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


Dov Murik
 

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>

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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