linux-kernel - Re: [RFC PATCH 01/11] ARM: kprobes: directly modify code if kprobe is not initialized.

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Date:	Wed, 14 Jan 2015 00:34:13 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	linux@....linux.org.uk, mingo@...hat.com, x86@...nel.org,
	anil.s.keshavamurthy@...el.com, davem@...emloft.net,
	ananth@...ibm.com, dave.long@...aro.org, tixy@...aro.org,
	lizefan@...wei.com, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 01/11] ARM: kprobes: directly modify code if kprobe
 is not initialized.

(2015/01/07 16:35), Wang Nan wrote:
> If kprobe is optimized before kprobe is initialized, there should
> be only one core, the probed instruction is not armed with breakpoint,
> so simply patch text is okay.

This patch looks very hacky. If kprobes is not initialized, why anyone
can optimize kprobes? I think you must introduce early kprobes init
routine and set init flag at that point.

Thank you,

> 
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> ---
>  arch/arm/probes/kprobes/opt-arm.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/probes/kprobes/opt-arm.c b/arch/arm/probes/kprobes/opt-arm.c
> index 15b37c0..a021474 100644
> --- a/arch/arm/probes/kprobes/opt-arm.c
> +++ b/arch/arm/probes/kprobes/opt-arm.c
> @@ -325,8 +325,17 @@ void __kprobes arch_optimize_kprobes(struct list_head *oplist)
>  		 * Similar to __arch_disarm_kprobe, operations which
>  		 * removing breakpoints must be wrapped by stop_machine
>  		 * to avoid racing.
> +		 *
> +		 * If this function is called before kprobes initialized,
> +		 * the kprobe should be an early kprobe, the instruction
> +		 * is not armed with breakpoint. There should be only
> +		 * one core now, so directly __patch_text is enough.
>  		 */
> -		kprobes_remove_breakpoint(op->kp.addr, insn);
> +		if (unlikely(!kprobes_initialized)) {
> +			BUG_ON(!(op->kp.flags & KPROBE_FLAG_EARLY));
> +			__patch_text(op->kp.addr, insn);
> +		} else
> +			kprobes_remove_breakpoint(op->kp.addr, insn);
>  
>  		list_del_init(&op->list);
>  	}
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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