linux-kernel - Re: [PATCH v2 1/1] kasan: Add memzero init for unaligned size under SLUB debug

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Date:   Mon, 28 Jun 2021 20:41:55 +0200
From:   Marco Elver <elver@...gle.com>
To:     yee.lee@...iatek.com
Cc:     andreyknvl@...il.com, wsd_upstream@...iatek.com,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "open list:KASAN" <kasan-dev@...glegroups.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v2 1/1] kasan: Add memzero init for unaligned size under
 SLUB debug

On Thu, 24 Jun 2021 at 13:27, <yee.lee@...iatek.com> wrote:
>
> From: Yee Lee <yee.lee@...iatek.com>
>
> Issue: when SLUB debug is on, hwtag kasan_unpoison() would overwrite
> the redzone of object with unaligned size.
>
> An additional memzero_explicit() path is added to replacing init by
> hwtag instruction for those unaligned size at SLUB debug mode.
>
> Signed-off-by: Yee Lee <yee.lee@...iatek.com>
> ---
>  mm/kasan/kasan.h | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 8f450bc28045..d1054f35838f 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -387,6 +387,12 @@ static inline void kasan_unpoison(const void *addr, size_t size, bool init)
>
>         if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
>                 return;
> +#if IS_ENABLED(CONFIG_SLUB_DEBUG)

Avoid the #if. I think none of the stuff referenced here is only
available if CONFIG_SLUB_DEBUG. In that case, please just write:

if (IS_ENABLED(CONFIG_SLUB_DEBUG) && init && .........) {

The compiler will correctly optimize out the branch if the config
option is not enabled. But the benefit is we compile-test this code
with all configs.

> +       if (init && ((unsigned long)size & KASAN_GRANULE_MASK)) {
> +               init = false;
> +               memzero_explicit((void *)addr, size);
> +       }
> +#endif

Thanks,
-- Marco