linux-kernel - Re: [PATCH 2/2] kprobes: disabling optimized kprobes for entry text section

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Message-ID: <4D632BE9.6090108@hitachi.com>
Date:	Tue, 22 Feb 2011 12:22:17 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	mingo@...e.hu, acme@...hat.com, fweisbec@...il.com, hpa@...or.com,
	ananth@...ibm.com, davem@...emloft.net,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	a.p.zijlstra@...llo.nl, eric.dumazet@...il.com,
	2nddept-manager@....hitachi.co.jp,
	"2nddept-manager@....hitachi.co.jp" 
	<2nddept-manager@....hitachi.co.jp>
Subject: Re: [PATCH 2/2] kprobes: disabling optimized kprobes for entry text
 section

(2011/02/21 23:25), Jiri Olsa wrote:
> You can crash the kernel using kprobe tracer by running:
> 
> echo "p system_call_after_swapgs" > ./kprobe_events
> echo 1 > ./events/kprobes/enable
> 
> The reason is that at the system_call_after_swapgs label, the kernel
> stack is not set up. If optimized kprobes are enabled, the user space
> stack is being used in this case (see optimized kprobe template) and
> this might result in a crash.
> 
> There are several places like this over the entry code (entry_$BIT).
> As it seems there's no any reasonable/maintainable way to disable only
> those places where the stack is not ready, I switched off the whole
> entry code from kprobe optimizing.

Thank you very much!

> 
> wbr,
> jirka
> 
> 
> Signed-off-by: Jiri Olsa <jolsa@...hat.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

> ---
>  arch/x86/kernel/kprobes.c |    8 ++++++++
>  1 files changed, 8 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
> index d91c477..d03bc1e 100644
> --- a/arch/x86/kernel/kprobes.c
> +++ b/arch/x86/kernel/kprobes.c
> @@ -1276,6 +1276,14 @@ static int __kprobes can_optimize(unsigned long paddr)
>  	if (!kallsyms_lookup_size_offset(paddr, &size, &offset))
>  		return 0;
>  
> +	/*
> +	 * Do not optimize in the entry code due to the unstable
> +	 * stack handling.
> +	 */
> +	if ((paddr >= (unsigned long ) __entry_text_start) &&
> +	    (paddr <  (unsigned long ) __entry_text_end))
> +		return 0;
> +
>  	/* Check there is enough space for a relative jump. */
>  	if (size - offset < RELATIVEJUMP_SIZE)
>  		return 0;


-- 
Masami HIRAMATSU
2nd Dept. Linux Technology Center
Hitachi, Ltd., Systems Development Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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