Hello Gred
On 11/19/2025 12:49 PM, Gerd Hoffmann wrote:
On Mon, Nov 10, 2025 at 03:20:13PM -0600, Tom Lendacky wrote:
What is occurring is ValidateFvHeader() is supplied the address from
PcdOvmfFlashNvStorageVariableBase, which is an MMIO address. A #VC is
generated when the code accesses this memory. However, the memory is
accessed with a CMP instruction, which is an unsupported MMIO
instruction, resulting in the assert.
Thanks for the analysis. Does this help?
https://github.com/tianocore/edk2/pull/11770
That patch did not apply cleanly on current edk2 master[46548b1]. I
could manually do the changes:
--- a/OvmfPkg/EmuVariableFvbRuntimeDxe/Fvb.c
+++ b/OvmfPkg/EmuVariableFvbRuntimeDxe/Fvb.c
@@ -565,17 +565,25 @@ ValidateFvHeader (
IN EFI_FIRMWARE_VOLUME_HEADER *FwVolHeader
)
{
- UINT16 Checksum;
+ UINT16 Checksum;
+ EFI_FIRMWARE_VOLUME_HEADER Hdr;
+
+ //
+ // Instruction emulation in the #VC handler does not support cmp
instructions.
+ // So avoid accessing the header (which might be an mmio address)
directly
+ // with cmp, copy to stack and compare fields in the copy instead.
+ //
+ CopyMem (&Hdr, FwVolHeader, sizeof (Hdr));
//
// Verify the header revision, header signature, length
// Length of FvBlock cannot be 2**64-1
// HeaderLength cannot be an odd number
//
- if ((FwVolHeader->Revision != EFI_FVH_REVISION) ||
- (FwVolHeader->Signature != EFI_FVH_SIGNATURE) ||
- (FwVolHeader->FvLength != EMU_FVB_SIZE) ||
- (FwVolHeader->HeaderLength != EMU_FV_HEADER_LENGTH)
+ if ((Hdr.Revision != EFI_FVH_REVISION) ||
+ (Hdr.Signature != EFI_FVH_SIGNATURE) ||
+ (Hdr.FvLength != EMU_FVB_SIZE) ||
+ (Hdr.HeaderLength != EMU_FV_HEADER_LENGTH)
)
{
DEBUG ((DEBUG_INFO, "EMU Variable FVB: Basic FV headers were
invalid\n"));
Still SEV-ES guest boot crashes, with below trace:
InstallProtocolInterface: 5B1B31A1-9562-11D2-8E3F-00A0C969723B 7F0E41C0
Loading driver at 0x0007F6D4000 EntryPoint=0x0007F6D6642
EmuVariableFvbRuntimeDxe.efi
InstallProtocolInterface: BC62157E-3E33-4FEC-9920-2D3B36D750DF 7F0E4918
ProtectUefiImageCommon - 0x7F0E41C0
- 0x000000007F6D4000 - 0x0000000000006000
EMU Variable FVB Started
EMU Variable FVB: Using pre-reserved block at 7FB7A000
EMU Variable FVB: Basic FV headers were invalid
Invalid MMIO opcode (A5)
ASSERT [CpuDxe] CcExitVcHandler.c(498): ((BOOLEAN)(0==1))
take care,
Gerd
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