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

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Date:   Fri, 2 Dec 2016 08:01:47 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.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 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.

-- 
Josh