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Date:   Tue, 21 Nov 2023 17:47:03 +0100
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     David Rientjes <rientjes@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Marco Elver <elver@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Kees Cook <keescook@...omium.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        cgroups@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 03/21] KASAN: remove code paths guarded by CONFIG_SLAB

On Mon, Nov 20, 2023 at 7:34 PM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> With SLAB removed and SLUB the only remaining allocator, we can clean up
> some code that was depending on the choice.
>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Reviewed-by: Marco Elver <elver@...gle.com>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>  mm/kasan/common.c     | 13 ++-----------
>  mm/kasan/kasan.h      |  3 +--
>  mm/kasan/quarantine.c |  7 -------
>  3 files changed, 3 insertions(+), 20 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 256930da578a..5d95219e69d7 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -153,10 +153,6 @@ void __kasan_poison_object_data(struct kmem_cache *cache, void *object)
>   * 2. A cache might be SLAB_TYPESAFE_BY_RCU, which means objects can be
>   *    accessed after being freed. We preassign tags for objects in these
>   *    caches as well.
> - * 3. For SLAB allocator we can't preassign tags randomly since the freelist
> - *    is stored as an array of indexes instead of a linked list. Assign tags
> - *    based on objects indexes, so that objects that are next to each other
> - *    get different tags.
>   */
>  static inline u8 assign_tag(struct kmem_cache *cache,
>                                         const void *object, bool init)
> @@ -171,17 +167,12 @@ static inline u8 assign_tag(struct kmem_cache *cache,
>         if (!cache->ctor && !(cache->flags & SLAB_TYPESAFE_BY_RCU))
>                 return init ? KASAN_TAG_KERNEL : kasan_random_tag();
>
> -       /* 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_slab(object), (void *)object);
> -#else
>         /*
> -        * For SLUB assign a random tag during slab creation, otherwise reuse
> +        * For caches that either have a constructor or SLAB_TYPESAFE_BY_RCU,
> +        * assign a random tag during slab creation, otherwise reuse
>          * the already assigned tag.
>          */
>         return init ? kasan_random_tag() : get_tag(object);
> -#endif
>  }
>
>  void * __must_check __kasan_init_slab_obj(struct kmem_cache *cache,
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 8b06bab5c406..eef50233640a 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -373,8 +373,7 @@ void kasan_set_track(struct kasan_track *track, gfp_t flags);
>  void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags);
>  void kasan_save_free_info(struct kmem_cache *cache, void *object);
>
> -#if defined(CONFIG_KASAN_GENERIC) && \
> -       (defined(CONFIG_SLAB) || defined(CONFIG_SLUB))
> +#ifdef CONFIG_KASAN_GENERIC
>  bool kasan_quarantine_put(struct kmem_cache *cache, void *object);
>  void kasan_quarantine_reduce(void);
>  void kasan_quarantine_remove_cache(struct kmem_cache *cache);
> diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
> index ca4529156735..138c57b836f2 100644
> --- a/mm/kasan/quarantine.c
> +++ b/mm/kasan/quarantine.c
> @@ -144,10 +144,6 @@ static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
>  {
>         void *object = qlink_to_object(qlink, cache);
>         struct kasan_free_meta *meta = kasan_get_free_meta(cache, object);
> -       unsigned long flags;
> -
> -       if (IS_ENABLED(CONFIG_SLAB))
> -               local_irq_save(flags);
>
>         /*
>          * If init_on_free is enabled and KASAN's free metadata is stored in
> @@ -166,9 +162,6 @@ static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
>         *(u8 *)kasan_mem_to_shadow(object) = KASAN_SLAB_FREE;
>
>         ___cache_free(cache, object, _THIS_IP_);
> -
> -       if (IS_ENABLED(CONFIG_SLAB))
> -               local_irq_restore(flags);
>  }
>
>  static void qlist_free_all(struct qlist_head *q, struct kmem_cache *cache)
>
> --
> 2.42.1
>

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

Very nice to see SLAB-induced complexity being gone :)

Thank you!

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