Re: [edk2-devel] [PATCH v6 04/14] MdeModulePkg: Define the VarCheckPolicyLib and SMM interface

["Bret Barkelew" <bret.barkelew@microsoft.com>]

[-- Attachment #1: Type: text/plain, Size: 26904 bytes --]

1.[Dandan]: This should be a NULL class library, not an instance of VarCheck Lib.

Agreed. Will update.

- Bret

From: Dandan Bi via groups.io<mailto:dandan.bi=intel.com@groups.io>
Sent: Wednesday, July 1, 2020 7:13 PM
To: devel@edk2.groups.io<mailto:devel@edk2.groups.io>; bret@corthon.com<mailto:bret@corthon.com>
Cc: Wang, Jian J<mailto:jian.j.wang@intel.com>; Wu, Hao A<mailto:hao.a.wu@intel.com>; liming.gao<mailto:liming.gao@intel.com>
Subject: [EXTERNAL] Re: [edk2-devel] [PATCH v6 04/14] MdeModulePkg: Define the VarCheckPolicyLib and SMM interface

1 comment inline, please check.



Thanks,
Dandan
> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Bret
> Barkelew
> Sent: Tuesday, June 23, 2020 2:41 PM
> To: devel@edk2.groups.io
> Cc: Wang, Jian J <jian.j.wang@intel.com>; Wu, Hao A <hao.a.wu@intel.com>;
> Gao, Liming <liming.gao@intel.com>
> Subject: [edk2-devel] [PATCH v6 04/14] MdeModulePkg: Define the
> VarCheckPolicyLib and SMM interface
>
> https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D2522&amp;data=02%7C01%7CBret.Barkelew%40microsoft.com%7Cc2c1537a2d7f41247b0308d81e2d8238%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637292528098010318&amp;sdata=yj3Z6JZariiNwPNLzp1Phb7bQHvtPYPA7U%2BjFkQMJ3k%3D&amp;reserved=0
>
> VariablePolicy is an updated interface to
> replace VarLock and VarCheckProtocol.
>
> This is an instance of a VarCheckLib that is backed by the
> VariablePolicyLib business logic. It also publishes the SMM
> calling interface for messages from the DXE protocol.
>
> 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>
> ---
>  MdeModulePkg/Library/VarCheckPolicyLib/VarCheckPolicyLib.c   | 320
> ++++++++++++++++++++
>  MdeModulePkg/Include/Guid/VarCheckPolicyMmi.h                |  54 ++++
>  MdeModulePkg/Library/VarCheckPolicyLib/VarCheckPolicyLib.inf |  42 +++
>  MdeModulePkg/Library/VarCheckPolicyLib/VarCheckPolicyLib.uni |  12 +
>  MdeModulePkg/MdeModulePkg.dec                                |   4 +
>  MdeModulePkg/MdeModulePkg.dsc                                |   2 +
>  6 files changed, 434 insertions(+)
>
> diff --git a/MdeModulePkg/Library/VarCheckPolicyLib/VarCheckPolicyLib.c
> b/MdeModulePkg/Library/VarCheckPolicyLib/VarCheckPolicyLib.c
> new file mode 100644
> index 000000000000..b64fc5f45332
> --- /dev/null
> +++ b/MdeModulePkg/Library/VarCheckPolicyLib/VarCheckPolicyLib.c
> @@ -0,0 +1,320 @@
> +/** @file -- VarCheckPolicyLib.c
>
> +This is an instance of a VarCheck lib that leverages the business logic behind
1.[Dandan]: This should be a NULL class library, not an instance of VarCheck Lib.

>
> +the VariablePolicy code to make its decisions.
>
> +
>
> +Copyright (c) Microsoft Corporation.
