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Date:   Thu, 23 Nov 2023 11:58:02 +0900
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Andrey Konovalov <andreyknvl@...il.com>
Cc:     andrey.konovalov@...ux.dev,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marco Elver <elver@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>, kasan-dev@...glegroups.com,
        Evgenii Stepanov <eugenis@...gle.com>,
        Oscar Salvador <osalvador@...e.de>,
        Feng Tang <feng.tang@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH mm] slub, kasan: improve interaction of KASAN and
 slub_debug poisoning

On Thu, Nov 23, 2023 at 11:31 AM Andrey Konovalov <andreyknvl@...il.com> wrote:
>
> On Thu, Nov 23, 2023 at 1:39 AM Hyeonggon Yoo <42.hyeyoo@...il.com> wrote:
> >
> > On Thu, Nov 23, 2023 at 8:12 AM <andrey.konovalov@...ux.dev> wrote:
> > >
> > > From: Andrey Konovalov <andreyknvl@...gle.com>
> > >
> > > When both KASAN and slub_debug are enabled, when a free object is being
> > > prepared in setup_object, slub_debug poisons the object data before KASAN
> > > initializes its per-object metadata.
> > >
> > > Right now, in setup_object, KASAN only initializes the alloc metadata,
> > > which is always stored outside of the object. slub_debug is aware of
> > > this and it skips poisoning and checking that memory area.
> > >
> > > However, with the following patch in this series, KASAN also starts
> > > initializing its free medata in setup_object. As this metadata might be
> > > stored within the object, this initialization might overwrite the
> > > slub_debug poisoning. This leads to slub_debug reports.
> > >
> > > Thus, skip checking slub_debug poisoning of the object data area that
> > > overlaps with the in-object KASAN free metadata.
> > >
> > > Also make slub_debug poisoning of tail kmalloc redzones more precise when
> > > KASAN is enabled: slub_debug can still poison and check the tail kmalloc
> > > allocation area that comes after the KASAN free metadata.
> > >
> > > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> >
> > Thank you for looking at this quickly!
> > Unfortunately the problem isn't fixed yet with the patch.
> >
> > I applied this on top of linux-next and built a kernel with the same config,
> > it is still stuck at boot.
>
> Ah, this is caused by a buggy version of "kasan: improve free meta
> storage in Generic KASAN", which made its way into linux-next.
> Reverting that patch should fix the issue. My patch that you bisected
> to exposes the buggy behavior.

1. I reverted the commit "kasan: improve free meta storage in Generic KASAN",
    on top of linux-next (next-20231122), and it is still stuck at boot.

2. I reverted the commit "kasan: improve free meta storage in Generic KASAN",
    on top of linux-next (next-20231122),
   _and_ applied this patch on top of it, now it boots fine!

--
Hyeonggon

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