You comments will be warmly welcomed and we will continuously update the slides based on the feedbacks.



Thank you

Yao Jiewen







[-- Attachment #2: Type: text/html, Size: 5270 bytes --]

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[James Bottomley]

On Thu, 2021-06-10 at 22:30 +0000, Xu, Min M wrote:
> Hi, All
> Thanks much for the valuable comments and discussion about the
> design.
> We have updated the slides (v0.9) in below link. If some comments or
> concerns are not answered/addressed in the new slides, please don't
> hesitate to tell us. We do want to answer/address all the
> comments/concerns. But to be honest it is a rather complicated one
> and we appreciate your feedbacks.
> https://edk2.groups.io/g/devel/files/Designs/2021/0611/TDVF_Design_Review%28v0.9%29.pptx

What's the url of the meeting?  Apparently it isn't in the calendar
entry.

James

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Yao, Jiewen]

[-- Attachment #1: Type: text/plain, Size: 2587 bytes --]

Hi James.
I attached the invitation and copied all content below:

==================================
## TOPIC

1. NA

For more info, see here: https://www.tianocore.org/design-meeting/

---
## Microsoft Teams meeting

### Join on your computer or mobile app

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==================================





> -----Original Message-----
> From: James Bottomley <jejb@linux.ibm.com>
> Sent: Friday, June 11, 2021 9:33 AM
> To: Xu, Min M <min.m.xu@intel.com>; devel@edk2.groups.io; Yao, Jiewen
> <jiewen.yao@intel.com>; rfc@edk2.groups.io
> Cc: Laszlo Ersek <lersek@redhat.com>; Brijesh Singh <brijesh.singh@amd.com>;
> Tom Lendacky <thomas.lendacky@amd.com>; erdemaktas@google.com;
> cho@microsoft.com; bret.barkelew@microsoft.com; Jon Lange
> <jlange@microsoft.com>; Karen Noel <knoel@redhat.com>; Paolo Bonzini
> <pbonzini@redhat.com>; Nathaniel McCallum <npmccallum@redhat.com>; Dr.
> David Alan Gilbert <dgilbert@redhat.com>; Ademar de Souza Reis Jr.
> <areis@redhat.com>
> Subject: Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF
> 
> On Thu, 2021-06-10 at 22:30 +0000, Xu, Min M wrote:
> > Hi, All
> > Thanks much for the valuable comments and discussion about the
> > design.
> > We have updated the slides (v0.9) in below link. If some comments or
> > concerns are not answered/addressed in the new slides, please don't
> > hesitate to tell us. We do want to answer/address all the
> > comments/concerns. But to be honest it is a rather complicated one
> > and we appreciate your feedbacks.
> >
> https://edk2.groups.io/g/devel/files/Designs/2021/0611/TDVF_Design_Review
> %28v0.9%29.pptx
> 
> What's the url of the meeting?  Apparently it isn't in the calendar
> entry.
> 
> James
> 


[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
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 anocore.org/design-meeting/\n\n---\n## Microsoft Teams meeting\n\n### Joi
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 n\nFor more info\, see here: https://www.tianocore.org/design-meeting/\n\
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DTSTART:20210611T013000Z
DTEND:20210611T023000Z
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 https://www.tianocore.org/design-meeting/\n\n---\n## Microsoft Teams meet
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Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[James Bottomley]

On Fri, 2021-06-11 at 01:36 +0000, Yao, Jiewen wrote:
> Hi James.
> I attached the invitation and copied all content below:
> 
> ==================================
> ## TOPIC
> 
> 1. NA
> 
> For more info, see here: https://www.tianocore.org/design-meeting/
> 
> ---
> ## Microsoft Teams meeting
> 
> ### Join on your computer or mobile app
> 
> [Click here to join the meeting](
> https://teams.microsoft.com/l/meetup-join/19%3ameeting_OTNmZTNhMWEtOWQwNi00ZTdkLWI5NDgtYTFmYjNkOWI0ZDg4%40thread.v2/0?context=%7b%22Tid%22%3a%2246c98d88-e344-4ed4-8496-4ed7712e255d%22%2c%22Oid%22%3a%2255d36a50-78be-4ced-bc27-3d06c576cc19%22%7d
> )

Apparently it's not possible to join from a web browser: is there a
dial in?

James

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[James Bottomley]

On Thu, 2021-06-10 at 21:38 -0400, James Bottomley wrote:
> On Fri, 2021-06-11 at 01:36 +0000, Yao, Jiewen wrote:
> > Hi James.
> > I attached the invitation and copied all content below:
> > 
> > ==================================
> > ## TOPIC
> > 
> > 1. NA
> > 
> > For more info, see here: https://www.tianocore.org/design-meeting/
> > 
> > ---
> > ## Microsoft Teams meeting
> > 
> > ### Join on your computer or mobile app
> > 
> > [Click here to join the meeting](
> > https://teams.microsoft.com/l/meetup-join/19%3ameeting_OTNmZTNhMWEtOWQwNi00ZTdkLWI5NDgtYTFmYjNkOWI0ZDg4%40thread.v2/0?context=%7b%22Tid%22%3a%2246c98d88-e344-4ed4-8496-4ed7712e255d%22%2c%22Oid%22%3a%2255d36a50-78be-4ced-bc27-3d06c576cc19%22%7d
> > )
> 
> Apparently it's not possible to join from a web browser: is there a
> dial in?

