From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@suse.de>,
Josh Poimboeuf <jpoimboe@kernel.org>,
linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: CONFIG_RETHUNK int3 filling prevents kprobes in function body
Date: Tue, 6 Sep 2022 10:33:29 +0900 [thread overview]
Message-ID: <20220906103329.a2e79b1763bad299c0e1f11e@kernel.org> (raw)
In-Reply-To: <YxYbPTmN1TCp4En5@hirez.programming.kicks-ass.net>
On Mon, 5 Sep 2022 17:52:29 +0200
Peter Zijlstra <peterz@infradead.org> wrote:
> On Mon, Sep 05, 2022 at 05:09:16PM +0200, Peter Zijlstra wrote:
>
> > > This is because kprobes decodes function body to ensure the probed address
> > > is an instruction boundary, and if it finds the 0xcc (int3), it stops
> > > decoding and reject probing because the int3 is usually used for a
> > > software breakpoint and is replacing some other instruction. Without
> > > recovering the instruction, it can not continue decoding safely.
> >
> > I can't follow this logic. Decoding the single byte int3 instruction is
> > trivial. If you want a sanity check, follow the branches you found while
> > decoding the instruction starting at +0.
>
> Specifically, kprobe is the only one scribbling random [*] instructions
> with int3 in kernel text, so if kprobes doesn't know about the int3, it
> must be padding.
No, kgdb is also handles int3 for its breakpoint. Of course we can
ignore it or ask kgdb to expose the API to decode it.
>
> [*] there's also static_call, jump_label and ftrace that use
> text_poke_bp() to scribble instructions but those are well known
> locations.
Yeah, but it is a temporal use, so user can try it again.
Thank you,
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
next prev parent reply other threads:[~2022-09-06 1:33 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-04 14:07 CONFIG_RETHUNK int3 filling prevents kprobes in function body Masami Hiramatsu
2022-09-05 14:57 ` Steven Rostedt
2022-09-05 15:10 ` Peter Zijlstra
2022-09-05 15:20 ` Peter Zijlstra
2022-09-06 1:30 ` Masami Hiramatsu
2022-09-05 15:09 ` Peter Zijlstra
2022-09-05 15:15 ` Peter Zijlstra
2022-09-05 15:52 ` Peter Zijlstra
2022-09-06 1:33 ` Masami Hiramatsu [this message]
2022-09-06 8:44 ` Peter Zijlstra
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