linux-kernel - Re: [PATCH v2] x86/suspend: fix false positive KASAN warning on suspend/resume

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Date:   Fri, 2 Dec 2016 15:02:46 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        linux-pm@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Scott Bauer <scott.bauer@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH v2] x86/suspend: fix false positive KASAN warning on suspend/resume

On Fri, Dec 2, 2016 at 3:01 PM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> On Fri, Dec 02, 2016 at 04:41:09PM +0300, Andrey Ryabinin wrote:
>>
>>
>> On 12/01/2016 11:31 PM, Josh Poimboeuf wrote:
>>
>> >  arch/x86/kernel/acpi/wakeup_64.S | 16 ++++++++++++++++
>> >  1 file changed, 16 insertions(+)
>> >
>> > diff --git a/arch/x86/kernel/acpi/wakeup_64.S b/arch/x86/kernel/acpi/wakeup_64.S
>> > index 169963f..1df9b75 100644
>> > --- a/arch/x86/kernel/acpi/wakeup_64.S
>> > +++ b/arch/x86/kernel/acpi/wakeup_64.S
>> > @@ -109,6 +109,22 @@ ENTRY(do_suspend_lowlevel)
>> >     movq    pt_regs_r14(%rax), %r14
>> >     movq    pt_regs_r15(%rax), %r15
>> >
>> > +#ifdef CONFIG_KASAN
>> > +   /*
>> > +    * The suspend path may have poisoned some areas deeper in the stack,
>> > +    * which we now need to unpoison.
>> > +    *
>> > +    * We can't call kasan_unpoison_task_stack_below() because it uses %gs
>> > +    * for 'current', which hasn't been set up yet.  Instead, calculate the
>> > +    * stack range manually and call kasan_unpoison_shadow().
>> > +    */
>> > +   movq    %rsp, %rdi
>> > +   andq    $CURRENT_MASK, %rdi
>> > +   movq    %rsp, %rsi
>> > +   xorq    %rdi, %rsi
>> > +   call    kasan_unpoison_shadow
>> > +#endif
>> > +
>>
>> Looks good, but in fact we can use kasan_unpoison_task_stack_below(). We just need to change it a little:
>>
>> diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
>> index 70c0097..e779236 100644
>> --- a/mm/kasan/kasan.c
>> +++ b/mm/kasan/kasan.c
>> @@ -80,7 +80,9 @@ void kasan_unpoison_task_stack(struct task_struct *task)
>>  /* Unpoison the stack for the current task beyond a watermark sp value. */
>>  asmlinkage void kasan_unpoison_task_stack_below(const void *watermark)
>>  {
>> -       __kasan_unpoison_stack(current, watermark);
>> +       void *base = (void *)((unsigned long)watermark & ~(THREAD_SIZE - 1));
>> +
>> +       kasan_unpoison_shadow(base, watermark - base);
>>  }
>>
>>
>> With this we don't have to calculate stack range in assembly.
>
> That is better indeed, will do a v3.

agree