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 4346ba160409 ("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 <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/
Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer")
Cc: [email protected]
Cc: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/175852292275.307379.9040117316112640553.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Tested-by: Menglong Dong <[email protected]>
Acked-by: Menglong Dong <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

0 files changed, 0 insertions, 0 deletions