Re: [PATCH 3/3] MdeModulePkg/Core: add use-after-free memory detection

["Zeng, Star" <star.zeng@intel.com>]

On 2018/10/19 9:50, Jian J Wang wrote:
> UAF (Use-After-Free) memory detection is new feature introduced to
> detect illegal access to memory which has been freed. The principle
> behind is similar to heap guard feature, that is the core turn all pool
> memory allocation to page allocation and mark them to be not-present
> once they are freed.
> 
> This also implies that, once a page is allocated and freed, it cannot
> be re-allocated. This will bring another issue, which is that there's
> risk that memory space will be used out. To address it, the memory
> service add logic to put part (at most 64 pages a time) of freed pages
> back into page pool, so that the memory service can still have memory
> to allocate, when all memory space have been allocated once. This is
> called memory promotion. The promoted pages are always from the eldest
> pages which haven been freed.
> 
> To use this feature, one can simply set following PCD to 1
>    gEfiMdeModulePkgTokenSpaceGuid.PcdUseAfterFreeDetectionPropertyMask
> 
> Please note this feature cannot be used with heap guard feature controlled
> by PCD gEfiMdeModulePkgTokenSpaceGuid.PcdHeapGuardPropertyMask.
> 
> Cc: Star Zeng <star.zeng@intel.com>
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Jian J Wang <jian.j.wang@intel.com>

I did not review the whole patch thoroughly. But I suggest that putting 
the code for UAF in a separated file if it is feasible. I am aware that 
UAF will be sharing much code with HeapGuard, so could we have Uaf.c, 
HeapGuard.c and GuardPage.c (this file name is just for example)?

> ---
>   MdeModulePkg/Core/Dxe/DxeMain.h              |   1 +
>   MdeModulePkg/Core/Dxe/DxeMain.inf            |   1 +
>   MdeModulePkg/Core/Dxe/Gcd/Gcd.c              |   8 +
>   MdeModulePkg/Core/Dxe/Mem/HeapGuard.c        | 393 ++++++++++++++++++++++++++-
>   MdeModulePkg/Core/Dxe/Mem/HeapGuard.h        |  66 +++++
>   MdeModulePkg/Core/Dxe/Mem/Page.c             |  39 ++-
>   MdeModulePkg/Core/Dxe/Mem/Pool.c             |  21 +-
>   MdeModulePkg/Core/Dxe/Misc/PropertiesTable.c |  16 +-
>   8 files changed, 519 insertions(+), 26 deletions(-)
> 
> diff --git a/MdeModulePkg/Core/Dxe/DxeMain.h b/MdeModulePkg/Core/Dxe/DxeMain.h
> index 2dec9da5e3..ae75cc5b25 100644
> --- a/MdeModulePkg/Core/Dxe/DxeMain.h
> +++ b/MdeModulePkg/Core/Dxe/DxeMain.h
> @@ -92,6 +92,7 @@ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
>   #include <Library/DxeServicesLib.h>
>   #include <Library/DebugAgentLib.h>
>   #include <Library/CpuExceptionHandlerLib.h>
> +#include <Library/DebugPrintErrorLevelLib.h>
>   
>   
>   //
> diff --git a/MdeModulePkg/Core/Dxe/DxeMain.inf b/MdeModulePkg/Core/Dxe/DxeMain.inf
> index 10375443c0..d91258c087 100644
> --- a/MdeModulePkg/Core/Dxe/DxeMain.inf
> +++ b/MdeModulePkg/Core/Dxe/DxeMain.inf
> @@ -198,6 +198,7 @@
>     gEfiMdeModulePkgTokenSpaceGuid.PcdHeapGuardPoolType                       ## CONSUMES
>     gEfiMdeModulePkgTokenSpaceGuid.PcdHeapGuardPropertyMask                   ## CONSUMES
>     gEfiMdeModulePkgTokenSpaceGuid.PcdCpuStackGuard                           ## CONSUMES
> +  gEfiMdeModulePkgTokenSpaceGuid.PcdUseAfterFreeDetectionPropertyMask       ## CONSUMES
>   
>   # [Hob]
>   # RESOURCE_DESCRIPTOR   ## CONSUMES
> diff --git a/MdeModulePkg/Core/Dxe/Gcd/Gcd.c b/MdeModulePkg/Core/Dxe/Gcd/Gcd.c
> index d9c65a8045..e43ec74010 100644
> --- a/MdeModulePkg/Core/Dxe/Gcd/Gcd.c
> +++ b/MdeModulePkg/Core/Dxe/Gcd/Gcd.c
> @@ -160,6 +160,10 @@ CoreDumpGcdMemorySpaceMap (
>       EFI_GCD_MEMORY_SPACE_DESCRIPTOR  *MemorySpaceMap;
>       UINTN                            Index;
>   
> +    if ((GetDebugPrintErrorLevel () & DEBUG_GCD) == 0) {
> +      return;
> +    }

I am aware the purpose of this change to optimize some code when 
DEBUG_GCD is not set.
