linux-kernel - Re: Re: Re: [PATCH -tip v6 06/22] [BUGFIX] x86: Prohibit probing on memcpy/memset

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Date:	Tue, 24 Dec 2013 14:39:29 +0800
From:	Jovi Zhangwei <jovi.zhangwei@...il.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-arch@...r.kernel.org,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>, x86@...nel.org,
	lkml <linux-kernel@...r.kernel.org>,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>, systemtap@...rceware.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: Re: Re: [PATCH -tip v6 06/22] [BUGFIX] x86: Prohibit probing on memcpy/memset

On Mon, Dec 23, 2013 at 6:59 PM, Masami Hiramatsu
<masami.hiramatsu.pt@...achi.com> wrote:
> (2013/12/23 13:51), Jovi Zhangwei wrote:
>> On Fri, Dec 20, 2013 at 5:21 PM, Masami Hiramatsu
>> <masami.hiramatsu.pt@...achi.com> wrote:
>>> (2013/12/20 17:31), Jovi Zhangwei wrote:
>>>> On Fri, Dec 20, 2013 at 12:42 PM, Masami Hiramatsu
>>>> <masami.hiramatsu.pt@...achi.com> wrote:
>>>>> (2013/12/20 12:07), Jovi Zhangwei wrote:
>>>>>> On Fri, Dec 20, 2013 at 10:37 AM, Masami Hiramatsu
>>>>>> <masami.hiramatsu.pt@...achi.com> wrote:
>>>>>>> Hi Jovi,
>>>>>>>
>>>>>>> (2013/12/19 18:37), Jovi Zhangwei wrote:
>>>>>>>> Hi Masami,
>>>>>>>>
>>>>>>>> On Thu, Dec 19, 2013 at 5:04 PM, Masami Hiramatsu
>>>>>>>> <masami.hiramatsu.pt@...achi.com> wrote:
>>>>>>>>> memcpy/memset functions are fundamental functions and
>>>>>>>>> those are involved in kprobe's exception handling.
>>>>>>>>> Prohibit probing on them to avoid kernel crash.
>>>>>>>>>
>>>>>>>> Would you please let me know the LKML link of that bugfix, I cannot
>>>>>>>> find it in my LKML fold.
>>>>>>>
>>>>>>> Yeah, that was found in my testing environment.
>>>>>>>
>>>>>>>> No objection on this patch. :) just want to know more, It seems there
>>>>>>>> have no problem to probe memcpy in my box, maybe I didn't hit the
>>>>>>>> crash code path.
>>>>>>>
>>>>>>> Ah, I see. Originally the problem happened when I put a probe on
>>>>>>> __memcpy. And it looks the instances of memcpy and __memcpy are
>>>>>>> same on x86-64. Thus I decided to blacklist both. (memset/__memset too)
>>>>>>> Have you ever tried to probe __memcpy on your box?
>>>>>>>
>>>>>> Hmm, still no crash, __memcpy and __memset are both tested.
>>>>>>
>>>>>> I use below kprobe related config:
>>>>>>
>>>>>> CONFIG_KPROBES=y
>>>>>> CONFIG_JUMP_LABEL=y
>>>>>> CONFIG_OPTPROBES=y
>>>>>> CONFIG_KPROBES_ON_FTRACE=y
>>>>>
>>>>> Hmm, I've added some debugging options.
>>>>>
>>>>> CONFIG_SLUB_DEBUG=y
>>>>> CONFIG_X86_DEBUGCTLMSR=y
>>>>> CONFIG_PNP_DEBUG_MESSAGES=y
>>>>> CONFIG_DEBUG_INFO=y
>>>>> CONFIG_DEBUG_FS=y
>>>>> CONFIG_DEBUG_KERNEL=y
>>>>> CONFIG_DEBUG_STACK_USAGE=y
>>>>> CONFIG_DEBUG_MEMORY_INIT=y
>>>>> CONFIG_DEBUG_STACKOVERFLOW=y
>>>>> CONFIG_DEBUG_SPINLOCK=y
>>>>> CONFIG_DEBUG_MUTEXES=y
>>>>> CONFIG_DEBUG_LOCK_ALLOC=y
>>>>> CONFIG_DEBUG_LOCKDEP=y
>>>>> CONFIG_DEBUG_BUGVERBOSE=y
>>>>> CONFIG_DEBUG_RODATA=y
>>>>> CONFIG_DEBUG_BOOT_PARAMS=y
>>>>>
>>>>> I guess some of them might cause it.
>>>>>
>>>> I recompiled the kernel with those config enabled, unfortunately still no crash,
>>>> I tested on 3.13.0-rc4, a fedora kvm box.
>>>
>>> Hmm, it's very odd. I'm running 3.13.0-rc4 x86-64 on the fedora
>>> kvm box too. here is the full of my kconfig.
>>>
>> That configuration is still working for me, no crash for memcpy kprobe test.
>
> Would you do __memcpy test? or memcpy test? I only had a crash on the
> __memcpy(__memset).
>
Still no crash, use your kernel config.
memcpy and __memcpy have same address in /proc/kallsyms.

Looks like a interesting problem.

Thanks,

Jovi.
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