OvfmPkg/VmgExitLib: Properly decode MMIO MOVZX and MOVSX opcodes

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

The MOVZX and MOVSX instructions use the ModRM byte in the instruction,
but the instruction decoding support was not decoding it. This resulted
in invalid decoding and failing of the MMIO operation. Also, when
performing the zero-extend or sign-extend operation, the memory operation
should be using the size, and not the size enumeration value.

Add the ModRM byte decoding for the MOVZX and MOVSX opcodes and use the
true data size to perform the extend operations. Additionally, add a
DEBUG statement identifying the MMIO address being flagged as encrypted
during the MMIO address validation.

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: Erdem Aktas <erdemaktas@google.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Min Xu <min.m.xu@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <5949d54cb2c9ab69256f67ed5654b32654c0501c.1619716333.git.thomas.lendacky@amd.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
index 24259060fd..b716541ad1 100644
--- a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
+++ b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
@@ -643,6 +643,9 @@ ValidateMmioMemory (
   //

   // Any state other than unencrypted is an error, issue a #GP.

   //

+  DEBUG ((DEBUG_ERROR,

+    "MMIO using encrypted memory: %lx\n",

+    (UINT64) MemoryAddress));

   GpEvent.Uint64 = 0;

   GpEvent.Elements.Vector = GP_EXCEPTION;

   GpEvent.Elements.Type   = GHCB_EVENT_INJECTION_TYPE_EXCEPTION;

@@ -817,6 +820,7 @@ MmioExit (
     // fall through

     //

   case 0xB7:

+    DecodeModRm (Regs, InstructionData);

     Bytes = (Bytes != 0) ? Bytes : 2;

 

     Status = ValidateMmioMemory (Ghcb, InstructionData->Ext.RmData, Bytes);

@@ -835,7 +839,7 @@ MmioExit (
     }

 

     Register = GetRegisterPointer (Regs, InstructionData->Ext.ModRm.Reg);

-    SetMem (Register, InstructionData->DataSize, 0);

+    SetMem (Register, (UINTN) (1 << InstructionData->DataSize), 0);

     CopyMem (Register, Ghcb->SharedBuffer, Bytes);

     break;

 

@@ -848,6 +852,7 @@ MmioExit (
     // fall through

     //

   case 0xBF:

+    DecodeModRm (Regs, InstructionData);

     Bytes = (Bytes != 0) ? Bytes : 2;

 

     Status = ValidateMmioMemory (Ghcb, InstructionData->Ext.RmData, Bytes);

@@ -878,7 +883,7 @@ MmioExit (
     }

 

     Register = GetRegisterPointer (Regs, InstructionData->Ext.ModRm.Reg);

-    SetMem (Register, InstructionData->DataSize, SignByte);

+    SetMem (Register, (UINTN) (1 << InstructionData->DataSize), SignByte);

     CopyMem (Register, Ghcb->SharedBuffer, Bytes);

     break;