Hi
I do not think NULL pointer is related to NX.
As long as NullPointer PCD is true and IA32PAE is supported, we can build page
table.
+ BuildPageTablesIa32Pae = (BOOLEAN) (IsIa32PaeSupport ()
+ && IsExecuteDisableBitAvailable ()
+ && (PcdGetBool (PcdSetNxForStack)
+ || IsNullDetectionEnabled ()));
> -----Original Message-----
> From: Wang, Jian J
> Sent: Thursday, September 21, 2017 1:20 PM
> To: edk2-devel@lists.01.org
> Cc: Zeng, Star <star.z...@intel.com>; Dong, Eric <eric.d...@intel.com>; Laszlo
> Ersek <ler...@redhat.com>; Yao, Jiewen <jiewen....@intel.com>; Kinney,
> Michael D <michael.d.kin...@intel.com>; Justen, Jordan L
> <jordan.l.jus...@intel.com>; Wolman, Ayellet <ayellet.wol...@intel.com>
> Subject: [PATCH v2 2/6] MdeModulePkg/DxeIpl: Implement NULL pointer
> detection
>
> NULL pointer detection is done by making use of paging mechanism of CPU.
> During page table setup, if enabled, the first 4-K page (0-4095) will be
> marked as NOT PRESENT. Any code which unintentionally access memory
> between
> 0-4095 will trigger a Page Fault exception which warns users that there's
> potential illegal code in BIOS.
>
> This also means that legacy code which has to access memory between 0-4095
> should be cautious to temporarily disable this feature before the access
> and re-enable it afterwards; or disalbe this feature at all.
>
> Cc: Star Zeng <star.z...@intel.com>
> Cc: Eric Dong <eric.d...@intel.com>
> Cc: Laszlo Ersek <ler...@redhat.com>
> Cc: Jiewen Yao <jiewen....@intel.com>
> Cc: Michael Kinney <michael.d.kin...@intel.com>
> Cc: Jordan Justen <jordan.l.jus...@intel.com>
> Cc: Ayellet Wolman <ayellet.wol...@intel.com>
> Suggested-by: Ayellet Wolman <ayellet.wol...@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Jian J Wang <jian.j.w...@intel.com>
> ---
> MdeModulePkg/Core/DxeIplPeim/DxeIpl.h | 25 +++++++++
> MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf | 1 +
> MdeModulePkg/Core/DxeIplPeim/DxeLoad.c | 65
> ++++++++++++++++++++++++
> MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c | 11 +++-
> MdeModulePkg/Core/DxeIplPeim/X64/DxeLoadFunc.c | 2 +
> MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c | 31 ++++++++---
> 6 files changed, 126 insertions(+), 9 deletions(-)
>
> diff --git a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h
> b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h
> index 72d2532f50..1654bcd2dc 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h
> +++ b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.h
> @@ -240,4 +240,29 @@ Decompress (
> OUT UINTN *OutputSize
> );
>
> +/**
> + Clear legacy memory located at the first 4K-page.
> +
> + 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 HoStart The start of HobList passed to DxeCore.
> +
> +**/
> +VOID
> +ClearLegacyMemory (
> + IN VOID *HobStart
> + );
> +
> +/**
> + 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
> + );
> +
> #endif
> diff --git a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
> b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
> index c54afe4aa6..9d0e76a293 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
> +++ b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
> @@ -115,6 +115,7 @@
> [Pcd.IA32,Pcd.X64]
> gEfiMdeModulePkgTokenSpaceGuid.PcdUse1GPageTable
> ## SOMETIMES_CONSUMES
>
> gEfiMdeModulePkgTokenSpaceGuid.PcdPteMemoryEncryptionAddressOrMask
> ## CONSUMES
> + gEfiMdeModulePkgTokenSpaceGuid.PcdNullPointerDetectionPropertyMask
> ## CONSUMES
>
> [Pcd.IA32,Pcd.X64,Pcd.ARM,Pcd.AARCH64]
> gEfiMdeModulePkgTokenSpaceGuid.PcdSetNxForStack ##
> SOMETIMES_CONSUMES
> diff --git a/MdeModulePkg/Core/DxeIplPeim/DxeLoad.c
> b/MdeModulePkg/Core/DxeIplPeim/DxeLoad.c
> index 50b5440d15..0a71b1f3de 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/DxeLoad.c
> +++ b/MdeModulePkg/Core/DxeIplPeim/DxeLoad.c
> @@ -825,3 +825,68 @@ UpdateStackHob (
> Hob.Raw = GET_NEXT_HOB (Hob);
> }
> }
> +
> +/**
> + 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 HoStart The start of HobList passed to
> DxeCore.
> +
> +**/
> +VOID
> +ClearLegacyMemory (
> + 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;
> +}
> +
> +BOOLEAN
> +IsNullDetectionEnabled (
> + VOID
> + )
> +{
> + return (((PcdGet8 (PcdNullPointerDetectionPropertyMask) & BIT0) != 0) ?
> + TRUE : FALSE);
> +}
> +
> diff --git a/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> b/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> index 1957326caf..503cf88382 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> +++ b/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> @@ -123,7 +123,9 @@ Create4GPageTablesIa32Pae (
> PageDirectoryPointerEntry->Bits.Present = 1;
>
> for (IndexOfPageDirectoryEntries = 0; IndexOfPageDirectoryEntries < 512;
> IndexOfPageDirectoryEntries++, PageDirectoryEntry++, PhysicalAddress +=
> SIZE_2MB) {
> - if ((PhysicalAddress < StackBase + StackSize) && ((PhysicalAddress +
> SIZE_2MB) > StackBase)) {
> + if ((IsNullDetectionEnabled () && PhysicalAddress == 0)
> + || ((PhysicalAddress < StackBase + StackSize)
> + && ((PhysicalAddress + SIZE_2MB) > StackBase))) {
> //
> // Need to split this 2M page that covers stack range.