>
> +SPDX-License-Identifier: BSD-2-Clause-Patent
>
> +
>
> +**/
>
> +
>
> +#include <Library/VarCheckLib.h>
>
> +#include <Library/BaseLib.h>
>
> +#include <Library/DebugLib.h>
>
> +#include <Library/SafeIntLib.h>
>
> +#include <Library/MmServicesTableLib.h>
>
> +#include <Library/BaseMemoryLib.h>
>
> +#include <Library/MemoryAllocationLib.h>
>
> +
>
> +#include <Protocol/MmCommunication.h>
>
> +
>
> +#include <Protocol/VariablePolicy.h>
>
> +#include <Library/VariablePolicyLib.h>
>
> +
>
> +#include <Guid/VarCheckPolicyMmi.h>
>
> +
>
> +//================================================
>
> +// As a VarCheck library, we're linked into the VariableServices
>
> +// and may not be able to call them indirectly. To get around this,
>
> +// use the internal GetVariable function to query the variable store.
>
> +//================================================
>
> +EFI_STATUS
>
> +EFIAPI
>
> +VariableServiceGetVariable (
>
> +  IN      CHAR16            *VariableName,
>
> +  IN      EFI_GUID          *VendorGuid,
>
> +  OUT     UINT32            *Attributes OPTIONAL,
>
> +  IN OUT  UINTN             *DataSize,
>
> +  OUT     VOID              *Data
>
> +  );
>
> +
>
> +
>
> +/**
>
> +  MM Communication Handler to recieve commands from the DXE protocol
> for
>
> +  Variable Policies. This communication channel is used to register new
> policies
>
> +  and poll and toggle the enforcement of variable policies.
>
> +
>
> +  @param[in]      DispatchHandle      All parameters standard to MM
> communications convention.
>
> +  @param[in]      RegisterContext     All parameters standard to MM
> communications convention.
>
> +  @param[in,out]  CommBuffer          All parameters standard to MM
> communications convention.
>
> +  @param[in,out]  CommBufferSize      All parameters standard to MM
> communications convention.
>
> +
>
> +  @retval     EFI_SUCCESS
>
> +  @retval     EFI_INVALID_PARAMETER   CommBuffer or CommBufferSize is
> null pointer.
>
> +  @retval     EFI_INVALID_PARAMETER   CommBuffer size is wrong.
>
> +  @retval     EFI_INVALID_PARAMETER   Revision or signature don't match.
>
> +
>
> +**/
>
> +STATIC
>
> +EFI_STATUS
>
> +EFIAPI
>
> +VarCheckPolicyLibMmiHandler (
>
> +  IN     EFI_HANDLE                   DispatchHandle,
>
> +  IN     CONST VOID                   *RegisterContext,
>
> +  IN OUT VOID                         *CommBuffer,
>
> +  IN OUT UINTN                        *CommBufferSize
>
> +  )
>
> +{
>
> +  EFI_STATUS                                Status;
>
> +  EFI_STATUS                                SubCommandStatus;
>
> +  VAR_CHECK_POLICY_COMM_HEADER              *PolicyCommmHeader;
>
> +  VAR_CHECK_POLICY_COMM_IS_ENABLED_PARAMS   *IsEnabledParams;
>
> +  VAR_CHECK_POLICY_COMM_DUMP_PARAMS         *DumpParams;
>
> +  UINT8                                     *DumpInputBuffer;
>
> +  UINT8                                     *DumpOutputBuffer;
>
> +  UINTN                                     DumpTotalPages;
>
> +  VARIABLE_POLICY_ENTRY                     *PolicyEntry;
>
> +  UINTN                                     ExpectedSize;
>
> +  // Pagination Cache Variables
>
> +  static UINT8                              *PaginationCache = NULL;
>
> +  static UINTN                              PaginationCacheSize = 0;
>
> +  static UINT32                             CurrentPaginationCommand = 0;
>
> +
>
> +  Status = EFI_SUCCESS;
>
> +
>
> +  //
>
> +  // Validate some input parameters.
>
> +  //
>
> +  // If either of the pointers are NULL, we can't proceed.
>
> +  if (CommBuffer == NULL || CommBufferSize == NULL) {
>
> +    DEBUG(( DEBUG_INFO, "%a - Invalid comm buffer pointers!\n",
> __FUNCTION__ ));
>
> +    return EFI_INVALID_PARAMETER;
>
> +  }
>
> +  // If the size does not meet a minimum threshold, we cannot proceed.
