If CET shadows stack feature enabled in SMM and stack switch is enabled. When code execute from SMM handler to SMM exception, CPU will check SMM exception shadow stack token busy bit if it is cleared or not. If it is set, it will trigger #DF exception. If it is not set, CPU will set the busy bit when enter SMM exception. So, the busy bit should be cleared when return back form SMM exception to SMM handler. Otherwise, keeping busy bit 1 will cause to trigger #DF exception when enter SMM exception next time. So, we use instruction SAVEPREVSSP, CLRSSBSY and RSTORSSP to clear the shadow stack token busy bit before RETF instruction in SMM exception.
REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3192 Signed-off-by: Sheng Wei <w.sh...@intel.com> Cc: Eric Dong <eric.d...@intel.com> Cc: Ray Ni <ray...@intel.com> Cc: Laszlo Ersek <ler...@redhat.com> Cc: Rahul Kumar <rahul1.ku...@intel.com> Cc: Jiewen Yao <jiewen....@intel.com> Cc: Roger Feng <roger.f...@intel.com> --- .../DxeCpuExceptionHandlerLib.inf | 3 ++ .../PeiCpuExceptionHandlerLib.inf | 3 ++ .../SecPeiCpuExceptionHandlerLib.inf | 4 ++ .../SmmCpuExceptionHandlerLib.inf | 3 ++ .../X64/Xcode5ExceptionHandlerAsm.nasm | 48 ++++++++++++++++++++-- .../Xcode5SecPeiCpuExceptionHandlerLib.inf | 4 ++ UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c | 5 ++- 7 files changed, 66 insertions(+), 4 deletions(-) diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/DxeCpuExceptionHandlerLib.inf b/UefiCpuPkg/Library/CpuExceptionHandlerLib/DxeCpuExceptionHandlerLib.inf index 07b34c92a8..e7a81bebdb 100644 --- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/DxeCpuExceptionHandlerLib.inf +++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/DxeCpuExceptionHandlerLib.inf @@ -43,6 +43,9 @@ gUefiCpuPkgTokenSpaceGuid.PcdCpuStackSwitchExceptionList gUefiCpuPkgTokenSpaceGuid.PcdCpuKnownGoodStackSize +[FeaturePcd] + gUefiCpuPkgTokenSpaceGuid.PcdCpuSmmStackGuard ## CONSUMES + [Packages] MdePkg/MdePkg.dec MdeModulePkg/MdeModulePkg.dec diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuExceptionHandlerLib.inf b/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuExceptionHandlerLib.inf index feae7b3e06..cf5bfe4083 100644 --- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuExceptionHandlerLib.inf +++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/PeiCpuExceptionHandlerLib.inf @@ -57,3 +57,6 @@ [Pcd] gEfiMdeModulePkgTokenSpaceGuid.PcdCpuStackGuard # CONSUMES +[FeaturePcd] + gUefiCpuPkgTokenSpaceGuid.PcdCpuSmmStackGuard ## CONSUMES + diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/SecPeiCpuExceptionHandlerLib.inf b/UefiCpuPkg/Library/CpuExceptionHandlerLib/SecPeiCpuExceptionHandlerLib.inf index 967cb61ba6..8ae4feae62 100644 --- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/SecPeiCpuExceptionHandlerLib.inf +++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/SecPeiCpuExceptionHandlerLib.inf @@ -49,3 +49,7 @@ LocalApicLib PeCoffGetEntryPointLib VmgExitLib + +[FeaturePcd] + gUefiCpuPkgTokenSpaceGuid.PcdCpuSmmStackGuard ## CONSUMES + diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/SmmCpuExceptionHandlerLib.inf b/UefiCpuPkg/Library/CpuExceptionHandlerLib/SmmCpuExceptionHandlerLib.inf index 4cdb11c04e..5c3d1f7cfd 100644 --- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/SmmCpuExceptionHandlerLib.inf +++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/SmmCpuExceptionHandlerLib.inf @@ -53,3 +53,6 @@ DebugLib VmgExitLib +[FeaturePcd] + gUefiCpuPkgTokenSpaceGuid.PcdCpuSmmStackGuard ## CONSUMES + diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/Xcode5ExceptionHandlerAsm.nasm b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/Xcode5ExceptionHandlerAsm.nasm index 26cae56cc5..05a802a633 100644 --- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/Xcode5ExceptionHandlerAsm.nasm +++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/Xcode5ExceptionHandlerAsm.nasm @@ -1,5 +1,5 @@ ;------------------------------------------------------------------------------ ; -; Copyright (c) 2012 - 2018, Intel Corporation. All rights reserved.<BR> +; Copyright (c) 2012 - 2021, Intel Corporation. All rights reserved.