In the absence of a dial in, I'll view the recording.  I did most of my
comments in the email thread anyway and I'll be boarding my next flight
soon.

However, next time can we hold meetings with usable web based meeting
technologies, like zoom or webex?  It's not feasible to demand
downloading gigabytes of app from a remote location ... even when it
works, which this one doesn't seem to do: the app download just keeps
going back to the meeting screen.

Thanks,

James

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Min Xu]

[-- Attachment #1: Type: text/plain, Size: 4527 bytes --]

In today's TianoCore Design Meeting we reviewed the Overview Section (from slide 1 to 20). Thanks much for the valuable feedbacks and comments. The meeting minutes will be sent out soon.

To address the concerns of the *one binary* solution in previous discussion, we propose 2 Configurations for TDVF to upstream. (slide 6 - 8)



Config-A:

  *   Merge the *basic* TDVF feature to existing OvmfX64Pkg.dsc. (Align with existing SEV)
  *   Threat model: VMM is NOT out of TCB. (We don't make things worse.)
  *   The OvmfX64Pkg.dsc includes SEV/TDX/normal OVMF basic boot capability. The final binary can run on SEV/TDX/normal OVMF
  *   No changes to existing OvmfPkgX64 image layout.
  *   No need to add additional security features if they do not exist today
  *   No need to remove features if they exist today.
  *   RTMR is not supported
  *   PEI phase is NOT skipped in either Td or Non-Td



Config-B:

  *   Add a standalone IntelTdx.dsc to a TDX specific directory for a *full* feature TDVF. (Align with existing SEV)
  *   Threat model: VMM is out of TCB. (We need necessary change to prevent attack from VMM)
  *   IntelTdx.dsc includes TDX/normal OVMF basic boot capability. The final binary can run on TDX/normal OVMF
  *   It might eventually merge with AmdSev.dsc, but NOT at this point of time. And we don't know when it will happen. We need sync with AMD in the community, after both of us think the solutions are mature to merge.
  *   Need to add necessary security feature as mandatory requirement, such as RTMR based Trusted Boot support
  *   Need to remove unnecessary attack surfaces, such as network stack.


From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Min Xu
Sent: Friday, June 11, 2021 6:30 AM
To: devel@edk2.groups.io; Yao, Jiewen <jiewen.yao@intel.com>; rfc@edk2.groups.io
Cc: jejb@linux.ibm.com; Laszlo Ersek <lersek@redhat.com>; Brijesh Singh <brijesh.singh@amd.com>; Tom Lendacky <thomas.lendacky@amd.com>; erdemaktas@google.com; cho@microsoft.com; bret.barkelew@microsoft.com; Jon Lange <jlange@microsoft.com>; Karen Noel <knoel@redhat.com>; Paolo Bonzini <pbonzini@redhat.com>; Nathaniel McCallum <npmccallum@redhat.com>; Dr. David Alan Gilbert <dgilbert@redhat.com>; Ademar de Souza Reis Jr. <areis@redhat.com>
Subject: Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

Hi, All
Thanks much for the valuable comments and discussion about the design.
We have updated the slides (v0.9) in below link. If some comments or concerns are not answered/addressed in the new slides, please don't hesitate to tell us. We do want to answer/address all the comments/concerns. But to be honest it is a rather complicated one and we appreciate your feedbacks.
https://edk2.groups.io/g/devel/files/Designs/2021/0611/TDVF_Design_Review%28v0.9%29.pptx

Thanks much!

Xu Min


From: devel@edk2.groups.io<mailto:devel@edk2.groups.io> <devel@edk2.groups.io<mailto:devel@edk2.groups.io>> On Behalf Of Yao, Jiewen
Sent: Thursday, June 3, 2021 9:51 PM
To: rfc@edk2.groups.io<mailto:rfc@edk2.groups.io>; devel@edk2.groups.io<mailto:devel@edk2.groups.io>
Cc: jejb@linux.ibm.com<mailto:jejb@linux.ibm.com>; Laszlo Ersek <lersek@redhat.com<mailto:lersek@redhat.com>>; Brijesh Singh <brijesh.singh@amd.com<mailto:brijesh.singh@amd.com>>; Tom Lendacky <thomas.lendacky@amd.com<mailto:thomas.lendacky@amd.com>>; erdemaktas@google.com<mailto:erdemaktas@google.com>; cho@microsoft.com<mailto:cho@microsoft.com>; bret.barkelew@microsoft.com<mailto:bret.barkelew@microsoft.com>; Jon Lange <jlange@microsoft.com<mailto:jlange@microsoft.com>>; Karen Noel <knoel@redhat.com<mailto:knoel@redhat.com>>; Paolo Bonzini <pbonzini@redhat.com<mailto:pbonzini@redhat.com>>; Nathaniel McCallum <npmccallum@redhat.com<mailto:npmccallum@redhat.com>>; Dr. David Alan Gilbert <dgilbert@redhat.com<mailto:dgilbert@redhat.com>>; Ademar de Souza Reis Jr. <areis@redhat.com<mailto:areis@redhat.com>>
Subject: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

Hi, All
We plan to do a design review for TDVF in OVMF package.


The TDVF Design slides for TinaoCore Design Review Meeting (Jun 11) is now available in blow link: https://edk2.groups.io/g/devel/files/Designs/2021/0611.

