Re: [PATCH 2/3] OvmfPkg/VmgExitLib: Add support for new MMIO MOV opcodes


Laszlo Ersek
 

On 04/21/21 00:54, Lendacky, Thomas wrote:
From: Tom Lendacky <thomas.lendacky@amd.com>

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3345

Enabling TPM support results in guest termination of an SEV-ES guest
because it uses MMIO opcodes that are not currently supported.

Add support for the new MMIO opcodes (0xA0 - 0xA3), MOV instructions which
use a memory offset directly encoded in the instruction. Also, add a DEBUG
statement to identify an unsupported MMIO opcode being used.

Fixes: c45f678a1ea2080344e125dc55b14e4b9f98483d
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Min Xu <min.m.xu@intel.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c | 99 +++++++++++++++++++
1 file changed, 99 insertions(+)

diff --git a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
index 273f36499988..f9660b757d8e 100644
--- a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
+++ b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
@@ -678,6 +678,7 @@ MmioExit (
UINTN Bytes;
UINT64 *Register;
UINT8 OpCode, SignByte;
+ UINTN Address;

Bytes = 0;

@@ -727,6 +728,51 @@ MmioExit (
}
break;

+ //
+ // MMIO write (MOV moffsetX, aX)
+ //
+ case 0xA2:
+ Bytes = 1;
+ //
+ // fall through
+ //
+ case 0xA3:
+ Bytes = ((Bytes != 0) ? Bytes :
+ (InstructionData->DataSize == Size16Bits) ? 2 :
+ (InstructionData->DataSize == Size32Bits) ? 4 :
+ (InstructionData->DataSize == Size64Bits) ? 8 :
+ 0);
+
+ InstructionData->ImmediateSize = (UINTN) (1 << InstructionData->AddrSize);
+ InstructionData->End += (UINTN) (1 << InstructionData->AddrSize);
+
+ if (InstructionData->AddrSize == Size8Bits) {
+ Address = *(UINT8 *) InstructionData->Immediate;
+ } else if (InstructionData->AddrSize == Size16Bits) {
+ Address = *(UINT16 *) InstructionData->Immediate;
+ } else if (InstructionData->AddrSize == Size32Bits) {
+ Address = *(UINT32 *) InstructionData->Immediate;
+ } else {
+ Address = *(UINTN *) InstructionData->Immediate;
+ }
(1) Can we simplify this as follows?

InstructionData->ImmediateSize = 1 << InstructionData->AddrSize;
InstructionData->End += InstructionData->ImmediateSize;
Address = 0;
CopyMem (&Address, InstructionData->Immediate,
InstructionData->ImmediateSize);

+
+ Status = ValidateMmioMemory (Ghcb, Address, Bytes);
+ if (Status != 0) {
+ return Status;
+ }
+
+ ExitInfo1 = Address;
+ ExitInfo2 = Bytes;
+ CopyMem (Ghcb->SharedBuffer, &Regs->Rax, Bytes);
+
+ Ghcb->SaveArea.SwScratch = (UINT64) Ghcb->SharedBuffer;
+ VmgSetOffsetValid (Ghcb, GhcbSwScratch);
+ Status = VmgExit (Ghcb, SVM_EXIT_MMIO_WRITE, ExitInfo1, ExitInfo2);
+ if (Status != 0) {
+ return Status;
+ }
+ break;
+
//
// MMIO write (MOV reg/memX, immX)
//
@@ -809,6 +855,58 @@ MmioExit (
CopyMem (Register, Ghcb->SharedBuffer, Bytes);
break;

+ //
+ // MMIO read (MOV aX, moffsetX)
+ //
+ case 0xA0:
+ Bytes = 1;
+ //
+ // fall through
+ //
+ case 0xA1:
+ Bytes = ((Bytes != 0) ? Bytes :
+ (InstructionData->DataSize == Size16Bits) ? 2 :
+ (InstructionData->DataSize == Size32Bits) ? 4 :
+ (InstructionData->DataSize == Size64Bits) ? 8 :
+ 0);
+
+ InstructionData->ImmediateSize = (UINTN) (1 << InstructionData->AddrSize);
+ InstructionData->End += (UINTN) (1 << InstructionData->AddrSize);
+
+ if (InstructionData->AddrSize == Size8Bits) {
+ Address = *(UINT8 *) InstructionData->Immediate;
+ } else if (InstructionData->AddrSize == Size16Bits) {
+ Address = *(UINT16 *) InstructionData->Immediate;
+ } else if (InstructionData->AddrSize == Size32Bits) {
+ Address = *(UINT32 *) InstructionData->Immediate;
+ } else {
+ Address = *(UINTN *) InstructionData->Immediate;
+ }
(2) Similar question as (1).

+
+ Status = ValidateMmioMemory (Ghcb, Address, Bytes);
+ if (Status != 0) {
+ return Status;
+ }
+
+ ExitInfo1 = Address;
+ ExitInfo2 = Bytes;
+
+ Ghcb->SaveArea.SwScratch = (UINT64) Ghcb->SharedBuffer;
+ VmgSetOffsetValid (Ghcb, GhcbSwScratch);
+ Status = VmgExit (Ghcb, SVM_EXIT_MMIO_READ, ExitInfo1, ExitInfo2);
+ if (Status != 0) {
+ return Status;
+ }
+
+ if (Bytes == 4) {
+ //
+ // Zero-extend for 32-bit operation
+ //
+ Regs->Rax = 0;
+ }
(3) This is also seen with opcode 0x8B, but can you remind me please why
we ignore (Bytes == 1) and (Bytes == 2) for zero extension?

+ CopyMem (&Regs->Rax, Ghcb->SharedBuffer, Bytes);
+ break;
+
//
// MMIO read w/ zero-extension ((MOVZX regX, reg/memX)
//
@@ -886,6 +984,7 @@ MmioExit (
break;

default:
+ DEBUG ((DEBUG_INFO, "Invalid MMIO opcode (%x)\n", OpCode));
Status = GP_EXCEPTION;
ASSERT (FALSE);
}
(4) We should use the DEBUG_ERROR log mask here.

Thanks
Laszlo

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