X-Git-Url: https://git.proxmox.com/?a=blobdiff_plain;f=MdeModulePkg%2FCore%2FDxeIplPeim%2FX64%2FVirtualMemory.c;h=d7a86c0d305d16bfc37f31dab22973514880811c;hb=9db7e9fd97c30242e22d50f534c835c9c7d98169;hp=ab1e91462ea7a563fdf15bdb3bdc586421369b0f;hpb=5630cdfe9fcaf54f704be05f0311987bfcae4dc2;p=mirror_edk2.git
diff --git a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
index ab1e91462e..d7a86c0d30 100644
--- a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
+++ b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
@@ -15,7 +15,9 @@
2) IA-32 Intel(R) Architecture Software Developer's Manual Volume 2:Instruction Set Reference, Intel
3) IA-32 Intel(R) Architecture Software Developer's Manual Volume 3:System Programmer's Guide, Intel
-Copyright (c) 2006 - 2015, Intel Corporation. All rights reserved.
+Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.
+Copyright (c) 2017, AMD Incorporated. 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
@@ -29,6 +31,81 @@ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
#include "DxeIpl.h"
#include "VirtualMemory.h"
+//
+// Global variable to keep track current available memory used as page table.
+//
+PAGE_TABLE_POOL *mPageTablePool = NULL;
+
+/**
+ Clear legacy memory located at the first 4K-page, if available.
+
+ This function traverses the whole HOB list to check if memory from 0 to 4095
+ exists and has not been allocated, and then clear it if so.
+
+ @param HobStart The start of HobList passed to DxeCore.
+
+**/
+VOID
+ClearFirst4KPage (
+ IN VOID *HobStart
+ )
+{
+ EFI_PEI_HOB_POINTERS RscHob;
+ EFI_PEI_HOB_POINTERS MemHob;
+ BOOLEAN DoClear;
+
+ RscHob.Raw = HobStart;
+ MemHob.Raw = HobStart;
+ DoClear = FALSE;
+
+ //
+ // Check if page 0 exists and free
+ //
+ while ((RscHob.Raw = GetNextHob (EFI_HOB_TYPE_RESOURCE_DESCRIPTOR,
+ RscHob.Raw)) != NULL) {
+ if (RscHob.ResourceDescriptor->ResourceType == EFI_RESOURCE_SYSTEM_MEMORY &&
+ RscHob.ResourceDescriptor->PhysicalStart == 0) {
+ DoClear = TRUE;
+ //
+ // Make sure memory at 0-4095 has not been allocated.
+ //
+ while ((MemHob.Raw = GetNextHob (EFI_HOB_TYPE_MEMORY_ALLOCATION,
+ MemHob.Raw)) != NULL) {
+ if (MemHob.MemoryAllocation->AllocDescriptor.MemoryBaseAddress
+ < EFI_PAGE_SIZE) {
+ DoClear = FALSE;
+ break;
+ }
+ MemHob.Raw = GET_NEXT_HOB (MemHob);
+ }
+ break;
+ }
+ RscHob.Raw = GET_NEXT_HOB (RscHob);
+ }
+
+ if (DoClear) {
+ DEBUG ((DEBUG_INFO, "Clearing first 4K-page!\r\n"));
+ SetMem (NULL, EFI_PAGE_SIZE, 0);
+ }
+
+ return;
+}
+
+/**
+ Return configure status of NULL pointer detection feature.
+
+ @return TRUE NULL pointer detection feature is enabled
+ @return FALSE NULL pointer detection feature is disabled
+
+**/
+BOOLEAN
+IsNullDetectionEnabled (
+ VOID
+ )
+{
+ return ((PcdGet8 (PcdNullPointerDetectionPropertyMask) & BIT0) != 0);
+}
+
/**
Enable Execute Disable Bit.
@@ -45,6 +122,148 @@ EnableExecuteDisableBit (
AsmWriteMsr64 (0xC0000080, MsrRegisters);
}
+/**
+ The function will check if page table entry should be splitted to smaller
+ granularity.
+
+ @param Address Physical memory address.
+ @param Size Size of the given physical memory.
+ @param StackBase Base address of stack.
+ @param StackSize Size of stack.
+
+ @retval TRUE Page table should be split.
