linux-kernel - Re: [PATCH] riscv: kprobes/ftrace: Add recursion protection to the ftrace callback

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Date:   Sun, 11 Apr 2021 18:09:07 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     jszhang3@...l.ustc.edu.cn
CC:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        mhiramat@...nel.org, rostedt@...dmis.org, guoren@...ux.alibaba.com,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject:     Re: [PATCH] riscv: kprobes/ftrace: Add recursion protection to the ftrace callback

On Mon, 29 Mar 2021 11:14:40 PDT (-0700), jszhang3@...l.ustc.edu.cn wrote:
> From: Jisheng Zhang <jszhang@...nel.org>
>
> Currently, the riscv's kprobes(powerred by ftrace) handler is
> preemptible. Futher check indicates we miss something similar as the
> commit c536aa1c5b17 ("kprobes/ftrace: Add recursion protection to the
> ftrace callback"), so do similar modifications as the commit does.
>
> Fixes: 829adda597fe ("riscv: Add KPROBES_ON_FTRACE supported")
> Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
> ---
>  arch/riscv/kernel/probes/ftrace.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/probes/ftrace.c b/arch/riscv/kernel/probes/ftrace.c
> index 17ca5e923bb0..aab85a82f419 100644
> --- a/arch/riscv/kernel/probes/ftrace.c
> +++ b/arch/riscv/kernel/probes/ftrace.c
> @@ -9,10 +9,16 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
>  	struct kprobe *p;
>  	struct pt_regs *regs;
>  	struct kprobe_ctlblk *kcb;
> +	int bit;
>
> +	bit = ftrace_test_recursion_trylock(ip, parent_ip);
> +	if (bit < 0)
> +		return;
> +
> +	preempt_disable_notrace();
>  	p = get_kprobe((kprobe_opcode_t *)ip);
>  	if (unlikely(!p) || kprobe_disabled(p))
> -		return;
> +		goto out;
>
>  	regs = ftrace_get_regs(fregs);
>  	kcb = get_kprobe_ctlblk();
> @@ -45,6 +51,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
>  		 */
>  		__this_cpu_write(current_kprobe, NULL);
>  	}
> +out:
> +	preempt_enable_notrace();
> +	ftrace_test_recursion_unlock(bit);
>  }
>  NOKPROBE_SYMBOL(kprobe_ftrace_handler);

Thanks, this is on fixes.