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OvmfPkg: Move kernel hashes section to end 

When launching a SEV-SNP VM, the ROM is not all that must be measured.
The OvmfSevMetadata sections describe ranges of memory that must be
measured with different types than PAGE_TYPE_NORMAL, except one. The
SevSnpKernelHashes page is also PAGE_TYPE_NORMAL, but is populated by
the VMM from configuration data that is separate from the OVMF build
itself. To more compactly provide reference values for the measurement
of the firmware separately from the kernel hashes, it's advantageous to
measure as much known information as possible first.

Whereas VMMs are permitted to measure these sections in any order they
prefer, the normative order of how they appear in the .fd is easiest to
follow. This change is semantics-preserving. Measurement calculation
tools that do not follow the normative ordering would need updating to
accommodate, but I don't know of any. The accounting for EC2 moving the
CPUID page to the end of measurement would be unchanged.

This change is to improve performance of a proposed launch update event
log to separate responsibility for initially measured data before VM
launch, application/vnd.amd.sevsnp.launch-updates+cbor:

https://github.com/deeglaze/draft-deeglaze-amd-sev-snp-corim-profile

Signed-off-by: Dionna Glaze <dionnaglaze@google.com>
This commit is contained in:
Dionna Glaze 2024-08-06 15:44:54 +00:00 committed by mergify[bot]
parent 662272ef41
commit 5c63e22a9f
1 changed files with 6 additions and 5 deletions
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11
OvmfPkg/ResetVector/X64/OvmfSevMetadata.asm
View File

@ -76,6 +76,12 @@ SvsmCaa:
DD SVSM_CAA_SIZE
DD OVMF_SECTION_TYPE_SVSM_CAA
; Region need to be pre-validated by the hypervisor
PreValidate3:
DD SNP_SEC_MEM_BASE_DESC_3
DD SNP_SEC_MEM_SIZE_DESC_3
DD OVMF_SECTION_TYPE_SNP_SEC_MEM
%if (SEV_SNP_KERNEL_HASHES_BASE > 0)
; Kernel hashes for measured direct boot, or zero page if
; there are no kernel hashes / SEV secrets
@ -85,10 +91,5 @@ SevSnpKernelHashes:
DD OVMF_SECTION_TYPE_KERNEL_HASHES
%endif
; Region need to be pre-validated by the hypervisor
PreValidate3:
DD SNP_SEC_MEM_BASE_DESC_3
DD SNP_SEC_MEM_SIZE_DESC_3
DD OVMF_SECTION_TYPE_SNP_SEC_MEM
OvmfSevGuidedStructureEnd:
ALIGN 16