linux-kernel - Re: [PATCH RFC v2 19/21] kasan: don't round

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Date:   Wed, 28 Oct 2020 18:01:49 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Serban Constantinescu <serbanc@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Elena Petrova <lenaptr@...gle.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-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v2 19/21] kasan: don't round_up too much

On Thu, Oct 22, 2020 at 3:20 PM Andrey Konovalov <andreyknvl@...gle.com> wrote:
>
> For tag-based mode kasan_poison_memory() already rounds up the size. Do
> the same for software modes and remove round_up() from common code.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> Link: https://linux-review.googlesource.com/id/Ib397128fac6eba874008662b4964d65352db4aa4

Reviewed-by: Dmitry Vyukov <dvyukov@...gle.com>

> ---
>  mm/kasan/common.c | 8 ++------
>  mm/kasan/shadow.c | 1 +
>  2 files changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 5622b0ec0907..983383ebe32a 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -215,9 +215,7 @@ void __kasan_unpoison_object_data(struct kmem_cache *cache, void *object)
>
>  void __kasan_poison_object_data(struct kmem_cache *cache, void *object)
>  {
> -       kasan_poison_memory(object,
> -                       round_up(cache->object_size, KASAN_GRANULE_SIZE),
> -                       KASAN_KMALLOC_REDZONE);
> +       kasan_poison_memory(object, cache->object_size, KASAN_KMALLOC_REDZONE);
>  }
>
>  /*
> @@ -290,7 +288,6 @@ static bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
>  {
>         u8 tag;
>         void *tagged_object;
> -       unsigned long rounded_up_size;
>
>         tag = get_tag(object);
>         tagged_object = object;
> @@ -311,8 +308,7 @@ static bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
>                 return true;
>         }
>
> -       rounded_up_size = round_up(cache->object_size, KASAN_GRANULE_SIZE);
> -       kasan_poison_memory(object, rounded_up_size, KASAN_KMALLOC_FREE);
> +       kasan_poison_memory(object, cache->object_size, KASAN_KMALLOC_FREE);
>
>         if (static_branch_unlikely(&kasan_stack)) {
>                 if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) ||
> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> index 616ac64c4a21..ab1d39c566b9 100644
> --- a/mm/kasan/shadow.c
> +++ b/mm/kasan/shadow.c
> @@ -82,6 +82,7 @@ void kasan_poison_memory(const void *address, size_t size, u8 value)
>          * addresses to this function.
>          */
>         address = reset_tag(address);
> +       size = round_up(size, KASAN_GRANULE_SIZE);
>
>         shadow_start = kasan_mem_to_shadow(address);
>         shadow_end = kasan_mem_to_shadow(address + size);
> --
> 2.29.0.rc1.297.gfa9743e501-goog
>