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

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Date:   Wed, 23 Jun 2021 11:17:55 +0800
From:   Kuan-Ying Lee <Kuan-Ying.Lee@...iatek.com>
To:     Andrey Konovalov <andreyknvl@...il.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 Tue, 2021-06-22 at 16:54 +0300, Andrey Konovalov wrote:
> 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.
> 

Got it.

> > --- /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.
> 

Ok. I will refactor in v4.
Thanks for suggestions.

> > +{
> > +#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";
> > +}