Re: [PATCH mm] slub, kasan: improve interaction of KASAN and slub_debug poisoning

Andrey Konovalov
2023-11-23T02:32:26Z

On Thu, Nov 23, 2023 at 1:39 AM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote:
>
> On Thu, Nov 23, 2023 at 8:12 AM <andrey.konovalov@linux.dev> wrote:
> >
> > From: Andrey Konovalov <andreyknvl@google.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@google.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.

Thanks!