Re: [PATCH RFC v2 20/21] kasan: simplify assign_tag and set_tag calls

[Dmitry Vyukov]

On Thu, Oct 22, 2020 at 3:20 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
>
> set_tag() already ignores the tag for the generic mode, so just call it
> as is. Add a check for the generic mode to assign_tag(), and simplify its
> call in ____kasan_kmalloc().
>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Link: https://linux-review.googlesource.com/id/I18905ca78fb4a3d60e1a34a4ca00247272480438

Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>

> ---
>  mm/kasan/common.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 983383ebe32a..3cd56861eb11 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -235,6 +235,9 @@ void __kasan_poison_object_data(struct kmem_cache *cache, void *object)
>  static u8 assign_tag(struct kmem_cache *cache, const void *object,
>                         bool init, bool keep_tag)
>  {
> +       if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +               return 0xff;
> +
>         /*
>          * 1. When an object is kmalloc()'ed, two hooks are called:
>          *    kasan_slab_alloc() and kasan_kmalloc(). We assign the
> @@ -277,8 +280,8 @@ void * __must_check __kasan_init_slab_obj(struct kmem_cache *cache,
>                 __memset(alloc_meta, 0, sizeof(*alloc_meta));
>         }
>
> -       if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) || IS_ENABLED(CONFIG_KASAN_HW_TAGS))
> -               object = set_tag(object, assign_tag(cache, object, true, false));
> +       /* Tag is ignored in set_tag() without CONFIG_KASAN_SW/HW_TAGS */
> +       object = set_tag(object, assign_tag(cache, object, true, false));
>
>         return (void *)object;
>  }
> @@ -360,9 +363,7 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
>                                 KASAN_GRANULE_SIZE);
>         redzone_end = round_up((unsigned long)object + cache->object_size,
>                                 KASAN_GRANULE_SIZE);
> -
> -       if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) || IS_ENABLED(CONFIG_KASAN_HW_TAGS))
> -               tag = assign_tag(cache, object, false, keep_tag);
> +       tag = assign_tag(cache, object, false, keep_tag);
>
>         /*
>          * Don't unpoison the object when keeping the tag. Tag is kept for:
> --
> 2.29.0.rc1.297.gfa9743e501-goog
>