NonMmramMapDxeSmm.c

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#include "PiSmmCpuCommon.h"
#include <Library/DxeServicesTableLib.h>
#include <Library/UefiBootServicesTableLib.h>
#include <Library/UefiRuntimeServicesTableLib.h>
 
//
// attributes for reserved memory before it is promoted to system memory
//
#define EFI_MEMORY_PRESENT      0x0100000000000000ULL
#define EFI_MEMORY_INITIALIZED  0x0200000000000000ULL
#define EFI_MEMORY_TESTED       0x0400000000000000ULL
 
#define PREVIOUS_MEMORY_DESCRIPTOR(MemoryDescriptor, Size) \
  ((EFI_MEMORY_DESCRIPTOR *)((UINT8 *)(MemoryDescriptor) - (Size)))
 
EFI_MEMORY_DESCRIPTOR  *mUefiMemoryMap;
UINTN                  mUefiMemoryMapSize;
UINTN                  mUefiDescriptorSize;
 
EFI_GCD_MEMORY_SPACE_DESCRIPTOR  *mGcdMemSpace       = NULL;
UINTN                            mGcdMemNumberOfDesc = 0;
 
EFI_MEMORY_ATTRIBUTES_TABLE  *mUefiMemoryAttributesTable = NULL;
 
STATIC
VOID
SortMemoryMap (
  IN OUT EFI_MEMORY_DESCRIPTOR  *MemoryMap,
  IN UINTN                      MemoryMapSize,
  IN UINTN                      DescriptorSize
  )
{
  EFI_MEMORY_DESCRIPTOR  *MemoryMapEntry;
  EFI_MEMORY_DESCRIPTOR  *NextMemoryMapEntry;
  EFI_MEMORY_DESCRIPTOR  *MemoryMapEnd;
  EFI_MEMORY_DESCRIPTOR  TempMemoryMap;
 
  MemoryMapEntry     = MemoryMap;
  NextMemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (MemoryMapEntry, DescriptorSize);
  MemoryMapEnd       = (EFI_MEMORY_DESCRIPTOR *)((UINT8 *)MemoryMap + MemoryMapSize);
  while (MemoryMapEntry < MemoryMapEnd) {
    while (NextMemoryMapEntry < MemoryMapEnd) {
      if (MemoryMapEntry->PhysicalStart > NextMemoryMapEntry->PhysicalStart) {
        CopyMem (&TempMemoryMap, MemoryMapEntry, sizeof (EFI_MEMORY_DESCRIPTOR));
        CopyMem (MemoryMapEntry, NextMemoryMapEntry, sizeof (EFI_MEMORY_DESCRIPTOR));
        CopyMem (NextMemoryMapEntry, &TempMemoryMap, sizeof (EFI_MEMORY_DESCRIPTOR));
      }
 
      NextMemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (NextMemoryMapEntry, DescriptorSize);
    }
 
    MemoryMapEntry     = NEXT_MEMORY_DESCRIPTOR (MemoryMapEntry, DescriptorSize);
    NextMemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (MemoryMapEntry, DescriptorSize);
  }
}
 
BOOLEAN
IsUefiPageNotPresent (
  IN EFI_MEMORY_DESCRIPTOR  *MemoryMap
  )
{
  switch (MemoryMap->Type) {
    case EfiLoaderCode:
    case EfiLoaderData:
    case EfiBootServicesCode:
    case EfiBootServicesData:
    case EfiConventionalMemory:
    case EfiUnusableMemory:
    case EfiACPIReclaimMemory:
      return TRUE;
    default:
      return FALSE;
  }
}
 
STATIC
VOID
MergeMemoryMapForNotPresentEntry (
  IN OUT EFI_MEMORY_DESCRIPTOR  *MemoryMap,
  IN OUT UINTN                  *MemoryMapSize,
  IN UINTN                      DescriptorSize
  )
{
  EFI_MEMORY_DESCRIPTOR  *MemoryMapEntry;
  EFI_MEMORY_DESCRIPTOR  *MemoryMapEnd;
  UINT64                 MemoryBlockLength;
  EFI_MEMORY_DESCRIPTOR  *NewMemoryMapEntry;
  EFI_MEMORY_DESCRIPTOR  *NextMemoryMapEntry;
 
