linux-kernel - Re: [PATCH 2/2] kprobes/x86: Check for invalid ftrace location in __recover_probed

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Message-ID: <20150220101925.GB25076@gmail.com>
Date:	Fri, 20 Feb 2015 11:19:25 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Petr Mladek <pmladek@...e.cz>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"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
Subject: Re: [PATCH 2/2] kprobes/x86: Check for invalid ftrace location in
 __recover_probed_insn()


* Petr Mladek <pmladek@...e.cz> 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.
> 
> Suggested-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Signed-off-by: Petr Mladek <pmladek@...e.cz>
> Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> ---
>  arch/x86/kernel/kprobes/core.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> 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);

Crashing the system with a BUG_ON() makes users very sad. 
Please use a construct like:

	if (WARN_ON(faddr && faddr != addr))
		return gently;

I've picked up your first patch.

Thanks,

	Ingo
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