The Bugzilla is https://bugzilla.tianocore.org/show_bug.cgi?id=3429



You can have an offline review first. You comments will be warmly welcomed and we will continuously update the slides based on the feedbacks.



Thank you

Yao Jiewen







[-- Attachment #2: Type: text/html, Size: 14808 bytes --]

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Laszlo Ersek]

Hi,

On 06/11/21 08:37, Xu, Min M wrote:
> In today's TianoCore Design Meeting we reviewed the Overview Section (from slide 1 to 20). Thanks much for the valuable feedbacks and comments. The meeting minutes will be sent out soon.
> 
> To address the concerns of the *one binary* solution in previous discussion, we propose 2 Configurations for TDVF to upstream. (slide 6 - 8)
> 
> 
> 
> Config-A:
> 
>   *   Merge the *basic* TDVF feature to existing OvmfX64Pkg.dsc. (Align with existing SEV)
>   *   Threat model: VMM is NOT out of TCB. (We don't make things worse.)
>   *   The OvmfX64Pkg.dsc includes SEV/TDX/normal OVMF basic boot capability. The final binary can run on SEV/TDX/normal OVMF
>   *   No changes to existing OvmfPkgX64 image layout.
>   *   No need to add additional security features if they do not exist today
>   *   No need to remove features if they exist today.
>   *   RTMR is not supported
>   *   PEI phase is NOT skipped in either Td or Non-Td

(so this is "Config-A / Option B", per slide 9 in the v0.9 slide deck)

> 
> 
> 
> Config-B:
> 
>   *   Add a standalone IntelTdx.dsc to a TDX specific directory for a *full* feature TDVF. (Align with existing SEV)
>   *   Threat model: VMM is out of TCB. (We need necessary change to prevent attack from VMM)
>   *   IntelTdx.dsc includes TDX/normal OVMF basic boot capability. The final binary can run on TDX/normal OVMF
>   *   It might eventually merge with AmdSev.dsc, but NOT at this point of time. And we don't know when it will happen. We need sync with AMD in the community, after both of us think the solutions are mature to merge.
>   *   Need to add necessary security feature as mandatory requirement, such as RTMR based Trusted Boot support
>   *   Need to remove unnecessary attack surfaces, such as network stack.

After reading the above, and checking slides 6 through 10 of the v0.9
slide deck:

- I prefer Config-B (IntelTdx.dsc).

This is in accordance with what I wrote earlier about "OvmfPkgX64.dsc"
maintainability and regressions.

Additionally (given that a full-featured TDVF is the ultimate goal), I
see the advance from "Config-A / option B" to "Config-B" a lot less
*incremental* than the step from "OvmfPkgX64.dsc" to "AmdSev.dsc" was.

Put differently, I think that any TDX work targeted at "OvmfPkgX64.dsc"
is going to prove less useful for the final "IntelTdx.dsc" than how
reusable SEV work from "OvmfPkgX64.dsc" did for "AmdSev.dsc".

Put yet differently, I'm concerned that a part of the TDX work for
"OvmfPkgX64.dsc" might be a waste, with an eye towards the ultimate TDVF
feature set ("IntelTdx.dsc").


- I could (very cautiously) live with "Config-A / option B" as the
initial approach. However, we'de have to be ready to make the full split
(the switch-over to "IntelTdx.dsc") at *any point* during development,
in case something turns out to be too intrusive. (And yes, "too
intrusive" is subjective.)

By this I mean that any particular patch towards "Config-A / option B"
could cause me to ask, "please create IntelTdx.dsc now". Note that the
later we make the switch the more painful it could be (= the more
invested in "OvmfPkgX64.dsc" we could be, at that point).

For example, as I stated earlier, "OvmfPkg/AcpiPlatformDxe" is a driver
where I'd like to see zero changes, for either SEV or TDX. If the TD
Mailbox location has to be reported to the OS via the MADT, and QEMU
cannot (or must not) populate that field in the MADT, then a separate,
TDX-specific edk2 driver should locate the MADT (installed technically
by "OvmfPkg/AcpiPlatformDxe", earlier), and update the field.

