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

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Date:   Fri, 2 Dec 2016 16:41:09 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
CC:     "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 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.