linux-kernel - Re: [PATCH v3 2/3] kasan: integrate the common part of two KASAN tag-based modes

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Date:   Tue, 22 Jun 2021 16:54:34 +0300
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Kuan-Ying Lee <Kuan-Ying.Lee@...iatek.com>
Cc:     Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-mediatek@...ts.infradead.org, wsd_upstream@...iatek.com,
        chinwen.chang@...iatek.com, nicholas.tang@...iatek.com
Subject: Re: [PATCH v3 2/3] kasan: integrate the common part of two KASAN
 tag-based modes

On Sun, Jun 20, 2021 at 2:48 PM Kuan-Ying Lee
<Kuan-Ying.Lee@...iatek.com> wrote:
>
> 1. Move kasan_get_free_track() and kasan_set_free_info()
>    into tags.c

Please mention that the patch doesn't only move but also combines
these functions for SW_TAGS and HW_TAGS modes.

> --- /dev/null
> +++ b/mm/kasan/report_tags.h
> @@ -0,0 +1,55 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (c) 2014 Samsung Electronics Co., Ltd.
> + * Copyright (c) 2020 Google, Inc.
> + */
> +#ifndef __MM_KASAN_REPORT_TAGS_H
> +#define __MM_KASAN_REPORT_TAGS_H
> +
> +#include "kasan.h"
> +#include "../slab.h"
> +
> +const char *kasan_get_bug_type(struct kasan_access_info *info)

As mentioned by Alex, don't put this implementation into a header. Put
it into report_tags.c. The declaration is already in kasan.h.


> +{
> +#ifdef CONFIG_KASAN_TAGS_IDENTIFY
> +       struct kasan_alloc_meta *alloc_meta;
> +       struct kmem_cache *cache;
> +       struct page *page;
> +       const void *addr;
> +       void *object;
> +       u8 tag;
> +       int i;
> +
> +       tag = get_tag(info->access_addr);
> +       addr = kasan_reset_tag(info->access_addr);
> +       page = kasan_addr_to_page(addr);
> +       if (page && PageSlab(page)) {
> +               cache = page->slab_cache;
> +               object = nearest_obj(cache, page, (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.
> +        *
> +        * Casting negative numbers to size_t would indeed turn up as
> +        * a large size_t and its value will be larger than ULONG_MAX/2,
> +        * so that this can qualify as out-of-bounds.
> +        */
> +       if (info->access_addr + info->access_size < info->access_addr)
> +               return "out-of-bounds";
> +
> +       return "invalid-access";
> +}