  MemoryMapEntry    = MemoryMap;
  NewMemoryMapEntry = MemoryMap;
  MemoryMapEnd      = (EFI_MEMORY_DESCRIPTOR *)((UINT8 *)MemoryMap + *MemoryMapSize);
  while ((UINTN)MemoryMapEntry < (UINTN)MemoryMapEnd) {
    CopyMem (NewMemoryMapEntry, MemoryMapEntry, sizeof (EFI_MEMORY_DESCRIPTOR));
    NextMemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (MemoryMapEntry, DescriptorSize);
 
    do {
      MemoryBlockLength = (UINT64)(EFI_PAGES_TO_SIZE ((UINTN)MemoryMapEntry->NumberOfPages));
      if (((UINTN)NextMemoryMapEntry < (UINTN)MemoryMapEnd) &&
          IsUefiPageNotPresent (MemoryMapEntry) && IsUefiPageNotPresent (NextMemoryMapEntry) &&
          ((MemoryMapEntry->PhysicalStart + MemoryBlockLength) == NextMemoryMapEntry->PhysicalStart))
      {
        MemoryMapEntry->NumberOfPages += NextMemoryMapEntry->NumberOfPages;
        if (NewMemoryMapEntry != MemoryMapEntry) {
          NewMemoryMapEntry->NumberOfPages += NextMemoryMapEntry->NumberOfPages;
        }
 
        NextMemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (NextMemoryMapEntry, DescriptorSize);
        continue;
      } else {
        MemoryMapEntry = PREVIOUS_MEMORY_DESCRIPTOR (NextMemoryMapEntry, DescriptorSize);
        break;
      }
    } while (TRUE);
 
    MemoryMapEntry    = NEXT_MEMORY_DESCRIPTOR (MemoryMapEntry, DescriptorSize);
    NewMemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (NewMemoryMapEntry, DescriptorSize);
  }
 
  *MemoryMapSize = (UINTN)NewMemoryMapEntry - (UINTN)MemoryMap;
 
  return;
}
 
VOID
GetGcdMemoryMap (
  VOID
  )
{
  UINTN                            NumberOfDescriptors;
  EFI_GCD_MEMORY_SPACE_DESCRIPTOR  *MemSpaceMap;
  EFI_STATUS                       Status;
  UINTN                            Index;
 
  Status = gDS->GetMemorySpaceMap (&NumberOfDescriptors, &MemSpaceMap);
  if (EFI_ERROR (Status)) {
    return;
  }
 
  mGcdMemNumberOfDesc = 0;
  for (Index = 0; Index < NumberOfDescriptors; Index++) {
    if ((MemSpaceMap[Index].GcdMemoryType == EfiGcdMemoryTypeReserved) &&
        ((MemSpaceMap[Index].Capabilities & (EFI_MEMORY_PRESENT | EFI_MEMORY_INITIALIZED | EFI_MEMORY_TESTED)) ==
         (EFI_MEMORY_PRESENT | EFI_MEMORY_INITIALIZED))
        )
    {
      mGcdMemNumberOfDesc++;
    }
  }
 
  mGcdMemSpace = AllocateZeroPool (mGcdMemNumberOfDesc * sizeof (EFI_GCD_MEMORY_SPACE_DESCRIPTOR));
  ASSERT (mGcdMemSpace != NULL);
  if (mGcdMemSpace == NULL) {
    mGcdMemNumberOfDesc = 0;
    gBS->FreePool (MemSpaceMap);
    return;
  }
 
  mGcdMemNumberOfDesc = 0;
  for (Index = 0; Index < NumberOfDescriptors; Index++) {
    if ((MemSpaceMap[Index].GcdMemoryType == EfiGcdMemoryTypeReserved) &&
        ((MemSpaceMap[Index].Capabilities & (EFI_MEMORY_PRESENT | EFI_MEMORY_INITIALIZED | EFI_MEMORY_TESTED)) ==
         (EFI_MEMORY_PRESENT | EFI_MEMORY_INITIALIZED))
        )
    {
      CopyMem (
        &mGcdMemSpace[mGcdMemNumberOfDesc],
        &MemSpaceMap[Index],
        sizeof (EFI_GCD_MEMORY_SPACE_DESCRIPTOR)
        );
      mGcdMemNumberOfDesc++;
    }
  }
 
  gBS->FreePool (MemSpaceMap);
}
 
VOID
GetUefiMemoryAttributesTable (
  VOID
  )
{
  EFI_STATUS                   Status;
  EFI_MEMORY_ATTRIBUTES_TABLE  *MemoryAttributesTable;
  UINTN                        MemoryAttributesTableSize;
 