But I do not suggest we newly introduce the dependency to 
DebugPrintErrorLevelLib, I think this check should be hidden in the 
instance of DebugLib. Maybe a new macro DEBUG_CODE_ERROR_LEVEL (this 
macro name is just for example) can be introduced if we really want to 
do that.


Thanks,
Star

> +
>       Status = CoreGetMemorySpaceMap (&NumberOfDescriptors, &MemorySpaceMap);
>       ASSERT (Status == EFI_SUCCESS && MemorySpaceMap != NULL);
>   
> @@ -202,6 +206,10 @@ CoreDumpGcdIoSpaceMap (
>       EFI_GCD_IO_SPACE_DESCRIPTOR  *IoSpaceMap;
>       UINTN                        Index;
>   
> +    if ((GetDebugPrintErrorLevel () & DEBUG_GCD) == 0) {
> +      return;
> +    }
> +
>       Status = CoreGetIoSpaceMap (&NumberOfDescriptors, &IoSpaceMap);
>       ASSERT (Status == EFI_SUCCESS && IoSpaceMap != NULL);
>   
> diff --git a/MdeModulePkg/Core/Dxe/Mem/HeapGuard.c b/MdeModulePkg/Core/Dxe/Mem/HeapGuard.c
> index 663f969c0d..b120c04f8f 100644
> --- a/MdeModulePkg/Core/Dxe/Mem/HeapGuard.c
> +++ b/MdeModulePkg/Core/Dxe/Mem/HeapGuard.c
> @@ -44,6 +44,11 @@ GLOBAL_REMOVE_IF_UNREFERENCED UINTN mLevelShift[GUARDED_HEAP_MAP_TABLE_DEPTH]
>   GLOBAL_REMOVE_IF_UNREFERENCED UINTN mLevelMask[GUARDED_HEAP_MAP_TABLE_DEPTH]
>                                       = GUARDED_HEAP_MAP_TABLE_DEPTH_MASKS;
>   
> +//
> +// Used for Use-After-Free memory detection to promote freed but not used pages.
> +//
> +GLOBAL_REMOVE_IF_UNREFERENCED EFI_PHYSICAL_ADDRESS mLastPromotedPage = BASE_4GB;
> +
>   /**
>     Set corresponding bits in bitmap table to 1 according to the address.
>   
> @@ -379,7 +384,7 @@ ClearGuardedMemoryBits (
>   
>     @return An integer containing the guarded memory bitmap.
>   **/
> -UINTN
> +UINT64
>   GetGuardedMemoryBits (
>     IN EFI_PHYSICAL_ADDRESS    Address,
>     IN UINTN                   NumberOfPages
> @@ -387,7 +392,7 @@ GetGuardedMemoryBits (
>   {
>     UINT64            *BitMap;
>     UINTN             Bits;
> -  UINTN             Result;
> +  UINT64            Result;
>     UINTN             Shift;
>     UINTN             BitsToUnitEnd;
>   
> @@ -1203,6 +1208,373 @@ SetAllGuardPages (
>     }
>   }
>   
> +/**
> +  Check to see if the Use-After-Free (UAF) feature is enabled or not.
> +
> +  @return TRUE/FALSE.
> +**/
> +BOOLEAN
> +IsUafEnabled (
> +  VOID
> +  )
> +{
> +  ASSERT (!IsHeapGuardEnabled());
> +  return ((PcdGet8 (PcdUseAfterFreeDetectionPropertyMask) & BIT0) != 0);
> +}
> +
> +/**
> +  Find the address of top-most guarded free page.
> +
> +  @param[out]  Address    Start address of top-most guarded free page.
> +
> +  @return VOID.
> +**/
> +VOID
> +GetLastGuardedFreePageAddress (
> +  OUT EFI_PHYSICAL_ADDRESS      *Address
> +  )
> +{
> +  EFI_PHYSICAL_ADDRESS    AddressGranularity;
> +  EFI_PHYSICAL_ADDRESS    BaseAddress;
> +  UINTN                   Level;
> +  UINT64                  Map;
> +  INTN                    Index;
> +
> +  ASSERT (mMapLevel >= 1);
> +
> +  BaseAddress = 0;
> +  Map = mGuardedMemoryMap;
> +  for (Level = GUARDED_HEAP_MAP_TABLE_DEPTH - mMapLevel;
> +       Level < GUARDED_HEAP_MAP_TABLE_DEPTH;
> +       ++Level) {
> +    AddressGranularity = LShiftU64 (1, mLevelShift[Level]);
> +
> +    //
> +    // Find the non-NULL entry at largest index.
