[PATCH v3 0/2] Enable page table write protection

[PATCH v3 0/2] Enable page table write protection

[Jian J Wang]

> v3 changes:
>  a. According to code review comments, remove the public definitions of
>     page table pool. Now the DxeIpl and CpuDxe will have their own page
>     table pool but in the same mechanism. Related PCDs, GUDI and headers
>     are also removed.
>  b. Apply protection to all page tables, including new ones added in
>     CpuDxe driver.
>  c. Code/comments cleanup.

> v2 changes:
>  a. Enable protection on any newly added page table after DxeIpl.
>  b. Introduce page table pool concept to make page table allocation
>     and protection easier and error free.

Write Protect feature (CR0.WP) is always enabled in driver UefiCpuPkg/CpuDxe.
But the memory pages used for page table are not set as read-only in the driver
DxeIplPeim, after the paging is setup. This might jeopardize the page table
integrity if there's buffer overflow occured in other part of system.

This patch series will change this situation by clearing R/W bit in page attribute
of the pages used as page table.

Validation works include booting Windows (10/server 2016) and Linux (Fedora/Ubuntu)
on OVMF and Intel real platform.

Jian J Wang (2):
  MdeModulePkg/DxeIpl: Mark page table as read-only
  UefiCpuPkg/CpuDxe: Enable protection for newly added page table

 MdeModulePkg/Core/DxeIplPeim/DxeIpl.h            |  34 +++
 MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c  |   8 +-
 MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c | 301 ++++++++++++++++++++++-
 MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h |  26 ++
 UefiCpuPkg/CpuDxe/CpuDxe.c                       |  17 +-
 UefiCpuPkg/CpuDxe/CpuDxe.h                       |   2 +
 UefiCpuPkg/CpuDxe/CpuPageTable.c                 | 226 ++++++++++++++++-
 UefiCpuPkg/CpuDxe/CpuPageTable.h                 |  34 +++
 8 files changed, 635 insertions(+), 13 deletions(-)

-- 
2.15.1.windows.2

[PATCH v3 1/2] MdeModulePkg/DxeIpl: Mark page table as read-only

[Jian J Wang]

> v3:
>    Remove the public definition of PAGE_TABLE_POOL_HEADER but keep similar
>    concept locally. CpuDxe has its own page table pool.

> v2:
>    Introduce page table pool to ease the page table memory allocation and
>    protection, which replaces the direct calling of AllocatePages().

This patch will set the memory pages used for page table as read-only
memory after the paging is setup. CR0.WP must set to let it take into
effect.

A simple page table memory management mechanism, page table pool concept,
is introduced to simplify the page table memory allocation and protection.
It will also help to reduce the potential recursive "split" action during
updating memory paging attributes.

The basic idea is to allocate a bunch of continuous pages of memory in
advance as one or more page table pools, and all future page tables
consumption will happen in those pool instead of system memory. If the page
pool is reserved at the boundary of 2MB page and with same size of 2MB page,
there's no page granularity "split" operation will be needed, because the
memory of new page tables (if needed) will be usually in the same page as
target page table you're working on.

And since we have centralized page tables (a few 2MB pages), it's easier
to protect them by changing their attributes to be read-only once and for
all. There's no need to apply the protection for new page tables any more
as long as the pool has free pages available.

Once current page table pool has been used up, one can allocate another 2MB
memory pool and just set this new 2MB memory block to be read-only instead of
setting the new page tables one page by one page.

Two new PCDs PcdPageTablePoolUnitSize and PcdPageTablePoolAlignment are used
to specify the size and alignment for page table pool. For IA32 processor
0x200000 (2MB) is the only choice for both of them to meet the requirement of
page table pool.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
---
 MdeModulePkg/Core/DxeIplPeim/DxeIpl.h            |  34 +++
 MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c  |   8 +-
 MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c | 301 ++++++++++++++++++++++-
 MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h |  26 ++
 4 files changed, 365 insertions(+), 4 deletions(-)

diff --git a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h
index f3aabdb7e0..9dc80b1508 100644
--- a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h
+++ b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h
@@ -265,4 +265,38 @@ IsNullDetectionEnabled (
   VOID
   );
 
+/**
+  Prevent the memory pages used for page table from been overwritten.
+
+  @param[in] PageTableBase    Base address of page table (CR3).
+
+**/
+VOID
+EnablePageTableProtection (
+  IN  UINTN     PageTableBase,
+  IN  BOOLEAN   Level4Paging
+  );
+
+/**
+  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
+  );
+
 #endif
diff --git a/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c b/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
index 5649265367..13fff28e93 100644
--- a/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
+++ b/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
@@ -99,7 +99,7 @@ Create4GPageTablesIa32Pae (
   NumberOfPdpEntriesNeeded = (UINT32) LShiftU64 (1, (PhysicalAddressBits - 30));
 
   TotalPagesNum = NumberOfPdpEntriesNeeded + 1;
-  PageAddress = (UINTN) AllocatePages (TotalPagesNum);
+  PageAddress = (UINTN) AllocatePageTableMemory (TotalPagesNum);
   ASSERT (PageAddress != 0);
 
   PageMap = (VOID *) PageAddress;
@@ -149,6 +149,12 @@ Create4GPageTablesIa32Pae (
       );
   }
 
+  //
+  // Protect the page table by marking the memory used for page table to be
+  // read-only.
+  //
+  EnablePageTableProtection ((UINTN)PageMap, FALSE);
+
   return (UINTN) PageMap;
 }
 
diff --git a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
index 29b6205e88..4ef3521224 100644
--- a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
+++ b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
@@ -31,6 +31,11 @@ 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.
 
@@ -117,6 +122,112 @@ EnableExecuteDisableBit (
   AsmWriteMsr64 (0xC0000080, MsrRegisters);
 }
 
+/**
+  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 512 (= SIZE_2MB) and at the
+  boundary of SIZE_2MB. 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 512 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 (512).
+  //
+  if (PoolPages <= PAGE_TABLE_POOL_UNIT_PAGES) {
+    PoolPages = PAGE_TABLE_POOL_UNIT_PAGES;
+  } else {
+    PoolPages = ((PoolPages + PAGE_TABLE_POOL_UNIT_PAGES) %
+                 PAGE_TABLE_POOL_UNIT_PAGES) * 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.
 