Thanks,
Laszlo

> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Min Xu
> Sent: Friday, June 11, 2021 6:30 AM
> To: devel@edk2.groups.io; Yao, Jiewen <jiewen.yao@intel.com>; rfc@edk2.groups.io
> Cc: jejb@linux.ibm.com; Laszlo Ersek <lersek@redhat.com>; Brijesh Singh <brijesh.singh@amd.com>; Tom Lendacky <thomas.lendacky@amd.com>; erdemaktas@google.com; cho@microsoft.com; bret.barkelew@microsoft.com; Jon Lange <jlange@microsoft.com>; Karen Noel <knoel@redhat.com>; Paolo Bonzini <pbonzini@redhat.com>; Nathaniel McCallum <npmccallum@redhat.com>; Dr. David Alan Gilbert <dgilbert@redhat.com>; Ademar de Souza Reis Jr. <areis@redhat.com>
> Subject: Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF
> 
> Hi, All
> Thanks much for the valuable comments and discussion about the design.
> We have updated the slides (v0.9) in below link. If some comments or concerns are not answered/addressed in the new slides, please don't hesitate to tell us. We do want to answer/address all the comments/concerns. But to be honest it is a rather complicated one and we appreciate your feedbacks.
> https://edk2.groups.io/g/devel/files/Designs/2021/0611/TDVF_Design_Review%28v0.9%29.pptx
> 
> Thanks much!
> 
> Xu Min
> 
> 
> From: devel@edk2.groups.io<mailto:devel@edk2.groups.io> <devel@edk2.groups.io<mailto:devel@edk2.groups.io>> On Behalf Of Yao, Jiewen
> Sent: Thursday, June 3, 2021 9:51 PM
> To: rfc@edk2.groups.io<mailto:rfc@edk2.groups.io>; devel@edk2.groups.io<mailto:devel@edk2.groups.io>
> Cc: jejb@linux.ibm.com<mailto:jejb@linux.ibm.com>; Laszlo Ersek <lersek@redhat.com<mailto:lersek@redhat.com>>; Brijesh Singh <brijesh.singh@amd.com<mailto:brijesh.singh@amd.com>>; Tom Lendacky <thomas.lendacky@amd.com<mailto:thomas.lendacky@amd.com>>; erdemaktas@google.com<mailto:erdemaktas@google.com>; cho@microsoft.com<mailto:cho@microsoft.com>; bret.barkelew@microsoft.com<mailto:bret.barkelew@microsoft.com>; Jon Lange <jlange@microsoft.com<mailto:jlange@microsoft.com>>; Karen Noel <knoel@redhat.com<mailto:knoel@redhat.com>>; Paolo Bonzini <pbonzini@redhat.com<mailto:pbonzini@redhat.com>>; Nathaniel McCallum <npmccallum@redhat.com<mailto:npmccallum@redhat.com>>; Dr. David Alan Gilbert <dgilbert@redhat.com<mailto:dgilbert@redhat.com>>; Ademar de Souza Reis Jr. <areis@redhat.com<mailto:areis@redhat.com>>
> Subject: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF
> 
> Hi, All
> We plan to do a design review for TDVF in OVMF package.
> 
> 
> The TDVF Design slides for TinaoCore Design Review Meeting (Jun 11) is now available in blow link: https://edk2.groups.io/g/devel/files/Designs/2021/0611.
> 
> The Bugzilla is https://bugzilla.tianocore.org/show_bug.cgi?id=3429
> 
> 
> 
> You can have an offline review first. You comments will be warmly welcomed and we will continuously update the slides based on the feedbacks.
> 
> 
> 
> Thank you
> 
> Yao Jiewen
> 
> 
> 
> 
> 
> 
> 

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Laszlo Ersek]

On 06/22/21 15:34, Laszlo Ersek wrote:
> Hi,
> 
> On 06/11/21 08:37, Xu, Min M wrote:
>> In today's TianoCore Design Meeting we reviewed the Overview Section (from slide 1 to 20). Thanks much for the valuable feedbacks and comments. The meeting minutes will be sent out soon.
>>
>> To address the concerns of the *one binary* solution in previous discussion, we propose 2 Configurations for TDVF to upstream. (slide 6 - 8)
>>
>>
>>
>> Config-A:
>>
>>   *   Merge the *basic* TDVF feature to existing OvmfX64Pkg.dsc. (Align with existing SEV)
>>   *   Threat model: VMM is NOT out of TCB. (We don't make things worse.)
>>   *   The OvmfX64Pkg.dsc includes SEV/TDX/normal OVMF basic boot capability. The final binary can run on SEV/TDX/normal OVMF
>>   *   No changes to existing OvmfPkgX64 image layout.
>>   *   No need to add additional security features if they do not exist today
>>   *   No need to remove features if they exist today.
>>   *   RTMR is not supported
>>   *   PEI phase is NOT skipped in either Td or Non-Td
> 
> (so this is "Config-A / Option B", per slide 9 in the v0.9 slide deck)
> 
>>
>>
>>
>> Config-B:
>>
>>   *   Add a standalone IntelTdx.dsc to a TDX specific directory for a *full* feature TDVF. (Align with existing SEV)
>>   *   Threat model: VMM is out of TCB. (We need necessary change to prevent attack from VMM)
>>   *   IntelTdx.dsc includes TDX/normal OVMF basic boot capability. The final binary can run on TDX/normal OVMF
>>   *   It might eventually merge with AmdSev.dsc, but NOT at this point of time. And we don't know when it will happen. We need sync with AMD in the community, after both of us think the solutions are mature to merge.
>>   *   Need to add necessary security feature as mandatory requirement, such as RTMR based Trusted Boot support
>>   *   Need to remove unnecessary attack surfaces, such as network stack.
> 
> After reading the above, and checking slides 6 through 10 of the v0.9
> slide deck:
> 
> - I prefer Config-B (IntelTdx.dsc).

I should clarify: the relevant part of my preference is not that
"IntelTdx.dsc" contain the *complete* TDVF feature set. The relevant
part (for me) is that "OvmfPkgX64.dsc" *not* be over-complicated for the
sake of TDX, even considering only the "basic" TDVF feature set. It's
fine to implement TDX in two stages ("basic" and "complete"); my point
is that even "basic" should not over-complicate "OvmfPkgX64.dsc".