> +    //
> +    for (Index = (INTN)mLevelMask[Level]; Index >= 0 ; --Index) {
> +      if (((UINT64 *)(UINTN)Map)[Index] != 0) {
> +        BaseAddress += MultU64x32 (AddressGranularity, (UINT32)Index);
> +        Map = ((UINT64 *)(UINTN)Map)[Index];
> +        break;
> +      }
> +    }
> +  }
> +
> +  //
> +  // Find the non-zero MSB then get the page address.
> +  //
> +  while (Map != 0) {
> +    Map = RShiftU64 (Map, 1);
> +    BaseAddress += EFI_PAGES_TO_SIZE (1);
> +  }
> +
> +  *Address = BaseAddress;
> +}
> +
> +/**
> +  Record freed pages.
> +
> +  @param[in]  BaseAddress   Base address of just freed pages.
> +  @param[in]  Pages         Number of freed pages.
> +
> +  @return VOID.
> +**/
> +VOID
> +MarkFreedPages (
> +  IN EFI_PHYSICAL_ADDRESS     BaseAddress,
> +  IN UINTN                    Pages
> +  )
> +{
> +  SetGuardedMemoryBits (BaseAddress, Pages);
> +}
> +
> +/**
> +  Record freed pages as well as mark them as not-present, if possible.
> +
> +  @param[in]  BaseAddress   Base address of just freed pages.
> +  @param[in]  Pages         Number of freed pages.
> +
> +  @return VOID.
> +**/
> +VOID
> +EFIAPI
> +GuardFreedPages (
> +  IN  EFI_PHYSICAL_ADDRESS    BaseAddress,
> +  IN  UINTN                   Pages
> +  )
> +{
> +  EFI_STATUS      Status;
> +
> +  //
> +  // Do nothing if
> +  // - Use-After-Free detection is not enabled
> +  // - Freed memory is legacy memory lower than 1MB
> +  //
> +  if (!IsUafEnabled () || BaseAddress < BASE_1MB) {
> +    return;
> +  }
> +
> +  MarkFreedPages (BaseAddress, Pages);
> +  if (gCpu != NULL) {
> +    //
> +    // Set flag to make sure allocating memory without GUARD for page table
> +    // operation; otherwise infinite loops could be caused.
> +    //
> +    mOnGuarding = TRUE;
> +    //
> +    // Note: This might overwrite other attributes needed by other features,
> +    // such as NX memory protection.
> +    //
> +    Status = gCpu->SetMemoryAttributes (
> +                     gCpu,
> +                     BaseAddress,
> +                     EFI_PAGES_TO_SIZE(Pages),
> +                     EFI_MEMORY_RP
> +                     );
> +    //
> +    // Normally we should check the returned Status. But there might be memory
> +    // alloc/free involved in SetMemoryAttributes(), which would fail this
> +    // calling. It's rare case so it's OK to let a few tiny holes be not-guarded.
> +    //
> +    if (EFI_ERROR (Status)) {
> +      DEBUG ((DEBUG_WARN, "Failed to guard freed pages: %p (%d)\n", BaseAddress, Pages));
> +    }
> +    mOnGuarding = FALSE;
> +  }
> +}
> +
> +/**
> +  Mark all pages freed before CPU Arch Protocol as not-present.
