From nobody Wed Apr 15 04:15:15 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 984C7C04A68 for ; Wed, 27 Jul 2022 07:10:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229987AbiG0HK4 (ORCPT ); Wed, 27 Jul 2022 03:10:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49268 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229952AbiG0HKo (ORCPT ); Wed, 27 Jul 2022 03:10:44 -0400 Received: from mga12.intel.com (mga12.intel.com [192.55.52.136]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0F234205EC for ; Wed, 27 Jul 2022 00:10:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1658905843; x=1690441843; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=5dtJLggPAAYSrtbRQ0ZMDHXpMfjCXrc3LigkNW2lSbQ=; b=Ba3KL9PJddTLRyeuzz5C5CZxZYxJcDZlapioiq+I5boU8h/pX6gYegVv 9yGARTFUR6VKQBuesvLdbTjL1ITiFSEs5OLtZVacQTrEN/lt6nnNYwzGF jkij5xcdXflT7Lww7qUaW1eIBhq/puyt1tKmuJSR/YFJ5JoDaMRGqW9fI 8PxtNW0TAPyqpXci7xHxn3Zq6dAFCss/8kIkfXF4CsqDp44Vm8JQFoheE HDp5aBk5W/rrhxsB0RJ5c2lAanIstC1edCynkdyOjQD87z2UUmmZxO4cY UBEkLQgYXpV7Nwz4+Z8yfklkXath56VzfH7ivIxQZw5RRhD7n1bC7lJf3 g==; X-IronPort-AV: E=McAfee;i="6400,9594,10420"; a="267931695" X-IronPort-AV: E=Sophos;i="5.93,195,1654585200"; d="scan'208";a="267931695" Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Jul 2022 00:10:42 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.93,195,1654585200"; d="scan'208";a="550737918" Received: from shbuild999.sh.intel.com ([10.239.146.138]) by orsmga003.jf.intel.com with ESMTP; 27 Jul 2022 00:10:39 -0700 From: Feng Tang To: Andrew Morton , Vlastimil Babka , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Dave Hansen , Robin Murphy , John Garry , Kefeng Wang , Feng Tang Subject: [PATCH v3 1/3] mm/slub: enable debugging memory wasting of kmalloc Date: Wed, 27 Jul 2022 15:10:40 +0800 Message-Id: <20220727071042.8796-2-feng.tang@intel.com> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20220727071042.8796-1-feng.tang@intel.com> References: <20220727071042.8796-1-feng.tang@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" kmalloc's API family is critical for mm, with one nature that it will round up the request size to a fixed one (mostly power of 2). Say=20 when user requests memory for '2^n + 1' bytes, actually 2^(n+1) bytes could be allocated, so in worst case, there is around 50% memory space waste. The wastage is not a big issue for requests that get allocated/freed=20 quickly, but may cause problems with objects that have longer life time. We've met a kernel boot OOM panic (v5.10), and from the dumped slab info: [ 26.062145] kmalloc-2k 814056KB 814056KB From debug we found there are huge number of 'struct iova_magazine', whose size is 1032 bytes (1024 + 8), so each allocation will waste 1016 bytes. Though the issue was solved by giving the right (bigger) size of RAM, it is still nice to optimize the size (either use a kmalloc friendly size or create a dedicated slab for it). And from lkml archive, there was another crash kernel OOM case [1] back in 2019, which seems to be related with the similar slab waste situation, as the log is similar: [ 4.332648] iommu: Adding device 0000:20:02.0 to group 16 [ 4.338946] swapper/0 invoked oom-killer: gfp_mask=3D0x6040c0(GFP_KE= RNEL|__GFP_COMP), nodemask=3D(null), order=3D0, oom_score_adj=3D0 ... [ 4.857565] kmalloc-2048 59164KB 59164KB The crash kernel only has 256M memory, and 59M is pretty big here. (Note: the related