Thanks
Laszlo


> 
> This is in accordance with what I wrote earlier about "OvmfPkgX64.dsc"
> maintainability and regressions.
> 
> Additionally (given that a full-featured TDVF is the ultimate goal), I
> see the advance from "Config-A / option B" to "Config-B" a lot less
> *incremental* than the step from "OvmfPkgX64.dsc" to "AmdSev.dsc" was.
> 
> Put differently, I think that any TDX work targeted at "OvmfPkgX64.dsc"
> is going to prove less useful for the final "IntelTdx.dsc" than how
> reusable SEV work from "OvmfPkgX64.dsc" did for "AmdSev.dsc".
> 
> Put yet differently, I'm concerned that a part of the TDX work for
> "OvmfPkgX64.dsc" might be a waste, with an eye towards the ultimate TDVF
> feature set ("IntelTdx.dsc").
> 
> 
> - I could (very cautiously) live with "Config-A / option B" as the
> initial approach. However, we'de have to be ready to make the full split
> (the switch-over to "IntelTdx.dsc") at *any point* during development,
> in case something turns out to be too intrusive. (And yes, "too
> intrusive" is subjective.)
> 
> By this I mean that any particular patch towards "Config-A / option B"
> could cause me to ask, "please create IntelTdx.dsc now". Note that the
> later we make the switch the more painful it could be (= the more
> invested in "OvmfPkgX64.dsc" we could be, at that point).
> 
> For example, as I stated earlier, "OvmfPkg/AcpiPlatformDxe" is a driver
> where I'd like to see zero changes, for either SEV or TDX. If the TD
> Mailbox location has to be reported to the OS via the MADT, and QEMU
> cannot (or must not) populate that field in the MADT, then a separate,
> TDX-specific edk2 driver should locate the MADT (installed technically
> by "OvmfPkg/AcpiPlatformDxe", earlier), and update the field.
> 
> Thanks,
> Laszlo
> 
>> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Min Xu
>> Sent: Friday, June 11, 2021 6:30 AM
>> To: devel@edk2.groups.io; Yao, Jiewen <jiewen.yao@intel.com>; rfc@edk2.groups.io
>> Cc: jejb@linux.ibm.com; Laszlo Ersek <lersek@redhat.com>; Brijesh Singh <brijesh.singh@amd.com>; Tom Lendacky <thomas.lendacky@amd.com>; erdemaktas@google.com; cho@microsoft.com; bret.barkelew@microsoft.com; Jon Lange <jlange@microsoft.com>; Karen Noel <knoel@redhat.com>; Paolo Bonzini <pbonzini@redhat.com>; Nathaniel McCallum <npmccallum@redhat.com>; Dr. David Alan Gilbert <dgilbert@redhat.com>; Ademar de Souza Reis Jr. <areis@redhat.com>
>> Subject: Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF
>>
>> Hi, All
>> Thanks much for the valuable comments and discussion about the design.
>> We have updated the slides (v0.9) in below link. If some comments or concerns are not answered/addressed in the new slides, please don't hesitate to tell us. We do want to answer/address all the comments/concerns. But to be honest it is a rather complicated one and we appreciate your feedbacks.
>> https://edk2.groups.io/g/devel/files/Designs/2021/0611/TDVF_Design_Review%28v0.9%29.pptx
>>
>> Thanks much!
>>
>> Xu Min
>>
>>
>> From: devel@edk2.groups.io<mailto:devel@edk2.groups.io> <devel@edk2.groups.io<mailto:devel@edk2.groups.io>> On Behalf Of Yao, Jiewen
>> Sent: Thursday, June 3, 2021 9:51 PM
>> To: rfc@edk2.groups.io<mailto:rfc@edk2.groups.io>; devel@edk2.groups.io<mailto:devel@edk2.groups.io>
>> Cc: jejb@linux.ibm.com<mailto:jejb@linux.ibm.com>; Laszlo Ersek <lersek@redhat.com<mailto:lersek@redhat.com>>; Brijesh Singh <brijesh.singh@amd.com<mailto:brijesh.singh@amd.com>>; Tom Lendacky <thomas.lendacky@amd.com<mailto:thomas.lendacky@amd.com>>; erdemaktas@google.com<mailto:erdemaktas@google.com>; cho@microsoft.com<mailto:cho@microsoft.com>; bret.barkelew@microsoft.com<mailto:bret.barkelew@microsoft.com>; Jon Lange <jlange@microsoft.com<mailto:jlange@microsoft.com>>; Karen Noel <knoel@redhat.com<mailto:knoel@redhat.com>>; Paolo Bonzini <pbonzini@redhat.com<mailto:pbonzini@redhat.com>>; Nathaniel McCallum <npmccallum@redhat.com<mailto:npmccallum@redhat.com>>; Dr. David Alan Gilbert <dgilbert@redhat.com<mailto:dgilbert@redhat.com>>; Ademar de Souza Reis Jr. <areis@redhat.com<mailto:areis@redhat.com>>
>> Subject: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF
>>
>> Hi, All
>> We plan to do a design review for TDVF in OVMF package.
>>
>>
>> The TDVF Design slides for TinaoCore Design Review Meeting (Jun 11) is now available in blow link: https://edk2.groups.io/g/devel/files/Designs/2021/0611.
>>
>> The Bugzilla is https://bugzilla.tianocore.org/show_bug.cgi?id=3429
>>
>>
>>
>> You can have an offline review first. You comments will be warmly welcomed and we will continuously update the slides based on the feedbacks.
>>
>>
>>
>> Thank you
>>
>> Yao Jiewen
>>
>>
>>
>>
>>
>> 
>>
> 

