OpenCorePkg/Library/OcMemoryLib/MemoryAttributes.c

/** @file
  Copyright (C) 2019, vit9696. All rights reserved.

  All rights reserved.

  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 <Uefi.h>

#include <Guid/MemoryAttributesTable.h>
#include <Library/BaseMemoryLib.h>
#include <Library/DebugLib.h>
#include <Library/MemoryAllocationLib.h>
#include <Library/OcGuardLib.h>
#include <Library/OcMemoryLib.h>
#include <Library/UefiBootServicesTableLib.h>
#include <Library/UefiLib.h>

/**
  Determine actual memory type from the attribute.

  @param[in]  MemoryAttribute  Attribute to inspect.
**/
STATIC
UINT32
OcRealMemoryType (
  IN EFI_MEMORY_DESCRIPTOR  *MemoryAttribte
  )
{
  ASSERT (MemoryAttribte->Type == EfiRuntimeServicesCode
    || MemoryAttribte->Type == EfiRuntimeServicesData);

  //
  // Use code for write-protected areas.
  //
  if ((MemoryAttribte->Attribute & EFI_MEMORY_RO) != 0) {
    return EfiRuntimeServicesCode;
  }

  //
  // Use data for executable-protected areas.
  //
  if ((MemoryAttribte->Attribute & EFI_MEMORY_XP) != 0) {
    return EfiRuntimeServicesData;
  }

  //
  // Use whatever is set.
  //
  return MemoryAttribte->Type;
}

/**
  Split memory map descriptor by attribute.

  @param[in,out] RetMemoryMapEntry    Pointer to descriptor in the memory map, updated to next proccessed.
  @param[in,out] CurrentEntryIndex    Current index of the descriptor in the memory map, updated on increase.
  @param[in,out] CurrentEntryCount    Number of descriptors in the memory map, updated on increase.
  @param[in]     TotalEntryCount      Max number of descriptors in the memory map.
  @param[in]     MemoryAttribute      Memory attribute used for splitting.
  @param[in]     DescriptorSize       Memory map descriptor size.

  @retval EFI_SUCCESS on success.
  @retval EFI_OUT_OF_RESOURCES when there are not enough free descriptor slots.
**/
STATIC
EFI_STATUS
OcSplitMemoryEntryByAttribute (
  IN OUT EFI_MEMORY_DESCRIPTOR  **RetMemoryMapEntry,
  IN OUT UINTN                  *CurrentEntryIndex,
  IN OUT UINTN                  *CurrentEntryCount,
  IN     UINTN                  TotalEntryCount,
  IN     EFI_MEMORY_DESCRIPTOR  *MemoryAttribute,
  IN     UINTN                  DescriptorSize

  )
{
  EFI_MEMORY_DESCRIPTOR  *MemoryMapEntry;
  EFI_MEMORY_DESCRIPTOR  *NewMemoryMapEntry;
  UINTN                  DiffPages;

  MemoryMapEntry = *RetMemoryMapEntry;

  //
  // Memory attribute starts after our descriptor.
  // Shorten the existing descriptor and insert the new one after it.
  // [DESC1] -> [DESC1][DESC2]
  //
  if (MemoryAttribute->PhysicalStart > MemoryMapEntry->PhysicalStart) {
    if (*CurrentEntryCount == TotalEntryCount) {
      return EFI_OUT_OF_RESOURCES;
    }

    NewMemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (MemoryMapEntry, DescriptorSize);
    DiffPages         = (UINTN) EFI_SIZE_TO_PAGES (MemoryAttribute->PhysicalStart - MemoryMapEntry->PhysicalStart);
    CopyMem (
      NewMemoryMapEntry,
      MemoryMapEntry,
      DescriptorSize * (*CurrentEntryCount - *CurrentEntryIndex)
      );
    MemoryMapEntry->NumberOfPages     = DiffPages;
    NewMemoryMapEntry->PhysicalStart  = MemoryAttribute->PhysicalStart;
    NewMemoryMapEntry->NumberOfPages -= DiffPages;

    MemoryMapEntry = NewMemoryMapEntry;

    //
    // Current processed entry is now the one we inserted.
    //
    ++(*CurrentEntryIndex);
    ++(*CurrentEntryCount);
  }

  ASSERT (MemoryAttribute->PhysicalStart == MemoryMapEntry->PhysicalStart);