@@ -144,7 +255,7 @@ Split2MPageTo4K (
   //
   AddressEncMask = PcdGet64 (PcdPteMemoryEncryptionAddressOrMask) & PAGING_1G_ADDRESS_MASK_64;
 
-  PageTableEntry = AllocatePages (1);
+  PageTableEntry = AllocatePageTableMemory (1);
   ASSERT (PageTableEntry != NULL);
 
   //
@@ -204,7 +315,7 @@ Split1GPageTo2M (
   //
   AddressEncMask = PcdGet64 (PcdPteMemoryEncryptionAddressOrMask) & PAGING_1G_ADDRESS_MASK_64;
 
-  PageDirectoryEntry = AllocatePages (1);
+  PageDirectoryEntry = AllocatePageTableMemory (1);
   ASSERT (PageDirectoryEntry != NULL);
 
   //
@@ -234,6 +345,184 @@ 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.
+      //
+      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 > 1) {
+          NewPageTable[EntryIndex] |= IA32_PG_PS;
+        }
+        PhysicalAddress += LevelSize[Level];
+      }
+
+      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.
@@ -329,7 +618,7 @@ CreateIdentityMappingPageTables (
   } else {
     TotalPagesNum = NumberOfPml4EntriesNeeded + 1;
   }
-  BigPageAddress = (UINTN) AllocatePages (TotalPagesNum);
+  BigPageAddress = (UINTN) AllocatePageTableMemory (TotalPagesNum);
   ASSERT (BigPageAddress != 0);
 
   //
@@ -430,6 +719,12 @@ 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 ();
   }
diff --git a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h
index 7c9bb49e3e..9f14ac6007 100644
--- a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h
+++ b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h
@@ -148,11 +148,37 @@ typedef union {
 
 #pragma pack()
 
+#define CR0_WP                      BIT16
+
 #define IA32_PG_P                   BIT0
 #define IA32_PG_RW                  BIT1
+#define IA32_PG_PS                  BIT7
+
+#define PAGING_PAE_INDEX_MASK       0x1FF
 
+#define PAGING_4K_ADDRESS_MASK_64   0x000FFFFFFFFFF000ull
+#define PAGING_2M_ADDRESS_MASK_64   0x000FFFFFFFE00000ull
 #define PAGING_1G_ADDRESS_MASK_64   0x000FFFFFC0000000ull
 
+#define PAGING_L1_ADDRESS_SHIFT     12
+#define PAGING_L2_ADDRESS_SHIFT     21
+#define PAGING_L3_ADDRESS_SHIFT     30
+#define PAGING_L4_ADDRESS_SHIFT     39
+
+#define PAGING_PML4E_NUMBER         4
+
+#define PAGE_TABLE_POOL_ALIGNMENT   BASE_2MB
+#define PAGE_TABLE_POOL_UNIT_SIZE   SIZE_2MB
+#define PAGE_TABLE_POOL_UNIT_PAGES  EFI_SIZE_TO_PAGES (SIZE_2MB)
+#define PAGE_TABLE_POOL_ALIGN_MASK  \
+  (~(EFI_PHYSICAL_ADDRESS)(PAGE_TABLE_POOL_ALIGNMENT - 1))
+
+typedef struct {
+  VOID            *NextPool;
+  UINTN           Offset;
+  UINTN           FreePages;
+} PAGE_TABLE_POOL;
+
 /**
   Enable Execute Disable Bit.
 
-- 
2.15.1.windows.2

Re: [PATCH v3 1/2] MdeModulePkg/DxeIpl: Mark page table as read-only

[Ni, Ruiyu]

On 12/5/2017 4:16 PM, Jian J Wang wrote:
>> v3:
>>     Remove the public definition of PAGE_TABLE_POOL_HEADER but keep similar
>>     concept locally. CpuDxe has its own page table pool.
> 
>> v2:
>>     Introduce page table pool to ease the page table memory allocation and
>>     protection, which replaces the direct calling of AllocatePages().
> 
> This patch will set the memory pages used for page table as read-only
> memory after the paging is setup. CR0.WP must set to let it take into
> effect.
> 
> A simple page table memory management mechanism, page table pool concept,
> is introduced to simplify the page table memory allocation and protection.
> It will also help to reduce the potential recursive "split" action during
> updating memory paging attributes.
> 
> The basic idea is to allocate a bunch of continuous pages of memory in
> advance as one or more page table pools, and all future page tables
> consumption will happen in those pool instead of system memory. If the page
> pool is reserved at the boundary of 2MB page and with same size of 2MB page,
> there's no page granularity "split" operation will be needed, because the
> memory of new page tables (if needed) will be usually in the same page as
> target page table you're working on.
> 
> And since we have centralized page tables (a few 2MB pages), it's easier
> to protect them by changing their attributes to be read-only once and for
> all. There's no need to apply the protection for new page tables any more
> as long as the pool has free pages available.
> 
> Once current page table pool has been used up, one can allocate another 2MB
> memory pool and just set this new 2MB memory block to be read-only instead of
> setting the new page tables one page by one page.
> 
> Two new PCDs PcdPageTablePoolUnitSize and PcdPageTablePoolAlignment are used
> to specify the size and alignment for page table pool. For IA32 processor
> 0x200000 (2MB) is the only choice for both of them to meet the requirement of
> page table pool.
> 
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Star Zeng <star.zeng@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
> ---
>   MdeModulePkg/Core/DxeIplPeim/DxeIpl.h            |  34 +++
>   MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c  |   8 +-
>   MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c | 301 ++++++++++++++++++++++-
>   MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h |  26 ++
>   4 files changed, 365 insertions(+), 4 deletions(-)
> 
> diff --git a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h
> index f3aabdb7e0..9dc80b1508 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h
> +++ b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h
> @@ -265,4 +265,38 @@ IsNullDetectionEnabled (
>     VOID
>     );
>   
> +/**
> +  Prevent the memory pages used for page table from been overwritten.
> +
> +  @param[in] PageTableBase    Base address of page table (CR3).
> +
> +**/
> +VOID
> +EnablePageTableProtection (
> +  IN  UINTN     PageTableBase,
> +  IN  BOOLEAN   Level4Paging
> +  );
> +
> +/**
> +  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
> +  );
> +
>   #endif
> diff --git a/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c b/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> index 5649265367..13fff28e93 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> +++ b/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> @@ -99,7 +99,7 @@ Create4GPageTablesIa32Pae (
>     NumberOfPdpEntriesNeeded = (UINT32) LShiftU64 (1, (PhysicalAddressBits - 30));
>   
>     TotalPagesNum = NumberOfPdpEntriesNeeded + 1;
> -  PageAddress = (UINTN) AllocatePages (TotalPagesNum);
> +  PageAddress = (UINTN) AllocatePageTableMemory (TotalPagesNum);
>     ASSERT (PageAddress != 0);
>   
>     PageMap = (VOID *) PageAddress;
> @@ -149,6 +149,12 @@ Create4GPageTablesIa32Pae (
>         );
>     }
>   
> +  //
> +  // Protect the page table by marking the memory used for page table to be
> +  // read-only.
> +  //
> +  EnablePageTableProtection ((UINTN)PageMap, FALSE);
> +
>     return (UINTN) PageMap;
>   }
>   
> diff --git a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> index 29b6205e88..4ef3521224 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> +++ b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> @@ -31,6 +31,11 @@ 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.
>   
> @@ -117,6 +122,112 @@ EnableExecuteDisableBit (
>     AsmWriteMsr64 (0xC0000080, MsrRegisters);
>   }
>   
> +/**
> +  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 512 (= SIZE_2MB) and at the
> +  boundary of SIZE_2MB. 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 512 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 (512).
> +  //
> +  if (PoolPages <= PAGE_TABLE_POOL_UNIT_PAGES) {
> +    PoolPages = PAGE_TABLE_POOL_UNIT_PAGES;
> +  } else {
> +    PoolPages = ((PoolPages + PAGE_TABLE_POOL_UNIT_PAGES - 1) /
> +                 PAGE_TABLE_POOL_UNIT_PAGES) * PAGE_TABLE_POOL_UNIT_PAGES;