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Min Xu]

On 06/22/2021 9:39 PM, Laszlo wrote:
> 
> I should clarify: the relevant part of my preference is not that "IntelTdx.dsc"
> contain the *complete* TDVF feature set. The relevant part (for me) is that
> "OvmfPkgX64.dsc" *not* be over-complicated for the sake of TDX, even
> considering only the "basic" TDVF feature set. It's fine to implement TDX in two
> stages ("basic" and "complete"); my point is that even "basic" should not over-
> complicate "OvmfPkgX64.dsc".
> 
Thanks much for the comments and we don't want to make OvmfPkgX64.dsc
over-complicated either. 
We have updated the design slides to V0.95 and Slides 6-15 are discussing the
Config-A and Config-B. 
https://edk2.groups.io/g/devel/files/Designs/2021/0611/TDVF_Design_Review%28v0.95%29.pptx
Your comment is always welcome!

Thanks!
Min

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[James Bottomley]

On Thu, 2021-06-24 at 00:24 +0000, Min Xu wrote:
> On 06/22/2021 9:39 PM, Laszlo wrote:
> > I should clarify: the relevant part of my preference is not that
> > "IntelTdx.dsc"
> > contain the *complete* TDVF feature set. The relevant part (for me)
> > is that
> > "OvmfPkgX64.dsc" *not* be over-complicated for the sake of TDX,
> > even
> > considering only the "basic" TDVF feature set. It's fine to
> > implement TDX in two
> > stages ("basic" and "complete"); my point is that even "basic"
> > should not over-
> > complicate "OvmfPkgX64.dsc".
> > 
> Thanks much for the comments and we don't want to make OvmfPkgX64.dsc
> over-complicated either. 
> We have updated the design slides to V0.95 and Slides 6-15 are
> discussing the
> Config-A and Config-B. 
> https://edk2.groups.io/g/devel/files/Designs/2021/0611/TDVF_Design_Review%28v0.95%29.pptx
> Your comment is always welcome!

The mailing list still won't give me that file, can you update it in
the bugzilla:

https://bugzilla.tianocore.org/show_bug.cgi?id=3429

As well, please?

Thanks,

James

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Min Xu]

On 06/24/2021 8:36 AM, James Bottomley wrote: 
> On Thu, 2021-06-24 at 00:24 +0000, Min Xu wrote:
> > On 06/22/2021 9:39 PM, Laszlo wrote:
> > > I should clarify: the relevant part of my preference is not that
> > > "IntelTdx.dsc"
> > > contain the *complete* TDVF feature set. The relevant part (for me)
> > > is that "OvmfPkgX64.dsc" *not* be over-complicated for the sake of
> > > TDX, even considering only the "basic" TDVF feature set. It's fine
> > > to implement TDX in two stages ("basic" and "complete"); my point is
> > > that even "basic"
> > > should not over-
> > > complicate "OvmfPkgX64.dsc".
> > >
> > Thanks much for the comments and we don't want to make OvmfPkgX64.dsc
> > over-complicated either.
> > We have updated the design slides to V0.95 and Slides 6-15 are
> > discussing the Config-A and Config-B.
> > https://edk2.groups.io/g/devel/files/Designs/2021/0611/TDVF_Design_Rev
> > iew%28v0.95%29.pptx
> > Your comment is always welcome!
> 
> The mailing list still won't give me that file, can you update it in the bugzilla:
> 
> https://bugzilla.tianocore.org/show_bug.cgi?id=3429
> 
> As well, please?
>
Sure. TDVF Design Review v0.95 is uploaded to
https://bugzilla.tianocore.org/show_bug.cgi?id=3429
>
Thanks
Min

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Min Xu]

Thanks much everyone who attended 2 sessions of TDVF design review meeting
and lots of valuable comments and feedbacks received. These 2 meetings were
recorded and now uploaded to below link:
Session 1:
https://drive.google.com/file/d/100__tNVe5erNzExySq2SJOprvBN7zz8u/view?usp=sharing
Session 2:
https://drive.google.com/file/d/1aDvtLhLxzniOISljXwjZH0YT_m7EBn8b/view?usp=sharing

Thank you!
Min

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Min Xu]

On 06/22/2021 9:35 PM, Laszlo wrote: 
> 
> For example, as I stated earlier, "OvmfPkg/AcpiPlatformDxe" is a driver where
> I'd like to see zero changes, for either SEV or TDX. If the TD Mailbox location has
> to be reported to the OS via the MADT, and QEMU cannot (or must not)
> populate that field in the MADT, then a separate, TDX-specific edk2 driver should
> locate the MADT (installed technically by "OvmfPkg/AcpiPlatformDxe", earlier),
> and update the field.
> 
We have updated the design of AcpiPlatformDxe. Please see the slides in below link.
https://edk2.groups.io/g/devel/files/Designs/2021/0611/TDVF_Design_Review-AcpiPlatformDxe.pptx

Because MailboxAddress in MADT table is determined in runtime in Tdx, so we 
separate the update of the MADT table in TdxDxe driver and keep AcpiPlatformDxe clean
and shim.
>
>
> Thanks,
> Laszlo
> 
Thanks
Min

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Laszlo Ersek]

On 06/23/21 04:44, Xu, Min M wrote:
> On 06/22/2021 9:35 PM, Laszlo wrote:
>>
>> For example, as I stated earlier, "OvmfPkg/AcpiPlatformDxe" is a
>> driver where I'd like to see zero changes, for either SEV or TDX. If
>> the TD Mailbox location has to be reported to the OS via the MADT,
>> and QEMU cannot (or must not) populate that field in the MADT, then a
>> separate, TDX-specific edk2 driver should locate the MADT (installed
>> technically by "OvmfPkg/AcpiPlatformDxe", earlier), and update the
>> field.
>>
> We have updated the design of AcpiPlatformDxe. Please see the slides
> in below link.
> https://edk2.groups.io/g/devel/files/Designs/2021/0611/TDVF_Design_Review-AcpiPlatformDxe.pptx

Thanks, let me mark this with [1].

