Re: [edk2-devel] [PATCH 2/3] OvmfPkg/VmgExitLib: Add support for new MMIO MOV opcodes

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

On 4/22/21 12:50 AM, Laszlo Ersek via groups.io wrote:
> On 04/21/21 00:54, Lendacky, Thomas wrote:
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>
>> BZ: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D3345&amp;data=04%7C01%7Cthomas.lendacky%40amd.com%7C19a7d97e2a7b461830ed08d905528472%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637546674232278910%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=znSezOvpnItW7mHAJkr%2FtJtkQNFc2H0dG9STpmOpVqU%3D&amp;reserved=0
>>
>> 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);

Yup, that can be done.

> 
>> +
>> +    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).

Will do.

> 
>> +
>> +    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?

That comes from the APM Vol 3, Table B-1, that says, in 64-bit mode, for a
32-bit operand size the 32-bit register results are zero-extended to 64-bits.

> 
>> +    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.

Will change.

Thanks,
Tom

> 
> Thanks
> Laszlo
> 
> 
> 
> 
> 
>