[PATCH 5/5] OvmfPkg: improve SMM comms security with adaptive MemoryTypeInformation

["Laszlo Ersek" <lersek@redhat.com>]

* In the Intel whitepaper:

--v--
A Tour Beyond BIOS -- Secure SMM Communication

https://github.com/tianocore/tianocore.github.io/wiki/EDK-II-Security-White-Papers
https://github.com/tianocore-docs/Docs/raw/master/White_Papers/A_Tour_Beyond_BIOS_Secure_SMM_Communication.pdf
--^--

bullet#3 in section "Assumption and Recommendation", and bullet#4 in "Call
for action", recommend enabling the (adaptive) Memory Type Information
feature.

* In the Intel whitepaper:

--v--
A Tour Beyond BIOS -- Memory Map and Practices in UEFI BIOS

https://github.com/tianocore/tianocore.github.io/wiki/EDK-II-white-papers
https://github.com/tianocore-docs/Docs/raw/master/White_Papers/A_Tour_Beyond_BIOS_Memory_Map_And_Practices_in_UEFI_BIOS_V2.pdf
--^--

figure#6 describes the Memory Type Information feature in detail; namely
as a feedback loop between the Platform PEIM, the DXE IPL PEIM, the DXE
Core, and BDS.

Implement the missing PlatformPei functionality in OvmfPkg, for fulfilling
the Secure SMM Communication recommendation.

In the longer term, OVMF should install the WSMT ACPI table, and this
patch contributes to that.

Notes:

- the step in figure#6 where the UEFI variable is copied into the HOB is
  covered by the DXE IPL PEIM, in the DxeLoadCore() function,

- "PcdResetOnMemoryTypeInformationChange" must be reverted to the DEC
  default TRUE value, because both whitepapers indicate that BDS needs to
  reset the system if the Memory Type Information changes.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=386
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 OvmfPkg/OvmfPkgIa32.dsc             |   2 +
 OvmfPkg/OvmfPkgIa32X64.dsc          |   2 +
 OvmfPkg/OvmfPkgX64.dsc              |   2 +
 OvmfPkg/PlatformPei/PlatformPei.inf |   2 +
 OvmfPkg/PlatformPei/Platform.h      |   5 +
 OvmfPkg/PlatformPei/MemTypeInfo.c   | 147 ++++++++++++++++++++
 OvmfPkg/PlatformPei/Platform.c      |  23 +--
 7 files changed, 161 insertions(+), 22 deletions(-)

diff --git a/OvmfPkg/OvmfPkgIa32.dsc b/OvmfPkg/OvmfPkgIa32.dsc
index 4c9ff419c462..02ca17db8b2a 100644
--- a/OvmfPkg/OvmfPkgIa32.dsc
+++ b/OvmfPkg/OvmfPkgIa32.dsc
@@ -448,7 +448,9 @@ [PcdsFeatureFlag]
 
 [PcdsFixedAtBuild]
   gEfiMdeModulePkgTokenSpaceGuid.PcdStatusCodeMemorySize|1
+!if $(SMM_REQUIRE) == FALSE
   gEfiMdeModulePkgTokenSpaceGuid.PcdResetOnMemoryTypeInformationChange|FALSE
+!endif
   gEfiMdePkgTokenSpaceGuid.PcdMaximumGuidedExtractHandler|0x10
 !if ($(FD_SIZE_IN_KB) == 1024) || ($(FD_SIZE_IN_KB) == 2048)
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x2000
diff --git a/OvmfPkg/OvmfPkgIa32X64.dsc b/OvmfPkg/OvmfPkgIa32X64.dsc
index 56681e9e4580..d08cf558c6aa 100644
--- a/OvmfPkg/OvmfPkgIa32X64.dsc
+++ b/OvmfPkg/OvmfPkgIa32X64.dsc
@@ -452,7 +452,9 @@ [PcdsFeatureFlag]
 
 [PcdsFixedAtBuild]
   gEfiMdeModulePkgTokenSpaceGuid.PcdStatusCodeMemorySize|1
+!if $(SMM_REQUIRE) == FALSE
   gEfiMdeModulePkgTokenSpaceGuid.PcdResetOnMemoryTypeInformationChange|FALSE
+!endif
   gEfiMdePkgTokenSpaceGuid.PcdMaximumGuidedExtractHandler|0x10
 !if ($(FD_SIZE_IN_KB) == 1024) || ($(FD_SIZE_IN_KB) == 2048)
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x2000
diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
index 0e74b6f4d26c..b2dccc40a865 100644
--- a/OvmfPkg/OvmfPkgX64.dsc
+++ b/OvmfPkg/OvmfPkgX64.dsc
@@ -452,7 +452,9 @@ [PcdsFeatureFlag]
 