>
> +  ExpectedSize = sizeof(VAR_CHECK_POLICY_COMM_HEADER);
>
> +  if (*CommBufferSize < ExpectedSize) {
>
> +    DEBUG(( DEBUG_INFO, "%a - Bad comm buffer size! %d < %d\n",
> __FUNCTION__, *CommBufferSize, ExpectedSize ));
>
> +    return EFI_INVALID_PARAMETER;
>
> +  }
>
> +  // Check the revision and the signature of the comm header.
>
> +  PolicyCommmHeader = CommBuffer;
>
> +  if (PolicyCommmHeader->Signature != VAR_CHECK_POLICY_COMM_SIG
> ||
>
> +      PolicyCommmHeader->Revision !=
> VAR_CHECK_POLICY_COMM_REVISION) {
>
> +    DEBUG(( DEBUG_INFO, "%a - Signature or revision are incorrect!\n",
> __FUNCTION__ ));
>
> +    // We have verified the buffer is not null and have enough size to hold
> Result field.
>
> +    PolicyCommmHeader->Result = EFI_INVALID_PARAMETER;
>
> +    return EFI_SUCCESS;
>
> +  }
>
> +
>
> +  // If we're in the middle of a paginated dump and any other command is
> sent,
>
> +  // pagination cache must be cleared.
>
> +  if (PaginationCache != NULL && PolicyCommmHeader->Command !=
> CurrentPaginationCommand) {
>
> +    FreePool (PaginationCache);
>
> +    PaginationCache = NULL;
>
> +    PaginationCacheSize = 0;
>
> +    CurrentPaginationCommand = 0;
>
> +  }
>
> +
>
> +  //
>
> +  // Now we can process the command as it was sent.
>
> +  //
>
> +  PolicyCommmHeader->Result = EFI_ABORTED;    // Set a default return for
> incomplete commands.
>
> +  switch(PolicyCommmHeader->Command) {
>
> +    case VAR_CHECK_POLICY_COMMAND_DISABLE:
>
> +      PolicyCommmHeader->Result = DisableVariablePolicy();
>
> +      break;
>
> +
>
> +    case VAR_CHECK_POLICY_COMMAND_IS_ENABLED:
>
> +      // Make sure that we're dealing with a reasonable size.
>
> +      // This add should be safe because these are fixed sizes so far.
>
> +      ExpectedSize +=
> sizeof(VAR_CHECK_POLICY_COMM_IS_ENABLED_PARAMS);
>
> +      if (*CommBufferSize < ExpectedSize) {
>
> +        DEBUG(( DEBUG_INFO, "%a - Bad comm buffer size! %d < %d\n",
> __FUNCTION__, *CommBufferSize, ExpectedSize ));
>
> +        PolicyCommmHeader->Result = EFI_INVALID_PARAMETER;
>
> +        break;
>
> +      }
>
> +
>
> +      // Now that we know we've got a valid size, we can fill in the rest of the
> data.
>
> +      IsEnabledParams =
> (VAR_CHECK_POLICY_COMM_IS_ENABLED_PARAMS*)((UINT8*)CommBuff
> er + sizeof(VAR_CHECK_POLICY_COMM_HEADER));
>
> +      IsEnabledParams->State = IsVariablePolicyEnabled();
>
> +      PolicyCommmHeader->Result = EFI_SUCCESS;
>
> +      break;
>
> +
>
> +    case VAR_CHECK_POLICY_COMMAND_REGISTER:
>
> +      // Make sure that we're dealing with a reasonable size.
>
> +      // This add should be safe because these are fixed sizes so far.
>
> +      ExpectedSize += sizeof(VARIABLE_POLICY_ENTRY);
>
> +      if (*CommBufferSize < ExpectedSize) {
>
> +        DEBUG(( DEBUG_INFO, "%a - Bad comm buffer size! %d < %d\n",
> __FUNCTION__, *CommBufferSize, ExpectedSize ));
>
> +        PolicyCommmHeader->Result = EFI_INVALID_PARAMETER;
>
> +        break;
>
> +      }
>
> +
>
> +      // At the very least, we can assume that we're working with a valid policy
> entry.