>
> Because MailboxAddress in MADT table is determined in runtime in Tdx,
> so we separate the update of the MADT table in TdxDxe driver and keep
> AcpiPlatformDxe clean and shim.

I've now read

  4.3.4 AP information reporting from TDVF to OS

from

  https://software.intel.com/content/dam/develop/external/us/en/documents/tdx-virtual-firmware-design-guide-rev-1.pdf

That section does not go into much detail about the expected MADT
updates / entries.

I've also checked the various MADT subtable types here:

  https://uefi.org/specs/ACPI/6.4/05_ACPI_Software_Programming_Model/ACPI_Software_Programming_Model.html#interrupt-controller-structure-types

It seems that the TDVF spec speaks about subtable type 0 (Processor
Local APIC):

  https://uefi.org/specs/ACPI/6.4/05_ACPI_Software_Programming_Model/ACPI_Software_Programming_Model.html#processor-local-apic-structure

I've also checked "acpidump -b; iasl -d" in a normal guest, to remind
myself of the actual MADT contents that QEMU currently generates. I see
minimally the following subtable types:

  Subtable Type : 00 [Processor Local APIC]
  Subtable Type : 01 [I/O APIC]
  Subtable Type : 02 [Interrupt Source Override]
  Subtable Type : 04 [Local APIC NMI]

Thus, the TDVF spec creates the extremely unfortunate situation where
subtables of types different from 0 are expected from QEMU, but
subtables of type 0 are expected from the firmware.

In this case, QEMU should likely not populate the MADT with any LAPIC (=
type 0) subtables. Then, Option-3 from slide#5 in [1] (uninstalling the
MADT, *extending* the MADT with LAPIC subtables, installing the new
MADT) seems relatively workable.

(

  Note that uninstalling an ACPI table (with EFI_ACPI_TABLE_PROTOCOL)
  that was installed by a different driver previously requires the use
  of EFI_ACPI_SDT_PROTOCOL. That's because the TableKey parameter taken
  by EFI_ACPI_TABLE_PROTOCOL.UninstallAcpiTable() is only available from
  EFI_ACPI_TABLE_PROTOCOL.InstallAcpiTable() -- which the TDX driver
  will not have called --, or from EFI_ACPI_SDT_PROTOCOL.GetAcpiTable().

  EFI_ACPI_SDT_PROTOCOL.RegisterNotify() also exists, but it should be
  avoided. It should not be used to immediately modify or replace the
  MADT as soon as the MADT appears. That's because, upon encountering an
  error, OvmfPkg/AcpiPlatformDxe rolls back all tables it installed up
  to the error. It wouldn't be great if the rollback attempted to remove
  a different MADT than what was installed.

)


Another approach (which sounds quite horrible) might be for QEMU to
pre-populate the MADT with just the right *count* of LAPIC subtables,
and then the TDX driver would patch the MADT *in-place* with the proper
LAPIC subtable contents (and then re-checksum the table manually). This
sounds horrible indeed.


Modifying the InstallAcpiTables() function in OvmfPkg/AcpiPlatformDxe,
so that it install a custom NULL protocol when InstallQemuFwCfgTables()
succeeds, seems tolerable. (In order to trigger the TdxDxe driver's MADT
patching.) However, I don't understand the following comment from
slide#5:

> Open: This method is not practicable if parameters cannot be
> transferred when trigger the notify function.

What parameters are we talking about here? The TDVF design guide speaks
about TD_VCPU_INFO_HOB, regarding the information required for filling
in the LAPIC entries in the MADT. But the same HOB should be available
to the TDX DXE driver too.


It would be much better if TDX specific code were added to QEMU that
prevented the generation of the MADT altogether, when running a TDX
guest. Then the firmware would fully own the MADT, and the TDX DXE
driver would only have to wait for the availability of
EFI_ACPI_TABLE_PROTOCOL (simple depex). In this case, of course, the TDX
driver would be responsible for all other subtable types too, not just
type 0 (LAPIC).


If all else fails, you can also copy "OvmfPkg/AcpiPlatformDxe" to
"OvmfPkg/TdxAcpiPlatformDxe", and customize it in any way (e.g. as
described on slides #3 and #4 [1]; Options 1 and 2). In this case,
TdxAcpiPlatformDxe would only be used in "IntelTdx.dsc", not the
pre-existent OvmfPkg*.dsc files.


Summary:

- Options 1 and 2 from [1] are not acceptable for
  OvmfPkg/AcpiPlatformDxe.

- Option 3 from [1] is acceptable for OvmfPkg/AcpiPlatformDxe with a
  custom NULL protocol instance, but:

  - I don't understand the "parameter passing problem".