 [PcdsFixedAtBuild]
   gEfiMdeModulePkgTokenSpaceGuid.PcdStatusCodeMemorySize|1
+!if $(SMM_REQUIRE) == FALSE
   gEfiMdeModulePkgTokenSpaceGuid.PcdResetOnMemoryTypeInformationChange|FALSE
+!endif
   gEfiMdePkgTokenSpaceGuid.PcdMaximumGuidedExtractHandler|0x10
 !if ($(FD_SIZE_IN_KB) == 1024) || ($(FD_SIZE_IN_KB) == 2048)
   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x2000
diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
index c51a6176aa2e..8531c63995c1 100644
--- a/OvmfPkg/PlatformPei/PlatformPei.inf
+++ b/OvmfPkg/PlatformPei/PlatformPei.inf
@@ -30,6 +30,7 @@ [Sources]
   FeatureControl.c
   Fv.c
   MemDetect.c
+  MemTypeInfo.c
   Platform.c
   Platform.h
   Xen.c
@@ -112,6 +113,7 @@ [FeaturePcd]
 [Ppis]
   gEfiPeiMasterBootModePpiGuid
   gEfiPeiMpServicesPpiGuid
+  gEfiPeiReadOnlyVariable2PpiGuid
 
 [Depex]
   TRUE
diff --git a/OvmfPkg/PlatformPei/Platform.h b/OvmfPkg/PlatformPei/Platform.h
index 43f20f067f22..0484ec9e6b4c 100644
--- a/OvmfPkg/PlatformPei/Platform.h
+++ b/OvmfPkg/PlatformPei/Platform.h
@@ -82,6 +82,11 @@ PeiFvInitialization (
   VOID
   );
 
+VOID
+MemTypeInfoInitialization (
+  VOID
+  );
+
 VOID
 InstallFeatureControlCallback (
   VOID
diff --git a/OvmfPkg/PlatformPei/MemTypeInfo.c b/OvmfPkg/PlatformPei/MemTypeInfo.c
new file mode 100644
index 000000000000..c709236a457a
--- /dev/null
+++ b/OvmfPkg/PlatformPei/MemTypeInfo.c
@@ -0,0 +1,147 @@
+/** @file
+  Produce a default memory type information HOB unless we can determine, from
+  the existence of the "MemoryTypeInformation" variable, that the DXE IPL PEIM
+  will produce the HOB.
+
+  Copyright (C) 2017-2020, Red Hat, Inc.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+#include <Guid/MemoryTypeInformation.h>
+#include <Library/BaseLib.h>
+#include <Library/DebugLib.h>
+#include <Library/HobLib.h>
+#include <Library/PcdLib.h>
+#include <Library/PeiServicesLib.h>
+#include <Ppi/ReadOnlyVariable2.h>
+#include <Uefi/UefiMultiPhase.h>
+
+#include "Platform.h"
+
+STATIC EFI_MEMORY_TYPE_INFORMATION mDefaultMemoryTypeInformation[] = {
+  { EfiACPIMemoryNVS,       0x004 },
+  { EfiACPIReclaimMemory,   0x008 },
+  { EfiReservedMemoryType,  0x004 },
+  { EfiRuntimeServicesData, 0x024 },
+  { EfiRuntimeServicesCode, 0x030 },
+  { EfiBootServicesCode,    0x180 },
+  { EfiBootServicesData,    0xF00 },
+  { EfiMaxMemoryType,       0x000 }
+};
+
+STATIC
+VOID
+BuildMemTypeInfoHob (
+  VOID
+  )
+{
+  BuildGuidDataHob (
+    &gEfiMemoryTypeInformationGuid,
+    mDefaultMemoryTypeInformation,
+    sizeof mDefaultMemoryTypeInformation
+    );
+  DEBUG ((DEBUG_INFO, "%a: default memory type information HOB built\n",
+    __FUNCTION__));
+}
+
+/**
+  Notification function called when EFI_PEI_READ_ONLY_VARIABLE2_PPI becomes
+  available.
+
+  @param[in] PeiServices      Indirect reference to the PEI Services Table.
+  @param[in] NotifyDescriptor Address of the notification descriptor data
+                              structure.
+  @param[in] Ppi              Address of the PPI that was installed.
+
+  @return  Status of the notification. The status code returned from this
+           function is ignored.
+**/
+STATIC
+EFI_STATUS
+EFIAPI
+OnReadOnlyVariable2Available (
+  IN EFI_PEI_SERVICES           **PeiServices,
+  IN EFI_PEI_NOTIFY_DESCRIPTOR  *NotifyDescriptor,
+  IN VOID                       *Ppi
+  )
+{
+  EFI_PEI_READ_ONLY_VARIABLE2_PPI *ReadOnlyVariable2;
+  UINTN                           DataSize;
+  EFI_STATUS                      Status;
+
+  DEBUG ((DEBUG_VERBOSE, "%a\n", __FUNCTION__));
+
+  //
+  // Check if the "MemoryTypeInformation" variable exists, in the
+  // gEfiMemoryTypeInformationGuid namespace.
+  //
+  ReadOnlyVariable2 = Ppi;
+  DataSize = 0;
+  Status = ReadOnlyVariable2->GetVariable (
+                                ReadOnlyVariable2,
+                                EFI_MEMORY_TYPE_INFORMATION_VARIABLE_NAME,
+                                &gEfiMemoryTypeInformationGuid,
+                                NULL,
+                                &DataSize,
+                                NULL
+                                );
+  switch (Status) {
+  case EFI_BUFFER_TOO_SMALL:
+    //
+    // The variable exists; the DXE IPL PEIM will build the HOB from it.
+    //
+    break;
+  case EFI_NOT_FOUND:
+    //
+    // The variable does not exist; install the default memory type information
+    // HOB.
+    //
+    BuildMemTypeInfoHob ();
+    break;
+  default:
+    DEBUG ((DEBUG_ERROR, "%a: unexpected: GetVariable(): %r\n", __FUNCTION__,
+      Status));
+    ASSERT (FALSE);
+    CpuDeadLoop ();
+    break;
+  }
+
+  return EFI_SUCCESS;
+}
+
+//
+// Notification object for registering the callback, for when
+// EFI_PEI_READ_ONLY_VARIABLE2_PPI becomes available.
+//
+STATIC CONST EFI_PEI_NOTIFY_DESCRIPTOR mReadOnlyVariable2Notify = {
+  (EFI_PEI_PPI_DESCRIPTOR_NOTIFY_DISPATCH |
+   EFI_PEI_PPI_DESCRIPTOR_TERMINATE_LIST),  // Flags
+  &gEfiPeiReadOnlyVariable2PpiGuid,         // Guid
+  OnReadOnlyVariable2Available              // Notify
+};
+
+VOID
+MemTypeInfoInitialization (
+  VOID
+  )
+{
+  EFI_STATUS Status;
+
+  if (!FeaturePcdGet (PcdSmmSmramRequire)) {
+    //
+    // EFI_PEI_READ_ONLY_VARIABLE2_PPI will never be available; install
+    // the default memory type information HOB right away.
+    //
+    BuildMemTypeInfoHob ();
+    return;
+  }
+
+  Status = PeiServicesNotifyPpi (&mReadOnlyVariable2Notify);
+  if (EFI_ERROR (Status)) {
+    DEBUG ((DEBUG_ERROR, "%a: failed to set up R/O Variable 2 callback: %r\n",
+      __FUNCTION__, Status));
+    ASSERT (FALSE);
+    CpuDeadLoop ();
+  }
+}
diff --git a/OvmfPkg/PlatformPei/Platform.c b/OvmfPkg/PlatformPei/Platform.c
index 473af102783a..587ca68fc210 100644
--- a/OvmfPkg/PlatformPei/Platform.c
+++ b/OvmfPkg/PlatformPei/Platform.c
@@ -28,7 +28,6 @@
 #include <Library/QemuFwCfgLib.h>
 #include <Library/QemuFwCfgS3Lib.h>
 #include <Library/ResourcePublicationLib.h>
-#include <Guid/MemoryTypeInformation.h>
 #include <Ppi/MasterBootMode.h>
 #include <IndustryStandard/I440FxPiix4.h>
 #include <IndustryStandard/Pci22.h>
@@ -39,18 +38,6 @@
 #include "Platform.h"
 #include "Cmos.h"
 