>
> +      // Time to compare its internal size.
>
> +      PolicyEntry = (VARIABLE_POLICY_ENTRY*)((UINT8*)CommBuffer +
> sizeof(VAR_CHECK_POLICY_COMM_HEADER));
>
> +      if (PolicyEntry->Version != VARIABLE_POLICY_ENTRY_REVISION ||
>
> +          PolicyEntry->Size < sizeof(VARIABLE_POLICY_ENTRY) ||
>
> +
> EFI_ERROR(SafeUintnAdd(sizeof(VAR_CHECK_POLICY_COMM_HEADER),
> PolicyEntry->Size, &ExpectedSize)) ||
>
> +          *CommBufferSize < ExpectedSize) {
>
> +        DEBUG(( DEBUG_INFO, "%a - Bad policy entry contents!\n",
> __FUNCTION__ ));
>
> +        PolicyCommmHeader->Result = EFI_INVALID_PARAMETER;
>
> +        break;
>
> +      }
>
> +
>
> +      PolicyCommmHeader->Result = RegisterVariablePolicy( PolicyEntry );
>
> +      break;
>
> +
>
> +    case VAR_CHECK_POLICY_COMMAND_DUMP:
>
> +      // Make sure that we're dealing with a reasonable size.
>
> +      // This add should be safe because these are fixed sizes so far.
>
> +      ExpectedSize += sizeof(VAR_CHECK_POLICY_COMM_DUMP_PARAMS)
> + VAR_CHECK_POLICY_MM_DUMP_BUFFER_SIZE;
>
> +      if (*CommBufferSize < ExpectedSize) {
>
> +        DEBUG(( DEBUG_INFO, "%a - Bad comm buffer size! %d < %d\n",
> __FUNCTION__, *CommBufferSize, ExpectedSize ));
>
> +        PolicyCommmHeader->Result = EFI_INVALID_PARAMETER;
>
> +        break;
>
> +      }
>
> +
>
> +      // Now that we know we've got a valid size, we can fill in the rest of the
> data.
>
> +      DumpParams =
> (VAR_CHECK_POLICY_COMM_DUMP_PARAMS*)(PolicyCommmHeader + 1);
>
> +
>
> +      // If we're requesting the first page, initialize the cache and get the sizes.
>
> +      if (DumpParams->PageRequested == 0) {
>
> +        if (PaginationCache != NULL) {
>
> +          FreePool (PaginationCache);
>
> +          PaginationCache = NULL;
>
> +        }
>
> +
>
> +        // Determine what the required size is going to be.
>
> +        DumpParams->TotalSize = 0;
>
> +        DumpParams->PageSize = 0;
>
> +        DumpParams->HasMore = FALSE;
>
> +        SubCommandStatus = DumpVariablePolicy (NULL, &DumpParams-
> >TotalSize);
>
> +        if (SubCommandStatus == EFI_BUFFER_TOO_SMALL && DumpParams-
> >TotalSize > 0) {
>
> +          CurrentPaginationCommand =
> VAR_CHECK_POLICY_COMMAND_DUMP;
>
> +          PaginationCacheSize = DumpParams->TotalSize;
>
> +          PaginationCache = AllocatePool (PaginationCacheSize);
>
> +          if (PaginationCache == NULL) {
>
> +            SubCommandStatus = EFI_OUT_OF_RESOURCES;
>
> +          }
>
> +        }
>
> +
>
> +        // If we've allocated our pagination cache, we're good to cache.
>
> +        if (PaginationCache != NULL) {
>
> +          SubCommandStatus = DumpVariablePolicy (PaginationCache,
> &DumpParams->TotalSize);
>
> +        }
>
> +
>
> +        // Populate the remaining fields and we can boogie.
>
> +        if (!EFI_ERROR (SubCommandStatus) && PaginationCache != NULL) {
>
> +          DumpParams->HasMore = TRUE;
>
> +        }
>
> +      }
>
> +      else if (PaginationCache != NULL) {
>
> +        DumpParams->TotalSize = (UINT32)PaginationCacheSize;
>
> +        DumpParams->PageSize =
> VAR_CHECK_POLICY_MM_DUMP_BUFFER_SIZE;
>
> +        DumpOutputBuffer = (UINT8*)(DumpParams + 1);
>
> +
>
> +        // Make sure that we don't over-index the cache.