What does the above calculation mean?
If PoolPages equals to 513, new PoolPages = ((513 + 512) % 512) * 512
= 512.

Maybe the logic is trying to make PoolPages multiple of 512?
If it's an internal function, just assert when PoolPages is not multiple
of 512 should be good enough.

> +  }
> +
> +  Buffer = AllocateAlignedPages (PoolPages, PAGE_TABLE_POOL_ALIGNMENT);

PAGE_TABLE_POOL_UNIT_PAGES and PAGE_TABLE_POOL_ALIGNMENT actually do
have some relationship between. Maybe just use
EFI_SIZE_TO_PAGES (SIZE_2MB) to replace PAGE_TABLE_POOL_UNIT_PAGES and
SIZE_2MB to replace 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) {

Great to use FreePages to track the remaining free pages.
It's possible that when FreePages equals to 3, Pages
equals to 4, the 3 pages are wasted.
But I think it should be fine. Not a big waste of memory.

> +    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.
>   
> @@ -144,7 +255,7 @@ Split2MPageTo4K (
>     //
>     AddressEncMask = PcdGet64 (PcdPteMemoryEncryptionAddressOrMask) & PAGING_1G_ADDRESS_MASK_64;
>   
> -  PageTableEntry = AllocatePages (1);
> +  PageTableEntry = AllocatePageTableMemory (1);
>     ASSERT (PageTableEntry != NULL);
>   
>     //
> @@ -204,7 +315,7 @@ Split1GPageTo2M (
>     //
>     AddressEncMask = PcdGet64 (PcdPteMemoryEncryptionAddressOrMask) & PAGING_1G_ADDRESS_MASK_64;
>   
> -  PageDirectoryEntry = AllocatePages (1);
> +  PageDirectoryEntry = AllocatePageTableMemory (1);
>     ASSERT (PageDirectoryEntry != NULL);
>   
>     //
> @@ -234,6 +345,184 @@ 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.
> +      //
> +      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 > 1) {
> +          NewPageTable[EntryIndex] |= IA32_PG_PS;
> +        }
> +        PhysicalAddress += LevelSize[Level];
> +      }
> +
> +      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.
> @@ -329,7 +618,7 @@ CreateIdentityMappingPageTables (
>     } else {
>       TotalPagesNum = NumberOfPml4EntriesNeeded + 1;
>     }
> -  BigPageAddress = (UINTN) AllocatePages (TotalPagesNum);
> +  BigPageAddress = (UINTN) AllocatePageTableMemory (TotalPagesNum);
>     ASSERT (BigPageAddress != 0);
>   
>     //
> @@ -430,6 +719,12 @@ 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 ();
>     }
> diff --git a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h
> index 7c9bb49e3e..9f14ac6007 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h
> +++ b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h
> @@ -148,11 +148,37 @@ typedef union {
>   
>   #pragma pack()
>   
> +#define CR0_WP                      BIT16
> +
>   #define IA32_PG_P                   BIT0
>   #define IA32_PG_RW                  BIT1
> +#define IA32_PG_PS                  BIT7
> +
> +#define PAGING_PAE_INDEX_MASK       0x1FF
>   
> +#define PAGING_4K_ADDRESS_MASK_64   0x000FFFFFFFFFF000ull
> +#define PAGING_2M_ADDRESS_MASK_64   0x000FFFFFFFE00000ull
>   #define PAGING_1G_ADDRESS_MASK_64   0x000FFFFFC0000000ull
>   
> +#define PAGING_L1_ADDRESS_SHIFT     12
> +#define PAGING_L2_ADDRESS_SHIFT     21
> +#define PAGING_L3_ADDRESS_SHIFT     30
> +#define PAGING_L4_ADDRESS_SHIFT     39
> +
> +#define PAGING_PML4E_NUMBER         4
> +
> +#define PAGE_TABLE_POOL_ALIGNMENT   BASE_2MB
> +#define PAGE_TABLE_POOL_UNIT_SIZE   SIZE_2MB
> +#define PAGE_TABLE_POOL_UNIT_PAGES  EFI_SIZE_TO_PAGES (SIZE_2MB)
> +#define PAGE_TABLE_POOL_ALIGN_MASK  \
> +  (~(EFI_PHYSICAL_ADDRESS)(PAGE_TABLE_POOL_ALIGNMENT - 1))
> +
> +typedef struct {
> +  VOID            *NextPool;
> +  UINTN           Offset;
> +  UINTN           FreePages;
> +} PAGE_TABLE_POOL;
> +
>   /**
>     Enable Execute Disable Bit.
>   
> 


-- 
Thanks,
Ray

Re: [PATCH v3 1/2] MdeModulePkg/DxeIpl: Mark page table as read-only

[Wang, Jian J]

