linux-kernel - Re: CONFIG_RETHUNK int3 filling prevents kprobes in function body

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Message-ID: <YxYSexFjytTCIJ0i@hirez.programming.kicks-ass.net>
Date:   Mon, 5 Sep 2022 17:15:07 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Borislav Petkov <bp@...e.de>, Josh Poimboeuf <jpoimboe@...nel.org>,
        linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: CONFIG_RETHUNK int3 filling prevents kprobes in function body

On Mon, Sep 05, 2022 at 05:09:16PM +0200, Peter Zijlstra wrote:
> On Sun, Sep 04, 2022 at 11:07:13PM +0900, Masami Hiramatsu wrote:
> > Hi Peter,
> > 
> > I found that the CONFIG_RETHUNK code (path_return) fills the unused bytes
> > with int3 for padding. Unfortunately, this prevents kprobes on the function
> > body after the return code (e.g. branch blocks placed behind the return.)
> 
> Prior to that CONFIG_SLS would already use "ret; int3"

FWIW, there is a compiler option pending to also stick an int3 after
every unconditional jmp.