  - How exactly the TdxDxe driver implements the MADT update (or
    replacement) remains a question, impacting even QEMU (as QEMU and
    TdxDxe must not fight for ownership over the LAPIC subtables). Some
    possibilities are:

    - stop QEMU from generating the MADT, make TdxDxe own the MADT fully;

    - stop QEMU from generating LAPIC subtables;

    - make QEMU generate the right number of dummy MADT entries;

    - don't touch QEMU, but filter out its LAPIC subtables in TdxDxe.

- Options 1 and 2 from [1] are acceptable for a detached / distinct
  driver called "OvmfPkg/TdxAcpiPlatformDxe", but this driver could only
  be used in "IntelTdx.dsc".

Thanks
Laszlo

Re: [edk2-rfc] [edk2-devel] RFC: design review for TDVF in OVMF

[Min Xu]

On 06/22/2021 9:35 PM, Laszlo wrote:
> Hi,
> 
> On 06/11/21 08:37, Xu, Min M wrote:
> > In today's TianoCore Design Meeting we reviewed the Overview Section
> (from slide 1 to 20). Thanks much for the valuable feedbacks and comments.
> The meeting minutes will be sent out soon.
> >
> > To address the concerns of the *one binary* solution in previous
> > discussion, we propose 2 Configurations for TDVF to upstream. (slide 6
> > - 8)
> >
> >
> >
> > Config-A:
> >
> >   *   Merge the *basic* TDVF feature to existing OvmfX64Pkg.dsc. (Align
> with existing SEV)
> >   *   Threat model: VMM is NOT out of TCB. (We don't make things worse.)
> >   *   The OvmfX64Pkg.dsc includes SEV/TDX/normal OVMF basic boot
> capability. The final binary can run on SEV/TDX/normal OVMF
> >   *   No changes to existing OvmfPkgX64 image layout.
> >   *   No need to add additional security features if they do not exist today
> >   *   No need to remove features if they exist today.
> >   *   RTMR is not supported
> >   *   PEI phase is NOT skipped in either Td or Non-Td
> 
> (so this is "Config-A / Option B", per slide 9 in the v0.9 slide deck)
>
Yes,  in Config-A we chose to follow the standard EDK2 flow (SEC -> PEI -> DXE -> BDS)
So that the changes in Config-A is not too intrusive.
>
> 
> >
> >
> >
> > Config-B:
> >
> >   *   Add a standalone IntelTdx.dsc to a TDX specific directory for a *full*
> feature TDVF. (Align with existing SEV)
> >   *   Threat model: VMM is out of TCB. (We need necessary change to
> prevent attack from VMM)
> >   *   IntelTdx.dsc includes TDX/normal OVMF basic boot capability. The final
> binary can run on TDX/normal OVMF
> >   *   It might eventually merge with AmdSev.dsc, but NOT at this point of
> time. And we don't know when it will happen. We need sync with AMD in
> the community, after both of us think the solutions are mature to merge.
> >   *   Need to add necessary security feature as mandatory requirement,
> such as RTMR based Trusted Boot support
> >   *   Need to remove unnecessary attack surfaces, such as network stack.
> 
> After reading the above, and checking slides 6 through 10 of the v0.9 slide
> deck:
> 
> - I prefer Config-B (IntelTdx.dsc).
> 
> This is in accordance with what I wrote earlier about "OvmfPkgX64.dsc"
> maintainability and regressions.
> 
> Additionally (given that a full-featured TDVF is the ultimate goal), I see the
> advance from "Config-A / option B" to "Config-B" a lot less
> *incremental* than the step from "OvmfPkgX64.dsc" to "AmdSev.dsc" was.
> 
> Put differently, I think that any TDX work targeted at "OvmfPkgX64.dsc"
> is going to prove less useful for the final "IntelTdx.dsc" than how reusable
> SEV work from "OvmfPkgX64.dsc" did for "AmdSev.dsc".
>
> Put yet differently, I'm concerned that a part of the TDX work for
> "OvmfPkgX64.dsc" might be a waste, with an eye towards the ultimate TDVF
> feature set ("IntelTdx.dsc").
> 
Actually Config-A and Config-B share some common (or basic) TDX features,
for example, the ResetVector, Memory Accept in SEC phase, IoMMU/DMA in
DXE phase, and the base IoLib, etc.
Config-A supports the basic Tdx features (except the security features).
Config-B supports the full set of Tdx features.
>
> 
> - I could (very cautiously) live with "Config-A / option B" as the initial
> approach. However, we'de have to be ready to make the full split (the
> switch-over to "IntelTdx.dsc") at *any point* during development, in case
> something turns out to be too intrusive. (And yes, "too intrusive" is
> subjective.)
>
Yes, we will always keep in mind the maintainability and regressions about
"OvmfPkgX64.dsc". So as the initial approach, only the basic Tdx features will
be included in Config-A.
>
> By this I mean that any particular patch towards "Config-A / option B"
> could cause me to ask, "please create IntelTdx.dsc now". Note that the later
> we make the switch the more painful it could be (= the more invested in
> "OvmfPkgX64.dsc" we could be, at that point).
>
Yes we will submit the patch for Config-B when any particular patch towards
"Config-A", so that we will not have a big surprise in the future.
>

Thanks!
Min