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Date:   Fri, 9 Dec 2022 11:16:34 +0000
From:   Mark Rutland <mark.rutland@arm.com>
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Mark Brown <broonie@kernel.org>,
        Kalesh Singh <kaleshsingh@google.com>,
        Marc Zyngier <maz@kernel.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Sandeepa Prabhu <sandeepa.s.prabhu@gmail.com>
Subject: Re: [PATCH v2 1/3] arm64: Prohibit instrumentation on
 arch_stack_walk()
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On Tue, Dec 06, 2022 at 09:41:37AM +0900, Masami Hiramatsu wrote:
> On Fri, 2 Dec 2022 13:17:30 +0000
> Mark Rutland <mark.rutland@arm.com> wrote:
> > I had a go at testing this patch, and it fixes the crash with the reproducer
> > above, but there are plenty of other instances in stacktrace.c that lead to the
> > same sort of crash, e.g.
> > 
> > # echo p stackinfo_get_task >> ${TRACEFS}/kprobe_events
> > # echo 1 > ${TRACEFS}/events/kprobes/enable
> 
> Oops, thanks for pointing! Hmm, I thought stackinfo_get_task() is an
> inlined function usually. Maybe we should make it nokprobe_inline.
> But this is just one case. I need to scan all symbols to trace...

FWIW, due to other instrumentation issues I've started doing a larger noinstr
cleanup on arm64 which should address this, as fixing this properly involves
also modifying a bunch of underlying helpers (e.g. preempt_count()).

I can Cc you when sending that out, if you'd like? That'll probably be in the
new year.

Thanks,
Mark.