  Status = EfiGetSystemConfigurationTable (&gEfiMemoryAttributesTableGuid, (VOID **)&MemoryAttributesTable);
  if (!EFI_ERROR (Status) && (MemoryAttributesTable != NULL)) {
    MemoryAttributesTableSize  = sizeof (EFI_MEMORY_ATTRIBUTES_TABLE) + MemoryAttributesTable->DescriptorSize * MemoryAttributesTable->NumberOfEntries;
    mUefiMemoryAttributesTable = AllocateCopyPool (MemoryAttributesTableSize, MemoryAttributesTable);
    ASSERT (mUefiMemoryAttributesTable != NULL);
  }
}
 
VOID
GetUefiMemoryMap (
  VOID
  )
{
  EFI_STATUS             Status;
  UINTN                  MapKey;
  UINT32                 DescriptorVersion;
  EFI_MEMORY_DESCRIPTOR  *MemoryMap;
  UINTN                  UefiMemoryMapSize;
 
  DEBUG ((DEBUG_INFO, "GetUefiMemoryMap\n"));
 
  UefiMemoryMapSize = 0;
  MemoryMap         = NULL;
  Status            = gBS->GetMemoryMap (
                             &UefiMemoryMapSize,
                             MemoryMap,
                             &MapKey,
                             &mUefiDescriptorSize,
                             &DescriptorVersion
                             );
  ASSERT (Status == EFI_BUFFER_TOO_SMALL);
 
  do {
    Status = gBS->AllocatePool (EfiBootServicesData, UefiMemoryMapSize, (VOID **)&MemoryMap);
    ASSERT (MemoryMap != NULL);
    if (MemoryMap == NULL) {
      return;
    }
 
    Status = gBS->GetMemoryMap (
                    &UefiMemoryMapSize,
                    MemoryMap,
                    &MapKey,
                    &mUefiDescriptorSize,
                    &DescriptorVersion
                    );
    if (EFI_ERROR (Status)) {
      gBS->FreePool (MemoryMap);
      MemoryMap = NULL;
    }
  } while (Status == EFI_BUFFER_TOO_SMALL);
 
  if (MemoryMap == NULL) {
    return;
  }
 
  SortMemoryMap (MemoryMap, UefiMemoryMapSize, mUefiDescriptorSize);
  MergeMemoryMapForNotPresentEntry (MemoryMap, &UefiMemoryMapSize, mUefiDescriptorSize);
 
  mUefiMemoryMapSize = UefiMemoryMapSize;
  mUefiMemoryMap     = AllocateCopyPool (UefiMemoryMapSize, MemoryMap);
  ASSERT (mUefiMemoryMap != NULL);
 
  gBS->FreePool (MemoryMap);
 
  //
  // Get additional information from GCD memory map.
  //
  GetGcdMemoryMap ();
 
  //
  // Get UEFI memory attributes table.
  //
  GetUefiMemoryAttributesTable ();
}
 
VOID
UpdateUefiMemMapAttributes (
  VOID
  )
{
  BOOLEAN                WriteProtect;
  BOOLEAN                CetEnabled;
  EFI_STATUS             Status;
  UINTN                  Index;
  UINT64                 Limit;
  UINT64                 PreviousAddress;
  UINTN                  PageTable;
  UINT64                 Base;
  EFI_MEMORY_DESCRIPTOR  *MemoryMap;
  UINTN                  MemoryMapEntryCount;
  EFI_MEMORY_DESCRIPTOR  *Entry;
 
  DEBUG ((DEBUG_INFO, "UpdateUefiMemMapAttributes Start...\n"));
 
  WRITE_UNPROTECT_RO_PAGES (WriteProtect, CetEnabled);
 
  PageTable = AsmReadCr3 ();
  Limit     = LShiftU64 (1, mPhysicalAddressBits);
 
  //
  // [0, 4k] may be non-present.
  //
  PreviousAddress = ((FixedPcdGet8 (PcdNullPointerDetectionPropertyMask) & BIT1) != 0) ? BASE_4KB : 0;
 
  //
  // NonMmram shall be non-executable after the SmmReadyToLock event occurs, regardless of whether
  // RestrictedMemoryAccess is enabled, since all MM drivers located in NonMmram have already been dispatched and executed.
  //
  for (Index = 0; Index < mSmmCpuSmramRangeCount; Index++) {
    Base = mSmmCpuSmramRanges[Index].CpuStart;
    if (Base > PreviousAddress) {
      Status = ConvertMemoryPageAttributes (PageTable, mPagingMode, PreviousAddress, Base - PreviousAddress, EFI_MEMORY_XP, TRUE, NULL);
      ASSERT_RETURN_ERROR (Status);
    }
 
