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Mon, 27 Oct 2025 12:29:19 +0000 Received: from CH3PR10MB7329.namprd10.prod.outlook.com ([fe80::f238:6143:104c:da23]) by CH3PR10MB7329.namprd10.prod.outlook.com ([fe80::f238:6143:104c:da23%5]) with mapi id 15.20.9253.017; Mon, 27 Oct 2025 12:29:19 +0000 From: Harry Yoo To: akpm@linux-foundation.org, vbabka@suse.cz Cc: andreyknvl@gmail.com, cl@linux.com, dvyukov@google.com, glider@google.com, hannes@cmpxchg.org, linux-mm@kvack.org, mhocko@kernel.org, muchun.song@linux.dev, rientjes@google.com, roman.gushchin@linux.dev, ryabinin.a.a@gmail.com, shakeel.butt@linux.dev, surenb@google.com, vincenzo.frascino@arm.com, yeoreum.yun@arm.com, harry.yoo@oracle.com, tytso@mit.edu, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [RFC PATCH V3 5/7] mm/memcontrol,alloc_tag: handle slabobj_ext access under KASAN poison Date: Mon, 27 Oct 2025 21:28:45 +0900 Message-ID: <20251027122847.320924-6-harry.yoo@oracle.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251027122847.320924-1-harry.yoo@oracle.com> References: <20251027122847.320924-1-harry.yoo@oracle.com> Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: SL2P216CA0103.KORP216.PROD.OUTLOOK.COM (2603:1096:101:3::18) To CH3PR10MB7329.namprd10.prod.outlook.com (2603:10b6:610:12c::16) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH3PR10MB7329:EE_|MW4PR10MB6371:EE_ X-MS-Office365-Filtering-Correlation-Id: fb263cbf-b559-40e1-e641-08de1554736d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|366016|1800799024; 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charset="utf-8" In the near future, slabobj_ext may reside outside the allocated slab object range within a slab, which could be reported as an out-of-bounds access by KASAN. To prevent false positives, explicitly disable KASAN and KMSAN checks when accessing slabobj_ext. While an alternative approach could be to unpoison slabobj_ext, out-of-bounds accesses outside the slab allocator are generally more common. Move metadata_access_enable()/disable() helpers to mm/slab.h so that it can be used outside mm/slub.c. Wrap accesses to slabobj_ext metadata in memcg and alloc_tag code with these helpers. Call kasan_reset_tag() in slab_obj_ext() before returning the address to prevent SW or HW tag-based KASAN from reporting false positives. Suggested-by: Andrey Konovalov Signed-off-by: Harry Yoo --- mm/memcontrol.c | 15 ++++++++++++--- mm/slab.h | 24 +++++++++++++++++++++++- mm/slub.c | 33 +++++++++++++-------------------- 3 files changed, 48 insertions(+), 24 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 2a9dc246e802..38e6e9099ff5 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2570,17 +2570,22 @@ struct mem_cgroup *mem_cgroup_from_obj_folio(struct= folio *folio, void *p) struct slabobj_ext *obj_ext; struct slab *slab; unsigned int off; + struct mem_cgroup *memcg; =20 slab =3D folio_slab(folio); obj_exts =3D slab_obj_exts(slab); if (!obj_exts) return NULL; =20 + metadata_access_enable(); off =3D obj_to_index(slab->slab_cache, slab, p); obj_ext =3D slab_obj_ext(slab, obj_exts, off); - if (obj_ext->objcg) - return obj_cgroup_memcg(obj_ext->objcg); - + if (obj_ext->objcg) { + memcg =3D obj_cgroup_memcg(obj_ext->objcg); + metadata_access_disable(); + return memcg; + } + metadata_access_disable(); return NULL; } =20 @@ -3197,9 +3202,11 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache = *s, struct list_lru *lru, =20 obj_exts =3D slab_obj_exts(slab); off =3D obj_to_index(s, slab, p[i]); + metadata_access_enable(); obj_ext =3D slab_obj_ext(slab, obj_exts, off); obj_cgroup_get(objcg); obj_ext->objcg =3D objcg; + metadata_access_disable(); } =20 return true; @@ -3210,6 +3217,7 @@ void __memcg_slab_free_hook(struct kmem_cache *s, str= uct slab *slab, { size_t obj_size =3D obj_full_size(s); =20 + metadata_access_enable(); for (int i =3D 0; i < objects; i++) { struct obj_cgroup *objcg; struct slabobj_ext *obj_ext; @@ -3226,6 +3234,7 @@ void __memcg_slab_free_hook(struct kmem_cache *s, str= uct slab *slab, slab_pgdat(slab), cache_vmstat_idx(s)); obj_cgroup_put(objcg); } + metadata_access_disable(); } =20 /* diff --git a/mm/slab.h b/mm/slab.h index 22ee28cb55e1..13f4ca65cb42 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -591,10 +591,14 @@ static inline struct slabobj_ext *slab_obj_ext(struct= slab *slab, unsigned long obj_exts, unsigned int index) { + struct slabobj_ext *obj_ext; + VM_WARN_ON_ONCE(!slab_obj_exts(slab)); VM_WARN_ON_ONCE(obj_exts !