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

From: Andrey Ryabinin
Date: Tue Aug 28 2018 - 07:33:44 EST

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, 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.