    PreviousAddress = mSmmCpuSmramRanges[Index].CpuStart + mSmmCpuSmramRanges[Index].PhysicalSize;
  }
 
  if (PreviousAddress < Limit) {
    Status = ConvertMemoryPageAttributes (PageTable, mPagingMode, PreviousAddress, Limit - PreviousAddress, EFI_MEMORY_XP, TRUE, NULL);
    ASSERT_RETURN_ERROR (Status);
  }
 
  //
  // Set NonMmram to not-present by excluding "RT, Reserved and NVS" memory type when RestrictedMemoryAccess is enabled.
  //
  if (IsRestrictedMemoryAccess ()) {
    if (mUefiMemoryMap != NULL) {
      MemoryMapEntryCount = mUefiMemoryMapSize/mUefiDescriptorSize;
      MemoryMap           = mUefiMemoryMap;
      for (Index = 0; Index < MemoryMapEntryCount; Index++) {
        if (IsUefiPageNotPresent (MemoryMap)) {
          Status = ConvertMemoryPageAttributes (
                     PageTable,
                     mPagingMode,
                     MemoryMap->PhysicalStart,
                     EFI_PAGES_TO_SIZE ((UINTN)MemoryMap->NumberOfPages),
                     EFI_MEMORY_RP,
                     TRUE,
                     NULL
                     );
          DEBUG ((
            DEBUG_INFO,
            "UefiMemory protection: 0x%lx - 0x%lx %r\n",
            MemoryMap->PhysicalStart,
            MemoryMap->PhysicalStart + (UINT64)EFI_PAGES_TO_SIZE ((UINTN)MemoryMap->NumberOfPages),
            Status
            ));
        }
 
        MemoryMap = NEXT_MEMORY_DESCRIPTOR (MemoryMap, mUefiDescriptorSize);
      }
    }
 
    //
    // Do not free mUefiMemoryMap, it will be checked in IsSmmCommBufferForbiddenAddress().
    //
 
    //
    // Set untested NonMmram memory as not present.
    //
    if (mGcdMemSpace != NULL) {
      for (Index = 0; Index < mGcdMemNumberOfDesc; Index++) {
        Status = ConvertMemoryPageAttributes (
                   PageTable,
                   mPagingMode,
                   mGcdMemSpace[Index].BaseAddress,
                   mGcdMemSpace[Index].Length,
                   EFI_MEMORY_RP,
                   TRUE,
                   NULL
                   );
        DEBUG ((
          DEBUG_INFO,
          "GcdMemory protection: 0x%lx - 0x%lx %r\n",
          mGcdMemSpace[Index].BaseAddress,
          mGcdMemSpace[Index].BaseAddress + mGcdMemSpace[Index].Length,
          Status
          ));
      }
    }
 
    //
    // Do not free mGcdMemSpace, it will be checked in IsSmmCommBufferForbiddenAddress().
    //
 
    //
    // Above logic sets the whole RT memory as present.
    // Below logic is to set the RT code as not present.
    //
    if (mUefiMemoryAttributesTable != NULL) {
      Entry = (EFI_MEMORY_DESCRIPTOR *)(mUefiMemoryAttributesTable + 1);
      for (Index = 0; Index < mUefiMemoryAttributesTable->NumberOfEntries; Index++) {
        if ((Entry->Type == EfiRuntimeServicesCode) || (Entry->Type == EfiRuntimeServicesData)) {
          if ((Entry->Attribute & EFI_MEMORY_RO) != 0) {
            Status = ConvertMemoryPageAttributes (
                       PageTable,
                       mPagingMode,
                       Entry->PhysicalStart,
                       EFI_PAGES_TO_SIZE ((UINTN)Entry->NumberOfPages),
                       EFI_MEMORY_RP,
                       TRUE,
                       NULL
                       );
            DEBUG ((
              DEBUG_INFO,
              "UefiMemoryAttribute protection: 0x%lx - 0x%lx %r\n",
              Entry->PhysicalStart,
              Entry->PhysicalStart + (UINT64)EFI_PAGES_TO_SIZE ((UINTN)Entry->NumberOfPages),
              Status
              ));
          }
        }
 
        Entry = NEXT_MEMORY_DESCRIPTOR (Entry, mUefiMemoryAttributesTable->DescriptorSize);
      }
    }
 
