[PATCH v1 0/8] Measured SEV boot with kernel/initrd/cmdline


Dov Murik <dovmurik@...>
 

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 declares a new page in MEMFD 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 a new QEMU patch which will be submitted soon.

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.

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>

James Bottomley (8):
OvmfPkg/AmdSev/SecretDxe: fix header comment to generic naming
OvmfPkg: PlatformBootManagerLibGrub: Allow executing kernel via fw_cfg
OvmfPkg/AmdSev: add a page to the MEMFD for firmware config hashes
OvmfPkg/QemuKernelLoaderFsDxe: Add ability to verify loaded items
OvmfPkg/AmdSev: Add library to find encrypted hashes for the FwCfg
device
OvmfPkg/AmdSev: Add firmware file plugin to verifier
OvmfPkg: GenericQemuLoadImageLib: Allow verifying fw_cfg command line
OvmfPkg/AmdSev: add SevQemuLoadImageLib

OvmfPkg/OvmfPkg.dec | 10 ++
OvmfPkg/AmdSev/AmdSevX64.dsc | 9 +-
OvmfPkg/AmdSev/AmdSevX64.fdf | 3 +
OvmfPkg/AmdSev/Library/SevFwCfgVerifier/SevFwCfgVerifier.inf | 30 +++++
OvmfPkg/AmdSev/Library/SevHashFinderLib/SevHashFinderLib.inf | 34 ++++++
OvmfPkg/AmdSev/Library/SevQemuLoadImageLib/SevQemuLoadImageLib.inf | 30 +++++
OvmfPkg/Library/PlatformBootManagerLibGrub/PlatformBootManagerLibGrub.inf | 2 +
OvmfPkg/ResetVector/ResetVector.inf | 2 +
OvmfPkg/AmdSev/Include/Library/SevHashFinderLib.h | 47 ++++++++
OvmfPkg/Include/Library/QemuFwCfgLib.h | 35 ++++++
OvmfPkg/Library/PlatformBootManagerLibGrub/BdsPlatform.h | 11 ++
OvmfPkg/AmdSev/Library/SevFwCfgVerifier/SevFwCfgVerifier.c | 60 ++++++++++
OvmfPkg/AmdSev/Library/SevHashFinderLib/SevHashFinderLib.c | 126 ++++++++++++++++++++
OvmfPkg/AmdSev/Library/SevQemuLoadImageLib/SevQemuLoadImageLib.c | 52 ++++++++
OvmfPkg/AmdSev/SecretDxe/SecretDxe.c | 2 +-
OvmfPkg/Library/GenericQemuLoadImageLib/GenericQemuLoadImageLib.c | 29 +++++
OvmfPkg/Library/PlatformBootManagerLibGrub/BdsPlatform.c | 5 +
OvmfPkg/Library/PlatformBootManagerLibGrub/QemuKernel.c | 50 ++++++++
OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c | 31 +++++
OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm | 20 ++++
OvmfPkg/ResetVector/ResetVector.nasmb | 2 +
21 files changed, 587 insertions(+), 3 deletions(-)
create mode 100644 OvmfPkg/AmdSev/Library/SevFwCfgVerifier/SevFwCfgVerifier.inf
create mode 100644 OvmfPkg/AmdSev/Library/SevHashFinderLib/SevHashFinderLib.inf
create mode 100644 OvmfPkg/AmdSev/Library/SevQemuLoadImageLib/SevQemuLoadImageLib.inf
create mode 100644 OvmfPkg/AmdSev/Include/Library/SevHashFinderLib.h
create mode 100644 OvmfPkg/AmdSev/Library/SevFwCfgVerifier/SevFwCfgVerifier.c
create mode 100644 OvmfPkg/AmdSev/Library/SevHashFinderLib/SevHashFinderLib.c
create mode 100644 OvmfPkg/AmdSev/Library/SevQemuLoadImageLib/SevQemuLoadImageLib.c
create mode 100644 OvmfPkg/Library/PlatformBootManagerLibGrub/QemuKernel.c

--
2.25.1

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