Hi,

> -----Original Message-----
> From: Ni, Ruiyu
> Sent: Wednesday, December 06, 2017 6:05 PM
> To: Wang, Jian J <jian.j.wang@intel.com>; edk2-devel@lists.01.org
> Cc: Yao, Jiewen <jiewen.yao@intel.com>; Dong, Eric <eric.dong@intel.com>;
> Zeng, Star <star.zeng@intel.com>
> Subject: Re: [edk2] [PATCH v3 1/2] MdeModulePkg/DxeIpl: Mark page table as
> read-only
> 
> On 12/5/2017 4:16 PM, Jian J Wang wrote:
> >> v3:
> >>     Remove the public definition of PAGE_TABLE_POOL_HEADER but keep
> similar
> >>     concept locally. CpuDxe has its own page table pool.
> >
> >> v2:
> >>     Introduce page table pool to ease the page table memory allocation and
> >>     protection, which replaces the direct calling of AllocatePages().
> >
> > This patch will set the memory pages used for page table as read-only
> > memory after the paging is setup. CR0.WP must set to let it take into
> > effect.
> >
> > A simple page table memory management mechanism, page table pool
> concept,
> > is introduced to simplify the page table memory allocation and protection.
> > It will also help to reduce the potential recursive "split" action during
> > updating memory paging attributes.
> >
> > The basic idea is to allocate a bunch of continuous pages of memory in
> > advance as one or more page table pools, and all future page tables
> > consumption will happen in those pool instead of system memory. If the page
> > pool is reserved at the boundary of 2MB page and with same size of 2MB page,
> > there's no page granularity "split" operation will be needed, because the
> > memory of new page tables (if needed) will be usually in the same page as
> > target page table you're working on.
> >
> > And since we have centralized page tables (a few 2MB pages), it's easier
> > to protect them by changing their attributes to be read-only once and for
> > all. There's no need to apply the protection for new page tables any more
> > as long as the pool has free pages available.
> >
> > Once current page table pool has been used up, one can allocate another 2MB
> > memory pool and just set this new 2MB memory block to be read-only instead
> of
> > setting the new page tables one page by one page.
> >
> > Two new PCDs PcdPageTablePoolUnitSize and PcdPageTablePoolAlignment
> are used
> > to specify the size and alignment for page table pool. For IA32 processor
> > 0x200000 (2MB) is the only choice for both of them to meet the requirement
> of
> > page table pool.
> >
> > Cc: Jiewen Yao <jiewen.yao@intel.com>
> > Cc: Star Zeng <star.zeng@intel.com>
> > Cc: Eric Dong <eric.dong@intel.com>
> > Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
> > ---
> >   MdeModulePkg/Core/DxeIplPeim/DxeIpl.h            |  34 +++
> >   MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c  |   8 +-
> >   MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c | 301
> ++++++++++++++++++++++-
> >   MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h |  26 ++
> >   4 files changed, 365 insertions(+), 4 deletions(-)
> >
> > diff --git a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h
> b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h
> > index f3aabdb7e0..9dc80b1508 100644
> > --- a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h
> > +++ b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h
> > @@ -265,4 +265,38 @@ IsNullDetectionEnabled (
> >     VOID
> >     );
> >
> > +/**
> > +  Prevent the memory pages used for page table from been overwritten.
> > +
> > +  @param[in] PageTableBase    Base address of page table (CR3).
> > +
> > +**/
> > +VOID
> > +EnablePageTableProtection (
> > +  IN  UINTN     PageTableBase,
> > +  IN  BOOLEAN   Level4Paging
> > +  );
> > +
> > +/**
> > +  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
> > +  );
> > +
> >   #endif
> > diff --git a/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> b/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> > index 5649265367..13fff28e93 100644
> > --- a/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> > +++ b/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> > @@ -99,7 +99,7 @@ Create4GPageTablesIa32Pae (
> >     NumberOfPdpEntriesNeeded = (UINT32) LShiftU64 (1, (PhysicalAddressBits -
> 30));
> >
> >     TotalPagesNum = NumberOfPdpEntriesNeeded + 1;
> > -  PageAddress = (UINTN) AllocatePages (TotalPagesNum);
> > +  PageAddress = (UINTN) AllocatePageTableMemory (TotalPagesNum);
> >     ASSERT (PageAddress != 0);
> >
> >     PageMap = (VOID *) PageAddress;
> > @@ -149,6 +149,12 @@ Create4GPageTablesIa32Pae (
> >         );
> >     }
> >
> > +  //
> > +  // Protect the page table by marking the memory used for page table to be
> > +  // read-only.
> > +  //
> > +  EnablePageTableProtection ((UINTN)PageMap, FALSE);
> > +
> >     return (UINTN) PageMap;
> >   }
> >
> > diff --git a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> > index 29b6205e88..4ef3521224 100644
> > --- a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> > +++ b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> > @@ -31,6 +31,11 @@ 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.
> >
> > @@ -117,6 +122,112 @@ EnableExecuteDisableBit (
> >     AsmWriteMsr64 (0xC0000080, MsrRegisters);
> >   }
> >
> > +/**
> > +  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 512 (= SIZE_2MB) and at the
> > +  boundary of SIZE_2MB. 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 512 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 (512).
> > +  //
> > +  if (PoolPages <= PAGE_TABLE_POOL_UNIT_PAGES) {
> > +    PoolPages = PAGE_TABLE_POOL_UNIT_PAGES;
> > +  } else {
> > +    PoolPages = ((PoolPages + PAGE_TABLE_POOL_UNIT_PAGES - 1) /
> > +                 PAGE_TABLE_POOL_UNIT_PAGES) *
> PAGE_TABLE_POOL_UNIT_PAGES;
> 
> What does the above calculation mean?
> If PoolPages equals to 513, new PoolPages = ((513 + 512) % 512) * 512
> = 512.
> 
> Maybe the logic is trying to make PoolPages multiple of 512?
> If it's an internal function, just assert when PoolPages is not multiple
> of 512 should be good enough.
> 

I want to always get multiple times of 512 pages which is large than requested pages.
Because there's a chance (most likely at the first time of requesting page tables)
that more than 512 pages of page table will be requested, and we don't know for sure
how many page tables are required at each boot on different platform, I think it is safer
to let the InitiliazePageTablePool to calculate a right number pages to reserve in pool.

In addition, I think it'd be better not to expose the pool details to its users, who just need
to request desired number of pages for page table.

And you're right there's error in the calculation. Thanks for catching it.

> > +  }
> > +
> > +  Buffer = AllocateAlignedPages (PoolPages,
> PAGE_TABLE_POOL_ALIGNMENT);
> 
> PAGE_TABLE_POOL_UNIT_PAGES and PAGE_TABLE_POOL_ALIGNMENT actually
> do
> have some relationship between. Maybe just use
> EFI_SIZE_TO_PAGES (SIZE_2MB) to replace PAGE_TABLE_POOL_UNIT_PAGES
> and
> SIZE_2MB to replace PAGE_TABLE_POOL_ALIGNMENT?
> 

For IA processor, 2MB is actually our only choice for the pool unit size and alignment.
So I don't have strong opinion for this. Anyway works for me.