<BR> ; SPDX-License-Identifier: BSD-2-Clause-Patent ; ; Module Name: @@ -13,6 +13,7 @@ ; Notes: ; ;------------------------------------------------------------------------------ +%include "Nasm.inc" ; ; CommonExceptionHandler() @@ -23,6 +24,7 @@ extern ASM_PFX(mErrorCodeFlag) ; Error code flags for exceptions extern ASM_PFX(mDoFarReturnFlag) ; Do far return flag extern ASM_PFX(CommonExceptionHandler) +extern ASM_PFX(FeaturePcdGet (PcdCpuSmmStackGuard)) SECTION .data @@ -371,8 +373,48 @@ DoReturn: push qword [rax + 0x18] ; save EFLAGS in new location mov rax, [rax] ; restore rax popfq ; restore EFLAGS - DB 0x48 ; prefix to composite "retq" with next "retf" - retf ; far return + + ; The follow algorithm is used for clear shadow stack token busy bit. + ; The comment is based on the sample shadow stack. + ; The sample shadow stack layout : + ; Address | Context + ; +-------------------------+ + ; 0xFD0 | FREE | it is 0xFD8|0x02|(LMA & CS.L), after SAVEPREVSSP. + ; +-------------------------+ + ; 0xFD8 | Prev SSP | + ; +-------------------------+ + ; 0xFE0 | RIP | + ; +-------------------------+ + ; 0xFE8 | CS | + ; +-------------------------+ + ; 0xFF0 | 0xFF0 | BUSY | BUSY flag cleared after CLRSSBSY + ; +-------------------------+ + ; 0xFF8 | 0xFD8|0x02|(LMA & CS.L) | + ; +-------------------------+ + ; Instructions for Intel Control Flow Enforcement Technology (CET) are supported since NASM version 2.15.01. + push rax ; SSP should be 0xFD8 at this point + cmp byte [dword ASM_PFX(FeaturePcdGet (PcdCpuSmmStackGuard))], 0 + jz CetDone + mov rax, cr4 + and rax, 0x800000 ; check if CET is enabled + jz CetDone + mov rax, 0x04 ; advance past cs:lip:prevssp;supervisor shadow stack token + INCSSP_RAX ; After this SSP should be 0xFF8 + DB 0xF3, 0x0F, 0x01, 0xEA ; SAVEPREVSSP ; now the shadow stack restore token will be created at 0xFD0 + READSSP_RAX ; Read new SSP, SSP should be 0x1000 + push rax + sub rax, 0x10 + DB 0xF3, 0x0F, 0xAE, 0x30 ; CLRSSBSY RAX ; Clear token at 0xFF0 ; SSP should be 0 after this + sub rax, 0x20 + DB 0xF3, 0x0F, 0x01, 0x28 ; RSTORSSP RAX ; Restore to token at 0xFD0, new SSP will be 0xFD0 + pop rax + mov rax, 0x01 ; Pop off the new save token created + INCSSP_RAX ; SSP should be 0xFD8 now +CetDone: + pop rax ; restore rax + + DB 0x48 ; prefix to composite "retq" with next "retf" + retf ; far return DoIret: iretq diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/Xcode5SecPeiCpuExceptionHandlerLib.inf b/UefiCpuPkg/Library/CpuExceptionHandlerLib/Xcode5SecPeiCpuExceptionHandlerLib.inf index 743c2aa766..a15f125d5b 100644 --- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/Xcode5SecPeiCpuExceptionHandlerLib.inf +++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/Xcode5SecPeiCpuExceptionHandlerLib.inf @@ -54,3 +54,7 @@ LocalApicLib PeCoffGetEntryPointLib VmgExitLib + +[FeaturePcd] + gUefiCpuPkgTokenSpaceGuid.PcdCpuSmmStackGuard ## CONSUMES + diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c index 28f8e8e133..1aa1102f56 100644 --- a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c @@ -173,6 +173,7 @@ InitShadowStack ( { UINTN SmmShadowStackSize; UINT64 *InterruptSspTable; + UINT32 InterruptSsp; if ((PcdGet32 (PcdControlFlowEnforcementPropertyMask) != 0) && mCetSupported) { SmmShadowStackSize = EFI_PAGES_TO_SIZE (EFI_SIZE_TO_PAGES (PcdGet32 (PcdCpuSmmShadowStackSize))); @@ -191,7 +192,9 @@ InitShadowStack ( ASSERT (mSmmInterruptSspTables != 0); DEBUG ((DEBUG_INFO, "mSmmInterruptSspTables - 0x%x\n", mSmmInterruptSspTables)); } - mCetInterruptSsp = (UINT32)((UINTN)ShadowStack + EFI_PAGES_TO_SIZE(1) - sizeof(UINT64)); + InterruptSsp = (UINT32)((UINTN)ShadowStack + EFI_PAGES_TO_SIZE(1) - sizeof(UINT64)); + *(UINT32 *)(UINTN)InterruptSsp = (InterruptSsp - sizeof(UINT64) * 4) | 0x2; + mCetInterruptSsp = InterruptSsp - sizeof(UINT64); mCetInterruptSspTable = (UINT32)(UINTN)(mSmmInterruptSspTables + sizeof(UINT64) * 8 * CpuIndex); InterruptSspTable = (UINT64 *)(UINTN)mCetInterruptSspTable; InterruptSspTable[1] = mCetInterruptSsp; -- 2.16.2.windows.1 -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. 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