Re: [PATCH v3 00/11] Measured SEV boot with kernel/initrd/cmdline

["Ard Biesheuvel" <ardb@kernel.org>]

On Tue, 20 Jul 2021 at 19:22, Tom Lendacky <thomas.lendacky@amd.com> wrote:
>
> On 7/20/21 3:03 AM, Dov Murik wrote:
> > BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3457
>
> I believe the convention is that this line be in the individual patch
> commit messages just like this (i.e. with the BZ: tag and the first line),
> not as a Ref: tag at the end of the commit message.
>
> I'll let Ard decide on that, though.
>

Using Ref: in the signoff section of the patch is perfectly fine with me.

I'll go over this series on Thursday and merge it if everything looks ok.

Thanks all for the review.

> >
> > Booting with SEV prevented the loading of kernel, initrd, and kernel
> > command-line via QEMU fw_cfg interface because they arrive from the VMM
> > which is untrusted in SEV.
> >
> > However, in some cases the kernel, initrd, and cmdline are not secret
> > but should not be modified by the host.  In such a case, we want to
> > verify inside the trusted VM that the kernel, initrd, and cmdline are
> > indeed the ones expected by the Guest Owner, and only if that is the
> > case go on and boot them up (removing the need for grub inside OVMF in
> > that mode).
> >
> > This patch series reserves an area in MEMFD (previously the last 1KB of
> > the launch secret page) which will contain the hashes of these three
> > blobs (kernel, initrd, cmdline), each under its own GUID entry.  This
> > tables of hashes is populated by QEMU before launch, and encrypted as
> > part of the initial VM memory; this makes sure these hashes are part of
> > the SEV measurement (which has to be approved by the Guest Owner for
> > secret injection, for example).  Note that populating the hashes table
> > requires QEMU support [1].
> >
> > OVMF parses the table of hashes populated by QEMU (patch 10), and as it
> > reads the fw_cfg blobs from QEMU, it will verify each one against the
> > expected hash.  This is all done inside the trusted VM context.  If all
> > the hashes are correct, boot of the kernel is allowed to continue.
> >
> > Any attempt by QEMU to modify the kernel, initrd, cmdline (including
> > dropping one of them), or to modify the OVMF code that verifies those
> > hashes, will cause the initial SEV measurement to change and therefore
> > will be detectable by the Guest Owner during launch before secret
> > injection.
> >
> > Relevant part of OVMF serial log during boot with AmdSevX86 build and
> > QEMU with -kernel/-initrd/-append:
> >
> >   ...
> >   BlobVerifierLibSevHashesConstructor: Found injected hashes table in secure location
> >   Select Item: 0x17
> >   Select Item: 0x8
> >   FetchBlob: loading 7379328 bytes for "kernel"
> >   Select Item: 0x18
> >   Select Item: 0x11
> >   VerifyBlob: Found GUID 4DE79437-ABD2-427F-B835-D5B172D2045B in table
> >   VerifyBlob: Hash comparison succeeded for "kernel"
> >   Select Item: 0xB
> >   FetchBlob: loading 12483878 bytes for "initrd"
> >   Select Item: 0x12
> >   VerifyBlob: Found GUID 44BAF731-3A2F-4BD7-9AF1-41E29169781D in table
> >   VerifyBlob: Hash comparison succeeded for "initrd"
> >   Select Item: 0x14
> >   FetchBlob: loading 86 bytes for "cmdline"
> >   Select Item: 0x15
> >   VerifyBlob: Found GUID 97D02DD8-BD20-4C94-AA78-E7714D36AB2A in table
> >   VerifyBlob: Hash comparison succeeded for "cmdline"
> >   ...
> >
> > The patch series is organized as follows:
> >
> > 1:     Simple comment fix in adjacent area in the code.
> > 2:     Use GenericQemuLoadImageLib to gain one location for fw_cfg blob
> >        fetching.
> > 3:     Allow the (previously blocked) usage of -kernel in AmdSevX64.
> > 4-7:   Add BlobVerifierLib with null implementation and use it in the correct
> >        location in QemuKernelLoaderFsDxe.
> > 8-9:   Reserve memory for hashes table, declare this area in the reset vector.
> > 10-11: Add the secure implementation BlobVerifierLibSevHashes and use it in
> >        AmdSevX64 builds.
> >
> > [1] https://lore.kernel.org/qemu-devel/20210624102040.2015280-1-dovmurik@linux.ibm.com/
> >
> > Code is at
> > https://github.com/confidential-containers-demo/edk2/tree/sev-hashes-v3
> >
> > v3 changes:
> >  - Rename to BlobVerifierLibNull, use decimal INF_VERSION, remove unused
> >    DebugLib reference, fix doxygen comments, add missing IN attribute
> >  - Rename to BlobVerifierLibSevHashes, use decimal INF_VERSION, fix
> >    doxygen comments, add missing IN attribute,
> >    calculate buffer hash only when the guid is found in hashes table
> >  - SecretPei: use ALIGN_VALUE to round the hob size
> >  - Coding style fixes
> >  - Add missing 'Ref:' in patch 1 commit message
