[PATCH 1/1] OvmfPkg/VmgExitLib: HALT on #VE when access to private memory

["Min Xu" <min.m.xu@intel.com>]

From: Min M Xu <min.m.xu@intel.com>

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4125

EPT-violation #VE should be always on shared memory, which means the
shared bit of the GuestPA should be set. But in current #VE Handler
it is not checked. When it occurs, stop TD immediately and log out
the error.

Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>
---
 .../Library/VmgExitLib/VmTdExitVeHandler.c    | 40 ++++++++++++++-----
 1 file changed, 29 insertions(+), 11 deletions(-)

diff --git a/OvmfPkg/Library/VmgExitLib/VmTdExitVeHandler.c b/OvmfPkg/Library/VmgExitLib/VmTdExitVeHandler.c
index b73e877c093b..5bc0e9b3aa74 100644
--- a/OvmfPkg/Library/VmgExitLib/VmTdExitVeHandler.c
+++ b/OvmfPkg/Library/VmgExitLib/VmTdExitVeHandler.c
@@ -300,23 +300,41 @@ MmioExit (
   IN TDCALL_VEINFO_RETURN_DATA   *Veinfo
   )
 {
-  UINT64   Status;
-  UINT32   MmioSize;
-  UINT32   RegSize;
-  UINT8    OpCode;
-  BOOLEAN  SeenRex;
-  UINT64   *Reg;
-  UINT8    *Rip;
-  UINT64   Val;
-  UINT32   OpSize;
-  MODRM    ModRm;
-  REX      Rex;
+  UINT64          Status;
+  UINT32          MmioSize;
+  UINT32          RegSize;
+  UINT8           OpCode;
+  BOOLEAN         SeenRex;
+  UINT64          *Reg;
+  UINT8           *Rip;
+  UINT64          Val;
+  UINT32          OpSize;
+  MODRM           ModRm;
+  REX             Rex;
+  TD_RETURN_DATA  TdReturnData;
+  UINT8           Gpaw;
+  UINT64          TdSharedPageMask;
 
   Rip     = (UINT8 *)Regs->Rip;
   Val     = 0;
   Rex.Val = 0;
   SeenRex = FALSE;
 
+  Status = TdCall (TDCALL_TDINFO, 0, 0, 0, &TdReturnData);
+  if (Status == TDX_EXIT_REASON_SUCCESS) {
+    Gpaw             = (UINT8)(TdReturnData.TdInfo.Gpaw & 0x3f);
+    TdSharedPageMask = 1ULL << (Gpaw - 1);
+  } else {
+    DEBUG ((DEBUG_ERROR, "TDCALL failed with status=%llx\n", Status));
+    return Status;
+  }
+
+  if ((Veinfo->GuestPA & TdSharedPageMask) == 0) {
+    DEBUG ((DEBUG_ERROR, "EPT-violation #VE on private memory is a bug or an attack."));
+    ASSERT (FALSE);
+    TdVmCall (TDVMCALL_HALT, 0, 0, 0, 0, 0);
+  }
+
   //
   // Default to 32bit transfer
   //
-- 
2.29.2.windows.2