[PATCH -next v2] riscv: add VMAP_STACK overflow detection

[tongtiangen]

On 2021/7/23 12:40, Jisheng Zhang wrote:
> On Fri, 23 Jul 2021 12:29:25 +0800
> Jisheng Zhang <jszhang3 at mail.ustc.edu.cn> wrote:
>
>> On Fri, 23 Jul 2021 09:36:47 +0800
>> tongtiangen <tongtiangen at huawei.com> wrote:
>>
>>> On 2021/7/23 7:54, Jisheng Zhang wrote:
>>>> On Thu, 22 Jul 2021 17:42:52 +0200
>>>> Andreas Schwab <schwab at linux-m68k.org> wrote:
>>>>
>>>>> On Jul 22 2021, Jisheng Zhang wrote:
>>>>>
>>>>>> I think we need to pin the stack before calling get_wchan(), could you please
>>>>>> try below patch?
>>>>>
>>>>> Thanks, this fixes the crash for me.
>>>>>
>>>>> Andreas.
>>>>>
>>>>
>>>> Thanks for testing. I will send out formal patch later
>>>>
>>>> Thanks
>>>>
>>>> .
>>>>
>>>
>>> Hi all:
>>> I tried to reproduced this crash in openSUSE code repo（
>>> https://github.com/opensuse/kernel ）, but not reproduced successfully.
>>>
>>>  From the patch of problem repair, the crash is due to task->stack is
>>> released before calling get_wchan, the task state of maybe TASK_DEAD.
>>>
>>> VMAP_STACK is used to detect kernel stack overflow, there is no
>>> connection between the two, it makes me a little confused.
>>
>> I believe the bug exists from the first day of riscv mainlined.
>>
>> Since THREAD_INFO_IN_TASK=y in riscv, so when task stack can be freed
>> before being destroyed.
>
> typo: task stack can be freed before task is destroyed
>
>>
>> When VMAP_STACK=n, task's stack is allocated from linear mapping. When
>> task stack is freed, the corresponding mapping still exists, and since
>> get_wchan() only read, no harm is observed so far.
>>
>> When VMAP_STACK=y, task's stack is allocated from vmalloc area. When
>> task stack is freed, the corresponding mapping may not exist, so I expect
>> MMU fault here, thus the kernel panic.
>>
>> In summary, the bug isn't related with VMAP_STACK, but VMAP_STACK makes
>> the bug observable.
>>
>> Thanks

This explanation is understandable, it is necessary to perform a stack 
validity check before walk_stackframe.

Thanks

>>
>>
>>
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>
>
> .
>