  //
  // Memory attribute matches our descriptor.
  // Simply update its protection.
  // [DESC1] -> [DESC1*]
  //
  if (MemoryMapEntry->NumberOfPages == MemoryAttribute->NumberOfPages) {
    MemoryMapEntry->Type = OcRealMemoryType (MemoryAttribute);
    *RetMemoryMapEntry = MemoryMapEntry;
    return EFI_SUCCESS;
  }

  //
  // Memory attribute is shorter than our descriptor.
  // Shorten current descriptor, update its type, and inseret the new one after it.
  // [DESC1] -> [DESC1*][DESC2]
  //
  if (*CurrentEntryCount == TotalEntryCount) {
    return EFI_OUT_OF_RESOURCES;
  }

  NewMemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (MemoryMapEntry, DescriptorSize);
  CopyMem (
    NewMemoryMapEntry,
    MemoryMapEntry,
    DescriptorSize * (*CurrentEntryCount - *CurrentEntryIndex)
    );
  MemoryMapEntry->Type              = OcRealMemoryType (MemoryAttribute);
  MemoryMapEntry->NumberOfPages     = MemoryAttribute->NumberOfPages;
  NewMemoryMapEntry->PhysicalStart += EFI_PAGES_TO_SIZE (MemoryAttribute->NumberOfPages);
  NewMemoryMapEntry->NumberOfPages -= MemoryAttribute->NumberOfPages;

  //
  // Current processed entry is now the one we need to process.
  //
  ++(*CurrentEntryIndex);
  ++(*CurrentEntryCount);

  *RetMemoryMapEntry = NewMemoryMapEntry;

  return EFI_SUCCESS;
}

STATIC
EFI_STATUS
OcExpandAttributeWrite (
  IN OUT EFI_MEMORY_ATTRIBUTES_TABLE  *MemoryAttributesTable,
  IN OUT EFI_MEMORY_DESCRIPTOR        *MemoryAttributesEntry OPTIONAL,
  IN     UINTN                        MaxDescriptors,
  IN     EFI_MEMORY_DESCRIPTOR        *MemoryMapEntry,
  IN     EFI_PHYSICAL_ADDRESS         CurrentMapAddress
  )
{
  EFI_PHYSICAL_ADDRESS    NextMatAddress;

  //
  // Simply abort on failing to write any new entry.
  //
  if (MemoryAttributesTable->NumberOfEntries >= MaxDescriptors) {
    return EFI_OUT_OF_RESOURCES;
  }

  if (MemoryAttributesEntry != NULL) {
    //
    // Insert to the middle of MAT table at current MAT entry position.
    // Assert that this MAT entry follows this map entry.
    //
    ASSERT (MemoryAttributesEntry->PhysicalStart > CurrentMapAddress);

    //
    // Create a free MAT entry inbetween.
    //
    CopyMem (
      NEXT_MEMORY_DESCRIPTOR (MemoryAttributesEntry, MemoryAttributesTable->DescriptorSize),
      MemoryAttributesEntry,
      MemoryAttributesTable->NumberOfEntries * MemoryAttributesTable->DescriptorSize
        - ((UINTN) MemoryAttributesEntry - (UINTN) MemoryAttributesTable - sizeof (*MemoryAttributesTable))
      );

    //
    // Calculate the location of the next MAT entry to get the size of this one.
    // This MAT entry will either:
    // - fill the whole gap right away, by reaching the next MAT entry.
    //   MA: [   GAP   ][ MAT ]
    //   MM: [   MAP   ]
    // - fill part of the gap up to MAP entry end.
    //   MA: [   GAP      ][ MAT ]
    //   MM: [   MAP  ][ OTHER MAP ]
    //
    NextMatAddress = LAST_DESCRIPTOR_ADDR (MemoryMapEntry) + 1;
    if (MemoryAttributesEntry->PhysicalStart < NextMatAddress) {
      NextMatAddress = MemoryAttributesEntry->PhysicalStart;
    }
  } else {
    //
    // Append to the end of MAT table.
    //
    MemoryAttributesEntry = (VOID *) ((UINTN) MemoryAttributesTable + sizeof (*MemoryAttributesTable)
      + MemoryAttributesTable->NumberOfEntries * MemoryAttributesTable->DescriptorSize);
    NextMatAddress = LAST_DESCRIPTOR_ADDR (MemoryMapEntry) + 1;
  }

