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tracing: fgraph: Protect return handler from recursion loop

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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 4346ba1604 ("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: Menglong Dong <menglong8.dong@gmail.com>
Closes: https://lore.kernel.org/all/20250918120939.1706585-1-dongml2@chinatelecom.cn/
Fixes: 4346ba1604 ("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: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Menglong Dong <menglong8.dong@gmail.com>
Acked-by: Menglong Dong <menglong8.dong@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Masami Hiramatsu (Google) 2025-09-22 15:35:22 +09:00 committed by Steven Rostedt (Google)
parent 1da3f145ed
commit 0db0934e7f
1 changed files with 12 additions and 0 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

12
kernel/trace/fgraph.c
View file

@ -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