linux-hardening - Re: [PATCH] slub: Introduce CONFIG_SLUB_RCU

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Date:   Sat, 16 Sep 2023 18:18:54 +0200
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        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>,
        Alexander Potapenko <glider@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-hardening@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] slub: Introduce CONFIG_SLUB_RCU_DEBUG

On Mon, Aug 28, 2023 at 4:40 PM Jann Horn <jannh@...gle.com> wrote:
>
> > Can't we unpoision this rcu_head right before call_rcu() and repoison
> > after receiving the callback?
>
> Yeah, I think that should work. It looks like currently
> kasan_unpoison() is exposed in include/linux/kasan.h but
> kasan_poison() is not, and its inline definition probably means I
> can't just move it out of mm/kasan/kasan.h into include/linux/kasan.h;
> do you have a preference for how I should handle this? Hmm, and it
> also looks like code outside of mm/kasan/ anyway wouldn't know what
> are valid values for the "value" argument to kasan_poison().
> I also have another feature idea that would also benefit from having
> something like kasan_poison() available in include/linux/kasan.h, so I
> would prefer that over adding another special-case function inside
> KASAN for poisoning this piece of slab metadata...

This is a problem only for the Generic mode, right? You already call
kasan_reset_tag on the rcu_head, which should suppress the reporting
for the tag-based modes.

If so, would it be possible to reuse metadata_access_enable/disable?
They are used for accessing slub_debug metadata and seem to fit nicely
with this case as well.

I also second Macro's comment to add a test for the new functionality.

Thanks for working on this!