    //
    // Do not free mUefiMemoryAttributesTable, it will be checked in IsSmmCommBufferForbiddenAddress().
    //
  }
 
  //
  // Flush TLB
  //
  CpuFlushTlb ();
 
  //
  // Set execute-disable flag
  //
  mXdEnabled = TRUE;
 
  WRITE_PROTECT_RO_PAGES (WriteProtect, CetEnabled);
 
  DEBUG ((DEBUG_INFO, "UpdateUefiMemMapAttributes Done.\n"));
}
 
EFI_PHYSICAL_ADDRESS
GetSmmProfileData (
  IN OUT  UINT64  *Size
  )
{
  EFI_STATUS            Status;
  EFI_PHYSICAL_ADDRESS  Base;
 
  ASSERT (Size != NULL);
 
  *Size = PcdGet32 (PcdCpuSmmProfileSize);
 
  Base   = 0xFFFFFFFF;
  Status = gBS->AllocatePages (
                  AllocateMaxAddress,
                  EfiReservedMemoryType,
                  (UINTN)EFI_SIZE_TO_PAGES (*Size),
                  &Base
                  );
  ASSERT_EFI_ERROR (Status);
  ZeroMem ((VOID *)(UINTN)Base, (UINTN)*Size);
 
  return Base;
}
 
BOOLEAN
IsNonMmramLoggingAddress (
  IN UINT64  Address
  )
{
  ASSERT (FALSE);
 
  return TRUE;
}
 
BOOLEAN
IsSmmCommBufferForbiddenAddress (
  IN UINT64  Address
  )
{
  EFI_MEMORY_DESCRIPTOR  *MemoryMap;
  UINTN                  MemoryMapEntryCount;
  UINTN                  Index;
  EFI_MEMORY_DESCRIPTOR  *Entry;
 
  if (!IsRestrictedMemoryAccess ()) {
    return FALSE;
  }
 
  if (mUefiMemoryMap != NULL) {
    MemoryMap           = mUefiMemoryMap;
    MemoryMapEntryCount = mUefiMemoryMapSize/mUefiDescriptorSize;
    for (Index = 0; Index < MemoryMapEntryCount; Index++) {
      if (IsUefiPageNotPresent (MemoryMap)) {
        if ((Address >= MemoryMap->PhysicalStart) &&
            (Address < MemoryMap->PhysicalStart + EFI_PAGES_TO_SIZE ((UINTN)MemoryMap->NumberOfPages)))
        {
          return TRUE;
        }
      }
 
      MemoryMap = NEXT_MEMORY_DESCRIPTOR (MemoryMap, mUefiDescriptorSize);
    }
  }
 
  if (mGcdMemSpace != NULL) {
    for (Index = 0; Index < mGcdMemNumberOfDesc; Index++) {
      if ((Address >= mGcdMemSpace[Index].BaseAddress) &&
          (Address < mGcdMemSpace[Index].BaseAddress + mGcdMemSpace[Index].Length))
      {
        return TRUE;
      }
    }
  }
 
  if (mUefiMemoryAttributesTable != NULL) {
    Entry = (EFI_MEMORY_DESCRIPTOR *)(mUefiMemoryAttributesTable + 1);
    for (Index = 0; Index < mUefiMemoryAttributesTable->NumberOfEntries; Index++) {
      if ((Entry->Type == EfiRuntimeServicesCode) || (Entry->Type == EfiRuntimeServicesData)) {
        if ((Entry->Attribute & EFI_MEMORY_RO) != 0) {
          if ((Address >= Entry->PhysicalStart) &&
              (Address < Entry->PhysicalStart + LShiftU64 (Entry->NumberOfPages, EFI_PAGE_SHIFT)))
          {
            return TRUE;
          }
 
          Entry = NEXT_MEMORY_DESCRIPTOR (Entry, mUefiMemoryAttributesTable->DescriptorSize);
        }
      }
    }
  }
 
  return FALSE;
}
 
VOID
CreateExtendedProtectionRange (
  OUT MM_CPU_MEMORY_REGION  **MemoryRegion,
  OUT UINTN                 *MemoryRegionCount
  )
{
  UINTN                            Index;
  EFI_GCD_MEMORY_SPACE_DESCRIPTOR  *MemorySpaceMap;
  UINTN                            NumberOfSpaceDescriptors;
  UINTN                            MemoryRegionIndex;
  UINTN                            Count;
 
