Re: [edk2-devel] [PATCH v2 00/11] Measured SEV boot with kernel/initrd/cmdline

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

On Tue, 6 Jul 2021 at 10:55, Dov Murik <dovmurik@linux.ibm.com> wrote:
>
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3457
>
> 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
> theses hashes are part of the SEV measurement (which has to be approved
> by the Guest Owner for secret injection, for example).  Note that this
> requires QEMU support [1].
>
> OVMF parses the table of hashes populated by QEMU (patch 5), and as it
> reads the fw_cfg blobs from QEMU, it will verify each one against the
> expected hash (kernel and initrd verifiers are introduced in patch 6,
> and command-line verifier is introduced in patches 7+8).  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:
>
>   ...
>   SevHashesBlobVerifierLibConstructor: 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 entry '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 entry '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 entry '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 SevHashesBlobVerifierLib 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-v2
>
> 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: Laszlo Ersek <lersek@redhat.com>
> 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>
>

Anyone on the cc list care to review this?


> Dov Murik (8):
>   OvmfPkg/AmdSev: use GenericQemuLoadImageLib in AmdSev builds
>   OvmfPkg: add library class BlobVerifierLib with null implementation
>   OvmfPkg: add NullBlobVerifierLib to DSC
>   ArmVirtPkg: add NullBlobVerifierLib to DSC
>   OvmfPkg/QemuKernelLoaderFsDxe: call VerifyBlob after fetch from fw_cfg
>   OvmfPkg/AmdSev/SecretPei: build hob for full page
>   OvmfPkg: add SevHashesBlobVerifierLib
>   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/NullBlobVerifierLib.inf                             |  27 +++
>  OvmfPkg/Library/BlobVerifierLib/SevHashesBlobVerifierLib.inf                        |  36 ++++
>  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                                                |   9 +-
>  OvmfPkg/Library/BlobVerifierLib/NullBlobVerifier.c                                  |  34 ++++
>  OvmfPkg/Library/BlobVerifierLib/SevHashesBlobVerifier.c                             | 199 ++++++++++++++++++++
>  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, 434 insertions(+), 10 deletions(-)
>  create mode 100644 OvmfPkg/Library/BlobVerifierLib/NullBlobVerifierLib.inf
>  create mode 100644 OvmfPkg/Library/BlobVerifierLib/SevHashesBlobVerifierLib.inf
>  create mode 100644 OvmfPkg/Include/Library/BlobVerifierLib.h
>  create mode 100644 OvmfPkg/Library/BlobVerifierLib/NullBlobVerifier.c
>  create mode 100644 OvmfPkg/Library/BlobVerifierLib/SevHashesBlobVerifier.c
>  copy OvmfPkg/Library/{PlatformBootManagerLib => PlatformBootManagerLibGrub}/QemuKernel.c (100%)
>
> --
> 2.25.1
>
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