> >  - Fix phrasing and typos in commit messages
> >  - Remove Cc: Laszlo from series
> >
> > v2: https://edk2.groups.io/g/devel/message/77505
> > v2 changes:
> >  - Use the last 1KB of the existing SEV launch secret page for hashes table
> >    (instead of reserving a whole new MEMFD page).
> >  - Build on top of commit cf203024745f ("OvmfPkg/GenericQemuLoadImageLib: Read
> >    cmdline from QemuKernelLoaderFs", 2021-06-28) to have a single location in
> >    which all of kernel/initrd/cmdline are fetched from QEMU.
> >  - Use static linking of the two BlobVerifierLib implemenatations.
> >  - Reorganize series.
> >
> > v1: https://edk2.groups.io/g/devel/message/75567
> >
> > Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
> > Cc: Jordan Justen <jordan.l.justen@intel.com>
> > Cc: Ashish Kalra <ashish.kalra@amd.com>
> > Cc: Brijesh Singh <brijesh.singh@amd.com>
> > Cc: Erdem Aktas <erdemaktas@google.com>
> > Cc: James Bottomley <jejb@linux.ibm.com>
> > Cc: Jiewen Yao <jiewen.yao@intel.com>
> > Cc: Min Xu <min.m.xu@intel.com>
> > Cc: Tom Lendacky <thomas.lendacky@amd.com>
> > Cc: Leif Lindholm <leif@nuviainc.com>
> > Cc: Sami Mujawar <sami.mujawar@arm.com>
> >
> > Dov Murik (8):
> >   OvmfPkg/AmdSev: use GenericQemuLoadImageLib in AmdSev builds
> >   OvmfPkg: add library class BlobVerifierLib with null implementation
> >   OvmfPkg: add BlobVerifierLibNull to DSC
> >   ArmVirtPkg: add BlobVerifierLibNull to DSC
> >   OvmfPkg/QemuKernelLoaderFsDxe: call VerifyBlob after fetch from fw_cfg
> >   OvmfPkg/AmdSev/SecretPei: build hob for full page
> >   OvmfPkg: add BlobVerifierLibSevHashes
> >   OvmfPkg/AmdSev: Enforce hash verification of kernel blobs
> >
> > James Bottomley (3):
> >   OvmfPkg/AmdSev/SecretDxe: fix header comment to generic naming
> >   OvmfPkg: PlatformBootManagerLibGrub: Allow executing kernel via fw_cfg
> >   OvmfPkg/AmdSev: reserve MEMFD space for for firmware config hashes
> >
> >  OvmfPkg/OvmfPkg.dec                                                                 |   9 +
> >  ArmVirtPkg/ArmVirtQemu.dsc                                                          |   5 +-
> >  ArmVirtPkg/ArmVirtQemuKernel.dsc                                                    |   5 +-
> >  OvmfPkg/AmdSev/AmdSevX64.dsc                                                        |   9 +-
> >  OvmfPkg/OvmfPkgIa32.dsc                                                             |   5 +-
> >  OvmfPkg/OvmfPkgIa32X64.dsc                                                          |   5 +-
> >  OvmfPkg/OvmfPkgX64.dsc                                                              |   5 +-
> >  OvmfPkg/AmdSev/AmdSevX64.fdf                                                        |   5 +-
> >  OvmfPkg/Library/BlobVerifierLib/BlobVerifierLibNull.inf                             |  24 +++
> >  OvmfPkg/Library/BlobVerifierLib/BlobVerifierLibSevHashes.inf                        |  37 ++++
> >  OvmfPkg/Library/PlatformBootManagerLibGrub/PlatformBootManagerLibGrub.inf           |   2 +
> >  OvmfPkg/ResetVector/ResetVector.inf                                                 |   2 +
> >  OvmfPkg/Include/Library/BlobVerifierLib.h                                           |  38 ++++
> >  OvmfPkg/Library/PlatformBootManagerLibGrub/BdsPlatform.h                            |  11 ++
> >  OvmfPkg/AmdSev/SecretDxe/SecretDxe.c                                                |   2 +-
> >  OvmfPkg/AmdSev/SecretPei/SecretPei.c                                                |   3 +-
> >  OvmfPkg/Library/BlobVerifierLib/BlobVerifierNull.c                                  |  33 ++++
> >  OvmfPkg/Library/BlobVerifierLib/BlobVerifierSevHashes.c                             | 200 ++++++++++++++++++++
> >  OvmfPkg/Library/PlatformBootManagerLibGrub/BdsPlatform.c                            |   5 +
> >  OvmfPkg/Library/{PlatformBootManagerLib => PlatformBootManagerLibGrub}/QemuKernel.c |   0
> >  OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c                               |   9 +
> >  OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm                                        |  20 ++
> >  OvmfPkg/ResetVector/ResetVector.nasmb                                               |   2 +
> >  23 files changed, 426 insertions(+), 10 deletions(-)
> >  create mode 100644 OvmfPkg/Library/BlobVerifierLib/BlobVerifierLibNull.inf
> >  create mode 100644 OvmfPkg/Library/BlobVerifierLib/BlobVerifierLibSevHashes.inf
> >  create mode 100644 OvmfPkg/Include/Library/BlobVerifierLib.h
> >  create mode 100644 OvmfPkg/Library/BlobVerifierLib/BlobVerifierNull.c
> >  create mode 100644 OvmfPkg/Library/BlobVerifierLib/BlobVerifierSevHashes.c
> >  copy OvmfPkg/Library/{PlatformBootManagerLib => PlatformBootManagerLibGrub}/QemuKernel.c (100%)
> >