=3D slab_obj_exts(slab)); =20 - return (struct slabobj_ext *)(obj_exts + slab_get_stride(slab) * index); + obj_ext =3D (struct slabobj_ext *)(obj_exts + + slab_get_stride(slab) * index); + return kasan_reset_tag(obj_ext); } =20 int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, @@ -625,6 +629,24 @@ static inline enum node_stat_item cache_vmstat_idx(str= uct kmem_cache *s) NR_SLAB_RECLAIMABLE_B : NR_SLAB_UNRECLAIMABLE_B; } =20 +/* + * slub is about to manipulate internal object metadata. This memory lies + * outside the range of the allocated object, so accessing it would normal= ly + * be reported by kasan as a bounds error. metadata_access_enable() is us= ed + * to tell kasan that these accesses are OK. + */ +static inline void metadata_access_enable(void) +{ + kasan_disable_current(); + kmsan_disable_current(); +} + +static inline void metadata_access_disable(void) +{ + kmsan_enable_current(); + kasan_enable_current(); +} + #ifdef CONFIG_MEMCG bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *l= ru, gfp_t flags, size_t size, void **p); diff --git a/mm/slub.c b/mm/slub.c index 4383740a4d34..13acc9437ef5 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -973,24 +973,6 @@ static slab_flags_t slub_debug; static char *slub_debug_string; static int disable_higher_order_debug; =20 -/* - * slub is about to manipulate internal object metadata. This memory lies - * outside the range of the allocated object, so accessing it would normal= ly - * be reported by kasan as a bounds error. metadata_access_enable() is us= ed - * to tell kasan that these accesses are OK. - */ -static inline void metadata_access_enable(void) -{ - kasan_disable_current(); - kmsan_disable_current(); -} - -static inline void metadata_access_disable(void) -{ - kmsan_enable_current(); - kasan_enable_current(); -} - /* * Object debugging */ @@ -2042,9 +2024,11 @@ static inline void mark_objexts_empty(struct slabobj= _ext *obj_exts) struct slabobj_ext *ext =3D slab_obj_ext(obj_exts_slab, slab_exts, offs); =20 + metadata_access_enable(); /* codetag should be NULL */ WARN_ON(ext->ref.ct); set_codetag_empty(&ext->ref); + metadata_access_disable(); } } =20 @@ -2245,8 +2229,11 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s= , void *object, gfp_t flags) * If other users appear then mem_alloc_profiling_enabled() * check should be added before alloc_tag_add(). */ - if (likely(obj_ext)) + if (likely(obj_ext)) { + metadata_access_enable(); alloc_tag_add(&obj_ext->ref, current->alloc_tag, s->size); + metadata_access_disable(); + } } =20 static inline void @@ -2272,11 +2259,13 @@ __alloc_tagging_slab_free_hook(struct kmem_cache *s= , struct slab *slab, void **p if (!obj_exts) return; =20 + metadata_access_enable(); for (i =3D 0; i < objects; i++) { unsigned int off =3D obj_to_index(s, slab, p[i]); =20 alloc_tag_sub(&slab_obj_ext(slab, obj_exts, off)->ref, s->size); } + metadata_access_disable(); } =20 static inline void @@ -2394,8 +2383,12 @@ bool memcg_slab_post_charge(void *p, gfp_t flags) if (obj_exts) { off =3D obj_to_index(s, slab, p); obj_ext =3D slab_obj_ext(slab, obj_exts, off); - if (unlikely(obj_ext->objcg)) + metadata_access_enable(); + if (unlikely(obj_ext->objcg)) { + metadata_access_disable(); return true; + } + metadata_access_disable(); } =20 return __memcg_slab_post_alloc_hook(s, NULL, flags, 1, &p); --=20 2.43.0