linux-kernel - Re: [PATCH] bpf: reject blacklisted symbols in kprobe

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Message-Id: <20230516133153.9627751457e0050159f077ab@kernel.org>
Date:   Tue, 16 May 2023 13:31:53 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Yonghong Song <yhs@...a.com>, Ze Gao <zegao2021@...il.com>,
        Jiri Olsa <olsajiri@...il.com>, Song Liu <song@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ze Gao <zegao@...cent.com>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] bpf: reject blacklisted symbols in kprobe_multi to
 avoid recursive trap

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

> On Fri, 12 May 2023 07:29:02 -0700
> Yonghong Song <yhs@...a.com> 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@...nel.org>