+ @retval FALSE Page table should not be split.
+**/
+BOOLEAN
+ToSplitPageTable (
+ IN EFI_PHYSICAL_ADDRESS Address,
+ IN UINTN Size,
+ IN EFI_PHYSICAL_ADDRESS StackBase,
+ IN UINTN StackSize
+ )
+{
+ if (IsNullDetectionEnabled () && Address == 0) {
+ return TRUE;
+ }
+
+ if (PcdGetBool (PcdCpuStackGuard)) {
+ if (StackBase >= Address && StackBase < (Address + Size)) {
+ return TRUE;
+ }
+ }
+
+ if (PcdGetBool (PcdSetNxForStack)) {
+ if ((Address < StackBase + StackSize) && ((Address + Size) > StackBase)) {
+ return TRUE;
+ }
+ }
+
+ return FALSE;
+}
+/**
+ Initialize a buffer pool for page table use only.
+
+ To reduce the potential split operation on page table, the pages reserved for
+ page table should be allocated in the times of PAGE_TABLE_POOL_UNIT_PAGES and
+ at the boundary of PAGE_TABLE_POOL_ALIGNMENT. So the page pool is always
+ initialized with number of pages greater than or equal to the given PoolPages.
+
+ Once the pages in the pool are used up, this method should be called again to
+ reserve at least another PAGE_TABLE_POOL_UNIT_PAGES. But usually this won't
+ happen in practice.
+
+ @param PoolPages The least page number of the pool to be created.
+
+ @retval TRUE The pool is initialized successfully.
+ @retval FALSE The memory is out of resource.
+**/
+BOOLEAN
+InitializePageTablePool (
+ IN UINTN PoolPages
+ )
+{
+ VOID *Buffer;
+
+ //
+ // Always reserve at least PAGE_TABLE_POOL_UNIT_PAGES, including one page for
+ // header.
+ //
+ PoolPages += 1; // Add one page for header.
+ PoolPages = ((PoolPages - 1) / PAGE_TABLE_POOL_UNIT_PAGES + 1) *
+ PAGE_TABLE_POOL_UNIT_PAGES;
+ Buffer = AllocateAlignedPages (PoolPages, PAGE_TABLE_POOL_ALIGNMENT);
+ if (Buffer == NULL) {
+ DEBUG ((DEBUG_ERROR, "ERROR: Out of aligned pages\r\n"));
+ return FALSE;
+ }
+
+ //
+ // Link all pools into a list for easier track later.
+ //
+ if (mPageTablePool == NULL) {
+ mPageTablePool = Buffer;
+ mPageTablePool->NextPool = mPageTablePool;
+ } else {
+ ((PAGE_TABLE_POOL *)Buffer)->NextPool = mPageTablePool->NextPool;
+ mPageTablePool->NextPool = Buffer;
+ mPageTablePool = Buffer;
+ }
+
+ //
+ // Reserve one page for pool header.
+ //
+ mPageTablePool->FreePages = PoolPages - 1;
+ mPageTablePool->Offset = EFI_PAGES_TO_SIZE (1);
+
+ return TRUE;
+}
+
+/**
+ This API provides a way to allocate memory for page table.
+
+ This API can be called more than once to allocate memory for page tables.
+
+ Allocates the number of 4KB pages and returns a pointer to the allocated
+ buffer. The buffer returned is aligned on a 4KB boundary.
+
+ If Pages is 0, then NULL is returned.
+ If there is not enough memory remaining to satisfy the request, then NULL is
+ returned.
+
+ @param Pages The number of 4 KB pages to allocate.
+
+ @return A pointer to the allocated buffer or NULL if allocation fails.
+
+**/
+VOID *
+AllocatePageTableMemory (
+ IN UINTN Pages
+ )
+{
+ VOID *Buffer;
+
+ if (Pages == 0) {
+ return NULL;
+ }
+
+ //
+ // Renew the pool if necessary.
+ //
+ if (mPageTablePool == NULL ||
+ Pages > mPageTablePool->FreePages) {
+ if (!InitializePageTablePool (Pages)) {
+ return NULL;
+ }
+ }
+
+ Buffer = (UINT8 *)mPageTablePool + mPageTablePool->Offset;
+
+ mPageTablePool->Offset += EFI_PAGES_TO_SIZE (Pages);
+ mPageTablePool->FreePages -= Pages;
+
+ return Buffer;
+}
+
/**
Split 2M page to 4K.