> +
> +**/
> +VOID
> +GuardAllFreedPages (
> +  VOID
> +  )
> +{
> +  UINTN     Entries[GUARDED_HEAP_MAP_TABLE_DEPTH];
> +  UINTN     Shifts[GUARDED_HEAP_MAP_TABLE_DEPTH];
> +  UINTN     Indices[GUARDED_HEAP_MAP_TABLE_DEPTH];
> +  UINT64    Tables[GUARDED_HEAP_MAP_TABLE_DEPTH];
> +  UINT64    Addresses[GUARDED_HEAP_MAP_TABLE_DEPTH];
> +  UINT64    TableEntry;
> +  UINT64    Address;
> +  UINT64    GuardPage;
> +  INTN      Level;
> +  UINTN     BitIndex;
> +  UINTN     GuardPageNumber;
> +
> +  if (mGuardedMemoryMap == 0 ||
> +      mMapLevel == 0 ||
> +      mMapLevel > GUARDED_HEAP_MAP_TABLE_DEPTH) {
> +    return;
> +  }
> +
> +  CopyMem (Entries, mLevelMask, sizeof (Entries));
> +  CopyMem (Shifts, mLevelShift, sizeof (Shifts));
> +
> +  SetMem (Tables, sizeof(Tables), 0);
> +  SetMem (Addresses, sizeof(Addresses), 0);
> +  SetMem (Indices, sizeof(Indices), 0);
> +
> +  Level           = GUARDED_HEAP_MAP_TABLE_DEPTH - mMapLevel;
> +  Tables[Level]   = mGuardedMemoryMap;
> +  Address         = 0;
> +  GuardPage       = (UINT64)-1;
> +  GuardPageNumber = 0;
> +
> +  while (TRUE) {
> +    if (Indices[Level] > Entries[Level]) {
> +      Tables[Level] = 0;
> +      Level        -= 1;
> +    } else {
> +      TableEntry  = ((UINT64 *)(UINTN)(Tables[Level]))[Indices[Level]];
> +      Address     = Addresses[Level];
> +
> +      if (Level < GUARDED_HEAP_MAP_TABLE_DEPTH - 1) {
> +        Level            += 1;
> +        Tables[Level]     = TableEntry;
> +        Addresses[Level]  = Address;
> +        Indices[Level]    = 0;
> +
> +        continue;
> +      } else {
> +        BitIndex = 1;
> +        while (BitIndex != 0) {
> +          if ((TableEntry & BitIndex) != 0) {
> +            if (GuardPage == (UINT64)-1) {
> +              GuardPage = Address;
> +            }
> +            ++GuardPageNumber;
> +          } else if (GuardPageNumber > 0) {
> +            GuardFreedPages (GuardPage, GuardPageNumber);
> +            GuardPageNumber = 0;
> +            GuardPage       = (UINT64)-1;
> +          }
> +
> +          if (TableEntry == 0) {
> +            break;
> +          }
> +
> +          Address += EFI_PAGES_TO_SIZE (1);
> +          BitIndex = LShiftU64(BitIndex, 1);
> +        }
> +      }
> +    }
> +
> +    if (Level < (GUARDED_HEAP_MAP_TABLE_DEPTH - (INTN)mMapLevel)) {
> +      break;
> +    }
> +
> +    Indices[Level] += 1;
> +    Address = (Level == 0) ? 0 : Addresses[Level - 1];
> +    Addresses[Level] = Address | LShiftU64(Indices[Level], Shifts[Level]);
> +
> +  }
> +
> +  //
> +  // Update the maximum address of freed page which can be used for memory
> +  // promotion upon out-of-memory-space.
> +  //
> +  GetLastGuardedFreePageAddress (&Address);
> +  if (Address != 0) {
> +    mLastPromotedPage = Address;
> +  }
> +}
> +
> +/**
> +  This function checks to see if the given memory map descriptor in a memory map
> +  can be merged with any guarded free pages.
> +
> +  @param  MemoryMapEntry    A pointer to a descriptor in MemoryMap.
> +  @param  MaxAddress        Maximum address to stop the merge.
> +
> +  @return VOID
> +
> +**/
> +VOID
> +MergeGuardPages (
> +  IN EFI_MEMORY_DESCRIPTOR      *MemoryMapEntry,
> +  IN EFI_PHYSICAL_ADDRESS       MaxAddress
> +  )
> +{
> +  EFI_PHYSICAL_ADDRESS        EndAddress;
> +  UINT64                      Bitmap;
> +  INTN                        Pages;
> +
> +  if (!IsUafEnabled () ||
> +      MemoryMapEntry->Type >= EfiMemoryMappedIO) {
> +    return;
> +  }
> +
> +  Bitmap = 0;
> +  Pages  = EFI_SIZE_TO_PAGES (MaxAddress - MemoryMapEntry->PhysicalStart);
> +  Pages -= MemoryMapEntry->NumberOfPages;
> +  while (Pages > 0) {
> +    if (Bitmap == 0) {
> +      EndAddress = MemoryMapEntry->PhysicalStart +
> +                   EFI_PAGES_TO_SIZE (MemoryMapEntry->NumberOfPages);
> +      Bitmap = GetGuardedMemoryBits(EndAddress, GUARDED_HEAP_MAP_ENTRY_BITS);
> +    }
> +
> +    if ((Bitmap & 1) == 0) {
> +      break;
> +    }
> +
> +    Pages--;
> +    MemoryMapEntry->NumberOfPages++;
> +    Bitmap = RShiftU64 (Bitmap, 1);
> +  }
> +}
> +
> +/**
> +  Put part (at most 64 pages a time) guarded free pages back to free page pool.
> +
> +  Use-After-Free detection makes use of 'Used then throw away' way to detect
> +  any illegal access to freed memory. The thrown-away memory will be marked as
> +  not-present so that any access to those memory (after free) will trigger
> +  page-fault.
