tracing, x86: fix fixup section to return to original code
Impact: fix to prevent a kernel crash on fault
If for some reason the pointer to the parent function on the
stack takes a fault, the fix up code will not return back to
the original faulting code. This can lead to unpredictable
results and perhaps even a kernel panic.
A fault should not happen, but if it does, we should simply
disable the tracer, warn, and continue running the kernel.
It should not lead to a kernel crash.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 1b43086..9d549e4 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -491,13 +491,15 @@
"1: " _ASM_MOV " (%[parent_old]), %[old]\n"
"2: " _ASM_MOV " %[return_hooker], (%[parent_replaced])\n"
" movl $0, %[faulted]\n"
+ "3:\n"
".section .fixup, \"ax\"\n"
- "3: movl $1, %[faulted]\n"
+ "4: movl $1, %[faulted]\n"
+ " jmp 3b\n"
".previous\n"
- _ASM_EXTABLE(1b, 3b)
- _ASM_EXTABLE(2b, 3b)
+ _ASM_EXTABLE(1b, 4b)
+ _ASM_EXTABLE(2b, 4b)
: [parent_replaced] "=r" (parent), [old] "=r" (old),
[faulted] "=r" (faulted)