@@ -65,22 +284,39 @@ Split2MPageTo4K (
EFI_PHYSICAL_ADDRESS PhysicalAddress4K;
UINTN IndexOfPageTableEntries;
PAGE_TABLE_4K_ENTRY *PageTableEntry;
+ UINT64 AddressEncMask;
+
+ //
+ // Make sure AddressEncMask is contained to smallest supported address field
+ //
+ AddressEncMask = PcdGet64 (PcdPteMemoryEncryptionAddressOrMask) & PAGING_1G_ADDRESS_MASK_64;
+
+ PageTableEntry = AllocatePageTableMemory (1);
+ ASSERT (PageTableEntry != NULL);
- PageTableEntry = AllocatePages (1);
//
// Fill in 2M page entry.
//
- *PageEntry2M = (UINT64) (UINTN) PageTableEntry | IA32_PG_P | IA32_PG_RW;
+ *PageEntry2M = (UINT64) (UINTN) PageTableEntry | AddressEncMask | IA32_PG_P | IA32_PG_RW;
PhysicalAddress4K = PhysicalAddress;
for (IndexOfPageTableEntries = 0; IndexOfPageTableEntries < 512; IndexOfPageTableEntries++, PageTableEntry++, PhysicalAddress4K += SIZE_4KB) {
//
// Fill in the Page Table entries
//
- PageTableEntry->Uint64 = (UINT64) PhysicalAddress4K;
+ PageTableEntry->Uint64 = (UINT64) PhysicalAddress4K | AddressEncMask;
PageTableEntry->Bits.ReadWrite = 1;
- PageTableEntry->Bits.Present = 1;
- if ((PhysicalAddress4K >= StackBase) && (PhysicalAddress4K < StackBase + StackSize)) {
+
+ if ((IsNullDetectionEnabled () && PhysicalAddress4K == 0) ||
+ (PcdGetBool (PcdCpuStackGuard) && PhysicalAddress4K == StackBase)) {
+ PageTableEntry->Bits.Present = 0;
+ } else {
+ PageTableEntry->Bits.Present = 1;
+ }
+
+ if (PcdGetBool (PcdSetNxForStack)
+ && (PhysicalAddress4K >= StackBase)
+ && (PhysicalAddress4K < StackBase + StackSize)) {
//
// Set Nx bit for stack.
//
@@ -109,25 +345,33 @@ Split1GPageTo2M (
EFI_PHYSICAL_ADDRESS PhysicalAddress2M;
UINTN IndexOfPageDirectoryEntries;
PAGE_TABLE_ENTRY *PageDirectoryEntry;
+ UINT64 AddressEncMask;
+
+ //
+ // Make sure AddressEncMask is contained to smallest supported address field
+ //
+ AddressEncMask = PcdGet64 (PcdPteMemoryEncryptionAddressOrMask) & PAGING_1G_ADDRESS_MASK_64;
+
+ PageDirectoryEntry = AllocatePageTableMemory (1);
+ ASSERT (PageDirectoryEntry != NULL);
- PageDirectoryEntry = AllocatePages (1);
//
// Fill in 1G page entry.
//
- *PageEntry1G = (UINT64) (UINTN) PageDirectoryEntry | IA32_PG_P | IA32_PG_RW;
+ *PageEntry1G = (UINT64) (UINTN) PageDirectoryEntry | AddressEncMask | IA32_PG_P | IA32_PG_RW;
PhysicalAddress2M = PhysicalAddress;
for (IndexOfPageDirectoryEntries = 0; IndexOfPageDirectoryEntries < 512; IndexOfPageDirectoryEntries++, PageDirectoryEntry++, PhysicalAddress2M += SIZE_2MB) {
- if ((PhysicalAddress2M < StackBase + StackSize) && ((PhysicalAddress2M + SIZE_2MB) > StackBase)) {
+ if (ToSplitPageTable (PhysicalAddress2M, SIZE_2MB, StackBase, StackSize)) {
//
- // Need to split this 2M page that covers stack range.
