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From:   Marco Elver <elver@google.com>
Date:   Mon, 20 Jun 2022 15:39:42 +0200
Message-ID: <CANpmjNNKKUkxOnOQBf5EZ3kCMv_wqd0V74R5Rx8K1+MhbXmSJQ@mail.gmail.com>
Subject: Re: [PATCH 05/32] kasan: drop CONFIG_KASAN_TAGS_IDENTIFY
To:     andrey.konovalov@linux.dev
Cc:     Alexander Potapenko <glider@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev@googlegroups.com, Peter Collingbourne <pcc@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Florian Mayer <fmayer@google.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
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On Mon, 13 Jun 2022 at 22:15, <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@google.com>
>
> Drop CONFIG_KASAN_TAGS_IDENTIFY and related code to simplify making
> changes to the reporting code.
>
> The dropped functionality will be restored in the following patches in
> this series.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

Reviewed-by: Marco Elver <elver@google.com>


> ---
>  lib/Kconfig.kasan      |  8 --------
>  mm/kasan/kasan.h       | 12 +-----------
>  mm/kasan/report_tags.c | 28 ----------------------------
>  mm/kasan/tags.c        | 21 ++-------------------
>  4 files changed, 3 insertions(+), 66 deletions(-)
>
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index f0973da583e0..ca09b1cf8ee9 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -167,14 +167,6 @@ config KASAN_STACK
>           as well, as it adds inline-style instrumentation that is run
>           unconditionally.
>
> -config KASAN_TAGS_IDENTIFY
> -       bool "Memory corruption type identification"
> -       depends on KASAN_SW_TAGS || KASAN_HW_TAGS
> -       help
> -         Enables best-effort identification of the bug types (use-after-free
> -         or out-of-bounds) at the cost of increased memory consumption.
> -         Only applicable for the tag-based KASAN modes.
> -
>  config KASAN_VMALLOC
>         bool "Check accesses to vmalloc allocations"
>         depends on HAVE_ARCH_KASAN_VMALLOC
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 610057e651d2..aa6b43936f8d 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -168,23 +168,13 @@ struct kasan_track {
>         depot_stack_handle_t stack;
>  };
>
> -#if defined(CONFIG_KASAN_TAGS_IDENTIFY) && defined(CONFIG_KASAN_SW_TAGS)
> -#define KASAN_NR_FREE_STACKS 5
> -#else
> -#define KASAN_NR_FREE_STACKS 1
> -#endif
> -
>  struct kasan_alloc_meta {
>         struct kasan_track alloc_track;
>         /* Generic mode stores free track in kasan_free_meta. */
>  #ifdef CONFIG_KASAN_GENERIC
>         depot_stack_handle_t aux_stack[2];
>  #else
> -       struct kasan_track free_track[KASAN_NR_FREE_STACKS];
> -#endif
> -#ifdef CONFIG_KASAN_TAGS_IDENTIFY
> -       u8 free_pointer_tag[KASAN_NR_FREE_STACKS];
> -       u8 free_track_idx;
> +       struct kasan_track free_track;
>  #endif
>  };
>
> diff --git a/mm/kasan/report_tags.c b/mm/kasan/report_tags.c
> index e25d2166e813..35cf3cae4aa4 100644
> --- a/mm/kasan/report_tags.c
> +++ b/mm/kasan/report_tags.c
> @@ -5,37 +5,9 @@
>   */
>
>  #include "kasan.h"
> -#include "../slab.h"
>
>  const char *kasan_get_bug_type(struct kasan_report_info *info)
>  {
> -#ifdef CONFIG_KASAN_TAGS_IDENTIFY
> -       struct kasan_alloc_meta *alloc_meta;
> -       struct kmem_cache *cache;
> -       struct slab *slab;
> -       const void *addr;
> -       void *object;
> -       u8 tag;
> -       int i;
> -
> -       tag = get_tag(info->access_addr);
> -       addr = kasan_reset_tag(info->access_addr);
> -       slab = kasan_addr_to_slab(addr);
> -       if (slab) {
> -               cache = slab->slab_cache;
> -               object = nearest_obj(cache, slab, (void *)addr);
> -               alloc_meta = kasan_get_alloc_meta(cache, object);
> -
> -               if (alloc_meta) {
> -                       for (i = 0; i < KASAN_NR_FREE_STACKS; i++) {
> -                               if (alloc_meta->free_pointer_tag[i] == tag)
> -                                       return "use-after-free";
> -                       }
> -               }
> -               return "out-of-bounds";
> -       }
> -#endif
> -
>         /*
>          * If access_size is a negative number, then it has reason to be
>          * defined as out-of-bounds bug type.
> diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
> index 1ba3c8399f72..e0e5de8ce834 100644
> --- a/mm/kasan/tags.c
> +++ b/mm/kasan/tags.c
> @@ -30,39 +30,22 @@ void kasan_save_free_info(struct kmem_cache *cache,
>                                 void *object, u8 tag)
>  {
>         struct kasan_alloc_meta *alloc_meta;
> -       u8 idx = 0;
>
>         alloc_meta = kasan_get_alloc_meta(cache, object);
>         if (!alloc_meta)
>                 return;
>
> -#ifdef CONFIG_KASAN_TAGS_IDENTIFY
> -       idx = alloc_meta->free_track_idx;
> -       alloc_meta->free_pointer_tag[idx] = tag;
> -       alloc_meta->free_track_idx = (idx + 1) % KASAN_NR_FREE_STACKS;
> -#endif
> -
> -       kasan_set_track(&alloc_meta->free_track[idx], GFP_NOWAIT);
> +       kasan_set_track(&alloc_meta->free_track, GFP_NOWAIT);
>  }
>
>  struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
>                                 void *object, u8 tag)
>  {
>         struct kasan_alloc_meta *alloc_meta;
> -       int i = 0;
>
>         alloc_meta = kasan_get_alloc_meta(cache, object);
>         if (!alloc_meta)
>                 return NULL;
>
> -#ifdef CONFIG_KASAN_TAGS_IDENTIFY
> -       for (i = 0; i < KASAN_NR_FREE_STACKS; i++) {
> -               if (alloc_meta->free_pointer_tag[i] == tag)
> -                       break;
> -       }
> -       if (i == KASAN_NR_FREE_STACKS)
> -               i = alloc_meta->free_track_idx;
> -#endif
> -
> -       return &alloc_meta->free_track[i];
> +       return &alloc_meta->free_track;
>  }
> --
> 2.25.1
>
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