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

[Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>]

(2013/12/24 15:39), Jovi Zhangwei wrote:
> On Mon, Dec 23, 2013 at 6:59 PM, Masami Hiramatsu
> <masami.hiramatsu.pt@hitachi.com> wrote:
>> (2013/12/23 13:51), Jovi Zhangwei wrote:
>>> On Fri, Dec 20, 2013 at 5:21 PM, Masami Hiramatsu
>>> <masami.hiramatsu.pt@hitachi.com> wrote:
>>>> (2013/12/20 17:31), Jovi Zhangwei wrote:
>>>>> On Fri, Dec 20, 2013 at 12:42 PM, Masami Hiramatsu
>>>>> <masami.hiramatsu.pt@hitachi.com> wrote:
>>>>>> (2013/12/20 12:07), Jovi Zhangwei wrote:
>>>>>>> On Fri, Dec 20, 2013 at 10:37 AM, Masami Hiramatsu
>>>>>>> <masami.hiramatsu.pt@hitachi.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@hitachi.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.

Agreed. In my case, those have same address, but only probing
__memcpy caused a kernel crash. I'm not sure why, but it is
safe to disable probing on it.

Thank you,

-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com