  //
  // Write the new attribute.
  //
  MemoryAttributesEntry->Type          = OcRealMemoryType (MemoryMapEntry);
  MemoryAttributesEntry->PhysicalStart = CurrentMapAddress;
  MemoryAttributesEntry->VirtualStart  = 0;
  MemoryAttributesEntry->NumberOfPages = EFI_SIZE_TO_PAGES (NextMatAddress - CurrentMapAddress);
  MemoryAttributesEntry->Attribute     = EFI_MEMORY_RUNTIME;
  if (MemoryAttributesEntry->Type == EfiRuntimeServicesCode) {
    MemoryAttributesEntry->Attribute |= EFI_MEMORY_RO;
  } else {
    MemoryAttributesEntry->Attribute |= EFI_MEMORY_XP;
  }

  ++MemoryAttributesTable->NumberOfEntries;

  return EFI_SUCCESS;
}

/**
  Expand attributes table by adding memory map runtime entries into it.
  Requires sorted memory map.

  @param[in,out]  MemoryAttributesTable   Memory attributes table.
  @param[in,out]  MemoryAttributesEntry   Memory attributes descriptor.
  @param[in]      MaxDescriptors          Maximum amount of descriptors in the attributes table.
  @param[in]      MemoryMapDescriptors    Memory map descriptor count.
  @param[in]      MemoryMap               Memory map.
  @param[in]      DescriptorSize          Memory map descriptor size.

  @retval EFI_SUCCESS on success.
  @retval EFI_NOT_FOUND nothing to do.
**/
STATIC
EFI_STATUS
OcExpandAttributesByMap (
  IN OUT EFI_MEMORY_ATTRIBUTES_TABLE  *MemoryAttributesTable,
  IN OUT EFI_MEMORY_DESCRIPTOR        *MemoryAttributesEntry,
  IN     UINTN                        MaxDescriptors,
  IN     UINTN                        MemoryMapDescriptors,
  IN     EFI_MEMORY_DESCRIPTOR        *MemoryMap,
  IN     UINTN                        DescriptorSize
  )
{
  EFI_STATUS             Status;
  UINTN                  MapIndex;
  UINTN                  MatIndex;
  EFI_PHYSICAL_ADDRESS   NextMapAddress;
  EFI_PHYSICAL_ADDRESS   LastMatAddress;
  EFI_PHYSICAL_ADDRESS   CurrentMapAddress;

  MatIndex = 0;
  Status   = EFI_NOT_FOUND;

  for (MapIndex = 0; MapIndex < MemoryMapDescriptors; ++MapIndex) {
    //
    // Skip MAP entries, which are not RTCode or RTData.
    //
    if (MemoryMap->Type != EfiRuntimeServicesCode
      && MemoryMap->Type != EfiRuntimeServicesData) {
      goto NEXT_MEMORY_MAP_DESCRIPTOR;
    }

    NextMapAddress    = LAST_DESCRIPTOR_ADDR (MemoryMap) + 1;
    CurrentMapAddress = MemoryMap->PhysicalStart;

    //
    // Iterate MAT entries till we are over them or till
    // we finish iterating this MAP entry memory.
    //
    while (MatIndex < MemoryAttributesTable->NumberOfEntries
      && CurrentMapAddress < NextMapAddress) {
      //
      // Skip MAT entries, which are not RTCode or RTData.
      //
      if (MemoryAttributesEntry->Type != EfiRuntimeServicesCode
        && MemoryAttributesEntry->Type != EfiRuntimeServicesData) {
        goto NEXT_MEMORY_ATTRIBUTE_DESCRIPTOR;
      }

      //
      // Skip MAT entries which end before this MAP entry. This should
      // not happen normally, as each MAT entry is supposed to be within
      // a single RTCode/RTData MAP entry according to UEFI spec, and
      // our memory map is sorted.
      //
      LastMatAddress = LAST_DESCRIPTOR_ADDR (MemoryAttributesEntry);
      if (LastMatAddress < MemoryMap->PhysicalStart) {
        goto NEXT_MEMORY_ATTRIBUTE_DESCRIPTOR;
      }