> > +  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) {
> 
> Great to use FreePages to track the remaining free pages.
> It's possible that when FreePages equals to 3, Pages
> equals to 4, the 3 pages are wasted.
> But I think it should be fine. Not a big waste of memory.
> 

Yes and No. Theoretically, pages will be wasted in your case. That's for sure.
But in actual current code, there's no chance to request more than 1 page
each time after the first page table memory request. So your case won't
happen.

Anyway, I think we don't need a complicated memory management here.
I agree that a little bit memory waste is acceptable.

> > +    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.
> >
> > @@ -144,7 +255,7 @@ Split2MPageTo4K (
> >     //
> >     AddressEncMask = PcdGet64 (PcdPteMemoryEncryptionAddressOrMask) &
> PAGING_1G_ADDRESS_MASK_64;
> >
> > -  PageTableEntry = AllocatePages (1);
> > +  PageTableEntry = AllocatePageTableMemory (1);
> >     ASSERT (PageTableEntry != NULL);
> >
> >     //
> > @@ -204,7 +315,7 @@ Split1GPageTo2M (
> >     //
> >     AddressEncMask = PcdGet64 (PcdPteMemoryEncryptionAddressOrMask) &
> PAGING_1G_ADDRESS_MASK_64;
> >
> > -  PageDirectoryEntry = AllocatePages (1);
> > +  PageDirectoryEntry = AllocatePageTableMemory (1);
> >     ASSERT (PageDirectoryEntry != NULL);
> >
> >     //
> > @@ -234,6 +345,184 @@ 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.
> > +      //
> > +      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 > 1) {
> > +          NewPageTable[EntryIndex] |= IA32_PG_PS;
> > +        }
> > +        PhysicalAddress += LevelSize[Level];
> > +      }
> > +
> > +      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.
> > @@ -329,7 +618,7 @@ CreateIdentityMappingPageTables (
> >     } else {
> >       TotalPagesNum = NumberOfPml4EntriesNeeded + 1;
> >     }
> > -  BigPageAddress = (UINTN) AllocatePages (TotalPagesNum);
> > +  BigPageAddress = (UINTN) AllocatePageTableMemory (TotalPagesNum);
> >     ASSERT (BigPageAddress != 0);
> >
> >     //
> > @@ -430,6 +719,12 @@ 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 ();
> >     }
> > diff --git a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h
> b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h
> > index 7c9bb49e3e..9f14ac6007 100644
> > --- a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h
> > +++ b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h
> > @@ -148,11 +148,37 @@ typedef union {
> >
> >   #pragma pack()
> >
> > +#define CR0_WP                      BIT16
> > +
> >   #define IA32_PG_P                   BIT0
> >   #define IA32_PG_RW                  BIT1
> > +#define IA32_PG_PS                  BIT7
> > +
> > +#define PAGING_PAE_INDEX_MASK       0x1FF
> >
> > +#define PAGING_4K_ADDRESS_MASK_64   0x000FFFFFFFFFF000ull
> > +#define PAGING_2M_ADDRESS_MASK_64   0x000FFFFFFFE00000ull
> >   #define PAGING_1G_ADDRESS_MASK_64   0x000FFFFFC0000000ull
> >
> > +#define PAGING_L1_ADDRESS_SHIFT     12
> > +#define PAGING_L2_ADDRESS_SHIFT     21
> > +#define PAGING_L3_ADDRESS_SHIFT     30
> > +#define PAGING_L4_ADDRESS_SHIFT     39
> > +
> > +#define PAGING_PML4E_NUMBER         4
> > +
> > +#define PAGE_TABLE_POOL_ALIGNMENT   BASE_2MB
> > +#define PAGE_TABLE_POOL_UNIT_SIZE   SIZE_2MB
> > +#define PAGE_TABLE_POOL_UNIT_PAGES  EFI_SIZE_TO_PAGES (SIZE_2MB)
> > +#define PAGE_TABLE_POOL_ALIGN_MASK  \
> > +  (~(EFI_PHYSICAL_ADDRESS)(PAGE_TABLE_POOL_ALIGNMENT - 1))
> > +
> > +typedef struct {
> > +  VOID            *NextPool;
> > +  UINTN           Offset;
> > +  UINTN           FreePages;
> > +} PAGE_TABLE_POOL;
> > +
> >   /**
> >     Enable Execute Disable Bit.
> >
> >
> 
> 
> --
> Thanks,
> Ray

[PATCH v3 2/2] UefiCpuPkg/CpuDxe: Enable protection for newly added page table

[Jian J Wang]

> v3:
>    Create driver's own page table pool instead of inheriting from DxeIpl.

> v2:
>    Use the page table pool to allocate new page tables and save code
>    to enable protection for them separately.

One of the functionalities of CpuDxe is to update memory paging attributes.
If page table protection is applied, it must be disabled temporarily before
any attributes update and enabled again afterwards.

This patch makes use of the same way as DxeIpl to allocate page table memory
from reserved memory pool, which helps to reduce potential "split" operation
and recursive calling of SetMemorySpaceAttributes().

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
---
 UefiCpuPkg/CpuDxe/CpuDxe.c       |  17 ++-
 UefiCpuPkg/CpuDxe/CpuDxe.h       |   2 +
 UefiCpuPkg/CpuDxe/CpuPageTable.c | 226 +++++++++++++++++++++++++++++++++++++--
 UefiCpuPkg/CpuDxe/CpuPageTable.h |  34 ++++++
 4 files changed, 270 insertions(+), 9 deletions(-)

diff --git a/UefiCpuPkg/CpuDxe/CpuDxe.c b/UefiCpuPkg/CpuDxe/CpuDxe.c
index 8ddebabd02..6ae2dcd1c7 100644
--- a/UefiCpuPkg/CpuDxe/CpuDxe.c
+++ b/UefiCpuPkg/CpuDxe/CpuDxe.c
@@ -25,6 +25,7 @@
 BOOLEAN                   InterruptState = FALSE;
 EFI_HANDLE                mCpuHandle = NULL;
 BOOLEAN                   mIsFlushingGCD;
+BOOLEAN                   mIsAllocatingPageTable = FALSE;
 UINT64                    mValidMtrrAddressMask;
 UINT64                    mValidMtrrBitsMask;
 UINT64                    mTimerPeriod = 0;
@@ -407,6 +408,20 @@ CpuSetMemoryAttributes (
     return EFI_SUCCESS;
   }
 
