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

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Date:   Fri, 2 Dec 2016 13:54:31 +0100
From:   Pavel Machek <pavel@....cz>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, 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

Hi!

> Resuming from a suspend operation is showing a KASAN false positive
> warning:

> KASAN instrumentation poisons the stack when entering a function and
> unpoisons it when exiting the function.  However, in the suspend path,
> some functions never return, so their stack never gets unpoisoned,
> resulting in stale KASAN shadow data which can cause later false
> positive warnings like the one above.
> 
> Reported-by: Scott Bauer <scott.bauer@...el.com>
> Suggested-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>

Acked-by: Pavel Machek <pavel@....cz>

> ---
>  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

Well... you may want to add note to kasan_unpoison_shadow()

/*
* This is called by early resume code, with cpu not yer properly
* resumed. In particular, %gs may not be set up, and thus current
* is not available.
*/

Thanks,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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