> +
> +  The problem is that this will consume lots of memory space. Once no memory
> +  left in pool to allocate, we have to restore part of the freed pages to their
> +  normal function. Otherwise the whole system will stop functioning.
> +
> +  @param  StartAddress    Start address of promoted memory.
> +  @param  EndAddress      End address of promoted memory.
> +
> +  @return TRUE    Succeeded to promote memory.
> +  @return FALSE   No free memory found.
> +
> +**/
> +BOOLEAN
> +PromoteGuardedFreePages (
> +  OUT EFI_PHYSICAL_ADDRESS      *StartAddress,
> +  OUT EFI_PHYSICAL_ADDRESS      *EndAddress
> +  )
> +{
> +  EFI_STATUS              Status;
> +  UINTN                   AvailablePages;
> +  UINT64                  Bitmap;
> +  EFI_PHYSICAL_ADDRESS    Start;
> +
> +  if (!IsUafEnabled ()) {
> +    return FALSE;
> +  }
> +
> +  //
> +  // Similar to memory allocation service, always search the freed pages in
> +  // descending direction.
> +  //
> +  Start           = mLastPromotedPage;
> +  AvailablePages  = 0;
> +  while (AvailablePages == 0) {
> +    Start -= EFI_PAGES_TO_SIZE(GUARDED_HEAP_MAP_ENTRY_BITS);
> +    //
> +    // If the address wraps around, try the really freed pages at top.
> +    //
> +    if (Start > mLastPromotedPage) {
> +      GetLastGuardedFreePageAddress (&Start);
> +      ASSERT (Start != 0);
> +      Start -= EFI_PAGES_TO_SIZE(GUARDED_HEAP_MAP_ENTRY_BITS);
> +    }
> +
> +    Bitmap = GetGuardedMemoryBits(Start, GUARDED_HEAP_MAP_ENTRY_BITS);
> +    while (Bitmap > 0) {
> +      if ((Bitmap & 1) != 0) {
> +        ++AvailablePages;
> +      } else if (AvailablePages == 0) {
> +        Start += EFI_PAGES_TO_SIZE (1);
> +      } else {
> +        break;
> +      }
> +
> +      Bitmap = RShiftU64(Bitmap, 1);
> +    }
> +  }
> +
> +  if (AvailablePages) {
> +    DEBUG((DEBUG_INFO, "Promoted pages: %lX (%X)\r\n", Start, AvailablePages));
> +    if (gCpu != NULL) {
> +      //
> +      // Set flag to make sure allocating memory without GUARD for page table
> +      // operation; otherwise infinite loops could be caused.
> +      //
> +      mOnGuarding = TRUE;
> +      Status = gCpu->SetMemoryAttributes (gCpu, Start, EFI_PAGES_TO_SIZE(AvailablePages), 0);
> +      ASSERT_EFI_ERROR (Status);
> +      mOnGuarding = FALSE;
> +    }
> +
> +    mLastPromotedPage = Start;
> +    *StartAddress     = Start;
> +    *EndAddress       = Start + EFI_PAGES_TO_SIZE (AvailablePages) - 1;
> +    return TRUE;
> +  }
> +
> +  return FALSE;
> +}
> +
>   /**
>     Notify function used to set all Guard pages before CPU Arch Protocol installed.
>   **/
> @@ -1212,7 +1584,14 @@ HeapGuardCpuArchProtocolNotify (
>     )
>   {
>     ASSERT (gCpu != NULL);
> -  SetAllGuardPages ();
> +
> +  if ((PcdGet8 (PcdHeapGuardPropertyMask) & 0x0F) != 0) {
> +    SetAllGuardPages ();
> +  }
> +
> +  if (IsUafEnabled ()) {
> +    GuardAllFreedPages ();
> +  }
>   }
>   
>   /**
> @@ -1264,6 +1643,14 @@ DumpGuardedMemoryBitmap (
>     CHAR8     *Ruler1;
>     CHAR8     *Ruler2;
>   
> +  if (!IsHeapGuardEnabled () && !IsUafEnabled ()) {
> +    return;
> +  }
> +
> +  if ((GetDebugPrintErrorLevel () & HEAP_GUARD_DEBUG_LEVEL) == 0) {
> +    return;
> +  }
> +
>     if (mGuardedMemoryMap == 0 ||
>         mMapLevel == 0 ||
>         mMapLevel > GUARDED_HEAP_MAP_TABLE_DEPTH) {
> diff --git a/MdeModulePkg/Core/Dxe/Mem/HeapGuard.h b/MdeModulePkg/Core/Dxe/Mem/HeapGuard.h
> index 8c34692439..3f2a5283c2 100644
> --- a/MdeModulePkg/Core/Dxe/Mem/HeapGuard.h
> +++ b/MdeModulePkg/Core/Dxe/Mem/HeapGuard.h
> @@ -407,6 +407,72 @@ HeapGuardCpuArchProtocolNotify (
>     VOID
>     );
>   
> +/**
> +  This function checks to see if the given memory map descriptor in a memory map
> +  can be merged with any guarded free pages.