  MemorySpaceMap           = NULL;
  NumberOfSpaceDescriptors = 0;
  Count                    = 0;
 
  ASSERT (MemoryRegion != NULL && MemoryRegionCount != NULL);
 
  *MemoryRegion      = NULL;
  *MemoryRegionCount = 0;
 
  //
  // Get MMIO ranges from GCD.
  //
  gDS->GetMemorySpaceMap (
         &NumberOfSpaceDescriptors,
         &MemorySpaceMap
         );
  for (Index = 0; Index < NumberOfSpaceDescriptors; Index++) {
    if (MemorySpaceMap[Index].GcdMemoryType == EfiGcdMemoryTypeMemoryMappedIo) {
      if (ADDRESS_IS_ALIGNED (MemorySpaceMap[Index].BaseAddress, SIZE_4KB) &&
          (MemorySpaceMap[Index].Length % SIZE_4KB == 0))
      {
        Count++;
      } else {
        //
        // Skip the MMIO range that BaseAddress and Length are not 4k aligned since
        // the minimum granularity of the page table is 4k
        //
        DEBUG ((
          DEBUG_WARN,
          "MMIO range [0x%lx, 0x%lx] is skipped since it is not 4k aligned.\n",
          MemorySpaceMap[Index].BaseAddress,
          MemorySpaceMap[Index].BaseAddress + MemorySpaceMap[Index].Length
          ));
      }
    }
  }
 
  *MemoryRegionCount = Count;
 
  *MemoryRegion = (MM_CPU_MEMORY_REGION *)AllocateZeroPool (sizeof (MM_CPU_MEMORY_REGION) * Count);
  ASSERT (*MemoryRegion != NULL);
 
  MemoryRegionIndex = 0;
  for (Index = 0; Index < NumberOfSpaceDescriptors; Index++) {
    if ((MemorySpaceMap[Index].GcdMemoryType == EfiGcdMemoryTypeMemoryMappedIo) &&
        ADDRESS_IS_ALIGNED (MemorySpaceMap[Index].BaseAddress, SIZE_4KB) &&
        (MemorySpaceMap[Index].Length % SIZE_4KB == 0))
    {
      (*MemoryRegion)[MemoryRegionIndex].Base   = MemorySpaceMap[Index].BaseAddress;
      (*MemoryRegion)[MemoryRegionIndex].Length = MemorySpaceMap[Index].Length;
      MemoryRegionIndex++;
    }
  }
 
  return;
}
 
VOID
CreateNonMmramMemMap (
  IN  UINT8                 PhysicalAddressBits,
  OUT MM_CPU_MEMORY_REGION  **MemoryRegion,
  OUT UINTN                 *MemoryRegionCount
  )
{
  UINT64  MaxLength;
  UINTN   Count;
  UINTN   Index;
  UINT64  PreviousAddress;
  UINT64  Base;
  UINT64  Length;
 
  ASSERT (MemoryRegion != NULL && MemoryRegionCount != NULL);
 
  *MemoryRegion      = NULL;
  *MemoryRegionCount = 0;
 
  MaxLength = LShiftU64 (1, PhysicalAddressBits);
 
  //
  // Build MemoryRegion to cover [0, 2^PhysicalAddressBits) by excluding all Smram range
  //
  Count = mSmmCpuSmramRangeCount + 1;
 
  *MemoryRegionCount = Count;
 
  *MemoryRegion = (MM_CPU_MEMORY_REGION *)AllocateZeroPool (sizeof (MM_CPU_MEMORY_REGION) * Count);
  ASSERT (*MemoryRegion != NULL);
 
  PreviousAddress = 0;
  for (Index = 0; Index < mSmmCpuSmramRangeCount; Index++) {
    Base   = mSmmCpuSmramRanges[Index].CpuStart;
    Length = mSmmCpuSmramRanges[Index].PhysicalSize;
 
    ASSERT (MaxLength > Base +  Length);
 
    if (Base > PreviousAddress) {
      (*MemoryRegion)[Index].Base      = PreviousAddress;
      (*MemoryRegion)[Index].Length    = Base - PreviousAddress;
      (*MemoryRegion)[Index].Attribute = 0;
    }
 
    PreviousAddress = Base + Length;
  }
 
  //
  // Set the last remaining range
  //
  if (PreviousAddress < MaxLength) {
    (*MemoryRegion)[Index].Base   = PreviousAddress;
    (*MemoryRegion)[Index].Length = MaxLength - PreviousAddress;
  }
}