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

Josh Poimboeuf
2016-12-02T14:01:51Z

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