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

["Dov Murik" <dovmurik@linux.ibm.com>]

On 19/07/2021 18:14, Tom Lendacky wrote:
> On 7/6/21 3:54 AM, Dov Murik wrote:
>> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3457
> 
> This BZ link should be part of all the commit messages in the series.
> 

Oh I missed a few.  I'll fix.  Thanks.


> Thanks,
> Tom
> 
>>
>> 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>
>>
>> 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%)
>>