      //
      // Advance MAP iterator if we found a MAT entry that follows the
      // current MAP entry address.
      //
      if (CurrentMapAddress == MemoryAttributesEntry->PhysicalStart) {
        //
        // MAT is required to be smaller or equal than MAP by UEFI spec.
        // For now just assert on this, but if we find anybody violating this,
        // we will have to adapt this code.
        //
        ASSERT (MemoryAttributesEntry->NumberOfPages <= MemoryMap->NumberOfPages);
        CurrentMapAddress = LastMatAddress + 1;
        goto NEXT_MEMORY_ATTRIBUTE_DESCRIPTOR;
      }

      //
      // At this step we have a hole between the current MAP entry address
      // and the MAT entry. Fill it in.
      //
      Status = OcExpandAttributeWrite (
        MemoryAttributesTable,
        MemoryAttributesEntry,
        MaxDescriptors,
        MemoryMap,
        CurrentMapAddress
        );
      if (EFI_ERROR (Status)) {
        return Status;
      }

      //
      // Advance MAP iterator with the entry we have just added and continue
      // processing the next MAT entry.
      //
      CurrentMapAddress = LAST_DESCRIPTOR_ADDR (MemoryAttributesEntry) + 1;

NEXT_MEMORY_ATTRIBUTE_DESCRIPTOR:
      MemoryAttributesEntry = NEXT_MEMORY_DESCRIPTOR (
        MemoryAttributesEntry,
        MemoryAttributesTable->DescriptorSize
        );
      ++MatIndex;
    }

    //
    // We completed to process this MAP entry, proceed to the next one.
    //
    if (CurrentMapAddress == NextMapAddress) {
      goto NEXT_MEMORY_MAP_DESCRIPTOR;
    }

    //
    // We have finished processing all the available MAT entries,
    // but this MAP entry has more memory, which is not reflected
    // in the MAT table. Add this memory and continue processing
    // the next MAP entry.
    //
    ASSERT (CurrentMapAddress < NextMapAddress);
    ASSERT (MatIndex == MemoryAttributesTable->NumberOfEntries);
    Status = OcExpandAttributeWrite (
      MemoryAttributesTable,
      NULL,
      MaxDescriptors,
      MemoryMap,
      CurrentMapAddress
      );
    if (EFI_ERROR (Status)) {
      return Status;
    }

    //
    // Increment MatIndex to ensure that we no longer enter the MAT entry
    // loop on the next iteration. Do not care updating CurrentMapAddress
    // as we will overwrite it immediate on the next MAP entry iteration.
    // Do not care updating MemoryAttribute as we will no longer use it.
    //
    ++MatIndex;

NEXT_MEMORY_MAP_DESCRIPTOR:
    MemoryMap = NEXT_MEMORY_DESCRIPTOR (
      MemoryMap,
      DescriptorSize
      );
  }

  return Status;
}

EFI_MEMORY_ATTRIBUTES_TABLE *
OcGetMemoryAttributes (
  OUT EFI_MEMORY_DESCRIPTOR  **MemoryAttributesEntry  OPTIONAL
  )
{
  EFI_MEMORY_ATTRIBUTES_TABLE  *MemoryAttributesTable; 
  UINTN                        Index;

  for (Index = 0; Index < gST->NumberOfTableEntries; ++Index) {
    if (CompareGuid (&gST->ConfigurationTable[Index].VendorGuid, &gEfiMemoryAttributesTableGuid)) {
      MemoryAttributesTable = gST->ConfigurationTable[Index].VendorTable;
      if (MemoryAttributesEntry != NULL) {
        *MemoryAttributesEntry = (EFI_MEMORY_DESCRIPTOR *) (MemoryAttributesTable + 1);
      }
      return MemoryAttributesTable;
    }
  }

  return NULL;
}

EFI_STATUS
OcRebuildAttributes (
  IN EFI_PHYSICAL_ADDRESS  Address,
  IN EFI_GET_MEMORY_MAP    GetMemoryMap  OPTIONAL
  )
{
  EFI_STATUS                         Status;
  EFI_MEMORY_ATTRIBUTES_TABLE        *MemoryAttributesTable;
  EFI_MEMORY_DESCRIPTOR              *MemoryAttributesEntry;
  UINTN                              MaxDescriptors;
  UINTN                              MemoryMapSize;
  EFI_MEMORY_DESCRIPTOR              *MemoryMap;
  UINTN                              DescriptorSize;
  UINTN                              MapKey;
  UINT32                             DescriptorVersion;