>
> +        DumpTotalPages = PaginationCacheSize / DumpParams->PageSize;
>
> +        if (PaginationCacheSize % DumpParams->PageSize) DumpTotalPages++;
>
> +        if (DumpParams->PageRequested > DumpTotalPages) {
>
> +          SubCommandStatus = EFI_INVALID_PARAMETER;
>
> +        }
>
> +        else {
>
> +          // Figure out how far into the page cache we need to go for our next
> page.
>
> +          // We know the blind subtraction won't be bad because we already
> checked for page 0.
>
> +          DumpInputBuffer = &PaginationCache[DumpParams->PageSize *
> (DumpParams->PageRequested - 1)];
>
> +          // If we're getting the last page, adjust the PageSize.
>
> +          if (DumpParams->PageRequested == DumpTotalPages) {
>
> +            DumpParams->PageSize = PaginationCacheSize % DumpParams-
> >PageSize;
>
> +          }
>
> +          CopyMem (DumpOutputBuffer, DumpInputBuffer, DumpParams-
> >PageSize);
>
> +          // If we just got the last page, settle up the cache.
>
> +          if (DumpParams->PageRequested == DumpTotalPages) {
>
> +            DumpParams->HasMore = FALSE;
>
> +            FreePool (PaginationCache);
>
> +            PaginationCache = NULL;
>
> +            PaginationCacheSize = 0;
>
> +            CurrentPaginationCommand = 0;
>
> +          }
>
> +          // Otherwise, we could do more here.
>
> +          else {
>
> +            DumpParams->HasMore = TRUE;
>
> +          }
>
> +
>
> +          // If we made it this far, we're basically good.
>
> +          SubCommandStatus = EFI_SUCCESS;
>
> +        }
>
> +      }
>
> +      // If we've requested any other page than 0 and the cache is empty, we
> must have timed out.
>
> +      else {
>
> +        DumpParams->TotalSize = 0;
>
> +        DumpParams->PageSize = 0;
>
> +        DumpParams->HasMore = FALSE;
>
> +        SubCommandStatus = EFI_TIMEOUT;
>
> +      }
>
> +
>
> +      // There's currently no use for this, but it shouldn't be hard to implement.
>
> +      PolicyCommmHeader->Result = SubCommandStatus;
>
> +      break;
>
> +
>
> +    case VAR_CHECK_POLICY_COMMAND_LOCK:
>
> +      PolicyCommmHeader->Result = LockVariablePolicy();
>
> +      break;
>
> +
>
> +    default:
>
> +      // Mark unknown requested command as EFI_UNSUPPORTED.
>
> +      DEBUG(( DEBUG_INFO, "%a - Invalid command requested! %d\n",
> __FUNCTION__, PolicyCommmHeader->Command ));
>
> +      PolicyCommmHeader->Result = EFI_UNSUPPORTED;
>
> +      break;
>
> +  }
>
> +
>
> +  DEBUG(( DEBUG_VERBOSE, "%a - Command %d returning %r.\n",
> __FUNCTION__,
>
> +          PolicyCommmHeader->Command, PolicyCommmHeader->Result ));
>
> +
>
> +  return Status;
>
> +}
>
> +
>
> +
>
> +/**
>
> +  Constructor function of VarCheckPolicyLib to register VarCheck handler
> and
>
> +  SW MMI handlers.
>
> +
>
> +  @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 executed correctly.
>
> +
>
> +**/
>
> +EFI_STATUS
>
> +EFIAPI
>
> +VarCheckPolicyLibConstructor (
>
> +  IN EFI_HANDLE             ImageHandle,
>
> +  IN EFI_SYSTEM_TABLE       *SystemTable
>
> +  )
>
> +{
>
> +  EFI_STATUS    Status;
>
> +  EFI_HANDLE    DiscardedHandle;
>
> +
>
> +  // Initialize the business logic with the internal GetVariable handler.
