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>

1 files changed, 5 insertions, 3 deletions

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 1b43086b097a..9d549e4fe880 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -491,13 +491,15 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
                 "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)