linux-kernel - Re: kprobes vs __ex

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Message-Id: <20170301011651.d9961aee415783f3c7b78b19@kernel.org>
Date:   Wed, 1 Mar 2017 01:16:51 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: kprobes vs __ex_table[]

Hi Peter,

On Fri, 24 Feb 2017 10:26:46 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> One more complication with __ex_table and optimized kprobes is that we
> need to be careful not to clobber __ex_table[].fixup. It would be very
> bad if the optimized probe were to clobber the address we let the fixup
> return to -- or that needs fixups too, _after_ running
> __ex_table[].handler().

This gave me a chance to read closer current code, and I found that
I made a mistake 5 years ago on kprobe-booster. The commit 464846888d9a
("x86/kprobes: Fix a bug which can modify kernel code permanently")
introduced another bug -- which passed the address of copied instruction
instead of probing address to search_exception_tables() when preparing
kprobe-booster (skips singlestep.)

I'll send a fix patch.

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>