>
> +  Status = InitVariablePolicyLib( VariableServiceGetVariable );
>
> +
>
> +  // Only proceed with init if the business logic could be initialized.
>
> +  if (!EFI_ERROR( Status )) {
>
> +    // Register the VarCheck handler for SetVariable filtering.
>
> +    // Forward the check to the business logic of the library.
>
> +    VarCheckLibRegisterSetVariableCheckHandler( ValidateSetVariable );
>
> +
>
> +    // Register the MMI handlers for receiving policy commands.
>
> +    DiscardedHandle = NULL;
>
> +    Status = gMmst->MmiHandlerRegister( VarCheckPolicyLibMmiHandler,
>
> +                                        &gVarCheckPolicyLibMmiHandlerGuid,
>
> +                                        &DiscardedHandle );
>
> +  }
>
> +  // Otherwise, there's not much we can do.
>
> +  else {
>
> +    DEBUG(( DEBUG_ERROR, "%a - Cannot Initialize VariablePolicyLib! %r\n",
> __FUNCTION__, Status ));
>
> +    ASSERT_EFI_ERROR( Status );
>
> +  }
>
> +
>
> +  return Status;
>
> +}
>
> diff --git a/MdeModulePkg/Include/Guid/VarCheckPolicyMmi.h
> b/MdeModulePkg/Include/Guid/VarCheckPolicyMmi.h
> new file mode 100644
> index 000000000000..77bcc62f3ccf
> --- /dev/null
> +++ b/MdeModulePkg/Include/Guid/VarCheckPolicyMmi.h
> @@ -0,0 +1,54 @@
> +/** @file -- VarCheckPolicyMmiCommon.h
>
> +This header contains communication definitions that are shared between
> DXE
>
> +and the MM component of VarCheckPolicy.
>
> +
>
> +Copyright (c) Microsoft Corporation.
>
> +SPDX-License-Identifier: BSD-2-Clause-Patent
>
> +**/
>
> +
>
> +#ifndef _VAR_CHECK_POLICY_MMI_COMMON_H_
>
> +#define _VAR_CHECK_POLICY_MMI_COMMON_H_
>
> +
>
> +#define   VAR_CHECK_POLICY_COMM_SIG       SIGNATURE_32('V', 'C', 'P', 'C')
>
> +#define   VAR_CHECK_POLICY_COMM_REVISION  1
>
> +
>
> +#pragma pack(push, 1)
>
> +
>
> +typedef struct _VAR_CHECK_POLICY_COMM_HEADER {
>
> +  UINT32      Signature;
>
> +  UINT32      Revision;
>
> +  UINT32      Command;
>
> +  EFI_STATUS  Result;
>
> +} VAR_CHECK_POLICY_COMM_HEADER;
>
> +
>
> +typedef struct _VAR_CHECK_POLICY_COMM_IS_ENABLED_PARAMS {
>
> +  BOOLEAN     State;
>
> +} VAR_CHECK_POLICY_COMM_IS_ENABLED_PARAMS;
>
> +
>
> +typedef struct _VAR_CHECK_POLICY_COMM_DUMP_PARAMS {
>
> +  UINT32      PageRequested;
>
> +  UINT32      TotalSize;
>
> +  UINT32      PageSize;
>
> +  BOOLEAN     HasMore;
>
> +} VAR_CHECK_POLICY_COMM_DUMP_PARAMS;
>
> +
>
> +#pragma pack(pop)
>
> +
>
> +// Make sure that we will hold at least the headers.
