function-graph: add stack frame test

In case gcc does something funny with the stack frames, or the return
from function code, we would like to detect that.

An arch may implement passing of a variable that is unique to the
function and can be saved on entering a function and can be tested
when exiting the function. Usually the frame pointer can be used for
this purpose.

This patch also implements this for x86. Where it passes in the stack
frame of the parent function, and will test that frame on exit.

There was a case in x86_32 with optimize for size (-Os) where, for a
few functions, gcc would align the stack frame and place a copy of the
return address into it. The function graph tracer modified the copy and
not the actual return address. On return from the funtion, it did not go
to the tracer hook, but returned to the parent. This broke the function
graph tracer, because the return of the parent (where gcc did not do
this funky manipulation) returned to the location that the child function
was suppose to. This caused strange kernel crashes.

This test detected the problem and pointed out where the issue was.

This modifies the parameters of one of the functions that the arch
specific code calls, so it includes changes to arch code to accommodate
the new prototype.

Note, I notice that the parsic arch implements its own push_return_trace.
This is now a generic function and the ftrace_push_return_trace should be
used instead. This patch does not touch that code.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Kyle McMartin <kyle@mcmartin.ca>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 39 insertions, 4 deletions

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 1eac85253ce9..b17ed8787ded 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -18,6 +18,13 @@ config HAVE_FUNCTION_TRACER
 config HAVE_FUNCTION_GRAPH_TRACER
         bool
 
+config HAVE_FUNCTION_GRAPH_FP_TEST
+        bool
+        help
+         An arch may pass in a unique value (frame pointer) to both the
+         entering and exiting of a function. On exit, the value is compared
+         and if it does not match, then it will panic the kernel.
+
 config HAVE_FUNCTION_TRACE_MCOUNT_TEST
         bool
         help
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 8b592418d8b2..d2249abafb53 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -57,7 +57,8 @@ static struct tracer_flags tracer_flags = {
 
 /* Add a function return address to the trace stack on thread info.*/
 int
-ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth)
+ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth,
+                         unsigned long frame_pointer)
 {
         unsigned long long calltime;
         int index;
@@ -85,6 +86,7 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth)
         current->ret_stack[index].func = func;
         current->ret_stack[index].calltime = calltime;
         current->ret_stack[index].subtime = 0;
+        current->ret_stack[index].fp = frame_pointer;
         *depth = index;
 
         return 0;
@@ -92,7 +94,8 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth)
 
 /* Retrieve a function return address to the trace stack on thread info.*/
 static void
-ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret)
+ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret,
+                        unsigned long frame_pointer)
 {
         int index;
 
@@ -106,6 +109,31 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret)
                 return;
         }
 
+#ifdef CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST
+        /*
+         * The arch may choose to record the frame pointer used
+         * and check it here to make sure that it is what we expect it
+         * to be. If gcc does not set the place holder of the return
+         * address in the frame pointer, and does a copy instead, then
+         * the function graph trace will fail. This test detects this
+         * case.
+         *
+         * Currently, x86_32 with optimize for size (-Os) makes the latest
+         * gcc do the above.
+         */
+        if (unlikely(current->ret_stack[index].fp != frame_pointer)) {
+                ftrace_graph_stop();
+                WARN(1, "Bad frame pointer: expected %lx, received %lx\n"
+                     "  from func %pF return to %lx\n",
+                     current->ret_stack[index].fp,
+                     frame_pointer,
+                     (void *)current->ret_stack[index].func,
+                     current->ret_stack[index].ret);
+                *ret = (unsigned long)panic;
+                return;
+        }
+#endif
+
         *ret = current->ret_stack[index].ret;
         trace->func = current->ret_stack[index].func;
         trace->calltime = current->ret_stack[index].calltime;
@@ -117,12 +145,12 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret)
  * Send the trace to the ring-buffer.
  * @return the original return address.
  */
-unsigned long ftrace_return_to_handler(void)
+unsigned long ftrace_return_to_handler(unsigned long frame_pointer)
 {
         struct ftrace_graph_ret trace;
         unsigned long ret;
 
-        ftrace_pop_return_trace(&trace, &ret);
+        ftrace_pop_return_trace(&trace, &ret, frame_pointer);
         trace.rettime = trace_clock_local();
         ftrace_graph_return(&trace);
         barrier();