Re: [PATCH] bpf: reject blacklisted symbols in kprobe_multi to avoid recursive trap

[Google]

On Sat, 13 May 2023 00:17:57 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> On Fri, 12 May 2023 07:29:02 -0700
> Yonghong Song <yhs@xxxxxxxx> wrote:
> 
> > A fprobe_blacklist might make sense indeed as fprobe and kprobe are 
> > quite different... Thanks for working on this.
> 
> Hmm, I think I see the problem:
> 
> fprobe_kprobe_handler() {
>    kprobe_busy_begin() {
>       preempt_disable() {
>          preempt_count_add() {  <-- trace
>             fprobe_kprobe_handler() {
> 		[ wash, rinse, repeat, CRASH!!! ]
> 
> Either the kprobe_busy_begin() needs to use preempt_disable_notrace()
> versions, or fprobe_kprobe_handle() needs a
> ftrace_test_recursion_trylock() call.

Oops, I got it. Is preempt_count_add() tracable? If so, kprobe_busy_begin()
should be updated.

Thanks,

> 
> -- Steve


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>