code has been changed and optimised in recent kernel [2], these logs are picked just to demo the problem) So add an way to track each kmalloc's memory waste info, and leverage the existing SLUB debug framework to show its call stack of original allocation, so that user can evaluate the waste situation, identify some hot spots and optimize accordingly, for a better utilization of memory. The waste info is integrated into existing interface: /sys/kernel/debug/slab/kmalloc-xx/alloc_traces, one example of 'kmalloc-4k' after boot is: 126 ixgbe_alloc_q_vector+0xa5/0x4a0 [ixgbe] waste=3D233856/1856 age=3D14933= 02/1493830/1494358 pid=3D1284 cpus=3D32 nodes=3D1 __slab_alloc.isra.86+0x52/0x80 __kmalloc_node+0x143/0x350 ixgbe_alloc_q_vector+0xa5/0x4a0 [ixgbe] ixgbe_init_interrupt_scheme+0x1a6/0x730 [ixgbe] ixgbe_probe+0xc8e/0x10d0 [ixgbe] local_pci_probe+0x42/0x80 work_for_cpu_fn+0x13/0x20 process_one_work+0x1c5/0x390 which means in 'kmalloc-4k' slab, there are 126 requests of 2240 bytes which got a 4KB space (wasting 1856 bytes each and 233856 bytes in total). And when system starts some real workload like multiple docker instances, there are more severe waste. [1]. https://lkml.org/lkml/2019/8/12/266 [2]. https://lore.kernel.org/lkml/2920df89-9975-5785-f79b-257d3052dfaf@huaw= ei.com/ [Thanks Hyeonggon for pointing out several bugs about sorting/format] [Thanks Vlastimil for suggesting way to reduce memory usage of orig_size and keep it only for kmalloc objects] Signed-off-by: Feng Tang --- include/linux/slab.h | 2 + mm/slub.c | 99 ++++++++++++++++++++++++++++++++++++-------- 2 files changed, 83 insertions(+), 18 deletions(-) diff --git a/include/linux/slab.h b/include/linux/slab.h index 0fefdf528e0d..a713b0e5bbcd 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -29,6 +29,8 @@ #define SLAB_RED_ZONE ((slab_flags_t __force)0x00000400U) /* DEBUG: Poison objects */ #define SLAB_POISON ((slab_flags_t __force)0x00000800U) +/* Indicate a kmalloc slab */ +#define SLAB_KMALLOC ((slab_flags_t __force)0x00001000U) /* Align objs on cache lines */ #define SLAB_HWCACHE_ALIGN ((slab_flags_t __force)0x00002000U) /* Use GFP_DMA memory */ diff --git a/mm/slub.c b/mm/slub.c index 862dbd9af4f5..2e046cc10b84 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -191,6 +191,12 @@ static inline bool kmem_cache_debug(struct kmem_cache = *s) return kmem_cache_debug_flags(s, SLAB_DEBUG_FLAGS); } =20 +static inline bool slub_debug_orig_size(struct kmem_cache *s) +{ + return (kmem_cache_debug_flags(s, SLAB_STORE_USER) && + (s->flags & SLAB_KMALLOC)); +} + void *fixup_red_left(struct kmem_cache *s, void *p) { if (kmem_cache_debug_flags(s, SLAB_RED_ZONE)) @@ -816,6 +822,33 @@ static void print_slab_info(const struct slab *slab) folio_flags(folio, 0)); } =20 +static inline void set_orig_size(struct kmem_cache *s, + void *object, unsigned int orig_size) +{ + void *p =3D kasan_reset_tag(object); + + if (!slub_debug_orig_size(s)) + return; + + p +=3D get_info_end(s); + p +=3D sizeof(struct track) * 2; + + *(unsigned int *)p =3D orig_size; +} + +static unsigned int get_orig_size(struct kmem_cache *s, void *object) +{ + void *p =3D kasan_reset_tag(object); + + if (!slub_debug_orig_size(s)) + return s->object_size; + + p +=3D get_info_end(s); + p +=3D sizeof(struct track) * 2; + + return *(unsigned int *)p; +} + static void slab_bug(struct kmem_cache *s, char *fmt, ...) { struct va_format vaf; @@ -875,6 +908,9 @@ static void print_trailer(struct kmem_cache *s, struct = slab *slab, u8 *p) if (s->flags & SLAB_STORE_USER) off +=3D 2 * sizeof(struct track); =20 + if (slub_debug_orig_size(s)) + off +=3D sizeof(unsigned int); + off +=3D kasan_metadata_size(s); =20 if (off !