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Date:   Fri, 9 Jul 2021 18:00:31 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Shaobo Huang <huangshaobo6@huawei.com>
Cc:     <gregkh@linuxfoundation.org>, <chenzefeng2@huawei.com>,
        <kepler.chenxin@huawei.com>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <linux@arm.linux.org.uk>,
        <liucheng32@huawei.com>, <mhiramat@kernel.org>,
        <nixiaoming@huawei.com>, <tixy@linaro.org>, <xiaoqian9@huawei.com>,
        <young.liuyang@huawei.com>, <zengweilin@huawei.com>
Subject: Re: [PATCH 4.4.y] arm: kprobes: Allow to handle reentered kprobe on
 single-stepping
Message-Id: <20210709180031.adc7260b54645b0292a6f02a@kernel.org>
In-Reply-To: <20210709024630.22268-1-huangshaobo6@huawei.com>
References: <YOcOcNBRou5KlbOR@kroah.com>
        <20210709024630.22268-1-huangshaobo6@huawei.com>
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Hi Shaobo,

Thanks for backporting!
Greg, it seems this patch can be applied to 4.9 too without any issue.

Thank you,

On Fri, 9 Jul 2021 10:46:30 +0800
Shaobo Huang <huangshaobo6@huawei.com> wrote:

> From: Masami Hiramatsu <mhiramat@kernel.org>
> 
> commit f3fbd7ec62dec1528fb8044034e2885f2b257941 upstream
> 
> This is arm port of commit 6a5022a56ac3 ("kprobes/x86: Allow to
> handle reentered kprobe on single-stepping")
> 
> Since the FIQ handlers can interrupt in the single stepping
> (or preparing the single stepping, do_debug etc.), we should
> consider a kprobe is hit in the NMI handler. Even in that
> case, the kprobe is allowed to be reentered as same as the
> kprobes hit in kprobe handlers
> (KPROBE_HIT_ACTIVE or KPROBE_HIT_SSDONE).
> 
> The real issue will happen when a kprobe hit while another
> reentered kprobe is processing (KPROBE_REENTER), because
> we already consumed a saved-area for the previous kprobe.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> Signed-off-by: Jon Medhurst <tixy@linaro.org>
> Fixes: 24ba613c9d6c ("ARM kprobes: core code")
> Cc: stable@vger.kernel.org #v2.6.25~v4.11
> Signed-off-by: huangshaobo <huangshaobo6@huawei.com>
> ---
>  arch/arm/probes/kprobes/core.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
> index 3eb018fa1a1f..c3362ddd6c4c 100644
> --- a/arch/arm/probes/kprobes/core.c
> +++ b/arch/arm/probes/kprobes/core.c
> @@ -270,6 +270,7 @@ void __kprobes kprobe_handler(struct pt_regs *regs)
>  			switch (kcb->kprobe_status) {
>  			case KPROBE_HIT_ACTIVE:
>  			case KPROBE_HIT_SSDONE:
> +			case KPROBE_HIT_SS:
>  				/* A pre- or post-handler probe got us here. */
>  				kprobes_inc_nmissed_count(p);
>  				save_previous_kprobe(kcb);
> @@ -278,6 +279,11 @@ void __kprobes kprobe_handler(struct pt_regs *regs)
>  				singlestep(p, regs, kcb);
>  				restore_previous_kprobe(kcb);
>  				break;
> +			case KPROBE_REENTER:
> +				/* A nested probe was hit in FIQ, it is a BUG */
> +				pr_warn("Unrecoverable kprobe detected at %p.\n",
> +					p->addr);
> +				/* fall through */
>  			default:
>  				/* impossible cases */
>  				BUG();
> -- 
> 2.12.3
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>