From 9711c9230b5485e3e652b21c5eb6da0e07e6394c Mon Sep 17 00:00:00 2001
From: Tom Lendacky <thomas.lendacky@amd.com>
Date: Wed, 12 Aug 2020 15:21:37 -0500
Subject: [PATCH] OvmfPkg/VmgExitLib: Add support for MSR_PROT NAE events

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: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>
---
 OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c | 65 +++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
index 476e94ce5f..f6cfd7fa29 100644
--- a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
+++ b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
@@ -374,6 +374,67 @@ 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
+  @return                          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);
+    //
+    // fall through
+    //
+  case 0x32: // RDMSR
+    Ghcb->SaveArea.Rcx = Regs->Rcx;
+    GhcbSetRegValid (Ghcb, GhcbRcx);
+    break;
+  default:
+    return UnsupportedExit (Ghcb, Regs, InstructionData);
+  }
+
+  Status = VmgExit (Ghcb, SVM_EXIT_MSR, ExitInfo1, 0);
+  if (Status != 0) {
+    return Status;
+  }
+
+  if (ExitInfo1 == 0) {
+    if (!GhcbIsRegValid (Ghcb, GhcbRax) ||
+        !GhcbIsRegValid (Ghcb, GhcbRdx)) {
+      return UnsupportedExit (Ghcb, Regs, InstructionData);
+    }
+    Regs->Rax = Ghcb->SaveArea.Rax;
+    Regs->Rdx = Ghcb->SaveArea.Rdx;
+  }
+
+  return 0;
+}
+
 /**
   Build the IOIO event information.
 
@@ -705,6 +766,10 @@ VmgExitHandleVc (
     NaeExit = IoioExit;
     break;
 
+  case SVM_EXIT_MSR:
+    NaeExit = MsrExit;
+    break;
+
   default:
     NaeExit = UnsupportedExit;
   }
-- 
2.39.5