> +
> +  @param  MemoryMapEntry    A pointer to a descriptor in MemoryMap.
> +  @param  MaxAddress        Maximum address to stop the merge.
> +
> +  @return VOID
> +
> +**/
> +VOID
> +MergeGuardPages (
> +  IN EFI_MEMORY_DESCRIPTOR      *MemoryMapEntry,
> +  IN EFI_PHYSICAL_ADDRESS       MaxAddress
> +  );
> +
> +/**
> +  Record freed pages as well as mark them as not-present, if possible.
> +
> +  @param[in]  BaseAddress   Base address of just freed pages.
> +  @param[in]  Pages         Number of freed pages.
> +
> +  @return VOID.
> +**/
> +VOID
> +EFIAPI
> +GuardFreedPages (
> +  IN  EFI_PHYSICAL_ADDRESS    BaseAddress,
> +  IN  UINTN                   Pages
> +  );
> +
> +/**
> +  Check to see if the use-after-free (UAF) feature is enabled or not.
> +
> +  @return TRUE/FALSE.
> +**/
> +BOOLEAN
> +IsUafEnabled (
> +  VOID
> +  );
> +
> +/**
> +  Put part (at most 64 pages a time) guarded free pages back to free page pool.
> +
> +  Use-After-Free detection makes use of 'Used then throw away' way to detect
> +  any illegal access to freed memory. The thrown-away memory will be marked as
> +  not-present so that any access to those memory (after free) will trigger
> +  page-fault.
> +
> +  The problem is that this will consume lots of memory space. Once no memory
> +  left in pool to allocate, we have to restore part of the freed pages to their
> +  normal function. Otherwise the whole system will stop functioning.
> +
> +  @param  StartAddress    Start address of promoted memory.
> +  @param  EndAddress      End address of promoted memory.
> +
> +  @return TRUE    Succeeded to promote memory.
> +  @return FALSE   No free memory found.
> +
> +**/
> +BOOLEAN
> +PromoteGuardedFreePages (
> +  OUT EFI_PHYSICAL_ADDRESS      *StartAddress,
> +  OUT EFI_PHYSICAL_ADDRESS      *EndAddress
> +  );
> +
>   extern BOOLEAN mOnGuarding;
>   
>   #endif
> diff --git a/MdeModulePkg/Core/Dxe/Mem/Page.c b/MdeModulePkg/Core/Dxe/Mem/Page.c
> index 3b4cc08e7c..9f4419fa5b 100644
> --- a/MdeModulePkg/Core/Dxe/Mem/Page.c
> +++ b/MdeModulePkg/Core/Dxe/Mem/Page.c
> @@ -401,9 +401,11 @@ PromoteMemoryResource (
>     VOID
>     )
>   {
> -  LIST_ENTRY         *Link;
> -  EFI_GCD_MAP_ENTRY  *Entry;
> -  BOOLEAN            Promoted;
> +  LIST_ENTRY            *Link;
> +  EFI_GCD_MAP_ENTRY     *Entry;
> +  BOOLEAN               Promoted;
> +  EFI_PHYSICAL_ADDRESS  StartAddress;
> +  EFI_PHYSICAL_ADDRESS  EndAddress;
>   
>     DEBUG ((DEBUG_PAGE, "Promote the memory resource\n"));
>   
> @@ -451,6 +453,24 @@ PromoteMemoryResource (
>   
>     CoreReleaseGcdMemoryLock ();
>   
> +  if (!Promoted) {
> +    //
> +    // If Use-After-Free detection is enabled, we might promote pages from
> +    // guarded free pages.
> +    //
> +    Promoted = PromoteGuardedFreePages (&StartAddress, &EndAddress);
> +    if (Promoted) {
> +      CoreAcquireGcdMemoryLock ();
> +      CoreAddRange (
> +        EfiConventionalMemory,
> +        StartAddress,
> +        EndAddress,
> +        EFI_MEMORY_UC | EFI_MEMORY_WC | EFI_MEMORY_WT | EFI_MEMORY_WB
> +        );
> +      CoreReleaseGcdMemoryLock ();
> +    }
> +  }
> +
>     return Promoted;
>   }
>   /**
> @@ -896,9 +916,13 @@ CoreConvertPagesEx (
>       }
>   
>       //
> -    // Add our new range in
> +    // Add our new range in. Don't do this for freed pages if Use-After-Free
> +    // detection is enabled.
