linux-kernel - Re: [PATCH] kprobes/x86: Check for invalid ftrace location in __recover_probed

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Date:	Wed, 04 Feb 2015 10:15:01 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Petr Mladek <pmladek@...e.cz>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	Ananth NMavinakayanahalli <ananth@...ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jiri Kosina <jkosina@...e.cz>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] kprobes/x86: Check for invalid ftrace location in
 __recover_probed_insn()

(2015/02/04 1:21), Petr Mladek wrote:
> __recover_probed_insn() should always be called from an address where
> an instructions starts. The check for ftrace_location() might help to
> discover a potential inconsistency. Something goes terribly wrong when
> an address inside the ftrace location is checked. Let's BUG() in this case.

Looks good to me :)

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

Thank you,

> 
> Suggested-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Signed-off-by: Petr Mladek <pmladek@...e.cz>
> ---
>  arch/x86/kernel/kprobes/core.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> 
> This is follow up for the patch ("[PATCH v2] kprobes/x86: Use 5-byte NOP
> when the code might be modified by ftrace") based on the Masami's
> suggestion, see https://lkml.org/lkml/2015/2/3/207
> 
> Let me know if I should merge this with the first patch and send v3.
> 
> 
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 2f464b56766a..124577dcf768 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -228,6 +228,12 @@ __recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
>  	kp = get_kprobe((void *)addr);
>  	faddr = ftrace_location(addr);
>  	/*
> +	 * Addresses inside the ftrace location are refused by
> +	 * arch_check_ftrace_location(). Something went terribly wrong
> +	 * if such an address is checked here.
> +	 */
> +	BUG_ON(faddr && faddr != addr);
> +	/*
>  	 * Use the current code if it is not modified by Kprobe
>  	 * and it cannot be modified by ftrace.
>  	 */
> 


-- 
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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