+ // Need to split this 2M page that covers NULL or stack range.
//
Split2MPageTo4K (PhysicalAddress2M, (UINT64 *) PageDirectoryEntry, StackBase, StackSize);
} else {
//
// Fill in the Page Directory entries
//
- PageDirectoryEntry->Uint64 = (UINT64) PhysicalAddress2M;
+ PageDirectoryEntry->Uint64 = (UINT64) PhysicalAddress2M | AddressEncMask;
PageDirectoryEntry->Bits.ReadWrite = 1;
PageDirectoryEntry->Bits.Present = 1;
PageDirectoryEntry->Bits.MustBe1 = 1;
@@ -135,6 +379,186 @@ Split1GPageTo2M (
}
}
+/**
+ Set one page of page table pool memory to be read-only.
+
+ @param[in] PageTableBase Base address of page table (CR3).
+ @param[in] Address Start address of a page to be set as read-only.
+ @param[in] Level4Paging Level 4 paging flag.
+
+**/
+VOID
+SetPageTablePoolReadOnly (
+ IN UINTN PageTableBase,
+ IN EFI_PHYSICAL_ADDRESS Address,
+ IN BOOLEAN Level4Paging
+ )
+{
+ UINTN Index;
+ UINTN EntryIndex;
+ UINT64 AddressEncMask;
+ EFI_PHYSICAL_ADDRESS PhysicalAddress;
+ UINT64 *PageTable;
+ UINT64 *NewPageTable;
+ UINT64 PageAttr;
+ UINT64 LevelSize[5];
+ UINT64 LevelMask[5];
+ UINTN LevelShift[5];
+ UINTN Level;
+ UINT64 PoolUnitSize;
+
+ ASSERT (PageTableBase != 0);
+
+ //
+ // Since the page table is always from page table pool, which is always
+ // located at the boundary of PcdPageTablePoolAlignment, we just need to
+ // set the whole pool unit to be read-only.
+ //
+ Address = Address & PAGE_TABLE_POOL_ALIGN_MASK;
+
+ LevelShift[1] = PAGING_L1_ADDRESS_SHIFT;
+ LevelShift[2] = PAGING_L2_ADDRESS_SHIFT;
+ LevelShift[3] = PAGING_L3_ADDRESS_SHIFT;
+ LevelShift[4] = PAGING_L4_ADDRESS_SHIFT;
+
+ LevelMask[1] = PAGING_4K_ADDRESS_MASK_64;
+ LevelMask[2] = PAGING_2M_ADDRESS_MASK_64;
+ LevelMask[3] = PAGING_1G_ADDRESS_MASK_64;
+ LevelMask[4] = PAGING_1G_ADDRESS_MASK_64;
+
+ LevelSize[1] = SIZE_4KB;
+ LevelSize[2] = SIZE_2MB;
+ LevelSize[3] = SIZE_1GB;
+ LevelSize[4] = SIZE_512GB;
+
+ AddressEncMask = PcdGet64 (PcdPteMemoryEncryptionAddressOrMask) &
+ PAGING_1G_ADDRESS_MASK_64;
+ PageTable = (UINT64 *)(UINTN)PageTableBase;
+ PoolUnitSize = PAGE_TABLE_POOL_UNIT_SIZE;
+
+ for (Level = (Level4Paging) ? 4 : 3; Level > 0; --Level) {
+ Index = ((UINTN)RShiftU64 (Address, LevelShift[Level]));
+ Index &= PAGING_PAE_INDEX_MASK;
+
+ PageAttr = PageTable[Index];
+ if ((PageAttr & IA32_PG_PS) == 0) {
+ //
+ // Go to next level of table.
+ //
+ PageTable = (UINT64 *)(UINTN)(PageAttr & ~AddressEncMask &
+ PAGING_4K_ADDRESS_MASK_64);
+ continue;
+ }
+
+ if (PoolUnitSize >= LevelSize[Level]) {
+ //
+ // Clear R/W bit if current page granularity is not larger than pool unit
+ // size.
+ //
+ if ((PageAttr & IA32_PG_RW) != 0) {
+ while (PoolUnitSize > 0) {
+ //
+ // PAGE_TABLE_POOL_UNIT_SIZE and PAGE_TABLE_POOL_ALIGNMENT are fit in
+ // one page (2MB). Then we don't need to update attributes for pages
+ // crossing page directory. ASSERT below is for that purpose.
