linux-kernel - Re: [PATCH v2 04/20] kasan, arm64: unpoison stack only with CONFIG_KASAN

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Date:   Thu, 12 Nov 2020 20:38:29 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Will Deacon <will.deacon@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 04/20] kasan, arm64: unpoison stack only with CONFIG_KASAN_STACK

On Thu, Nov 12, 2020 at 10:51 AM Catalin Marinas
<catalin.marinas@....com> wrote:
>
> On Tue, Nov 10, 2020 at 11:20:08PM +0100, Andrey Konovalov wrote:
> > There's a config option CONFIG_KASAN_STACK that has to be enabled for
> > KASAN to use stack instrumentation and perform validity checks for
> > stack variables.
> >
> > There's no need to unpoison stack when CONFIG_KASAN_STACK is not enabled.
> > Only call kasan_unpoison_task_stack[_below]() when CONFIG_KASAN_STACK is
> > enabled.
> >
> > Note, that CONFIG_KASAN_STACK is an option that is currently always
> > defined when CONFIG_KASAN is enabled, and therefore has to be tested
> > with #if instead of #ifdef.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> > Link: https://linux-review.googlesource.com/id/If8a891e9fe01ea543e00b576852685afec0887e3
> > ---
> >  arch/arm64/kernel/sleep.S        |  2 +-
> >  arch/x86/kernel/acpi/wakeup_64.S |  2 +-
> >  include/linux/kasan.h            | 10 ++++++----
> >  mm/kasan/common.c                |  2 ++
> >  4 files changed, 10 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/sleep.S b/arch/arm64/kernel/sleep.S
> > index ba40d57757d6..bdadfa56b40e 100644
> > --- a/arch/arm64/kernel/sleep.S
> > +++ b/arch/arm64/kernel/sleep.S
> > @@ -133,7 +133,7 @@ SYM_FUNC_START(_cpu_resume)
> >        */
> >       bl      cpu_do_resume
> >
> > -#ifdef CONFIG_KASAN
> > +#if defined(CONFIG_KASAN) && CONFIG_KASAN_STACK
> >       mov     x0, sp
> >       bl      kasan_unpoison_task_stack_below
> >  #endif
>
> I don't understand why CONFIG_KASAN_STACK is not a bool (do you plan to
> add more values to it?) but for arm64:

I don't remember if there's an actual reason. Perhaps this is
something that can be reworked later, but I don't want to get into
this in this series.

> Acked-by: Catalin Marinas <catalin.marinas@....com>

Thanks!