[PATCH 1/2] OvmfPkg/AmdSevDxe: Clear the C-bit from SMM Saved State

[Brijesh Singh <brijesh.singh@amd.com>]

When OVMF is built with SMM, SMMSaved State area (SMM_DEFAULT_SMBASE +
SMRAM_SAVE_STATE_MAP_OFFSET) contains data which need to be accessed by
both guest and hypervisor. Since the data need to be accessed by both
hence we must map the SMMSaved State area as unencrypted (i.e C-bit
cleared).

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 OvmfPkg/AmdSevDxe/AmdSevDxe.inf |  4 ++++
 OvmfPkg/AmdSevDxe/AmdSevDxe.c   | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/OvmfPkg/AmdSevDxe/AmdSevDxe.inf b/OvmfPkg/AmdSevDxe/AmdSevDxe.inf
index 41635a57a454..162ed98a2fbe 100644
--- a/OvmfPkg/AmdSevDxe/AmdSevDxe.inf
+++ b/OvmfPkg/AmdSevDxe/AmdSevDxe.inf
@@ -29,6 +29,7 @@ [Packages]
   MdePkg/MdePkg.dec
   MdeModulePkg/MdeModulePkg.dec
   OvmfPkg/OvmfPkg.dec
+  UefiCpuPkg/UefiCpuPkg.dec
 
 [LibraryClasses]
   BaseLib
@@ -41,3 +42,6 @@ [LibraryClasses]
 
 [Depex]
   TRUE
+
+[FeaturePcd]
+  gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire
diff --git a/OvmfPkg/AmdSevDxe/AmdSevDxe.c b/OvmfPkg/AmdSevDxe/AmdSevDxe.c
index e472096320ea..5ec727456526 100644
--- a/OvmfPkg/AmdSevDxe/AmdSevDxe.c
+++ b/OvmfPkg/AmdSevDxe/AmdSevDxe.c
@@ -25,6 +25,8 @@
 #include <Library/UefiBootServicesTableLib.h>
 #include <Library/DxeServicesTableLib.h>
 #include <Library/MemEncryptSevLib.h>
+#include <Register/SmramSaveStateMap.h>
+#include <Register/QemuSmramSaveStateMap.h>
 
 EFI_STATUS
 EFIAPI
@@ -71,5 +73,22 @@ AmdSevDxeEntryPoint (
     FreePool (AllDescMap);
   }
 
+  //
+  // When SMM is enabled, clear the C-bit from SMM Saved State Area
+  //
+  if (FeaturePcdGet (PcdSmmSmramRequire)) {
+    EFI_PHYSICAL_ADDRESS  SmmSavedStateAreaAddress;
+
+    SmmSavedStateAreaAddress = SMM_DEFAULT_SMBASE + SMRAM_SAVE_STATE_MAP_OFFSET;
+
+    Status = MemEncryptSevClearPageEncMask (
+               0,
+               SmmSavedStateAreaAddress,
+               EFI_SIZE_TO_PAGES (sizeof(QEMU_SMRAM_SAVE_STATE_MAP)),
+               FALSE
+               );
+    ASSERT_EFI_ERROR (Status);
+  }
+
   return EFI_SUCCESS;
 }
-- 
2.14.3