UefiCpuPkg/CpuExceptionHandlerLib: Setup single step in #PF handler
Once the #PF handler has set the page to be 'present', there should
be a way to reset it to 'not-present'. 'TF' bit in EFLAGS can be used
for this purpose. 'TF' bit will be set in interrupted function context
so that it can be triggered once the cpu control returns back to the
instruction causing #PF and re-execute it.
This is an necessary step to implement non-stop mode for Heap Guard
and NULL Pointer Detection feature.
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>
Reviewed-by: Eric Dong <eric.dong@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ExceptionHandlerAsm.nasm b/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ExceptionHandlerAsm.nasm
index 45d6474..6fcf5fb 100644
--- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ExceptionHandlerAsm.nasm
+++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ExceptionHandlerAsm.nasm
@@ -383,6 +383,13 @@
pop dword [ebp - 4]
mov esp, ebp
pop ebp
+
+; Enable TF bit after page fault handler runs
+ cmp dword [esp], 14 ; #PF?
+ jne .5
+ bts dword [esp + 16], 8 ; EFLAGS
+
+.5:
add esp, 8
cmp dword [esp - 16], 0 ; check EXCEPTION_HANDLER_CONTEXT.OldIdtHandler
jz DoReturn
diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ExceptionTssEntryAsm.nasm b/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ExceptionTssEntryAsm.nasm
index 62bcede..7aac29c 100644
--- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ExceptionTssEntryAsm.nasm
+++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ExceptionTssEntryAsm.nasm
@@ -355,10 +355,8 @@
movzx ebx, word [ecx + IA32_TSS._CS]
mov [eax - 0x8], ebx ; create CS in old stack
mov ebx, dword [ecx + IA32_TSS.EFLAGS]
- bts ebx, 8
+ bts ebx, 8 ; Set TF
mov [eax - 0x4], ebx ; create eflags in old stack
- mov dword [ecx + IA32_TSS.EFLAGS], ebx ; update eflags in old TSS
- mov eax, dword [ecx + IA32_TSS._ESP] ; Get old stack pointer
sub eax, 0xc ; minus 12 byte
mov dword [ecx + IA32_TSS._ESP], eax ; Set new stack pointer
diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.nasm b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.nasm
index 7b97810..f842af2 100644
--- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.nasm
+++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ExceptionHandlerAsm.nasm
@@ -336,6 +336,10 @@
pop r15
mov rsp, rbp
+ cmp qword [rbp + 8], 14 ; #PF?
+ jne .1
+ bts qword [rsp + 40], 8 ; RFLAGS.TF
+.1:
pop rbp
add rsp, 16
cmp qword [rsp - 32], 0 ; check EXCEPTION_HANDLER_CONTEXT.OldIdtHandler
