From 2a93cccc24cfca12c66f13a41d52fb0a82fb924e Mon Sep 17 00:00:00 2001 From: Jian J Wang Date: Thu, 28 Feb 2019 15:16:25 +0800 Subject: UefiCpuPkg: restore strict page attributes via #DB in nonstop mode only REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1576 The root cause of this issue is that non-stop mode of Heap Guard and NULL Detection set TF bit (single-step) in EFLAG unconditionally in the common handler in CpuExceptionLib. If PcdCpuSmmStaticPageTable is FALSE, the SMM will only create page table for memory below 4G. If SMM tries to access memory beyond 4G, a page fault exception will be triggered and the memory to access will be added to page table so that SMM code can continue the access. Because of above issue, the TF bit is set after the page fault is handled and then fall into another DEBUG exception. Since non-stop mode of Heap Guard and NULL Detection are not enabled, no special DEBUG exception handler is registered. The default handler just prints exception context and go into dead loop. Actually EFLAGS can be changed in any standard exception handler. There's no need to do single-step setup in assembly code. So the fix is to move the logic to C code part of page fault exception handler so that we can fully validate the configuration and prevent TF bit from being set unexpectedly. Fixes: dcc026217fdc363f55c217039fc43d344f69fed6 16b918bbaf51211a32ae04d9d8a5ba6ccca25a6a Test: - Pass special test of accessing memory beyond 4G in SMM mode - Boot to OS with Qemu emulator platform (Fedora27, Ubuntu18.04, Windows7, Windows10) Cc: Eric Dong Cc: Laszlo Ersek Cc: Ruiyu Ni Cc: Star Zeng Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Jian J Wang Acked-by: Laszlo Ersek Reviewed-by: Eric Dong --- UefiCpuPkg/CpuDxe/CpuPageTable.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) (limited to 'UefiCpuPkg/CpuDxe') diff --git a/UefiCpuPkg/CpuDxe/CpuPageTable.c b/UefiCpuPkg/CpuDxe/CpuPageTable.c index 4bee8c7772..812537417d 100644 --- a/UefiCpuPkg/CpuDxe/CpuPageTable.c +++ b/UefiCpuPkg/CpuDxe/CpuPageTable.c @@ -1300,7 +1300,16 @@ PageFaultExceptionHandler ( // Display ExceptionType, CPU information and Image information // DumpCpuContext (ExceptionType, SystemContext); - if (!NonStopMode) { + if (NonStopMode) { + // + // Set TF in EFLAGS + // + if (mPagingContext.MachineType == IMAGE_FILE_MACHINE_I386) { + SystemContext.SystemContextIa32->Eflags |= (UINT32)BIT8; + } else { + SystemContext.SystemContextX64->Rflags |= (UINT64)BIT8; + } + } else { CpuDeadLoop (); } } -- cgit v1.2.3