+ //
+ ASSERT (Index < EFI_PAGE_SIZE/sizeof (UINT64));
+
+ PageTable[Index] &= ~(UINT64)IA32_PG_RW;
+ PoolUnitSize -= LevelSize[Level];
+
+ ++Index;
+ }
+ }
+
+ break;
+
+ } else {
+ //
+ // The smaller granularity of page must be needed.
+ //
+ ASSERT (Level > 1);
+
+ NewPageTable = AllocatePageTableMemory (1);
+ ASSERT (NewPageTable != NULL);
+
+ PhysicalAddress = PageAttr & LevelMask[Level];
+ for (EntryIndex = 0;
+ EntryIndex < EFI_PAGE_SIZE/sizeof (UINT64);
+ ++EntryIndex) {
+ NewPageTable[EntryIndex] = PhysicalAddress | AddressEncMask |
+ IA32_PG_P | IA32_PG_RW;
+ if (Level > 2) {
+ NewPageTable[EntryIndex] |= IA32_PG_PS;
+ }
+ PhysicalAddress += LevelSize[Level - 1];
+ }
+
+ PageTable[Index] = (UINT64)(UINTN)NewPageTable | AddressEncMask |
+ IA32_PG_P | IA32_PG_RW;
+ PageTable = NewPageTable;
+ }
+ }
+}
+
+/**
+ Prevent the memory pages used for page table from been overwritten.
+
+ @param[in] PageTableBase Base address of page table (CR3).
+ @param[in] Level4Paging Level 4 paging flag.
+
+**/
+VOID
+EnablePageTableProtection (
+ IN UINTN PageTableBase,
+ IN BOOLEAN Level4Paging
+ )
+{
+ PAGE_TABLE_POOL *HeadPool;
+ PAGE_TABLE_POOL *Pool;
+ UINT64 PoolSize;
+ EFI_PHYSICAL_ADDRESS Address;
+
+ if (mPageTablePool == NULL) {
+ return;
+ }
+
+ //
+ // Disable write protection, because we need to mark page table to be write
+ // protected.
+ //
+ AsmWriteCr0 (AsmReadCr0() & ~CR0_WP);
+
+ //
+ // SetPageTablePoolReadOnly might update mPageTablePool. It's safer to
+ // remember original one in advance.
+ //
+ HeadPool = mPageTablePool;
+ Pool = HeadPool;
+ do {
+ Address = (EFI_PHYSICAL_ADDRESS)(UINTN)Pool;
+ PoolSize = Pool->Offset + EFI_PAGES_TO_SIZE (Pool->FreePages);
+
+ //
+ // The size of one pool must be multiple of PAGE_TABLE_POOL_UNIT_SIZE, which
+ // is one of page size of the processor (2MB by default). Let's apply the
+ // protection to them one by one.
+ //
+ while (PoolSize > 0) {
+ SetPageTablePoolReadOnly(PageTableBase, Address, Level4Paging);
+ Address += PAGE_TABLE_POOL_UNIT_SIZE;
+ PoolSize -= PAGE_TABLE_POOL_UNIT_SIZE;
+ }
+
+ Pool = Pool->NextPool;
+ } while (Pool != HeadPool);
+
+ //
+ // Enable write protection, after page table attribute updated.
+ //
+ AsmWriteCr0 (AsmReadCr0() | CR0_WP);
+}
+
/**
Allocates and fills in the Page Directory and Page Table Entries to
establish a 1:1 Virtual to Physical mapping.
