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Wed, 7 Aug 2024 21:26:23 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id w4k2E3/ms2bTYwAAD6G6ig (envelope-from ); Wed, 07 Aug 2024 21:26:23 +0000 Message-ID: Date: Wed, 7 Aug 2024 23:26:23 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 2/2] slub: Introduce CONFIG_SLUB_RCU_DEBUG Content-Language: en-US To: Jann Horn , Andrey Ryabinin , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, David Sterba Cc: Marco Elver , kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzbot+263726e59eab6b442723@syzkaller.appspotmail.com References: <20240802-kasan-tsbrcu-v6-0-60d86ea78416@google.com> <20240802-kasan-tsbrcu-v6-2-60d86ea78416@google.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spamd-Result: default: False [-2.79 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; XM_UA_NO_VERSION(0.01)[]; TAGGED_RCPT(0.00)[263726e59eab6b442723]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; FREEMAIL_TO(0.00)[google.com,gmail.com,arm.com,linux-foundation.org,linux.com,kernel.org,lge.com,linux.dev,suse.cz]; RCPT_COUNT_TWELVE(0.00)[19]; MID_RHS_MATCH_FROM(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; DBL_BLOCKED_OPENRESOLVER(0.00)[appspotmail.com:email] X-Spam-Score: -2.79 X-Spam-Flag: NO X-Spam-Level: On 8/2/24 22:31, 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.) > > Tested-by: syzbot+263726e59eab6b442723@syzkaller.appspotmail.com > Signed-off-by: Jann Horn Actually, wait a second... > +#ifdef CONFIG_SLUB_RCU_DEBUG > +static void slab_free_after_rcu_debug(struct rcu_head *rcu_head) > +{ > + struct rcu_delayed_free *delayed_free = > + container_of(rcu_head, struct rcu_delayed_free, head); > + void *object = delayed_free->object; > + struct slab *slab = virt_to_slab(object); > + struct kmem_cache *s; > + > + if (WARN_ON(is_kfence_address(object))) > + return; > + > + /* find the object and the cache again */ > + if (WARN_ON(!slab)) > + return; > + s = slab->slab_cache; > + if (WARN_ON(!(s->flags & SLAB_TYPESAFE_BY_RCU))) > + return; > + > + /* resume freeing */ > + if (!slab_free_hook(s, object, slab_want_init_on_free(s), true)) > + return; > + do_slab_free(s, slab, object, object, 1, _THIS_IP_); > + kfree(delayed_free); This will leak memory of delayed_free when slab_free_hook() returns false (such as because of KASAN quarantine), the kfree() needs to happen always. Even in the WARN_ON cases but that's somewhat less critical. Thanks to David Sterba for making me look again, as he's been asking me about recent OOMs in -next with heavy kmalloc-32 cache usage (delayed_free is 24 bytes) and CONFIG_SLUB_RCU_DEBUG was so far almost certainly confirmed. > +} > +#endif /* CONFIG_SLUB_RCU_DEBUG */ > + > #ifdef CONFIG_KASAN_GENERIC > void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr) > { > do_slab_free(cache, virt_to_slab(x), x, x, 1, addr); > } > #endif >