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OvmfPkg/PlatformPei: Move early GDT into ram when SEV-ES is enabled 

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198

The SEV support will clear the C-bit from non-RAM areas.  The early GDT
lives in a non-RAM area, so when an exception occurs (like a #VC) the GDT
will be read as un-encrypted even though it is encrypted. This will result
in a failure to be able to handle the exception.

Move the GDT into RAM so it can be accessed without error when running as
an SEV-ES guest.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>
This commit is contained in:
Tom Lendacky 2020-08-12 15:21:40 -05:00 committed by mergify[bot]
parent 449a6e4934
commit 13ed9e5fc0
1 changed files with 18 additions and 0 deletions
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18
OvmfPkg/PlatformPei/AmdSev.c
View File

@ -39,6 +39,8 @@ AmdSevEsInitialize (
PHYSICAL_ADDRESS GhcbBasePa;
UINTN GhcbPageCount, PageCount;
RETURN_STATUS PcdStatus, DecryptStatus;
IA32_DESCRIPTOR Gdtr;
VOID *Gdt;
if (!MemEncryptSevEsIsEnabled ()) {
return;
@ -83,6 +85,22 @@ AmdSevEsInitialize (
(UINT64)GhcbPageCount, GhcbBase));
AsmWriteMsr64 (MSR_SEV_ES_GHCB, GhcbBasePa);
//
// The SEV support will clear the C-bit from non-RAM areas. The early GDT
// lives in a non-RAM area, so when an exception occurs (like a #VC) the GDT
// will be read as un-encrypted even though it was created before the C-bit
// was cleared (encrypted). This will result in a failure to be able to
// handle the exception.
//
AsmReadGdtr (&Gdtr);
Gdt = AllocatePages (EFI_SIZE_TO_PAGES ((UINTN) Gdtr.Limit + 1));
ASSERT (Gdt != NULL);
CopyMem (Gdt, (VOID *) Gdtr.Base, Gdtr.Limit + 1);
Gdtr.Base = (UINTN) Gdt;
AsmWriteGdtr (&Gdtr);
}
/**