  MemoryAttributesTable = OcGetMemoryAttributes (&MemoryAttributesEntry);
  if (MemoryAttributesTable == NULL) {
    return EFI_UNSUPPORTED;
  }

  //
  // MAT is normally sorted, and so far nobody had issues
  // caused by unsorted MAT, but we do not want to risk.
  //
  OcSortMemoryMap (
    MemoryAttributesTable->NumberOfEntries * MemoryAttributesTable->DescriptorSize,
    MemoryAttributesEntry,
    MemoryAttributesTable->DescriptorSize
    );

  //
  // Some boards create entry duplicates and lose all non-PE entries
  // after loading runtime drivers after EndOfDxe.
  // REF: https://github.com/acidanthera/bugtracker/issues/491#issuecomment-609014334
  //
  MaxDescriptors = MemoryAttributesTable->NumberOfEntries;
  Status = OcDeduplicateDescriptors (
    &MemoryAttributesTable->NumberOfEntries,
    MemoryAttributesEntry,
    MemoryAttributesTable->DescriptorSize
    );
  if (!EFI_ERROR (Status)) {
    //
    // Statically allocate memory for the memory map to avoid allocations.
    //
    STATIC UINT8 mMemoryMap[OC_DEFAULT_MEMORY_MAP_SIZE];

    //
    // Assume effected and add missing entries.
    //
    if (GetMemoryMap == NULL) {
      GetMemoryMap = gBS->GetMemoryMap;
    }

    MemoryMapSize = sizeof (mMemoryMap);
    MemoryMap     = (EFI_MEMORY_DESCRIPTOR *) mMemoryMap;

    Status = GetMemoryMap (
      &MemoryMapSize,
      MemoryMap,
      &MapKey,
      &DescriptorSize,
      &DescriptorVersion
      );

    if (!EFI_ERROR (Status)) {
      OcSortMemoryMap (
        MemoryMapSize,
        MemoryMap,
        DescriptorSize
        );

      OcExpandAttributesByMap (
        MemoryAttributesTable,
        MemoryAttributesEntry,
        MaxDescriptors,
        MemoryMapSize / DescriptorSize,
        MemoryMap,
        DescriptorSize
        );
    } else {
      //
      // TODO: Scream in fear here? We cannot log, but for a fatal error it is "fine".
      //
    }
  }

  //
  // Some firmwares do not update MAT after loading runtime drivers after EndOfDxe.
  // Since the memory used to allocate runtime driver resides in BINs, MAT has whatever
  // permissions designated for unused memory. Mark unused memory containing our driver
  // as executable here.
  // REF: https://github.com/acidanthera/bugtracker/issues/491#issuecomment-606835337
  //
  if (Address != 0) {
    Status = OcUpdateDescriptors (
      MemoryAttributesTable->NumberOfEntries * MemoryAttributesTable->DescriptorSize,
      MemoryAttributesEntry,
      MemoryAttributesTable->DescriptorSize,
      Address,
      EfiRuntimeServicesCode,
      EFI_MEMORY_RO,
      EFI_MEMORY_XP
      );
  }

  return Status;
}

UINTN
OcCountSplitDescriptors (
  VOID
  )
{
  UINTN                             Index;
  UINTN                             DescriptorCount;
  CONST EFI_MEMORY_ATTRIBUTES_TABLE *MemoryAttributesTable;
  EFI_MEMORY_DESCRIPTOR             *MemoryAttributesEntry;

  MemoryAttributesTable = OcGetMemoryAttributes (&MemoryAttributesEntry);
  if (MemoryAttributesTable == NULL) {
    return 0;
  }

  DescriptorCount = 0;
  for (Index = 0; Index < MemoryAttributesTable->NumberOfEntries; ++Index) {
    if (MemoryAttributesEntry->Type == EfiRuntimeServicesCode
      || MemoryAttributesEntry->Type == EfiRuntimeServicesData) {
      ++DescriptorCount;
    }

