linux-kernel - Re: [PATCH v6 3/4] mm: kasan: Add free_meta size info in struct kasan

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Date:   Sat, 24 Sep 2022 20:05:04 +0200
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        "Sang, Oliver" <oliver.sang@...el.com>
Subject: Re: [PATCH v6 3/4] mm: kasan: Add free_meta size info in struct kasan_cache

On Wed, Sep 21, 2022 at 2:03 PM Feng Tang <feng.tang@...el.com> wrote:
>
> Agree, it's better not touch the internal fields in slub code.
>
> How about the following patch, it merge the 2 functions with one flag
> indicating in meta data or object. (I'm fine with 2 separate functions)

The overall approach sounds good. See some comments below.

> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index b092277bf48d..0ad05a34e708 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -150,11 +150,12 @@ static __always_inline void kasan_cache_create_kmalloc(struct kmem_cache *cache)
>                 __kasan_cache_create_kmalloc(cache);
>  }
>
> -size_t __kasan_metadata_size(struct kmem_cache *cache);
> -static __always_inline size_t kasan_metadata_size(struct kmem_cache *cache)
> +size_t __kasan_meta_size(struct kmem_cache *cache, bool in_slab_object);
> +static __always_inline size_t kasan_meta_size(struct kmem_cache *cache,
> +                                                       bool in_slab_object)

I would keep the name as kasan_metadata_size as it's more clear to
external users but rename in_slab_object to in_object to make the
declaration shorter.

>  {
>         if (kasan_enabled())
> -               return __kasan_metadata_size(cache);
> +               return  __kasan_meta_size(cache, in_slab_object);
>         return 0;
>  }
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 69f583855c8b..2a8710461ebb 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -218,14 +218,21 @@ void __kasan_cache_create_kmalloc(struct kmem_cache *cache)
>         cache->kasan_info.is_kmalloc = true;
>  }
>
> -size_t __kasan_metadata_size(struct kmem_cache *cache)
> +size_t __kasan_meta_size(struct kmem_cache *cache, bool in_slab_object)
>  {
>         if (!kasan_stack_collection_enabled())
>                 return 0;
> -       return (cache->kasan_info.alloc_meta_offset ?
> -               sizeof(struct kasan_alloc_meta) : 0) +
> -               (cache->kasan_info.free_meta_offset ?
> -               sizeof(struct kasan_free_meta) : 0);
> +
> +       if (in_slab_object)
> +               return (cache->kasan_info.alloc_meta_offset == 0 ?
> +                       sizeof(struct kasan_alloc_meta) : 0) +
> +                       (cache->kasan_info.free_meta_offset ?
> +                       sizeof(struct kasan_free_meta) : 0);
> +       else
> +               return (cache->kasan_info.alloc_meta_offset == 0 ?
> +                       sizeof(struct kasan_alloc_meta) : 0) +
> +                       (cache->kasan_info.free_meta_offset ?
> +                       sizeof(struct kasan_free_meta) : 0);

Something weird here: both if and else cases are the same.

The change also needs to be rebased onto [1].

Thanks!

[1] https://lore.kernel.org/linux-mm/c7b316d30d90e5947eb8280f4dc78856a49298cf.1662411799.git.andreyknvl@google.com/