>
> +#define   VAR_CHECK_POLICY_MM_COMM_BUFFER_SIZE
> MAX((OFFSET_OF(EFI_MM_COMMUNICATE_HEADER, Data) + sizeof
> (VAR_CHECK_POLICY_COMM_HEADER) + EFI_PAGES_TO_SIZE(1)),
> EFI_PAGES_TO_SIZE(4))
>
> +#define   VAR_CHECK_POLICY_MM_DUMP_BUFFER_SIZE
> (VAR_CHECK_POLICY_MM_COMM_BUFFER_SIZE - \
>
> +                                                    (OFFSET_OF(EFI_MM_COMMUNICATE_HEADER,
> Data) + \
>
> +                                                      sizeof(VAR_CHECK_POLICY_COMM_HEADER) + \
>
> +
> sizeof(VAR_CHECK_POLICY_COMM_DUMP_PARAMS)))
>
> +STATIC_ASSERT (
>
> +  VAR_CHECK_POLICY_MM_DUMP_BUFFER_SIZE <
> VAR_CHECK_POLICY_MM_COMM_BUFFER_SIZE,
>
> +  "an integer underflow may have occurred calculating
> VAR_CHECK_POLICY_MM_DUMP_BUFFER_SIZE"
>
> +  );
>
> +
>
> +#define   VAR_CHECK_POLICY_COMMAND_DISABLE      0x0001
>
> +#define   VAR_CHECK_POLICY_COMMAND_IS_ENABLED   0x0002
>
> +#define   VAR_CHECK_POLICY_COMMAND_REGISTER     0x0003
>
> +#define   VAR_CHECK_POLICY_COMMAND_DUMP         0x0004
>
> +#define   VAR_CHECK_POLICY_COMMAND_LOCK         0x0005
>
> +
>
> +#endif // _VAR_CHECK_POLICY_MMI_COMMON_H_
>
> diff --git a/MdeModulePkg/Library/VarCheckPolicyLib/VarCheckPolicyLib.inf
> b/MdeModulePkg/Library/VarCheckPolicyLib/VarCheckPolicyLib.inf
> new file mode 100644
> index 000000000000..077bcc8990ca
> --- /dev/null
> +++ b/MdeModulePkg/Library/VarCheckPolicyLib/VarCheckPolicyLib.inf
> @@ -0,0 +1,42 @@
> +## @file VarCheckPolicyLib.inf
>
> +# This is an instance of a VarCheck lib that leverages the business logic
> behind
>
> +# the VariablePolicy code to make its decisions.
>
> +#
>
> +# Copyright (c) Microsoft Corporation.
>
> +# SPDX-License-Identifier: BSD-2-Clause-Patent
>
> +##
>
> +
>
> +[Defines]
>
> +  INF_VERSION                    = 0x00010005
>
> +  BASE_NAME                      = VarCheckPolicyLib
>
> +  FILE_GUID                      = 9C28A48F-C884-4B1F-8B95-DEF125448023
>
> +  MODULE_TYPE                    = DXE_RUNTIME_DRIVER
>
> +  VERSION_STRING                 = 1.0
>
> +  LIBRARY_CLASS                  = NULL|DXE_RUNTIME_DRIVER
> DXE_SMM_DRIVER
>
> +  CONSTRUCTOR                    = VarCheckPolicyLibConstructor
>
> +
>
> +
>
> +[Sources]
>
> +  VarCheckPolicyLib.c
>
> +
>
> +
>
> +[Packages]
>
> +  MdePkg/MdePkg.dec
>
> +  MdeModulePkg/MdeModulePkg.dec
>
> +
>
> +
>
> +[LibraryClasses]
>
> +  BaseLib
>
> +  DebugLib
>
> +  BaseMemoryLib
>
> +  DxeServicesLib
>
> +  MemoryAllocationLib
>
> +  VarCheckLib
>
> +  VariablePolicyLib
>
> +  VariablePolicyHelperLib
>
> +  SafeIntLib
>
> +  MmServicesTableLib
>
> +
>
> +
>
> +[Guids]
>
> +  gVarCheckPolicyLibMmiHandlerGuid        ## CONSUME ## Used to register
> for MM Communication events.
>
> diff --git a/MdeModulePkg/Library/VarCheckPolicyLib/VarCheckPolicyLib.uni
> b/MdeModulePkg/Library/VarCheckPolicyLib/VarCheckPolicyLib.uni
> new file mode 100644
> index 000000000000..eedeeed15d31
> --- /dev/null
> +++ b/MdeModulePkg/Library/VarCheckPolicyLib/VarCheckPolicyLib.uni
> @@ -0,0 +1,12 @@
> +// /** @file
>
> +// VarCheckPolicyLib.uni
>
> +//
>
> +// Copyright (c) Microsoft Corporation.