    MemoryAttributesEntry = NEXT_MEMORY_DESCRIPTOR (
      MemoryAttributesEntry,
      MemoryAttributesTable->DescriptorSize
      );
  }

  return DescriptorCount;
}

EFI_STATUS
OcSplitMemoryMapByAttributes (
  IN     UINTN                  MaxMemoryMapSize,
  IN OUT UINTN                  *MemoryMapSize,
  IN OUT EFI_MEMORY_DESCRIPTOR  *MemoryMap,
  IN     UINTN                  DescriptorSize
  )
{
  EFI_STATUS                         Status;
  CONST EFI_MEMORY_ATTRIBUTES_TABLE  *MemoryAttributesTable;
  EFI_MEMORY_DESCRIPTOR              *MemoryAttributesEntry;
  EFI_MEMORY_DESCRIPTOR              *MemoryMapEntry;
  EFI_MEMORY_DESCRIPTOR              *LastAttributeEntry;
  UINTN                              LastAttributeIndex;
  UINTN                              Index;
  UINTN                              Index2;
  UINTN                              CurrentEntryCount;
  UINTN                              TotalEntryCount;
  UINTN                              AttributeCount;
  BOOLEAN                            CanSplit;
  BOOLEAN                            InDescAttrs;

  ASSERT (MaxMemoryMapSize >= *MemoryMapSize);

  MemoryAttributesTable = OcGetMemoryAttributes (&MemoryAttributesEntry);
  if (MemoryAttributesTable == NULL) {
    return EFI_UNSUPPORTED;
  }

  LastAttributeEntry = MemoryAttributesEntry;
  LastAttributeIndex = 0;
  MemoryMapEntry     = MemoryMap;
  CurrentEntryCount  = *MemoryMapSize / DescriptorSize;
  TotalEntryCount    = MaxMemoryMapSize / DescriptorSize;
  AttributeCount     = MemoryAttributesTable->NumberOfEntries;

  //
  // We assume that the memory map and attribute table are sorted.
  //
  Index = 0;
  while (Index < CurrentEntryCount) {
    //
    // Split entry by as many attributes as possible.
    //
    CanSplit = TRUE;
    while ((MemoryMapEntry->Type == EfiRuntimeServicesCode
      || MemoryMapEntry->Type == EfiRuntimeServicesData) && CanSplit) {
      //
      // Find corresponding memory attribute.
      //
      InDescAttrs = FALSE;
      MemoryAttributesEntry = LastAttributeEntry;
      for (Index2 = LastAttributeIndex; Index2 < AttributeCount; ++Index2) {
        if (MemoryAttributesEntry->Type == EfiRuntimeServicesCode
          || MemoryAttributesEntry->Type == EfiRuntimeServicesData) {
          //
          // UEFI spec says attribute entries are fully within memory map entries.
          // Find first one of a different type.
          //
          if (AREA_WITHIN_DESCRIPTOR (
            MemoryMapEntry,
            MemoryAttributesEntry->PhysicalStart,
            EFI_PAGES_TO_SIZE (MemoryAttributesEntry->NumberOfPages))) {
            //
            // We are within descriptor attribute sequence.
            //
            InDescAttrs = TRUE;
            //
            // No need to process the attribute of the same type.
            //
            if (OcRealMemoryType (MemoryAttributesEntry) != MemoryMapEntry->Type) {
              //
              // Start with the next attribute on the second iteration.
              //
              LastAttributeEntry = NEXT_MEMORY_DESCRIPTOR (
                MemoryAttributesEntry,
                MemoryAttributesTable->DescriptorSize
                );
              LastAttributeIndex = Index2 + 1;
              break;
            }
          } else if (InDescAttrs) {
            //
            // Reached the end of descriptor attribute sequence, abort.
            //
            InDescAttrs = FALSE;
            break;
          }
        }

        MemoryAttributesEntry = NEXT_MEMORY_DESCRIPTOR (
          MemoryAttributesEntry,
          MemoryAttributesTable->DescriptorSize
          );
      }

      if (Index2 < AttributeCount && InDescAttrs) {
        //
        // Split current memory map entry.
        //
        Status = OcSplitMemoryEntryByAttribute (
          &MemoryMapEntry,
          &Index,
          &CurrentEntryCount,
          TotalEntryCount,
          MemoryAttributesEntry,
          DescriptorSize
          );
        if (EFI_ERROR (Status)) {
          *MemoryMapSize = CurrentEntryCount * DescriptorSize;
          return Status;
        }
        continue;
      } else {
        //
        // Did not find a suitable attribute or processed all the attributes.
        //
        CanSplit = FALSE;
      }
    }

    MemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (
      MemoryMapEntry,
      DescriptorSize
      );
    ++Index;
  }

  *MemoryMapSize = CurrentEntryCount * DescriptorSize;
  return EFI_SUCCESS;
}