Re: [PATCH] x86/entry/64: wipe KASAN stack shadow in rewind_stack_do_exit()

From: Jann Horn
Date: Tue Aug 28 2018 - 08:54:07 EST

On Tue, Aug 28, 2018 at 1:33 PM Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> wrote:
> On 08/28/2018 01:38 PM, Jann Horn wrote:
> >> Why this has to be done in the rewind_stack_do_exit()?
> >> Are there any problems with calling the kasan_unpoison_task_stack(current) from oops_end(), before the rewind_stack_do_exit()?
> >
> > Ooh, good point! I didn't see that KASAN instrumentation is disabled
> > for dumpstack.c.
> It doesn't really matter. This would work with instrumented oops_end() as well.
> kasan_unpoison_task_stack() will unpoison everything including oops_end's stack.
> It would be also ok if kasan_unpoison_task_stack() instrumented,

But then that would rely on ASAN implementation details, so I'd be
hesitant to do that.

> or calling any number of instrumented functions
> in between kasan_unpoison_task_stack() and rewind_stack_do_exit(). As long as we return from these functions before
> the rewind_stack_do_exit(), the stack will be unpoisoned on return.

Yeah, I understand that. :)