linux-kernel - Re: [PATCH] kasan, slub: fix HW_TAGS zeroing with slub

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Date:   Thu, 6 Jul 2023 10:03:10 +0100
From:   Will Deacon <will@...nel.org>
To:     Andrey Konovalov <andreyknvl@...il.com>
Cc:     Marco Elver <elver@...gle.com>, andrey.konovalov@...ux.dev,
        Mark Rutland <mark.rutland@....com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        kasan-dev@...glegroups.com,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Catalin Marinas <catalin.marinas@....com>,
        Peter Collingbourne <pcc@...gle.com>,
        Feng Tang <feng.tang@...el.com>, stable@...r.kernel.org,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH] kasan, slub: fix HW_TAGS zeroing with slub_debug

On Wed, Jul 05, 2023 at 03:19:06PM +0200, Andrey Konovalov wrote:
> On Wed, Jul 5, 2023 at 2:51 PM Marco Elver <elver@...gle.com> wrote:
> >
> > On Wed, 5 Jul 2023 at 14:44, <andrey.konovalov@...ux.dev> wrote:
> > >
> > > From: Andrey Konovalov <andreyknvl@...gle.com>
> > >
> > > Commit 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated
> > > kmalloc space than requested") added precise kmalloc redzone poisoning
> > > to the slub_debug functionality.
> > >
> > > However, this commit didn't account for HW_TAGS KASAN fully initializing
> > > the object via its built-in memory initialization feature. Even though
> > > HW_TAGS KASAN memory initialization contains special memory initialization
> > > handling for when slub_debug is enabled, it does not account for in-object
> > > slub_debug redzones. As a result, HW_TAGS KASAN can overwrite these
> > > redzones and cause false-positive slub_debug reports.
> > >
> > > To fix the issue, avoid HW_TAGS KASAN memory initialization when slub_debug
> > > is enabled altogether. Implement this by moving the __slub_debug_enabled
> > > check to slab_post_alloc_hook. Common slab code seems like a more
> > > appropriate place for a slub_debug check anyway.
> > >
> > > Fixes: 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated kmalloc space than requested")
> > > Cc: <stable@...r.kernel.org>
> > > Reported-by: Mark Rutland <mark.rutland@....com>
> >
> > Is it fixing this issue:
> >
> >   https://lore.kernel.org/all/20230628154714.GB22090@willie-the-truck/
> 
> Yes, my bad, messed up the Reported-by tag. The correct one should be:
> 
> Reported-by: Will Deacon <will@...nel.org>
> 
> > Other than the question above, it looks sane:
> >
> > Acked-by: Marco Elver <elver@...gle.com>
> 
> Thank you, Marco!

Cheers, this seems to fix the splats for me:

Tested-by: Will Deacon <will@...nel.org>

Will