+  //
+  // During memory attributes updating, new pages may be allocated to setup
+  // smaller granularity of page table. Page allocation action might then cause
+  // another calling of CpuSetMemoryAttributes() recursively, due to memory
+  // protection policy configured (such as PcdDxeNxMemoryProtectionPolicy).
+  // Since this driver will always protect memory used as page table by itself,
+  // there's no need to apply protection policy requested from memory service.
+  // So it's safe to just return EFI_SUCCESS if this time of calling is caused
+  // by page table memory allocation.
+  //
+  if (mIsAllocatingPageTable) {
+    DEBUG((DEBUG_VERBOSE, "  Allocating page table memory\n"));
+    return EFI_SUCCESS;
+  }
 
   CacheAttributes = Attributes & CACHE_ATTRIBUTE_MASK;
   MemoryAttributes = Attributes & MEMORY_ATTRIBUTE_MASK;
@@ -487,7 +502,7 @@ CpuSetMemoryAttributes (
   //
   // Set memory attribute by page table
   //
-  return AssignMemoryPageAttributes (NULL, BaseAddress, Length, MemoryAttributes, AllocatePages);
+  return AssignMemoryPageAttributes (NULL, BaseAddress, Length, MemoryAttributes, NULL);
 }
 
 /**
diff --git a/UefiCpuPkg/CpuDxe/CpuDxe.h b/UefiCpuPkg/CpuDxe/CpuDxe.h
index 9c0d22359d..540f5f2dbf 100644
--- a/UefiCpuPkg/CpuDxe/CpuDxe.h
+++ b/UefiCpuPkg/CpuDxe/CpuDxe.h
@@ -273,5 +273,7 @@ RefreshGcdMemoryAttributesFromPaging (
   VOID
   );
 
+extern BOOLEAN mIsAllocatingPageTable;
+
 #endif
 
diff --git a/UefiCpuPkg/CpuDxe/CpuPageTable.c b/UefiCpuPkg/CpuDxe/CpuPageTable.c
index 9658ed74c5..57ec76378a 100644
--- a/UefiCpuPkg/CpuDxe/CpuPageTable.c
+++ b/UefiCpuPkg/CpuDxe/CpuPageTable.c
@@ -87,6 +87,8 @@ PAGE_ATTRIBUTE_TABLE mPageAttributeTable[] = {
   {Page1G,  SIZE_1GB, PAGING_1G_ADDRESS_MASK_64},
 };
 
+PAGE_TABLE_POOL   *mPageTablePool = NULL;
+
 /**
   Enable write protection function for AP.
 
@@ -172,10 +174,6 @@ GetCurrentPagingContext (
   }
   if ((AsmReadCr0 () & BIT31) != 0) {
     PagingContext->ContextData.X64.PageTableBase = (AsmReadCr3 () & PAGING_4K_ADDRESS_MASK_64);
-    if ((AsmReadCr0 () & BIT16) == 0) {
-      AsmWriteCr0 (AsmReadCr0 () | BIT16);
-      SyncMemoryPageAttributesAp (SyncCpuEnableWriteProtection);
-    }
   } else {
     PagingContext->ContextData.X64.PageTableBase = 0;
   }
@@ -561,6 +559,59 @@ SplitPage (
   }
 }
 
+/**
+ Check the WP status in CR0 register. This bit is used to lock or unlock write
+ access to pages marked as read-only.
+
+  @retval TRUE    Write protection is enabled.
+  @retval FALSE   Write protection is disabled.
+**/
+BOOLEAN
+IsReadOnlyPageWriteProtected (
+  VOID
+  )
+{
+  return ((AsmReadCr0 () & BIT16) != 0);
+}
+
+/**
+  Disable write protection function for AP.
+
+  @param[in,out] Buffer  The pointer to private data buffer.
+**/
+VOID
+EFIAPI
+SyncCpuDisableWriteProtection (
+  IN OUT VOID *Buffer
+  )
+{
+  AsmWriteCr0 (AsmReadCr0() & ~BIT16);
+}
+
+/**
+ Disable Write Protect on pages marked as read-only.
+**/
+VOID
+DisableReadOnlyPageWriteProtect (
+  VOID
+  )
+{
+  AsmWriteCr0 (AsmReadCr0() & ~BIT16);
+  SyncMemoryPageAttributesAp (SyncCpuDisableWriteProtection);
+}
+
+/**
+ Enable Write Protect on pages marked as read-only.
+**/
+VOID
+EnableReadOnlyPageWriteProtect (
+  VOID
+  )
+{
+  AsmWriteCr0 (AsmReadCr0() | BIT16);
+  SyncMemoryPageAttributesAp (SyncCpuEnableWriteProtection);
+}
+
 /**
   This function modifies the page attributes for the memory region specified by BaseAddress and
   Length from their current attributes to the attributes specified by Attributes.
@@ -609,6 +660,7 @@ ConvertMemoryPageAttributes (
   PAGE_ATTRIBUTE                    SplitAttribute;
   RETURN_STATUS                     Status;
   BOOLEAN                           IsEntryModified;
+  BOOLEAN                           IsWpEnabled;
 
   if ((BaseAddress & (SIZE_4KB - 1)) != 0) {
     DEBUG ((DEBUG_ERROR, "BaseAddress(0x%lx) is not aligned!\n", BaseAddress));
@@ -665,14 +717,27 @@ ConvertMemoryPageAttributes (
   if (IsModified != NULL) {
     *IsModified = FALSE;
   }
+  if (AllocatePagesFunc == NULL) {
+    AllocatePagesFunc = AllocatePageTableMemory;
+  }
+
+  //
+  // Make sure that the page table is changeable.
+  //
+  IsWpEnabled = IsReadOnlyPageWriteProtected ();
+  if (IsWpEnabled) {
+    DisableReadOnlyPageWriteProtect ();
+  }
 
