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From:   Andrey Konovalov <andreyknvl@gmail.com>
Date:   Sun, 3 Oct 2021 18:27:31 +0200
Message-ID: <CA+fCnZeJ1AdvEmNmwo8r+ue0qtQVUoQyeMSsq0DMXyK2EQxj5g@mail.gmail.com>
Subject: Re: [PATCH] kasan: Fix tag for large allocations when using CONFIG_SLAB
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc:     Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Fri, Oct 1, 2021 at 4:42 AM Matthew Wilcox (Oracle)
<willy@infradead.org> wrote:
>
> If an object is allocated on a tail page of a multi-page slab, kasan
> will get the wrong tag because page->s_mem is NULL for tail pages.
> I'm not quite sure what the user-visible effect of this might be.
>
> Fixes: 7f94ffbc4c6a ("kasan: add hooks implementation for tag-based mode")
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  mm/kasan/common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 2baf121fb8c5..41779ad109cd 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -298,7 +298,7 @@ static inline u8 assign_tag(struct kmem_cache *cache,
>         /* For caches that either have a constructor or SLAB_TYPESAFE_BY_RCU: */
>  #ifdef CONFIG_SLAB
>         /* For SLAB assign tags based on the object index in the freelist. */
> -       return (u8)obj_to_index(cache, virt_to_page(object), (void *)object);
> +       return (u8)obj_to_index(cache, virt_to_head_page(object), (void *)object);
>  #else
>         /*
>          * For SLUB assign a random tag during slab creation, otherwise reuse
> --
> 2.32.0
>

Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>