2 files changed, 127 insertions, 0 deletions
diff --git a/OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf b/OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf
new file mode 100644
index 0000000000..51ad6d0d05
--- /dev/null
+++ b/OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPei.inf
@@ -0,0 +1,40 @@
+## @file
+# Map TPM MMIO range unencrypted when SEV-ES is active.
+# Install gOvmfTpmMmioAccessiblePpiGuid unconditionally.
+#
+# Copyright (C) 2021, Advanced Micro Devices, Inc.
+#
+# SPDX-License-Identifier: BSD-2-Clause-Patent
+##
+
+[Defines]
+  INF_VERSION                    = 1.29
+  BASE_NAME                      = TpmMmioSevDecryptPei
+  FILE_GUID                      = F12F698A-E506-4A1B-B32E-6920E55DA1C4
+  MODULE_TYPE                    = PEIM
+  VERSION_STRING                 = 1.0
+  ENTRY_POINT                    = TpmMmioSevDecryptPeimEntryPoint
+
+[Sources]
+  TpmMmioSevDecryptPeim.c
+
+[Packages]
+  MdePkg/MdePkg.dec
+  OvmfPkg/OvmfPkg.dec
+  SecurityPkg/SecurityPkg.dec
+
+[LibraryClasses]
+  DebugLib
+  MemEncryptSevLib
+  PcdLib
+  PeimEntryPoint
+  PeiServicesLib
+
+[Ppis]
+  gOvmfTpmMmioAccessiblePpiGuid                      ## PRODUCES
+
+[FixedPcd]
+  gEfiSecurityPkgTokenSpaceGuid.PcdTpmBaseAddress    ## CONSUMES
+
+[Depex]
+  gEfiPeiMemoryDiscoveredPpiGuid
diff --git a/OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPeim.c b/OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPeim.c
new file mode 100644
index 0000000000..df2ad62330
--- /dev/null
+++ b/OvmfPkg/Tcg/TpmMmioSevDecryptPei/TpmMmioSevDecryptPeim.c
@@ -0,0 +1,87 @@
+/** @file
+  Map TPM MMIO range unencrypted when SEV-ES is active.
+  Install gOvmfTpmMmioAccessiblePpiGuid unconditionally.
+
+  Copyright (C) 2021, Advanced Micro Devices, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+
+#include <PiPei.h>
+
+#include <Library/DebugLib.h>
+#include <Library/MemEncryptSevLib.h>
+#include <Library/PcdLib.h>
+#include <Library/PeiServicesLib.h>
+
+STATIC CONST EFI_PEI_PPI_DESCRIPTOR  mTpmMmioRangeAccessible = {
+  EFI_PEI_PPI_DESCRIPTOR_PPI | EFI_PEI_PPI_DESCRIPTOR_TERMINATE_LIST,
+  &gOvmfTpmMmioAccessiblePpiGuid,
+  NULL
+};
+
+/**
+  The entry point for TPM MMIO range mapping driver.
+
+  @param[in]  FileHandle   Handle of the file being invoked.
+  @param[in]  PeiServices  Describes the list of possible PEI Services.
+
+  @retval  EFI_ABORTED  No need to keep this PEIM resident
+**/
+EFI_STATUS
+EFIAPI
+TpmMmioSevDecryptPeimEntryPoint (
+  IN       EFI_PEI_FILE_HANDLE  FileHandle,
+  IN CONST EFI_PEI_SERVICES     **PeiServices
+  )
+{
+  RETURN_STATUS                   DecryptStatus;
+  EFI_STATUS                      Status;
+
+  DEBUG ((DEBUG_INFO, "%a\n", __FUNCTION__));
+
+  //
+  // If SEV is active, MMIO succeeds against an encrypted physical address
+  // because the nested page fault (NPF) that occurs on access does not
+  // include the encryption bit in the guest physical address provided to the
+  // hypervisor.
+  //
+  // If SEV-ES is active, MMIO would succeed against an encrypted physical
+  // address because the #VC handler uses the virtual address (which is an
+  // identity mapped physical address without the encryption bit) as the guest
+  // physical address of the MMIO target in the VMGEXIT.
+  //
+  // However, if SEV-ES is active, before performing the actual MMIO, an
+  // additional MMIO mitigation check is performed in the #VC handler to ensure
+  // that MMIO is being done to/from an unencrypted address. To prevent guest
+  // termination in this scenario, mark the range unencrypted ahead of access.
+  //
+  if (MemEncryptSevEsIsEnabled ()) {
+    DEBUG ((DEBUG_INFO,
+      "%a: mapping TPM MMIO address range unencrypted\n",
+      __FUNCTION__));
+
+    DecryptStatus = MemEncryptSevClearPageEncMask (
+                      0,
+                      FixedPcdGet64 (PcdTpmBaseAddress),
+                      EFI_SIZE_TO_PAGES ((UINTN) 0x5000),
+                      FALSE
+                      );
+
+    if (RETURN_ERROR (DecryptStatus)) {
+      DEBUG ((DEBUG_ERROR,
+        "%a: failed to map TPM MMIO address range unencrypted\n",
+        __FUNCTION__));
+      ASSERT_RETURN_ERROR (DecryptStatus);
+    }
+  }
+
+  //
+  // MMIO range available
+  //
+  Status = PeiServicesInstallPpi (&mTpmMmioRangeAccessible);
+  ASSERT_EFI_ERROR (Status);
+
+  return EFI_ABORTED;
+}