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OvmfPkg/MemEncryptSevLib: Evict cache lines during SNP memory validation

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An SNP cache coherency vulnerability may require a mitigation to evict
cache lines after memory has been validated. Perform this mitigation
after having validated memory.

CVE-2024-36331

Signed-off-by: Michael Roth <michael.roth@amd.com>
Co-developed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
This commit is contained in:
Tom Lendacky 2025-08-12 14:43:32 -05:00 • committed by mergify[bot]
parent 406aeb5a97
commit 3b0d834db2
1 changed files with 40 additions and 1 deletions
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41
OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c
View file

@ -22,6 +22,8 @@
#include "SnpPageStateChange.h"
#define PAGES_PER_2MB_ENTRY 512
STATIC
UINTN
MemoryStateToGhcbOp (
@ -213,6 +215,33 @@ PageStateChange (
}
}
STATIC
VOID
SevEvictCache (
IN EFI_PHYSICAL_ADDRESS Address,
IN UINTN NumPages
)
{
#if defined (__GNUC__) || defined (__clang__)
volatile UINT8 Val __attribute__ ((__unused__));
#else
volatile UINT8 Val;
#endif
UINT8 *Bytes = (UINT8 *)Address;
UINTN PageIdx;
/*
* For SEV guests, a read from the first/last cache-lines of a 4K page
* using the guest key is sufficient to cause a flush of all cache-lines
* associated with that 4K page without incurring all the overhead of a
* full CLFLUSH sequence.
*/
for (PageIdx = 0; PageIdx < NumPages; PageIdx++) {
Val = Bytes[PageIdx * SIZE_4KB];
Val = Bytes[PageIdx * SIZE_4KB + SIZE_4KB - 1];
}
}
/**
The function is used to set the page state when SEV-SNP is active. The page state
transition consist of changing the page ownership in the RMP table, and using the
@ -231,8 +260,12 @@ InternalSetPageState (
IN UINTN PscBufferSize
)
{
EFI_PHYSICAL_ADDRESS NextAddress, EndAddress;
EFI_PHYSICAL_ADDRESS NextAddress;
EFI_PHYSICAL_ADDRESS EndAddress;
EFI_PHYSICAL_ADDRESS Address;
SNP_PAGE_STATE_CHANGE_INFO *Info;
UINTN RmpPageSize;
UINTN Index;
EndAddress = BaseAddress + EFI_PAGES_TO_SIZE (NumPages);
@ -281,6 +314,12 @@ InternalSetPageState (
//
if (State == SevSnpPagePrivate) {
AmdSvsmSnpPvalidate (Info);
for (Index = 0; Index <= Info->Header.EndEntry; Index++) {
Address = LShiftU64 ((UINT64)Info->Entry[Index].GuestFrameNumber, EFI_PAGE_SHIFT);
RmpPageSize = Info->Entry[Index].PageSize;
SevEvictCache (Address, RmpPageSize == PvalidatePageSize2MB ? PAGES_PER_2MB_ENTRY : 1);
}
}
}
}