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From: "James Bottomley" <jejb@linux.ibm.com>
To: Dov Murik <dovmurik@linux.vnet.ibm.com>,
	Laszlo Ersek <lersek@redhat.com>,
	devel@edk2.groups.io, brijesh.singh@amd.com
Cc: Min Xu <min.m.xu@intel.com>, Jiewen Yao <jiewen.yao@intel.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Jordan Justen <jordan.l.justen@intel.com>,
	Ard Biesheuvel <ardb+tianocore@kernel.org>,
	Erdem Aktas <erdemaktas@google.com>,
	"tobin@ibm.com" <tobin@ibm.com>
Subject: Re: [edk2-devel] [PATCH RFC v2 11/28] OvmfPkg: Reserve Secrets page in MEMFD
Date: Thu, 06 May 2021 09:12:01 -0700	[thread overview]
Message-ID: <aed7d3490fe6edee74440ed8e4cd5364fb2ba4af.camel@linux.ibm.com> (raw)
In-Reply-To: <c289a97f-ad39-b144-e133-1687afa26f96@linux.vnet.ibm.com>

On Thu, 2021-05-06 at 13:57 +0300, Dov Murik wrote:
> 
> On 05/05/2021 22:33, Laszlo Ersek wrote:
> > On 05/05/21 15:11, Brijesh Singh wrote:
> > > On 5/5/21 1:42 AM, Dov Murik wrote:
[...]
> > > > Would it make sense to always use EfiACPIMemoryNVS for the
> > > > injected secret area, even for regular SEV (non-SNP)?
> > > 
> > > Ideally yes. Maybe James had some reasons for choosing the
> > > EfiBootServicesData. If I had to guess, it was mainly because
> > > there no guest kernel support which consumes the SEV secrets
> > > page.
> > 
> > git-blame fingers commit bff2811c6d99 ("OvmfPkg/AmdSev: assign and
> > reserve the Sev Secret area", 2020-12-14).
> > 
> > Commit bff2811c6d99 makes it clear that the area in question lives
> > in MEMFD.
> > 
> > We're populating the area in the PEI phase. We don't want anything
> > in DXE to overwrite it.
> > 
> > Once the bootloader (and/or perhaps the kernel's EFI stub) fetched
> > the secret from that particular location, there is no need to
> > prevent later parts of the OS (the actual kernel) from repurposing
> > that area. That's why EfiBootServicesData was used.
> > 
> 
> The first use of the secret area was to hold the guest luks disk
> passphrase; this is used in the grub-inside-OVMF (AmdSev package),
> and there was no need to keep that page around for the guest kernel.
> 
> The reason I'm raising this whole point is that we're working now on
> guest-kernel support for reading secrets from that injected page (for
> plain SEV).  We considered either (a) modifying the secrets page
> memory type to reserved here, or (b) add code to the kernel EFI stub
> that would copy this page somewhere else for kernel's later use
> (which seems more work and not sure what's the advantage).

It mirrors the TPM boot log behaviour: the log is stored in boot time
only memory, so the kernel EFI stub has to copy it out.  The reason the
TPM boot log behaves this way is that if the kernel didn't want to
collect it, it still gets freed.  I imagine a similar rationale exists
for the boot secrets: if the kernel isn't interested in them for some
reason, we don't want them to persist.

> Option (b) seems harder and more fragile, and I'm not sure if there
> are any advantages (though I'm definitely not an expert in that
> area).

I think forcing the kernel to consume the secret before exit boot
services is still a good idea because 

   1. If the kernel can't consume the secret it gets freed
   2. Not all secrets are consumed by the kernel, so it can pick the ones
      it wants out and discard the rest
   3. If the kernel is using a secret protection mechanism, that may not
      work for the memfd page, so relocation of the secret might be a more
      secure mechanism.

James



  parent reply	other threads:[~2021-05-06 16:12 UTC|newest]

