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

["Laszlo Ersek" <lersek@redhat.com>]

On 04/22/21 17:42, Tom Lendacky wrote:
> On 4/22/21 9:15 AM, Tom Lendacky wrote:
>> 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.
> 
> "Address" is a type UINTN, but since this is X64 only code, an 8-byte copy
> isn't an issue. Should I add a comment about that above the setting of
> "Address"? Or should I convert "Address" to a UINT64 - although
> ValidateMmioMemory expects a UINTN...  Thoughts?

Yes, I had the exact same thought process :)

The comment looks good, but how about expressing it as a STATIC_ASSERT,
with sizeof (UINTN) and sizeof (UINT64) being equal? (Alternatively,
about MAX_UINT64 being equal to MAX_UINTN.)

If you find that too verbose, a comment is good enough too, of course.

Thanks!
Laszlo

> 
> Thanks,
> Tom
> 
>>
>>>
>>>> +
>>>> +    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
>>>
>>>
>>>
>>> 
>>>
>>>
>