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

Andrey Ryabinin
2016-12-02T18:14:36Z

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.