   //
   // Below logic is to check 2M/4K page to make sure we donot waist memory.
   //
+  Status = EFI_SUCCESS;
   while (Length != 0) {
     PageEntry = GetPageTableEntry (&CurrentPagingContext, BaseAddress, &PageAttribute);
     if (PageEntry == NULL) {
-      return RETURN_UNSUPPORTED;
+      Status = RETURN_UNSUPPORTED;
+      goto Done;
     }
     PageEntryLength = PageAttributeToLength (PageAttribute);
     SplitAttribute = NeedSplitPage (BaseAddress, Length, PageEntry, PageAttribute);
@@ -690,11 +755,13 @@ ConvertMemoryPageAttributes (
       Length -= PageEntryLength;
     } else {
       if (AllocatePagesFunc == NULL) {
-        return RETURN_UNSUPPORTED;
+        Status = RETURN_UNSUPPORTED;
+        goto Done;
       }
       Status = SplitPage (PageEntry, PageAttribute, SplitAttribute, AllocatePagesFunc);
       if (RETURN_ERROR (Status)) {
-        return RETURN_UNSUPPORTED;
+        Status = RETURN_UNSUPPORTED;
+        goto Done;
       }
       if (IsSplitted != NULL) {
         *IsSplitted = TRUE;
@@ -709,7 +776,14 @@ ConvertMemoryPageAttributes (
     }
   }
 
-  return RETURN_SUCCESS;
+Done:
+  //
+  // Restore page table write protection, if any.
+  //
+  if (IsWpEnabled) {
+    EnableReadOnlyPageWriteProtect ();
+  }
+  return Status;
 }
 
 /**
@@ -922,6 +996,130 @@ RefreshGcdMemoryAttributesFromPaging (
   FreePool (MemorySpaceMap);
 }
 
+/**
+  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 512 (= SIZE_2MB) and at the
+  boundary of SIZE_2MB. 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 512 pages. Usually this won't happen often in
+  practice.
+
+  @param[in] 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;
+  BOOLEAN                   IsModified;
+
+  //
+  // Always reserve at least PAGE_TABLE_POOL_UNIT_PAGES (512).
+  //
+  if (PoolPages <= PAGE_TABLE_POOL_UNIT_PAGES) {
+    PoolPages = PAGE_TABLE_POOL_UNIT_PAGES;
+  } else {
+    PoolPages = ((PoolPages + PAGE_TABLE_POOL_UNIT_PAGES) %
+                 PAGE_TABLE_POOL_UNIT_PAGES) * 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);
+
+  //
+  // Mark the whole pool pages as read-only.
+  //
+  ConvertMemoryPageAttributes (
+    NULL,
+    (PHYSICAL_ADDRESS)(UINTN)Buffer,
+    EFI_PAGES_TO_SIZE (PoolPages),
+    EFI_MEMORY_RO,
+    PageActionSet,
+    AllocatePageTableMemory,
+    NULL,
+    &IsModified
+    );
+  ASSERT (IsModified == TRUE);
+
+  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 *
+EFIAPI
+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;
+}
+
 /**
   Initialize the Page Table lib.
 **/
@@ -933,6 +1131,18 @@ InitializePageTableLib (
   PAGE_TABLE_LIB_PAGING_CONTEXT     CurrentPagingContext;
 
   GetCurrentPagingContext (&CurrentPagingContext);
+
+  //
+  // Reserve memory of page tables for future uses, if paging is enabled.
+  //
+  if (CurrentPagingContext.ContextData.X64.PageTableBase != 0 &&
+      (CurrentPagingContext.ContextData.Ia32.Attributes &
+       PAGE_TABLE_LIB_PAGING_CONTEXT_IA32_X64_ATTRIBUTES_PAE) != 0) {
+    DisableReadOnlyPageWriteProtect ();
+    InitializePageTablePool (PAGE_TABLE_POOL_UNIT_SIZE);
+    EnableReadOnlyPageWriteProtect ();
+  }
+
   DEBUG ((DEBUG_INFO, "CurrentPagingContext:\n", CurrentPagingContext.MachineType));
   DEBUG ((DEBUG_INFO, "  MachineType   - 0x%x\n", CurrentPagingContext.MachineType));
   DEBUG ((DEBUG_INFO, "  PageTableBase - 0x%x\n", CurrentPagingContext.ContextData.X64.PageTableBase));
diff --git a/UefiCpuPkg/CpuDxe/CpuPageTable.h b/UefiCpuPkg/CpuDxe/CpuPageTable.h
index eaff595b4c..2557ffaecf 100644
--- a/UefiCpuPkg/CpuDxe/CpuPageTable.h
+++ b/UefiCpuPkg/CpuDxe/CpuPageTable.h
@@ -50,6 +50,19 @@ typedef struct {
   PAGE_TABLE_LIB_PAGING_CONTEXT_DATA     ContextData;
 } PAGE_TABLE_LIB_PAGING_CONTEXT;
 
+#define PAGE_TABLE_POOL_ALIGNMENT   BASE_2MB
+#define PAGE_TABLE_POOL_UNIT_SIZE   SIZE_2MB
+#define PAGE_TABLE_POOL_UNIT_PAGES  EFI_SIZE_TO_PAGES (SIZE_2MB)
+#define PAGE_TABLE_POOL_ALIGN_MASK  \
+  (~(EFI_PHYSICAL_ADDRESS)(PAGE_TABLE_POOL_ALIGNMENT - 1))
+
+typedef struct {
+  VOID            *NextPool;
+  UINTN           Offset;
+  UINTN           FreePages;
+} PAGE_TABLE_POOL;
+
+
 /**
   Allocates one or more 4KB pages for page table.
 
@@ -110,4 +123,25 @@ InitializePageTableLib (
   VOID
   );
 
+/**
+  This API provides a way to allocate memory for page table.
+
+  This API can be called more once to allocate memory for page tables.
+
+  Allocates the number of 4KB pages of type EfiRuntimeServicesData 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 *
+EFIAPI
+AllocatePageTableMemory (
+  IN UINTN           Pages
+  );
+
 #endif
-- 
2.15.1.windows.2

Re: [PATCH v3 0/2] Enable page table write protection

[Laszlo Ersek]

