Based on the following patch from Brijesh Singh <brijesh.singh@amd.com>:

  [PATCH v2 1/2] OvmfPkg/AmdSevDxe: Clear the C-bit from SMM Saved State
  http://mid.mail-archive.com/20180228161415.28723-2-brijesh.singh@amd.com
  https://lists.01.org/pipermail/edk2-devel/2018-February/022016.html

Once PiSmmCpuDxeSmm relocates SMBASE for all VCPUs, the pages of the
initial SMRAM save state map can be re-encrypted (including zeroing them
out after setting the C-bit on them), and they can be released to DXE for
general use (undoing the allocation that we did in PlatformPei's
AmdSevInitialize() function).

The decryption of the same pages (which will occur chronologically
earlier) is implemented in the next patch; hence the "re-encryption" part
of this patch is currently a no-op. The series is structured like this in
order to be bisection-friendly. If the decryption patch preceded this
patch, then an info leak would be created while standing between the
patches.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.inf |  2 ++
 OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.c   | 38 ++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.inf b/OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.inf
index 5184abbf21bd..7c2aaa890b5e 100644
--- a/OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.inf
+++ b/OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.inf
@@ -19,21 +19,23 @@ [Defines]
   BASE_NAME                      = SmmCpuFeaturesLib
   MODULE_UNI_FILE                = SmmCpuFeaturesLib.uni
   FILE_GUID                      = AC9991BE-D77A-464C-A8DE-A873DB8A4836
   MODULE_TYPE                    = DXE_SMM_DRIVER
   VERSION_STRING                 = 1.0
   LIBRARY_CLASS                  = SmmCpuFeaturesLib
   CONSTRUCTOR                    = SmmCpuFeaturesLibConstructor
 
 [Sources]
   SmmCpuFeaturesLib.c
 
 [Packages]
   MdePkg/MdePkg.dec
   OvmfPkg/OvmfPkg.dec
   UefiCpuPkg/UefiCpuPkg.dec
 
 [LibraryClasses]
   BaseLib
   BaseMemoryLib
   DebugLib
+  MemEncryptSevLib
   SmmServicesTableLib
+  UefiBootServicesTableLib
diff --git a/OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.c b/OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.c
index 13d929a983be..59c319e01bfb 100644
--- a/OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.c
+++ b/OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.c
@@ -1,39 +1,41 @@
 /** @file
   The CPU specific programming for PiSmmCpuDxeSmm module.
 
   Copyright (c) 2010 - 2015, Intel Corporation. All rights reserved.<BR>
 
   This program and the accompanying materials are licensed and made available
   under the terms and conditions of the BSD License which accompanies this
   distribution.  The full text of the license may be found at
   http://opensource.org/licenses/bsd-license.php
 
   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT
   WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
 **/
 
 #include <Library/BaseLib.h>
 #include <Library/BaseMemoryLib.h>
 #include <Library/DebugLib.h>
+#include <Library/MemEncryptSevLib.h>
 #include <Library/SmmCpuFeaturesLib.h>
 #include <Library/SmmServicesTableLib.h>
+#include <Library/UefiBootServicesTableLib.h>
 #include <PiSmm.h>
 #include <Register/QemuSmramSaveStateMap.h>
 
 //
 // EFER register LMA bit
 //
 #define LMA BIT10
 
 /**
   The constructor function
 
   @param[in]  ImageHandle  The firmware allocated handle for the EFI image.
   @param[in]  SystemTable  A pointer to the EFI System Table.
 
   @retval EFI_SUCCESS      The constructor always returns EFI_SUCCESS.
 
 **/
 EFI_STATUS
 EFIAPI
 SmmCpuFeaturesLibConstructor (
@@ -168,40 +170,76 @@ SmmCpuFeaturesHookReturnFromSmm (
     if ((CpuSaveState->x64.AutoHALTRestart & BIT0) != 0) {
       CpuSaveState->x64.AutoHALTRestart &= ~BIT0;
     }
   }
   return OriginalInstructionPointer;
 }
 
 /**
   Hook point in normal execution mode that allows the one CPU that was elected
   as monarch during System Management Mode initialization to perform additional
   initialization actions immediately after all of the CPUs have processed their
   first SMI and called SmmCpuFeaturesInitializeProcessor() relocating SMBASE
   into a buffer in SMRAM and called SmmCpuFeaturesHookReturnFromSmm().
 **/
 VOID
 EFIAPI
 SmmCpuFeaturesSmmRelocationComplete (
   VOID
   )
 {
+  EFI_STATUS Status;
+  UINTN      MapPagesBase;
+  UINTN      MapPagesCount;
+
+  if (!MemEncryptSevIsEnabled ()) {
+    return;
+  }
+
+  //
+  // Now that SMBASE relocation is complete, re-encrypt the original SMRAM save
+  // state map's container pages, and release the pages to DXE. (The pages were
+  // allocated in PlatformPei.)
+  //
+  Status = MemEncryptSevLocateInitialSmramSaveStateMapPages (
+             &MapPagesBase,
+             &MapPagesCount
+             );
+  ASSERT_EFI_ERROR (Status);
+
+  Status = MemEncryptSevSetPageEncMask (
+             0,             // Cr3BaseAddress -- use current CR3
+             MapPagesBase,  // BaseAddress
+             MapPagesCount, // NumPages
+             TRUE           // Flush
+             );
+  if (EFI_ERROR (Status)) {
+    DEBUG ((DEBUG_ERROR, "%a: MemEncryptSevSetPageEncMask(): %r\n",
+      __FUNCTION__, Status));
+    ASSERT (FALSE);
+    CpuDeadLoop ();
+  }
+
+  ZeroMem ((VOID *)MapPagesBase, EFI_PAGES_TO_SIZE (MapPagesCount));
+
+  Status = gBS->FreePages (MapPagesBase, MapPagesCount);
+  ASSERT_EFI_ERROR (Status);
 }
 
 /**
   Return the size, in bytes, of a custom SMI Handler in bytes.  If 0 is
   returned, then a custom SMI handler is not provided by this library,
   and the default SMI handler must be used.
 
   @retval 0    Use the default SMI handler.
   @retval > 0  Use the SMI handler installed by
                SmmCpuFeaturesInstallSmiHandler(). The caller is required to
                allocate enough SMRAM for each CPU to support the size of the
                custom SMI handler.
 **/
 UINTN
 EFIAPI
 SmmCpuFeaturesGetSmiHandlerSize (
   VOID
   )
 {
   return 0;
-- 
2.14.1.3.gb7cf6e02401b


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