> //
> @@ -240,6 +242,8 @@ HandOffToDxeCore (
> EFI_PEI_VECTOR_HANDOFF_INFO_PPI *VectorHandoffInfoPpi;
> BOOLEAN BuildPageTablesIa32Pae;
>
> + ClearLegacyMemory (HobList.Raw);
> +
> Status = PeiServicesAllocatePages (EfiBootServicesData, EFI_SIZE_TO_PAGES
> (STACK_SIZE), &BaseOfStack);
> ASSERT_EFI_ERROR (Status);
>
> @@ -379,7 +383,10 @@ HandOffToDxeCore (
> TopOfStack = (EFI_PHYSICAL_ADDRESS) (UINTN) ALIGN_POINTER
> (TopOfStack, CPU_STACK_ALIGNMENT);
>
> PageTables = 0;
> - BuildPageTablesIa32Pae = (BOOLEAN) (PcdGetBool (PcdSetNxForStack) &&
> IsIa32PaeSupport () && IsExecuteDisableBitAvailable ());
> + BuildPageTablesIa32Pae = (BOOLEAN) (IsIa32PaeSupport ()
> + && IsExecuteDisableBitAvailable
> ()
> + && (PcdGetBool
> (PcdSetNxForStack)
> + || IsNullDetectionEnabled
> ()));
> if (BuildPageTablesIa32Pae) {
> PageTables = Create4GPageTablesIa32Pae (BaseOfStack, STACK_SIZE);
> EnableExecuteDisableBit ();
> diff --git a/MdeModulePkg/Core/DxeIplPeim/X64/DxeLoadFunc.c
> b/MdeModulePkg/Core/DxeIplPeim/X64/DxeLoadFunc.c
> index 6488880eab..d93a9c5a2d 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/X64/DxeLoadFunc.c
> +++ b/MdeModulePkg/Core/DxeIplPeim/X64/DxeLoadFunc.c
> @@ -42,6 +42,8 @@ HandOffToDxeCore (
> EFI_VECTOR_HANDOFF_INFO *VectorInfo;
> EFI_PEI_VECTOR_HANDOFF_INFO_PPI *VectorHandoffInfoPpi;
>
> + ClearLegacyMemory (HobList.Raw);
> +
> //
> // Get Vector Hand-off Info PPI and build Guided HOB
> //
> diff --git a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> index 48150be4e1..80c1821eca 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> +++ b/MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c
> @@ -90,8 +90,16 @@ Split2MPageTo4K (
> //
> PageTableEntry->Uint64 = (UINT64) PhysicalAddress4K | AddressEncMask;
> PageTableEntry->Bits.ReadWrite = 1;
> - PageTableEntry->Bits.Present = 1;
> - if ((PhysicalAddress4K >= StackBase) && (PhysicalAddress4K < StackBase +
> StackSize)) {
> +
> + if (IsNullDetectionEnabled () && PhysicalAddress4K == 0) {
> + PageTableEntry->Bits.Present = 0;
> + } else {
> + PageTableEntry->Bits.Present = 1;
> + }
> +
> + if (PcdGetBool (PcdSetNxForStack)
> + && (PhysicalAddress4K >= StackBase)
> + && (PhysicalAddress4K < StackBase + StackSize)) {
> //
> // Set Nx bit for stack.
> //
> @@ -137,9 +145,12 @@ Split1GPageTo2M (
>
> PhysicalAddress2M = PhysicalAddress;
> for (IndexOfPageDirectoryEntries = 0; IndexOfPageDirectoryEntries < 512;
> IndexOfPageDirectoryEntries++, PageDirectoryEntry++, PhysicalAddress2M +=
> SIZE_2MB) {
> - if ((PhysicalAddress2M < StackBase + StackSize) && ((PhysicalAddress2M +
> SIZE_2MB) > StackBase)) {
> + if ((IsNullDetectionEnabled () && PhysicalAddress2M == 0)
> + || (PcdGetBool (PcdSetNxForStack)
> + && (PhysicalAddress2M < StackBase + StackSize)
> + && ((PhysicalAddress2M + SIZE_2MB) > StackBase))) {
> //
> - // 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 {
> @@ -279,7 +290,10 @@ 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 ((IsNullDetectionEnabled () && PageAddress == 0)
> + || (PcdGetBool (PcdSetNxForStack)
> + && (PageAddress < StackBase + StackSize)
> + && ((PageAddress + SIZE_1GB) > StackBase))) {
> Split1GPageTo2M (PageAddress, (UINT64 *) PageDirectory1GEntry,
> StackBase, StackSize);
> } else {
> //
> @@ -308,9 +322,12 @@ CreateIdentityMappingPageTables (
> 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 ((IsNullDetectionEnabled () && PageAddress == 0)
> + || (PcdGetBool (PcdSetNxForStack)
> + && (PageAddress < StackBase + StackSize)
> + && ((PageAddress + SIZE_2MB) > StackBase))) {
> //
> - // 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 {
> --
> 2.14.1.windows.1
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