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From:   Jann Horn <jannh@google.com>
Date:   Tue, 28 Aug 2018 14:53:35 +0200
Message-ID: <CAG48ez2u9gH8skjFcNR-cBctxCEdfZckDjvej07-hooiCvBO8A@mail.gmail.com>
Subject: Re: [PATCH] x86/entry/64: wipe KASAN stack shadow in rewind_stack_do_exit()
To:     Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc:     Andy Lutomirski <luto@kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>, kasan-dev@googlegroups.com,
        Alexander Potapenko <glider@google.com>,
        Kees Cook <keescook@chromium.org>
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On Tue, Aug 28, 2018 at 1:33 PM Andrey Ryabinin <aryabinin@virtuozzo.com> 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. :)