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.
Cc: Eric Dong <eric.d...@intel.com>
Cc: Laszlo Ersek <ler...@redhat.com>
Cc: Ruiyu Ni <ruiyu...@intel.com>
Cc: Star Zeng <star.z...@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Jian J Wang <jian.j.w...@intel.com>
---
UefiCpuPkg/CpuDxe/CpuPageTable.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
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 ();
}
}
--
2.17.1.windows.2
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