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Thu, 25 Jul 2024 13:28:18 +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 EEqDAPJSomZlAgAAD6G6ig (envelope-from ); Thu, 25 Jul 2024 13:28:18 +0000 Message-ID: <9e05f9be-9e75-4b4d-84a4-1da52591574b@suse.cz> Date: Thu, 25 Jul 2024 15:28:17 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 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> Cc: Marco Elver , kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20240724-kasan-tsbrcu-v2-0-45f898064468@google.com> <20240724-kasan-tsbrcu-v2-2-45f898064468@google.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: <20240724-kasan-tsbrcu-v2-2-45f898064468@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: BCCE3120007 X-Stat-Signature: zzdya99fjkiyoiunt7i6gy8jrjtc5jjj X-Rspam-User: X-HE-Tag: 1721914099-350219 X-HE-Meta: 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 R1TCJlsx OcejRCi1HRjjUu6lJ+WCit8A+8uzKxjjXnTuAigrWYN7T7+g0wUZ6FIEyKXM1nDfilnH8vqVFgxPE0K48V6AImUju+uPuDyKwFMbrvYtz+d0NTyfspkTyMLMdzibbT2EHrA9GNGErLM2MgeS+AMuvEEwBiThPsGSLoHPzeeBxZTZvdvrn/OMh5Ng4t422xDVZzDCvuba0LjDo3sgh5QUHTWq/fYA/MA0F+kN1ePEdeV3JuqEHbUics0zUBjDndsTjuqMESDn3y7r5XqDrl2chzlW0Fp5YCqHZyk4WwX892nauAMZlyw1UnK2yG+lbnaZn4Ax/JufCli7qLFKPJJu1NhJkjaJD8RDGPBsgmFOjqiq+qPGZDWHX9F1RX/ocOOZrk8/cpU8h3aWo9xCc5sgvYo3QbZ3gIUUhbmyoTPhdfHeUpr5OYZGcjZiq1UD9vmhQAzfxz6VF4oKldHLCWJyw90XMRg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/24/24 6:34 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. > > Note that this creates an aligned 16-byte area in the middle of the slab > metadata area, which kinda sucks but seems to be necessary in order to be > able to store an rcu_head in there that can be unpoisoned while the RCU > callback is pending. An alternative could be a head-less variant of kfree_rcu_mightsleep() that would fail instead of go to reclaim if it can't allocate, and upon failure we would fall back ot the old behavior and give up on checking that object? But maybe it's just too complicated and we just pay the overhead. At least this doesn't concern kmalloc caches with their power-of-two alignment guarantees where extra metadata blows things up more. > (metadata_access_enable/disable doesn't work here because while the RCU > callback is pending, it will be accessed by asynchronous RCU processing.) > To be able to re-poison the area after the RCU callback is done executing, > a new helper kasan_poison_range_as_redzone() is necessary. > > 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 Acked-by: Vlastimil Babka #slab ... > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -450,6 +450,18 @@ static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work) > > static int shutdown_cache(struct kmem_cache *s) > { > + if (IS_ENABLED(CONFIG_SLUB_RCU_DEBUG) && > + (s->flags & SLAB_TYPESAFE_BY_RCU)) { > + /* > + * Under CONFIG_SLUB_RCU_DEBUG, when objects in a > + * SLAB_TYPESAFE_BY_RCU slab are freed, SLUB will internally > + * defer their freeing with call_rcu(). > + * Wait for such call_rcu() invocations here before actually > + * destroying the cache. > + */ > + rcu_barrier(); > + } I think once we have the series [1] settled (patch 5/6 specifically), the delayed destruction could handle this case too? [1] https://lore.kernel.org/linux-mm/20240715-b4-slab-kfree_rcu-destroy-v1-0-46b2984c2205@suse.cz/ > + > /* free asan quarantined objects */ > kasan_cache_shutdown(s); > > diff --git a/mm/slub.c b/mm/slub.c > index 34724704c52d..999afdc1cffb 100644