Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1245741

Re: [PATCH v2 2/2] x86/process: Silence KASAN warnings in get_wchan()

Show all headers | View raw

On Tue, Oct 13, 2015 at 3:48 PM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Andrey Ryabinin <aryabinin@virtuozzo.com> wrote:
>
>> get_wchan() is racy by design, it may access volatile stack
>> of running task, thus it may access redzone in a stack frame
>> and cause KASAN to warn about this.
>>
>> Use READ_ONCE_NOCHECK() to silence these warnings.
>>
>> Reported-by: Sasha Levin <sasha.levin@oracle.com>
>> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
>> ---
>>  arch/x86/kernel/process.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
>> index 39e585a..e28db18 100644
>> --- a/arch/x86/kernel/process.c
>> +++ b/arch/x86/kernel/process.c
>> @@ -550,14 +550,14 @@ unsigned long get_wchan(struct task_struct *p)
>>       if (sp < bottom || sp > top)
>>               return 0;
>>
>> -     fp = READ_ONCE(*(unsigned long *)sp);
>> +     fp = READ_ONCE_NOCHECK(*(unsigned long *)sp);
>>       do {
>>               if (fp < bottom || fp > top)
>>                       return 0;
>> -             ip = READ_ONCE(*(unsigned long *)(fp + sizeof(unsigned long)));
>> +             ip = READ_ONCE_NOCHECK(*(unsigned long *)(fp + sizeof(unsigned long)));
>>               if (!in_sched_functions(ip))
>>                       return ip;
>> -             fp = READ_ONCE(*(unsigned long *)fp);
>> +             fp = READ_ONCE_NOCHECK(*(unsigned long *)fp);
>>       } while (count++ < 16 && p->state != TASK_RUNNING);
>>       return 0;
>>  }
>
> Hm, exactly how is the 'red zone' defined? Is this about the current task mostly,
> or when doing get_wchan() on other tasks?


When code is compiled with AddressSanitizer, most variables on stack
have redzones around them, on entry function "poisons" these redzones
(any accesses to them will be flagged), on exit function "unpoisons"
these redzones.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH v2 2/2] x86/process: Silence KASAN warnings in get_wchan() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-13 14:40 +0200
  Re: [PATCH v2 2/2] x86/process: Silence KASAN warnings in get_wchan() Ingo Molnar <mingo@kernel.org> - 2015-10-13 15:50 +0200
    Re: [PATCH v2 2/2] x86/process: Silence KASAN warnings in get_wchan() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-13 16:00 +0200
    Re: [PATCH v2 2/2] x86/process: Silence KASAN warnings in get_wchan() Dmitry Vyukov <dvyukov@google.com> - 2015-10-13 16:00 +0200
      Re: [PATCH v2 2/2] x86/process: Silence KASAN warnings in get_wchan() Andrey Ryabinin <aryabinin@virtuozzo.com> - 2015-10-13 16:20 +0200
      Re: [PATCH v2 2/2] x86/process: Silence KASAN warnings in get_wchan() Ingo Molnar <mingo@kernel.org> - 2015-10-13 16:30 +0200

csiph-web