Commit 0db0934e authored by Masami Hiramatsu (Google)'s avatar Masami Hiramatsu (Google) Committed by Steven Rostedt (Google)
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tracing: fgraph: Protect return handler from recursion loop 



function_graph_enter_regs() prevents itself from recursion by
ftrace_test_recursion_trylock(), but __ftrace_return_to_handler(),
which is called at the exit, does not prevent such recursion.
Therefore, while it can prevent recursive calls from
fgraph_ops::entryfunc(), it is not able to prevent recursive calls
to fgraph from fgraph_ops::retfunc(), resulting in a recursive loop.
This can lead an unexpected recursion bug reported by Menglong.

 is_endbr() is called in __ftrace_return_to_handler -> fprobe_return
  -> kprobe_multi_link_exit_handler -> is_endbr.

To fix this issue, acquire ftrace_test_recursion_trylock() in the
__ftrace_return_to_handler() after unwind the shadow stack to mark
this section must prevent recursive call of fgraph inside user-defined
fgraph_ops::retfunc().

This is essentially a fix to commit 4346ba16 ("fprobe: Rewrite
fprobe on function-graph tracer"), because before that fgraph was
only used from the function graph tracer. Fprobe allowed user to run
any callbacks from fgraph after that commit.

Reported-by: default avatarMenglong Dong <menglong8.dong@gmail.com>
Closes: https://lore.kernel.org/all/20250918120939.1706585-1-dongml2@chinatelecom.cn/
Fixes: 4346ba16 ("fprobe: Rewrite fprobe on function-graph tracer")
Cc: stable@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/175852292275.307379.9040117316112640553.stgit@devnote2


Signed-off-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: default avatarJiri Olsa <jolsa@kernel.org>
Tested-by: default avatarMenglong Dong <menglong8.dong@gmail.com>
Acked-by: default avatarMenglong Dong <menglong8.dong@gmail.com>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 1da3f145

kernel/trace/fgraph.c

+12 −0
Original line number Diff line number Diff line
@@ -815,6 +815,7 @@ __ftrace_return_to_handler(struct ftrace_regs *fregs, unsigned long frame_pointe 
	unsigned long bitmap;

	unsigned long ret;

	int offset;

	int bit;

	int i;



	ret_stack = ftrace_pop_return_trace(&trace, &ret, frame_pointer, &offset);
@@ -829,6 +830,15 @@ __ftrace_return_to_handler(struct ftrace_regs *fregs, unsigned long frame_pointe 
	if (fregs)

		ftrace_regs_set_instruction_pointer(fregs, ret);



	bit = ftrace_test_recursion_trylock(trace.func, ret);

	/*

	 * This can fail because ftrace_test_recursion_trylock() allows one nest

	 * call. If we are already in a nested call, then we don't probe this and

	 * just return the original return address.

	 */

	if (unlikely(bit < 0))

		goto out;



#ifdef CONFIG_FUNCTION_GRAPH_RETVAL

	trace.retval = ftrace_regs_get_return_value(fregs);

#endif
@@ -852,6 +862,8 @@ __ftrace_return_to_handler(struct ftrace_regs *fregs, unsigned long frame_pointe 
		}

	}



	ftrace_test_recursion_unlock(bit);

out:

	/*

	 * The ftrace_graph_return() may still access the current

	 * ret_stack structure, we need to make sure the update of