Re: [PATCH] [RESEND v2] structleak: disable STRUCTLEAK_BYREF in combination with KASAN_STACK

From: Arnd Bergmann
Date: Mon Jul 22 2019 - 10:26:59 EST

On Mon, Jul 22, 2019 at 3:43 PM Alexander Potapenko <glider@xxxxxxxxxx> wrote:
> On Mon, Jul 22, 2019 at 1:41 PM Arnd Bergmann <arnd@xxxxxxxx> wrote:
> >
> > KASAN_STACK is currently implied by KASAN on gcc, but could be made a
> > user selectable option if we want to allow combining (non-stack) KASAN
> >
> > Note that it would be possible to specifically address the files that
> > print the warning, but presumably the overall stack usage is still
> > significantly higher than in other configurations, so this would not
> > address the full problem.
> >
> > I could not test this with CONFIG_INIT_STACK_ALL, which may or may not
> > suffer from a similar problem.
> We would love to be able to run KASAN together with
> CONFIG_INIT_STACK_ALL on syzbot, as this will potentially reduce the
> number of flaky errors.

Doesn't that just limit the usefulness of KASAN, as you no longer catch
actual accesses to unintialized variables that KASAN is designed to find?

> Given that we already increase the stack size in KASAN builds, how big
> of a problem are these warnings?
> Perhaps it's better to disable them in this configuration, or push the limit up?

I'm really hoping to lower the per-function limit for 'allmodconfig' builds,
since both a high limit and lots of bogus warnings prevent us from
noticing any newly introduced functions that use a lot of kernel stack
without KASAN.

An allmodconfig build (and ideally also any randconfig build) should always
complete without warnings to be useful for compile testing.