>
> +// SPDX-License-Identifier: BSD-2-Clause-Patent
>
> +//
>
> +// **/
>
> +
>
> +
>
> +#string STR_MODULE_ABSTRACT             #language en-US "NULL library
> implementation that conforms to the VarCheck interface to allow
> VariablePolicy engine to enforce policies"
>
> +
>
> +#string STR_MODULE_DESCRIPTION          #language en-US "NULL library
> implementation that conforms to the VarCheck interface to allow
> VariablePolicy engine to enforce policies"
>
> diff --git a/MdeModulePkg/MdeModulePkg.dec
> b/MdeModulePkg/MdeModulePkg.dec
> index b21cd78c8787..9a3c9fe642d3 100644
> --- a/MdeModulePkg/MdeModulePkg.dec
> +++ b/MdeModulePkg/MdeModulePkg.dec
> @@ -385,6 +385,10 @@ [Guids]
>    ## Include/Guid/EndofS3Resume.h
>
>    gEdkiiEndOfS3ResumeGuid = { 0x96f5296d, 0x05f7, 0x4f3c, {0x84, 0x67, 0xe4,
> 0x56, 0x89, 0x0e, 0x0c, 0xb5 } }
>
>
>
> +  ## Used (similar to Variable Services) to communicate policies to the
> enforcement engine.
>
> +  # {DA1B0D11-D1A7-46C4-9DC9-F3714875C6EB}
>
> +  gVarCheckPolicyLibMmiHandlerGuid = { 0xda1b0d11, 0xd1a7, 0x46c4,
> { 0x9d, 0xc9, 0xf3, 0x71, 0x48, 0x75, 0xc6, 0xeb }}
>
> +
>
>    ## Include/Guid/S3SmmInitDone.h
>
>    gEdkiiS3SmmInitDoneGuid = { 0x8f9d4825, 0x797d, 0x48fc, { 0x84, 0x71,
> 0x84, 0x50, 0x25, 0x79, 0x2e, 0xf6 } }
>
>
>
> diff --git a/MdeModulePkg/MdeModulePkg.dsc
> b/MdeModulePkg/MdeModulePkg.dsc
> index 37795b9e4f58..f0a75a3b337b 100644
> --- a/MdeModulePkg/MdeModulePkg.dsc
> +++ b/MdeModulePkg/MdeModulePkg.dsc
> @@ -313,6 +313,7 @@ [Components]
>    MdeModulePkg/Library/AuthVariableLibNull/AuthVariableLibNull.inf
>
>    MdeModulePkg/Library/VariablePolicyLib/VariablePolicyLib.inf
>
>    MdeModulePkg/Library/VariablePolicyLib/VariablePolicyLibRuntimeDxe.inf
>
> +  MdeModulePkg/Library/VarCheckPolicyLib/VarCheckPolicyLib.inf
>
>    MdeModulePkg/Library/VarCheckLib/VarCheckLib.inf
>
>    MdeModulePkg/Library/VarCheckHiiLib/VarCheckHiiLib.inf
>
>    MdeModulePkg/Library/VarCheckPcdLib/VarCheckPcdLib.inf
>
> @@ -458,6 +459,7 @@ [Components.IA32, Components.X64]
>    MdeModulePkg/Core/PiSmmCore/PiSmmCore.inf
>
>    MdeModulePkg/Universal/Variable/RuntimeDxe/VariableSmm.inf {
>
>      <LibraryClasses>
>
> +      NULL|MdeModulePkg/Library/VarCheckPolicyLib/VarCheckPolicyLib.inf
>
>        NULL|MdeModulePkg/Library/VarCheckUefiLib/VarCheckUefiLib.inf
>
>        NULL|MdeModulePkg/Library/VarCheckHiiLib/VarCheckHiiLib.inf
>
>        NULL|MdeModulePkg/Library/VarCheckPcdLib/VarCheckPcdLib.inf
>
> --
> 2.26.2.windows.1.8.g01c50adf56.20200515075929
>
>
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