linux-kernel - Re: [PATCH 1/2] x86/kprobes: Fix kprobes instruction boudary check with CONFIG

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Message-Id: <20220907224913.dfdbea2ec6cd637438dbd09a@kernel.org>
Date:   Wed, 7 Sep 2022 22:49:13 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Suleiman Souhlal <suleiman@...gle.com>,
        bpf <bpf@...r.kernel.org>, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...e.de>,
        Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org
Subject: Re: [PATCH 1/2] x86/kprobes: Fix kprobes instruction boudary check
 with CONFIG_RETHUNK

On Wed, 7 Sep 2022 14:56:52 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, Sep 07, 2022 at 09:55:21AM +0900, Masami Hiramatsu (Google) wrote:
> 
> >  	if (!kallsyms_lookup_size_offset(paddr, NULL, &offset))
> >  		return 0;
> >  
> 
> One more thing:
> 
>   https://lkml.kernel.org/r/20220902130951.853460809@infradead.org
> 
> can result in negative offsets. The expression:
> 
> 	'paddr - offset'
> 
> will still get you to +0, but I might not have fully considered things
> when I wrote that patch.

Hmm, isn't 'offset' unsigned? If 'paddr - offset' is still available
to find the function entry address, it is OK to me.

Thank you,


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>