-EFI_MEMORY_TYPE_INFORMATION mDefaultMemoryTypeInformation[] = {
-  { EfiACPIMemoryNVS,       0x004 },
-  { EfiACPIReclaimMemory,   0x008 },
-  { EfiReservedMemoryType,  0x004 },
-  { EfiRuntimeServicesData, 0x024 },
-  { EfiRuntimeServicesCode, 0x030 },
-  { EfiBootServicesCode,    0x180 },
-  { EfiBootServicesData,    0xF00 },
-  { EfiMaxMemoryType,       0x000 }
-};
-
-
 EFI_PEI_PPI_DESCRIPTOR   mPpiBootMode[] = {
   {
     EFI_PEI_PPI_DESCRIPTOR_PPI | EFI_PEI_PPI_DESCRIPTOR_TERMINATE_LIST,
@@ -162,15 +149,6 @@ MemMapInitialization (
   PciIoBase = 0xC000;
   PciIoSize = 0x4000;
 
-  //
-  // Create Memory Type Information HOB
-  //
-  BuildGuidDataHob (
-    &gEfiMemoryTypeInformationGuid,
-    mDefaultMemoryTypeInformation,
-    sizeof(mDefaultMemoryTypeInformation)
-    );
-
   //
   // Video memory + Legacy BIOS region
   //
@@ -811,6 +789,7 @@ InitializePlatform (
       ReserveEmuVariableNvStore ();
     }
     PeiFvInitialization ();
+    MemTypeInfoInitialization ();
     MemMapInitialization ();
     NoexecDxeInitialization ();
   }
-- 
2.19.1.3.g30247aa5d201