@@ -169,6 +593,12 @@ CreateIdentityMappingPageTables (
VOID *Hob;
BOOLEAN Page1GSupport;
PAGE_TABLE_1G_ENTRY *PageDirectory1GEntry;
+ UINT64 AddressEncMask;
+
+ //
+ // Make sure AddressEncMask is contained to smallest supported address field
+ //
+ AddressEncMask = PcdGet64 (PcdPteMemoryEncryptionAddressOrMask) & PAGING_1G_ADDRESS_MASK_64;
Page1GSupport = FALSE;
if (PcdGetBool(PcdUse1GPageTable)) {
@@ -224,7 +654,7 @@ CreateIdentityMappingPageTables (
} else {
TotalPagesNum = NumberOfPml4EntriesNeeded + 1;
}
- BigPageAddress = (UINTN) AllocatePages (TotalPagesNum);
+ BigPageAddress = (UINTN) AllocatePageTableMemory (TotalPagesNum);
ASSERT (BigPageAddress != 0);
//
@@ -246,7 +676,7 @@ CreateIdentityMappingPageTables (
//
// Make a PML4 Entry
//
- PageMapLevel4Entry->Uint64 = (UINT64)(UINTN)PageDirectoryPointerEntry;
+ PageMapLevel4Entry->Uint64 = (UINT64)(UINTN)PageDirectoryPointerEntry | AddressEncMask;
PageMapLevel4Entry->Bits.ReadWrite = 1;
PageMapLevel4Entry->Bits.Present = 1;
@@ -254,13 +684,13 @@ CreateIdentityMappingPageTables (
PageDirectory1GEntry = (VOID *) PageDirectoryPointerEntry;
for (IndexOfPageDirectoryEntries = 0; IndexOfPageDirectoryEntries < 512; IndexOfPageDirectoryEntries++, PageDirectory1GEntry++, PageAddress += SIZE_1GB) {
- if (PcdGetBool (PcdSetNxForStack) && (PageAddress < StackBase + StackSize) && ((PageAddress + SIZE_1GB) > StackBase)) {
+ if (ToSplitPageTable (PageAddress, SIZE_1GB, StackBase, StackSize)) {
Split1GPageTo2M (PageAddress, (UINT64 *) PageDirectory1GEntry, StackBase, StackSize);
} else {
//
// Fill in the Page Directory entries
//
- PageDirectory1GEntry->Uint64 = (UINT64)PageAddress;
+ PageDirectory1GEntry->Uint64 = (UINT64)PageAddress | AddressEncMask;
PageDirectory1GEntry->Bits.ReadWrite = 1;
PageDirectory1GEntry->Bits.Present = 1;
PageDirectory1GEntry->Bits.MustBe1 = 1;
@@ -278,21 +708,21 @@ CreateIdentityMappingPageTables (
//
// Fill in a Page Directory Pointer Entries
//
- PageDirectoryPointerEntry->Uint64 = (UINT64)(UINTN)PageDirectoryEntry;
+ PageDirectoryPointerEntry->Uint64 = (UINT64)(UINTN)PageDirectoryEntry | AddressEncMask;
PageDirectoryPointerEntry->Bits.ReadWrite = 1;
PageDirectoryPointerEntry->Bits.Present = 1;
for (IndexOfPageDirectoryEntries = 0; IndexOfPageDirectoryEntries < 512; IndexOfPageDirectoryEntries++, PageDirectoryEntry++, PageAddress += SIZE_2MB) {
- if (PcdGetBool (PcdSetNxForStack) && (PageAddress < StackBase + StackSize) && ((PageAddress + SIZE_2MB) > StackBase)) {
+ if (ToSplitPageTable (PageAddress, SIZE_2MB, StackBase, StackSize)) {
//
- // Need to split this 2M page that covers stack range.
+ // Need to split this 2M page that covers NULL or stack range.
//
Split2MPageTo4K (PageAddress, (UINT64 *) PageDirectoryEntry, StackBase, StackSize);
} else {
//
// Fill in the Page Directory entries
//
- PageDirectoryEntry->Uint64 = (UINT64)PageAddress;
+ PageDirectoryEntry->Uint64 = (UINT64)PageAddress | AddressEncMask;
PageDirectoryEntry->Bits.ReadWrite = 1;
PageDirectoryEntry->Bits.Present = 1;
PageDirectoryEntry->Bits.MustBe1 = 1;
@@ -319,6 +749,12 @@ CreateIdentityMappingPageTables (
);
}
+ //
+ // Protect the page table by marking the memory used for page table to be
+ // read-only.
+ //
+ EnablePageTableProtection ((UINTN)PageMap, TRUE);
+
if (PcdGetBool (PcdSetNxForStack)) {
EnableExecuteDisableBit ();
}