Re: [PATCH v2] x86/entry/64: wipe KASAN stack shadow before rewind_stack_do_exit()

From: Andrey Ryabinin
Date: Wed Aug 29 2018 - 04:33:30 EST

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@xxxxxxxxxx>
> ---

Acked-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>