linux-kernel - Re: [PATCH v2] x86/entry/64: wipe KASAN stack shadow before rewind_stack_do

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Message-ID: <73efb4f9-b2f8-703d-f1a0-eefc070bdefb@virtuozzo.com>
Date:   Wed, 29 Aug 2018 11:33:36 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Jann Horn <jannh@...gle.com>, Andy Lutomirski <luto@...nel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>
Cc:     kernel list <linux-kernel@...r.kernel.org>,
        kasan-dev@...glegroups.com,
        Alexander Potapenko <glider@...gle.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v2] x86/entry/64: wipe KASAN stack shadow before
 rewind_stack_do_exit()

On 08/28/2018 09:40 PM, Jann Horn wrote:
> Reset the KASAN shadow state of the task stack before rewinding RSP.
> Without this, a kernel oops will leave parts of the stack poisoned, and
> code running under do_exit() can trip over such poisoned regions and cause
> nonsensical false-positive KASAN reports about stack-out-of-bounds bugs.
> 
> This patch does not wipe exception stacks; if you oops on an exception
> stack, you might get random KASAN false-positives from other tasks
> afterwards. This is probably relatively uninteresting, since if you're
> oopsing on an exception stack, you likely have bigger things to worry
> about. It'd be more interesting if vmapped stacks and KASAN were
> compatible, since then handle_stack_overflow() would oops from exception
> stack context.
> 
> Fixes: 2deb4be28077 ("x86/dumpstack: When OOPSing, rewind the stack before do_exit()")
> Signed-off-by: Jann Horn <jannh@...gle.com>
> ---

Acked-by: Andrey Ryabinin <aryabinin@...tuozzo.com>