>       //
> -    CoreAddRange (MemType, Start, RangeEnd, Attribute);
> +    if (!IsUafEnabled () || !ChangingType || MemType != EfiConventionalMemory) {
> +      CoreAddRange (MemType, Start, RangeEnd, Attribute);
> +    }
> +
>       if (ChangingType && (MemType == EfiConventionalMemory)) {
>         //
>         // Avoid calling DEBUG_CLEAR_MEMORY() for an address of 0 because this
> @@ -1514,6 +1538,7 @@ CoreFreePages (
>   
>     Status = CoreInternalFreePages (Memory, NumberOfPages, &MemoryType);
>     if (!EFI_ERROR (Status)) {
> +    GuardFreedPages (Memory, NumberOfPages);
>       CoreUpdateProfile (
>         (EFI_PHYSICAL_ADDRESS) (UINTN) RETURN_ADDRESS (0),
>         MemoryProfileActionFreePages,
> @@ -1908,9 +1933,7 @@ Done:
>     *MemoryMapSize = BufferSize;
>   
>     DEBUG_CODE (
> -    if (PcdGet8 (PcdHeapGuardPropertyMask) & (BIT1|BIT0)) {
> -      DumpGuardedMemoryBitmap ();
> -    }
> +    DumpGuardedMemoryBitmap ();
>     );
>   
>     return Status;
> diff --git a/MdeModulePkg/Core/Dxe/Mem/Pool.c b/MdeModulePkg/Core/Dxe/Mem/Pool.c
> index 1ff2061f7f..0cd74267b3 100644
> --- a/MdeModulePkg/Core/Dxe/Mem/Pool.c
> +++ b/MdeModulePkg/Core/Dxe/Mem/Pool.c
> @@ -26,7 +26,8 @@ typedef struct {
>   } POOL_FREE;
>   
>   
> -#define POOL_HEAD_SIGNATURE   SIGNATURE_32('p','h','d','0')
> +#define POOL_HEAD_SIGNATURE       SIGNATURE_32('p','h','d','0')
> +#define POOLPAGE_HEAD_SIGNATURE   SIGNATURE_32('p','h','d','1')
>   typedef struct {
>     UINT32          Signature;
>     UINT32          Reserved;
> @@ -367,6 +368,7 @@ CoreAllocatePoolI (
>     UINTN       NoPages;
>     UINTN       Granularity;
>     BOOLEAN     HasPoolTail;
> +  BOOLEAN     PageAsPool;
>   
>     ASSERT_LOCKED (&mPoolMemoryLock);
>   
> @@ -386,6 +388,7 @@ CoreAllocatePoolI (
>   
>     HasPoolTail  = !(NeedGuard &&
>                      ((PcdGet8 (PcdHeapGuardPropertyMask) & BIT7) == 0));
> +  PageAsPool = (IsUafEnabled () && !mOnGuarding);
>   
>     //
>     // Adjusting the Size to be of proper alignment so that
> @@ -406,7 +409,7 @@ CoreAllocatePoolI (
>     // If allocation is over max size, just allocate pages for the request
>     // (slow)
>     //
> -  if (Index >= SIZE_TO_LIST (Granularity) || NeedGuard) {
> +  if (Index >= SIZE_TO_LIST (Granularity) || NeedGuard || PageAsPool) {
>       if (!HasPoolTail) {
>         Size -= sizeof (POOL_TAIL);
>       }
> @@ -498,7 +501,7 @@ Done:
>       //
>       // If we have a pool buffer, fill in the header & tail info
>       //
> -    Head->Signature = POOL_HEAD_SIGNATURE;
> +    Head->Signature = (PageAsPool) ? POOLPAGE_HEAD_SIGNATURE : POOL_HEAD_SIGNATURE;
>       Head->Size      = Size;
>       Head->Type      = (EFI_MEMORY_TYPE) PoolType;
>       Buffer          = Head->Data;
> @@ -615,6 +618,7 @@ CoreFreePoolPagesI (
>     CoreFreePoolPages (Memory, NoPages);
>     CoreReleaseMemoryLock ();
>   
> +  GuardFreedPages (Memory, NoPages);
>     ApplyMemoryProtectionPolicy (PoolType, EfiConventionalMemory,
>       (EFI_PHYSICAL_ADDRESS)(UINTN)Memory, EFI_PAGES_TO_SIZE (NoPages));
>   }
> @@ -685,15 +689,19 @@ CoreFreePoolI (
>     UINTN       Granularity;
>     BOOLEAN     IsGuarded;
>     BOOLEAN     HasPoolTail;
> +  BOOLEAN     PageAsPool;
>   
