linux-kernel - Re: [PATCH] arm64: kprobes: Fix Uexpected kernel BRK exception at EL1

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Date:   Fri, 22 Jan 2021 15:29:21 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: kprobes: Fix Uexpected kernel BRK exception at EL1

On 01/22/21 22:36, Masami Hiramatsu wrote:
> > Further analysis showed that kcb->kprobe_status is set to
> > KPROBE_REENTER when the error occurs. By teaching
> > kprobe_breakpoint_ss_handler() to handle this status I can no  longer
> > reproduce the problem.
> 
> Very good catch! Yes, this missed the reentered kprobe case.
> 
> Acked-by: Masami Hiramatsu <mhiramat@...nel.org>

Thanks!

> 
> > 
> > Fixes: ba090f9cafd5 ("arm64: kprobes: Remove redundant kprobe_step_ctx")
> > Signed-off-by: Qais Yousef <qais.yousef@....com>
> > ---
> > 
> > Another change in behavior I noticed is that before ba090f9cafd5 ("arm64:
> > kprobes: Remove redundant kprobe_step_ctx") if 'cur' was NULL we wouldn't
> > return DBG_HOOK_ERROR, but after the change we do.
> 
> It should not happen, since the KPROBES_BRK_SS_IMM must be used only for
> kprobes's second break which must happen on the trampoline instruction
> buffer, which must set current kprobes before execution.

I see. Thanks for the explanation!

Cheers

--
Qais Yousef