linux-kernel - Re: [PATCH v6 13/18] khwasan: add bug reporting routines

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Message-ID: <CAAeHK+xFV0x3g0_HUp_TtACR1dsjXCGdzFyw0BHEmrwqdXi-Og@mail.gmail.com>
Date:   Tue, 18 Sep 2018 19:36:35 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Dave Martin <dave.martin@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Ingo Molnar <mingo@...nel.org>,
        Paul Lawrence <paullawrence@...gle.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-sparse@...r.kernel.org, Linux-MM <linux-mm@...ck.org>,
        "open list:KERNEL BUILD + fi..." <linux-kbuild@...r.kernel.org>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Jann Horn <jannh@...gle.com>,
        Mark Brand <markbrand@...gle.com>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Vishwath Mohan <vishwath@...gle.com>
Subject: Re: [PATCH v6 13/18] khwasan: add bug reporting routines

On Wed, Sep 12, 2018 at 7:50 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <andreyknvl@...gle.com> wrote:

>> +#ifdef CONFIG_KASAN_HW
>
> We already have #ifdef CONFIG_KASAN_HW section below with additional
> functions for KASAN_HW and empty stubs otherwise. I would add this one
> there as well.

Will do in v7.

>
>> +void print_tags(u8 addr_tag, const void *addr);
>> +#else
>> +static inline void print_tags(u8 addr_tag, const void *addr) { }
>> +#endif

>> +void *find_first_bad_addr(void *addr, size_t size)
>> +{
>> +       u8 tag = get_tag(addr);
>> +       void *untagged_addr = reset_tag(addr);
>> +       u8 *shadow = (u8 *)kasan_mem_to_shadow(untagged_addr);
>> +       void *first_bad_addr = untagged_addr;
>> +
>> +       while (*shadow == tag && first_bad_addr < untagged_addr + size) {
>
> I think it's better to check that are within bounds before accessing
> shadow. Otherwise it's kinda potential out-of-bounds access ;)
> I know that we _should_ not do an oob here, but still.
> Also feels that this function can be shortened to something like:
>
> u8 tag = get_tag(addr);
> void *p = reset_tag(addr);
> void *end = p + size;
>
> while (p < end && tag == *(u8 *)kasan_mem_to_shadow(p))
>         p += KASAN_SHADOW_SCALE_SIZE;
> return p;

Will do in v7.