[edk2-devel] [PATCH v7 15/43] UefiCpuPkg/CpuExceptionHandler: Add support for MSR_PROT NAE events

[Lendacky, Thomas]

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

Under SEV-ES, a MSR_PROT intercept generates a #VC exception. VMGEXIT must
be used to allow the hypervisor to handle this intercept.

Add support to construct the required GHCB values to support an MSR_PROT
NAE event. Parse the instruction that generated the #VC exception to
determine whether it is RDMSR or WRMSR, setting the required register
register values in the GHCB and creating the proper SW_EXIT_INFO1 value in
the GHCB.

Cc: Eric Dong <eric.dong at intel.com>
Cc: Ray Ni <ray.ni at intel.com>
Cc: Laszlo Ersek <lersek at redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky at amd.com>
---
 .../X64/ArchAMDSevVcHandler.c                 | 63 +++++++++++++++++++
 1 file changed, 63 insertions(+)

diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchAMDSevVcHandler.c b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchAMDSevVcHandler.c
index 4324de152b82..8eae3633a31b 100644
--- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchAMDSevVcHandler.c
+++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchAMDSevVcHandler.c
@@ -404,6 +404,65 @@ UnsupportedExit (
   return Status;
 }
 
+/**
+  Handle an MSR event.
+
+  Use the VMGEXIT instruction to handle either a RDMSR or WRMSR event.
+
+  @param[in, out] Ghcb             Pointer to the Guest-Hypervisor Communication
+                                   Block
+  @param[in, out] Regs             x64 processor context
+  @param[in]      InstructionData  Instruction parsing context
+
+  @retval 0                        Event handled successfully
+  @retval Others                   New exception value to propagate
+
+**/
+STATIC
+UINT64
+MsrExit (
+  IN OUT GHCB                     *Ghcb,
+  IN OUT EFI_SYSTEM_CONTEXT_X64   *Regs,
+  IN     SEV_ES_INSTRUCTION_DATA  *InstructionData
+  )
+{
+  UINT64  ExitInfo1, Status;
+
+  ExitInfo1 = 0;
+
+  switch (*(InstructionData->OpCodes + 1)) {
+  case 0x30: // WRMSR
+    ExitInfo1 = 1;
+    Ghcb->SaveArea.Rax = Regs->Rax;
+    GhcbSetRegValid (Ghcb, GhcbRax);
+    Ghcb->SaveArea.Rdx = Regs->Rdx;
+    GhcbSetRegValid (Ghcb, GhcbRdx);
+    /* Fallthrough */
+  case 0x32: // RDMSR
+    Ghcb->SaveArea.Rcx = Regs->Rcx;
+    GhcbSetRegValid (Ghcb, GhcbRcx);
+    break;
+  default:
+    return UnsupportedExit (Ghcb, Regs, InstructionData);
+  }
+
+  Status = VmgExit (Ghcb, SvmExitMsr, ExitInfo1, 0);
+  if (Status) {
+    return Status;
+  }
+
+  if (!ExitInfo1) {
+    if (!GhcbIsRegValid (Ghcb, GhcbRax) ||
+        !GhcbIsRegValid (Ghcb, GhcbRdx)) {
+      return UnsupportedExit (Ghcb, Regs, InstructionData);
+    }
+    Regs->Rax = Ghcb->SaveArea.Rax;
+    Regs->Rdx = Ghcb->SaveArea.Rdx;
+  }
+
+  return 0;
+}
+
 #define IOIO_TYPE_STR       (1 << 2)
 #define IOIO_TYPE_IN        1
 #define IOIO_TYPE_INS       (IOIO_TYPE_IN | IOIO_TYPE_STR)
@@ -722,6 +781,10 @@ DoVcCommon (
     NaeExit = IoioExit;
     break;
 
+  case SvmExitMsr:
+    NaeExit = MsrExit;
+    break;
+
   default:
     NaeExit = UnsupportedExit;
   }
-- 
2.17.1


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