Messages in this thread Patch in this message | | | Date | Tue, 16 May 2023 13:25:16 +0900 | From | Masami Hiramatsu (Google) <> | Subject | Re: [PATCH 3/4] fprobe: add recursion detection in fprobe_exit_handler |
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On Mon, 15 May 2023 11:26:40 +0800 Ze Gao <zegao2021@gmail.com> wrote:
> fprobe_hander and fprobe_kprobe_handler has guarded ftrace recusion > detection but fprobe_exit_handler has not, which possibly introduce > recurive calls if the fprobe exit callback calls any traceable > functions. Checking in fprobe_hander or fprobe_kprobe_handler > is not enough and misses this case.
Good catch! Yes, this can fix such recursive call case because if we put a fprobe to the exit of the "func()", recursive call happens as below;
func() { } => rethook => fprobe_exit_handler() => fp->exit_handler() { func() { } => rethook => fprobe_exit_handler() => fp->exit_handler() { func() { } => rethook ...
Note that this should not happen with fprobe-based events because all the code (except for tests) under kernel/trace/ are marked notrace automatically.
kretprobe avoids this by setting itself to current_kprobe, thus the other kprobes recursively called from the rethook will be skipped.
> > So add recusion free guard the same way as fprobe_hander and also > mark fprobe_exit_handler notrace. Since ftrace recursion check does > not employ ips, so here use entry_ip and entry_parent_ip the same as > fprobe_handler.
Looks good to me.
Fixes: 5b0ab78998e3 ("fprobe: Add exit_handler support") Cc: stable@vger.kernel.org Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > Signed-off-by: Ze Gao <zegao@tencent.com> > --- > kernel/trace/fprobe.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c > index ad9a36c87ad9..cf982d4ab142 100644 > --- a/kernel/trace/fprobe.c > +++ b/kernel/trace/fprobe.c > @@ -17,6 +17,7 @@ > struct fprobe_rethook_node { > struct rethook_node node; > unsigned long entry_ip; > + unsigned long entry_parent_ip; > char data[]; > }; > > @@ -39,6 +40,7 @@ static inline notrace void __fprobe_handler(unsigned long ip, unsigned long > } > fpr = container_of(rh, struct fprobe_rethook_node, node); > fpr->entry_ip = ip; > + fpr->entry_parent_ip = parent_ip; > if (fp->entry_data_size) > entry_data = fpr->data; > } > @@ -109,19 +111,30 @@ static void notrace fprobe_kprobe_handler(unsigned long ip, unsigned long parent > ftrace_test_recursion_unlock(bit); > } > > -static void fprobe_exit_handler(struct rethook_node *rh, void *data, > +static void notrace fprobe_exit_handler(struct rethook_node *rh, void *data, > struct pt_regs *regs) > { > struct fprobe *fp = (struct fprobe *)data; > struct fprobe_rethook_node *fpr; > + int bit; > > if (!fp || fprobe_disabled(fp)) > return; > > fpr = container_of(rh, struct fprobe_rethook_node, node); > > + /* we need to assure no calls to traceable functions in-between the > + * end of fprobe_handler and the beginning of fprobe_exit_handler. > + */ > + bit = ftrace_test_recursion_trylock(fpr->entry_ip, fpr->entry_parent_ip); > + if (bit < 0) { > + fp->nmissed++; > + return; > + } > + > fp->exit_handler(fp, fpr->entry_ip, regs, > fp->entry_data_size ? (void *)fpr->data : NULL); > + ftrace_test_recursion_unlock(bit); > } > NOKPROBE_SYMBOL(fprobe_exit_handler); > > -- > 2.40.1 >
-- Masami Hiramatsu (Google) <mhiramat@kernel.org>
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