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[edk2-devel] [PATCH v5 00/11] Measured SEV boot with kernel/initrd/cmdline



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 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-v5

v5 changes:
 - rename the null implementation dir to OvmfPkg/Library/BlobVerifierLibNull
   (note that I didn't remove the R-b tags on these patches; please let me
   know if I should have acted otherwise)
 - move the SevHashes implementation to OvmfPkg/AmdSev/BlobVerifierLibSevHashes
 - BlobVerifierLib.h: fix #ifndef according to ECC warnings
 - separate variable declaration and assignment in
   BlobVerifierLibSevHashesConstructor (ECC warning)

v4: https://edk2.groups.io/g/devel/message/78075
v4 changes:
 - BlobVerifierSevHashes (patch 10): more comprehensive overflow tests
   when parsing the SEV hashes table structure

v3: https://edk2.groups.io/g/devel/message/77955
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/AmdSev: 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/AmdSev/BlobVerifierLibSevHashes/BlobVerifierLibSevHashes.inf                |  37 ++++
 OvmfPkg/Library/BlobVerifierLibNull/BlobVerifierLibNull.inf                         |  24 +++
 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/BlobVerifierLibSevHashes/BlobVerifierSevHashes.c                     | 202 ++++++++++++++++++++
 OvmfPkg/AmdSev/SecretDxe/SecretDxe.c                                                |   2 +-
 OvmfPkg/AmdSev/SecretPei/SecretPei.c                                                |   3 +-
 OvmfPkg/Library/BlobVerifierLibNull/BlobVerifierNull.c                              |  33 ++++
 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, 428 insertions(+), 10 deletions(-)
 create mode 100644 OvmfPkg/AmdSev/BlobVerifierLibSevHashes/BlobVerifierLibSevHashes.inf
 create mode 100644 OvmfPkg/Library/BlobVerifierLibNull/BlobVerifierLibNull.inf
 create mode 100644 OvmfPkg/Include/Library/BlobVerifierLib.h
 create mode 100644 OvmfPkg/AmdSev/BlobVerifierLibSevHashes/BlobVerifierSevHashes.c
 create mode 100644 OvmfPkg/Library/BlobVerifierLibNull/BlobVerifierNull.c
 copy OvmfPkg/Library/{PlatformBootManagerLib => PlatformBootManagerLibGrub}/QemuKernel.c (100%)

-- 
2.25.1



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