MdeModulePkg: Allow VariablePolicy state to delete protected variables

https://bugzilla.tianocore.org/show_bug.cgi?id=2522

TcgMorLockSmm provides special protections for
the TCG MOR variables. This will check
IsVariablePolicyEnabled() before enforcing
them to allow variable deletion when policy
engine is disabled.

Only allows deletion, not modification.

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Bret Barkelew <brbarkel@microsoft.com>
Signed-off-by: Bret Barkelew <brbarkel@microsoft.com>
Reviewed-by: Dandan Bi <dandan.bi@intel.com>
Acked-by: Jian J Wang <jian.j.wang@intel.com>

MdeModulePkg/Universal/Variable/RuntimeDxe/TcgMorLockSmm.c

@@ -5,6 +5,7 @@
   This module adds Variable Hook and check MemoryOverwriteRequestControlLock.
 
 Copyright (c) 2016 - 2018, Intel Corporation. All rights reserved.<BR>
+Copyright (c) Microsoft Corporation.
 SPDX-License-Identifier: BSD-2-Clause-Patent
 
 **/
@@ -17,6 +18,10 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 #include <Library/BaseMemoryLib.h>
 #include "Variable.h"
 
+#include <Protocol/VariablePolicy.h>
+
+#include <Library/VariablePolicyLib.h>
+
 typedef struct {
   CHAR16                                 *VariableName;
   EFI_GUID                               *VendorGuid;
@@ -341,6 +346,11 @@ SetVariableCheckHandlerMor (
     return EFI_SUCCESS;
   }
 
+  // Permit deletion when policy is disabled.
+  if (!IsVariablePolicyEnabled() && ((Attributes == 0) || (DataSize == 0))) {
+    return EFI_SUCCESS;
+  }
+
   //
   // MorLock variable
   //

MdeModulePkg/Universal/Variable/RuntimeDxe/VariableStandaloneMm.inf

@@ -20,6 +20,7 @@
 #
 # Copyright (c) 2010 - 2019, Intel Corporation. All rights reserved.<BR>
 # Copyright (c) 2018, Linaro, Ltd. All rights reserved.<BR>
+# Copyright (c) Microsoft Corporation.
 # SPDX-License-Identifier: BSD-2-Clause-Patent
 #
 ##
@@ -74,6 +75,7 @@
   StandaloneMmDriverEntryPoint
   SynchronizationLib
   VarCheckLib
+  VariablePolicyLib
 
 [Protocols]
   gEfiSmmFirmwareVolumeBlockProtocolGuid        ## CONSUMES