>     ASSERT(Buffer != NULL);
>     //
>     // Get the head & tail of the pool entry
>     //
> -  Head = CR (Buffer, POOL_HEAD, Data, POOL_HEAD_SIGNATURE);
> +  Head = BASE_CR (Buffer, POOL_HEAD, Data);
>     ASSERT(Head != NULL);
>   
> -  if (Head->Signature != POOL_HEAD_SIGNATURE) {
> +  if (Head->Signature != POOL_HEAD_SIGNATURE &&
> +      Head->Signature != POOLPAGE_HEAD_SIGNATURE) {
> +    ASSERT (Head->Signature == POOL_HEAD_SIGNATURE ||
> +            Head->Signature == POOLPAGE_HEAD_SIGNATURE);
>       return EFI_INVALID_PARAMETER;
>     }
>   
> @@ -701,6 +709,7 @@ CoreFreePoolI (
>                   IsMemoryGuarded ((EFI_PHYSICAL_ADDRESS)(UINTN)Head);
>     HasPoolTail = !(IsGuarded &&
>                     ((PcdGet8 (PcdHeapGuardPropertyMask) & BIT7) == 0));
> +  PageAsPool = (Head->Signature == POOLPAGE_HEAD_SIGNATURE);
>   
>     if (HasPoolTail) {
>       Tail = HEAD_TO_TAIL (Head);
> @@ -757,7 +766,7 @@ CoreFreePoolI (
>     //
>     // If it's not on the list, it must be pool pages
>     //
> -  if (Index >= SIZE_TO_LIST (Granularity) || IsGuarded) {
> +  if (Index >= SIZE_TO_LIST (Granularity) || IsGuarded || PageAsPool) {
>   
>       //
>       // Return the memory pages back to free memory
> diff --git a/MdeModulePkg/Core/Dxe/Misc/PropertiesTable.c b/MdeModulePkg/Core/Dxe/Misc/PropertiesTable.c
> index 05eb4f422b..f6595c90ed 100644
> --- a/MdeModulePkg/Core/Dxe/Misc/PropertiesTable.c
> +++ b/MdeModulePkg/Core/Dxe/Misc/PropertiesTable.c
> @@ -32,6 +32,7 @@ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
>   #include <Guid/PropertiesTable.h>
>   
>   #include "DxeMain.h"
> +#include "HeapGuard.h"
>   
>   #define PREVIOUS_MEMORY_DESCRIPTOR(MemoryDescriptor, Size) \
>     ((EFI_MEMORY_DESCRIPTOR *)((UINT8 *)(MemoryDescriptor) - (Size)))
> @@ -205,16 +206,13 @@ MergeMemoryMap (
>       NextMemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (MemoryMapEntry, DescriptorSize);
>   
>       do {
> -      MemoryBlockLength = (UINT64) (EfiPagesToSize (MemoryMapEntry->NumberOfPages));
> +      MergeGuardPages (NewMemoryMapEntry, NextMemoryMapEntry->PhysicalStart);
> +      MemoryBlockLength = (UINT64) (EfiPagesToSize (NewMemoryMapEntry->NumberOfPages));
>         if (((UINTN)NextMemoryMapEntry < (UINTN)MemoryMapEnd) &&
> -          (MemoryMapEntry->Type == NextMemoryMapEntry->Type) &&
> -          (MemoryMapEntry->Attribute == NextMemoryMapEntry->Attribute) &&
> -          ((MemoryMapEntry->PhysicalStart + MemoryBlockLength) == NextMemoryMapEntry->PhysicalStart)) {
> -        MemoryMapEntry->NumberOfPages += NextMemoryMapEntry->NumberOfPages;
> -        if (NewMemoryMapEntry != MemoryMapEntry) {
> -          NewMemoryMapEntry->NumberOfPages += NextMemoryMapEntry->NumberOfPages;
> -        }
> -
> +          (NewMemoryMapEntry->Type == NextMemoryMapEntry->Type) &&
> +          (NewMemoryMapEntry->Attribute == NextMemoryMapEntry->Attribute) &&
> +          ((NewMemoryMapEntry->PhysicalStart + MemoryBlockLength) == NextMemoryMapEntry->PhysicalStart)) {
> +        NewMemoryMapEntry->NumberOfPages += NextMemoryMapEntry->NumberOfPages;
>           NextMemoryMapEntry = NEXT_MEMORY_DESCRIPTOR (NextMemoryMapEntry, DescriptorSize);
>           continue;
>         } else {
>