linux-kernel - Re: [PATCH 4/4] mm/slub: free KFENCE objects in slab_free

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Date:   Mon, 11 Dec 2023 23:11:50 +0100
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Marco Elver <elver@...gle.com>
Cc:     Chengming Zhou <chengming.zhou@...ux.dev>,
        Vlastimil Babka <vbabka@...e.cz>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com
Subject: Re: [PATCH 4/4] mm/slub: free KFENCE objects in slab_free_hook()

On Wed, Dec 6, 2023 at 3:45 PM Marco Elver <elver@...gle.com> wrote:
>
> The is_kfence_address() implementation tolerates tagged addresses,
> i.e. if it receives a tagged non-kfence address, it will never return
> true.
>
> The KASAN_HW_TAGS patches and KFENCE patches were in development
> concurrently, and at the time there was some conflict resolution that
> happened when both were merged. The
> is_kfence_address(kasan_reset_tag(..)) initially came from [1] but was
> squashed into 2b8305260fb.
>
> [1] https://lore.kernel.org/all/9dc196006921b191d25d10f6e611316db7da2efc.1611946152.git.andreyknvl@google.com/
>
> Andrey, do you recall what issue you encountered that needed kasan_reset_tag()?

I don't remember at this point, but this could have been just a safety measure.

If is_kfence_address tolerates tagged addresses, we should be able to
drop these kasan_reset_tag calls.