linux-kernel - Re: [PATCH v5 2/2] slub: Introduce CONFIG_SLUB_RCU

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Message-ID: <6ae22d49-7dfd-44d4-8720-fd2903a05fee@suse.cz>
Date: Tue, 30 Jul 2024 13:30:47 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Jann Horn <jannh@...gle.com>, Andrey Ryabinin <ryabinin.a.a@...il.com>,
 Alexander Potapenko <glider@...gle.com>,
 Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>,
 Vincenzo Frascino <vincenzo.frascino@....com>,
 Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...ux.com>,
 Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>,
 Joonsoo Kim <iamjoonsoo.kim@....com>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc: Marco Elver <elver@...gle.com>, kasan-dev@...glegroups.com,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v5 2/2] slub: Introduce CONFIG_SLUB_RCU_DEBUG

On 7/30/24 1:06 PM, Jann Horn wrote:
> Currently, KASAN is unable to catch use-after-free in SLAB_TYPESAFE_BY_RCU
> slabs because use-after-free is allowed within the RCU grace period by
> design.
> 
> Add a SLUB debugging feature which RCU-delays every individual
> kmem_cache_free() before either actually freeing the object or handing it
> off to KASAN, and change KASAN to poison freed objects as normal when this
> option is enabled.
> 
> For now I've configured Kconfig.debug to default-enable this feature in the
> KASAN GENERIC and SW_TAGS modes; I'm not enabling it by default in HW_TAGS
> mode because I'm not sure if it might have unwanted performance degradation
> effects there.
> 
> Note that this is mostly useful with KASAN in the quarantine-based GENERIC
> mode; SLAB_TYPESAFE_BY_RCU slabs are basically always also slabs with a
> ->ctor, and KASAN's assign_tag() currently has to assign fixed tags for
> those, reducing the effectiveness of SW_TAGS/HW_TAGS mode.
> (A possible future extension of this work would be to also let SLUB call
> the ->ctor() on every allocation instead of only when the slab page is
> allocated; then tag-based modes would be able to assign new tags on every
> reallocation.)
> 
> Signed-off-by: Jann Horn <jannh@...gle.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz> #slab