Re: [PATCH v4] x86/suspend: fix false positive KASAN warning on suspend/resume

Josh Poimboeuf
2016-12-02T21:57:42Z

On Fri, Dec 02, 2016 at 10:09:03PM +0100, Pavel Machek wrote:
> On Fri 2016-12-02 11:42:21, Josh Poimboeuf wrote:
> > Resuming from a suspend operation is showing a KASAN false positive
> > warning:
> >
> >
> > Reported-by: Scott Bauer <scott.bauer@intel.com>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
>
> Acked-by: Pavel Machek <pavel@ucw.cz>
>
> > diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
> > index 0e9505f..b2a0cff 100644
> > --- a/mm/kasan/kasan.c
> > +++ b/mm/kasan/kasan.c
> > @@ -80,7 +80,14 @@ 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);
> > + /*
> > + * Calculate the task stack base address. Avoid using 'current'
> > + * because this function is called by early resume code which hasn't
> > + * yet set up the percpu register (%gs).
> > + */
> > + void *base = (void *)((unsigned long)watermark & ~(THREAD_SIZE - 1));
> > +
> > + kasan_unpoison_shadow(base, watermark - base);
> > }
> >
>
> I know you modified this code to be arch-independend... but is it
> really? I guess it is portable enough across architectures that run
> kasan today..

Yes, it's arch-independent as far as I know.

All the implementations of alloc_thread_stack_node() in kernel/fork.c
create THREAD_SIZE sized/aligned stacks.

ia64 has its own implementation of alloc_thread_stack_node(), which also
has a THREAD_SIZE sized/aligned stack, with task_struct stored at the
beginning.

For those architectures for which stack grows up, they would need to
call a different helper which unpoisons the stack above the watermark,
but that was also the case before my patch.

--
Josh