Thread overview: 81+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-30 11:51 [PATCH RFC v2 00/28] Add AMD Secure Nested Paging (SEV-SNP) support Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 01/28] MdePkg: Expand the SEV MSR to include the SNP definition Brijesh Singh
2021-05-03  8:39   ` [edk2-devel] " Laszlo Ersek
2021-05-03 11:42     ` Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 02/28] MdePkg: Define the GHCB Hypervisor features Brijesh Singh
2021-05-03 10:10   ` [edk2-devel] " Laszlo Ersek
2021-05-03 12:20     ` Brijesh Singh
2021-05-03 13:40       ` Laszlo Ersek
2021-04-30 11:51 ` [PATCH RFC v2 03/28] MdePkg: Define the GHCB GPA structure Brijesh Singh
2021-05-03 10:24   ` [edk2-devel] " Laszlo Ersek
2021-05-03 12:19     ` Laszlo Ersek
2021-05-03 12:55       ` Brijesh Singh
2021-05-03 13:50         ` Laszlo Ersek
2021-05-03 13:55           ` Laszlo Ersek
2021-04-30 11:51 ` [PATCH RFC v2 04/28] MdePkg: Define the Page State Change VMGEXIT structures Brijesh Singh
2021-05-04 12:33   ` [edk2-devel] " Laszlo Ersek
2021-05-04 13:59     ` Laszlo Ersek
2021-05-04 14:48       ` Lendacky, Thomas
2021-05-04 18:07         ` Laszlo Ersek
2021-05-04 18:53     ` Brijesh Singh
2021-05-05 18:24       ` Laszlo Ersek
2021-05-05 19:27         ` Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 05/28] MdePkg: Add AsmPvalidate() support Brijesh Singh
2021-05-04 13:58   ` [edk2-devel] " Laszlo Ersek
2021-05-04 14:09     ` Laszlo Ersek
2021-05-04 19:07     ` Brijesh Singh
2021-05-05 18:56       ` Laszlo Ersek
     [not found]     ` <167BF2A01FA60569.6407@groups.io>
2021-05-04 19:55       ` Brijesh Singh
2021-05-05 19:10         ` Laszlo Ersek
     [not found]       ` <167BF53DA09B327E.22277@groups.io>
2021-05-04 20:28         ` Brijesh Singh
2021-05-04 23:03           ` Brijesh Singh
2021-05-05 19:19             ` Laszlo Ersek
2021-05-05 19:17           ` Laszlo Ersek
2021-04-30 11:51 ` [PATCH RFC v2 06/28] OvmfPkg/BaseMemEncryptSevLib: Introduce MemEncryptSevClearMmioPageEncMask() Brijesh Singh
2021-05-06 10:39   ` [edk2-devel] " Laszlo Ersek
2021-05-06 19:18     ` Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 07/28] OvmfPkg: Use MemEncryptSevClearMmioPageEncMask() to clear EncMask from Mmio Brijesh Singh
2021-05-06 10:50   ` [edk2-devel] " Laszlo Ersek
2021-05-06 19:20     ` Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 08/28] OvmfPkg/BaseMemEncryptSevLib: Remove CacheFlush parameter Brijesh Singh
2021-05-06 11:08   ` [edk2-devel] " Laszlo Ersek
2021-04-30 11:51 ` [PATCH RFC v2 09/28] OvmfPkg/VmgExitLib: Allow PMBASE register access in Dxe phase Brijesh Singh
2021-05-06 14:08   ` [edk2-devel] " Laszlo Ersek
2021-05-06 14:12     ` Laszlo Ersek
2021-05-07 13:29     ` Brijesh Singh
2021-05-07 15:10       ` Laszlo Ersek
2021-05-07 15:19         ` Brijesh Singh
2021-05-07 15:47           ` Laszlo Ersek
2021-04-30 11:51 ` [PATCH RFC v2 10/28] OvmfPkg/MemEncryptSevLib: add MemEncryptSevSnpEnabled() Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 11/28] OvmfPkg: Reserve Secrets page in MEMFD Brijesh Singh
2021-05-05  6:42   ` [edk2-devel] " Dov Murik
2021-05-05 13:11     ` Brijesh Singh
2021-05-05 19:33       ` Laszlo Ersek
2021-05-06 10:57         ` Dov Murik
2021-05-06 15:06           ` Laszlo Ersek
2021-05-06 16:12           ` James Bottomley [this message]
2021-05-06 16:02         ` James Bottomley
2021-04-30 11:51 ` [PATCH RFC v2 12/28] OvmfPkg: Reserve CPUID page for the SEV-SNP guest Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 13/28] OvmfPkg: Validate the data pages used in the Reset vector and SEC phase Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 14/28] UefiCpuPkg: Define the SEV-SNP specific dynamic PCDs Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 15/28] OvmfPkg/MemEncryptSevLib: extend the workarea to include SNP enabled field Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 16/28] OvmfPkg/MemEncryptSevLib: Extend Es Workarea to include hv features Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 17/28] OvmfPkg/ResetVector: Invalidate the GHCB page Brijesh Singh
2021-05-03 13:05   ` Erdem Aktas
2021-05-03 14:28     ` Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 18/28] OvmfPkg: Add a library to support registering GHCB GPA Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 19/28] OvmfPkg: register GHCB gpa for the SEV-SNP guest Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 20/28] UefiCpuPkg/MpLib: add support to register GHCB GPA when SEV-SNP is enabled Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 21/28] OvmfPkg/MemEncryptSevLib: Add support to validate system RAM Brijesh Singh
2021-05-03 14:04   ` Erdem Aktas
2021-05-03 18:56     ` Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 22/28] OvmfPkg/BaseMemEncryptSevLib: Skip the pre-validated " Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 23/28] OvmfPkg/MemEncryptSevLib: Add support to validate > 4GB memory in PEI phase Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 24/28] OvmfPkg/SecMain: Pre-validate the memory used for decompressing Fv Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 25/28] OvmfPkg/PlatformPei: Validate the system RAM when SNP is active Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 26/28] OvmfPkg/MemEncryptSevLib: Change the page state in the RMP table Brijesh Singh
2021-04-30 11:51 ` [PATCH RFC v2 27/28] OvmfPkg/AmdSev: Expose the SNP reserved pages through configuration table Brijesh Singh
2021-05-05  7:10   ` [edk2-devel] " Dov Murik
2021-05-05 19:37     ` Laszlo Ersek
2021-04-30 11:51 ` [PATCH RFC v2 28/28] MdePkg/GHCB: Increase the GHCB protocol max version Brijesh Singh
2021-04-30 16:49 ` [edk2-devel] [PATCH RFC v2 00/28] Add AMD Secure Nested Paging (SEV-SNP) support Laszlo Ersek

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