On 12/05/17 09:16, Jian J Wang wrote:
>> v3 changes:
>>  a. According to code review comments, remove the public definitions of
>>     page table pool. Now the DxeIpl and CpuDxe will have their own page
>>     table pool but in the same mechanism. Related PCDs, GUDI and headers
>>     are also removed.
>>  b. Apply protection to all page tables, including new ones added in
>>     CpuDxe driver.
>>  c. Code/comments cleanup.
> 
>> v2 changes:
>>  a. Enable protection on any newly added page table after DxeIpl.
>>  b. Introduce page table pool concept to make page table allocation
>>     and protection easier and error free.
> 
> Write Protect feature (CR0.WP) is always enabled in driver UefiCpuPkg/CpuDxe.
> But the memory pages used for page table are not set as read-only in the driver
> DxeIplPeim, after the paging is setup. This might jeopardize the page table
> integrity if there's buffer overflow occured in other part of system.
> 
> This patch series will change this situation by clearing R/W bit in page attribute
> of the pages used as page table.
> 
> Validation works include booting Windows (10/server 2016) and Linux (Fedora/Ubuntu)
> on OVMF and Intel real platform.
> 
> Jian J Wang (2):
>   MdeModulePkg/DxeIpl: Mark page table as read-only
>   UefiCpuPkg/CpuDxe: Enable protection for newly added page table
> 
>  MdeModulePkg/Core/DxeIplPeim/DxeIpl.h            |  34 +++
>  MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c  |   8 +-
>  MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c | 301 ++++++++++++++++++++++-
>  MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h |  26 ++
>  UefiCpuPkg/CpuDxe/CpuDxe.c                       |  17 +-
>  UefiCpuPkg/CpuDxe/CpuDxe.h                       |   2 +
>  UefiCpuPkg/CpuDxe/CpuPageTable.c                 | 226 ++++++++++++++++-
>  UefiCpuPkg/CpuDxe/CpuPageTable.h                 |  34 +++
>  8 files changed, 635 insertions(+), 13 deletions(-)
> 

series
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>

Thanks
Laszlo

Re: [PATCH v3 0/2] Enable page table write protection

[Wang, Jian J]

Hi Laszlo,

Thanks for the test.

Jian
> -----Original Message-----
> From: Laszlo Ersek [mailto:lersek@redhat.com]
> Sent: Wednesday, December 06, 2017 4:05 AM
> To: Wang, Jian J <jian.j.wang@intel.com>; edk2-devel@lists.01.org
> Subject: Re: [edk2] [PATCH v3 0/2] Enable page table write protection
> 
> On 12/05/17 09:16, Jian J Wang wrote:
> >> v3 changes:
> >>  a. According to code review comments, remove the public definitions of
> >>     page table pool. Now the DxeIpl and CpuDxe will have their own page
> >>     table pool but in the same mechanism. Related PCDs, GUDI and headers
> >>     are also removed.
> >>  b. Apply protection to all page tables, including new ones added in
> >>     CpuDxe driver.
> >>  c. Code/comments cleanup.
> >
> >> v2 changes:
> >>  a. Enable protection on any newly added page table after DxeIpl.
> >>  b. Introduce page table pool concept to make page table allocation
> >>     and protection easier and error free.
> >
> > Write Protect feature (CR0.WP) is always enabled in driver
> UefiCpuPkg/CpuDxe.
> > But the memory pages used for page table are not set as read-only in the
> driver
> > DxeIplPeim, after the paging is setup. This might jeopardize the page table
> > integrity if there's buffer overflow occured in other part of system.
> >
> > This patch series will change this situation by clearing R/W bit in page attribute
> > of the pages used as page table.
> >
> > Validation works include booting Windows (10/server 2016) and Linux
> (Fedora/Ubuntu)
> > on OVMF and Intel real platform.
> >
> > Jian J Wang (2):
> >   MdeModulePkg/DxeIpl: Mark page table as read-only
> >   UefiCpuPkg/CpuDxe: Enable protection for newly added page table
> >
> >  MdeModulePkg/Core/DxeIplPeim/DxeIpl.h            |  34 +++
> >  MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c  |   8 +-
> >  MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c | 301
> ++++++++++++++++++++++-
> >  MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h |  26 ++
> >  UefiCpuPkg/CpuDxe/CpuDxe.c                       |  17 +-
> >  UefiCpuPkg/CpuDxe/CpuDxe.h                       |   2 +
> >  UefiCpuPkg/CpuDxe/CpuPageTable.c                 | 226 ++++++++++++++++-
> >  UefiCpuPkg/CpuDxe/CpuPageTable.h                 |  34 +++
> >  8 files changed, 635 insertions(+), 13 deletions(-)
> >
> 
> series
> Regression-tested-by: Laszlo Ersek <lersek@redhat.com>
> 
> Thanks
> Laszlo

Re: [PATCH v3 0/2] Enable page table write protection

[Yao, Jiewen]

Thanks you. It looks good to me.
Reviewed-by: Jiewen.yao@intel.com

I suggest CPU owner can have double check the code before check in.

Thank you
Yao Jiewen


> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Jian J
> Wang
> Sent: Tuesday, December 5, 2017 4:16 PM
> To: edk2-devel@lists.01.org
> Subject: [edk2] [PATCH v3 0/2] Enable page table write protection
> 
> > v3 changes:
> >  a. According to code review comments, remove the public definitions of
> >     page table pool. Now the DxeIpl and CpuDxe will have their own page
> >     table pool but in the same mechanism. Related PCDs, GUDI and headers
> >     are also removed.
> >  b. Apply protection to all page tables, including new ones added in
> >     CpuDxe driver.
> >  c. Code/comments cleanup.
> 
> > v2 changes:
> >  a. Enable protection on any newly added page table after DxeIpl.
> >  b. Introduce page table pool concept to make page table allocation
> >     and protection easier and error free.
> 
> Write Protect feature (CR0.WP) is always enabled in driver UefiCpuPkg/CpuDxe.
> But the memory pages used for page table are not set as read-only in the driver
> DxeIplPeim, after the paging is setup. This might jeopardize the page table
> integrity if there's buffer overflow occured in other part of system.
> 
> This patch series will change this situation by clearing R/W bit in page attribute
> of the pages used as page table.
> 
> Validation works include booting Windows (10/server 2016) and Linux
> (Fedora/Ubuntu)
> on OVMF and Intel real platform.
> 
> Jian J Wang (2):
>   MdeModulePkg/DxeIpl: Mark page table as read-only
>   UefiCpuPkg/CpuDxe: Enable protection for newly added page table
> 
>  MdeModulePkg/Core/DxeIplPeim/DxeIpl.h            |  34 +++
>  MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c  |   8 +-
>  MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c | 301
> ++++++++++++++++++++++-
>  MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h |  26 ++
>  UefiCpuPkg/CpuDxe/CpuDxe.c                       |  17 +-
>  UefiCpuPkg/CpuDxe/CpuDxe.h                       |   2 +
>  UefiCpuPkg/CpuDxe/CpuPageTable.c                 | 226
> ++++++++++++++++-
>  UefiCpuPkg/CpuDxe/CpuPageTable.h                 |  34 +++
>  8 files changed, 635 insertions(+), 13 deletions(-)
> 
> --
> 2.15.1.windows.2
> 
> _______________________________________________
> edk2-devel mailing list
> edk2-devel@lists.01.org
> https://lists.01.org/mailman/listinfo/edk2-devel