=3D size_from_object(s)) @@ -1026,10 +1062,14 @@ static int check_pad_bytes(struct kmem_cache *s, st= ruct slab *slab, u8 *p) { unsigned long off =3D get_info_end(s); /* The end of info */ =20 - if (s->flags & SLAB_STORE_USER) + if (s->flags & SLAB_STORE_USER) { /* We also have user information there */ off +=3D 2 * sizeof(struct track); =20 + if (s->flags & SLAB_KMALLOC) + off +=3D sizeof(unsigned int); + } + off +=3D kasan_metadata_size(s); =20 if (size_from_object(s) =3D=3D off) @@ -1325,7 +1365,8 @@ static inline int alloc_consistency_checks(struct kme= m_cache *s, =20 static noinline int alloc_debug_processing(struct kmem_cache *s, struct slab *slab, - void *object, unsigned long addr) + void *object, unsigned long addr, + unsigned int orig_size) { if (s->flags & SLAB_CONSISTENCY_CHECKS) { if (!alloc_consistency_checks(s, slab, object)) @@ -1335,6 +1376,9 @@ static noinline int alloc_debug_processing(struct kme= m_cache *s, /* Success perform special debug activities for allocs */ if (s->flags & SLAB_STORE_USER) set_track(s, object, TRACK_ALLOC, addr); + + set_orig_size(s, object, orig_size); + trace(s, slab, object, 1); init_object(s, object, SLUB_RED_ACTIVE); return 1; @@ -1661,7 +1705,8 @@ static inline void setup_slab_debug(struct kmem_cache *s, struct slab *slab, void *addr)= {} =20 static inline int alloc_debug_processing(struct kmem_cache *s, - struct slab *slab, void *object, unsigned long addr) { return 0; } + struct slab *slab, void *object, unsigned long addr, + unsigned int orig_size) { return 0; } =20 static inline int free_debug_processing( struct kmem_cache *s, struct slab *slab, @@ -2905,7 +2950,7 @@ static inline void *get_freelist(struct kmem_cache *s= , struct slab *slab) * already disabled (which is the case for bulk allocation). */ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, - unsigned long addr, struct kmem_cache_cpu *c) + unsigned long addr, struct kmem_cache_cpu *c, unsigned int orig_size) { void *freelist; struct slab *slab; @@ -3048,7 +3093,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_= t gfpflags, int node, check_new_slab: =20 if (kmem_cache_debug(s)) { - if (!alloc_debug_processing(s, slab, freelist, addr)) { + if (!alloc_debug_processing(s, slab, freelist, addr, orig_size)) { /* Slab failed checks. Next slab needed */ goto new_slab; } else { @@ -3102,7 +3147,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_= t gfpflags, int node, * pointer. */ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, - unsigned long addr, struct kmem_cache_cpu *c) + unsigned long addr, struct kmem_cache_cpu *c, unsigned int orig_size) { void *p; =20 @@ -3115,7 +3160,7 @@ static void *__slab_alloc(struct kmem_cache *s, gfp_t= gfpflags, int node, c =3D slub_get_cpu_ptr(s->cpu_slab); #endif =20 - p =3D ___slab_alloc(s, gfpflags, node, addr, c); + p =3D ___slab_alloc(s, gfpflags, node, addr, c, orig_size); #ifdef CONFIG_PREEMPT_COUNT slub_put_cpu_ptr(s->cpu_slab); #endif @@ -3206,7 +3251,7 @@ static __always_inline void *slab_alloc_node(struct k= mem_cache *s, struct list_l */ if (IS_ENABLED(CONFIG_PREEMPT_RT) || unlikely(!object || !slab || !node_match(slab, node))) { - object =3D __slab_alloc(s, gfpflags, node, addr, c); + object =3D __slab_alloc(s, gfpflags, node, addr, c, orig_size); } else { void *next_object =3D get_freepointer_safe(s, object); =20 @@ -3709,7 +3754,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t= flags, size_t size, * of re-populating per CPU c->freelist */ p[i] =3D ___slab_alloc(s, flags, NUMA_NO_NODE, - _RET_IP_, c); + _RET_IP_, c, s->object_size); if (unlikely(!p[i])) goto error; =20 @@ -4112,12 +4157,17 @@ static int calculate_sizes(struct kmem_cache *s) } =20 #ifdef CONFIG_SLUB_DEBUG - if (flags & SLAB_STORE_USER) + if (flags & SLAB_STORE_USER) { /* * Need to store information about allocs and frees after * the object. */ size +=3D 2 * sizeof(struct track); + + /* Save the original kmalloc request size */ + if (flags & SLAB_KMALLOC) + size +=3D sizeof(unsigned int); + } #endif =20 kasan_cache_create(s, &size, &s->flags); @@ -4842,7 +4892,7 @@ void __init kmem_cache_init(void) =20 /* Now we can use the kmem_cache to allocate kmalloc slabs */ setup_kmalloc_cache_index_table(); - create_kmalloc_caches(0); + create_kmalloc_caches(SLAB_KMALLOC); =20 /* Setup random freelists for each cache */ init_freelist_randomization(); @@ -5068,6 +5118,7 @@ struct location { depot_stack_handle_t handle; unsigned long count; unsigned long addr; + unsigned long waste; long long sum_time; long min_time; long max_time; @@ -5114,13 +5165,15 @@ static int alloc_loc_track(struct loc_track *t, uns= igned long max, gfp_t flags) } =20 static int add_location(struct loc_track *t, struct kmem_cache *s, - const struct track *track) + const struct track *track, + unsigned int orig_size) { long start, end, pos; struct location *l; - unsigned long caddr, chandle; + unsigned long caddr, chandle, cwaste; unsigned long age =3D jiffies - track->when; depot_stack_handle_t handle =3D 0; + unsigned int waste =3D s->object_size - orig_size; =20 #ifdef CONFIG_STACKDEPOT handle =3D READ_ONCE(track->handle); @@ -5138,11 +5191,13 @@ static int add_location(struct loc_track *t, struct= kmem_cache *s, if (pos =3D=3D end) break; =20 - caddr =3D t->loc[pos].addr; - chandle =3D t->loc[pos].handle; - if ((track->addr =3D=3D caddr) && (handle =3D=3D chandle)) { + l =3D &t->loc[pos]; + caddr =3D l->addr; + chandle =3D l->handle; + cwaste =3D l->waste; + if ((track->addr =3D=3D caddr) && (handle =3D=3D chandle) && + (waste =3D=3D cwaste)) { =20 - l =3D &t->loc[pos]; l->count++; if (track->when) { l->sum_time +=3D age; @@ -5167,6 +5222,9 @@ static int add_location(struct loc_track *t, struct k= mem_cache *s, end =3D pos; else if (track->addr =3D=3D caddr && handle < chandle) end =3D pos; + else if (track->addr =3D=3D caddr && handle =3D=3D chandle && + waste < cwaste) + end =3D pos; else start =3D pos; } @@ -5190,6 +5248,7 @@ static int add_location(struct loc_track *t, struct k= mem_cache *s, l->min_pid =3D track->pid; l->max_pid =3D track->pid; l->handle =3D handle; + l->waste =3D waste; cpumask_clear(to_cpumask(l->cpus)); cpumask_set_cpu(track->cpu, to_cpumask(l->cpus)); nodes_clear(l->nodes); @@ -5208,7 +5267,7 @@ static void process_slab(struct loc_track *t, struct = kmem_cache *s, =20 for_each_object(p, s, addr, slab->objects) if (!test_bit(__obj_to_index(s, addr, p), obj_map)) - add_location(t, s, get_track(s, p, alloc)); + add_location(t, s, get_track(s, p, alloc), get_orig_size(s, p)); } #endif /* CONFIG_DEBUG_FS */ #endif /* CONFIG_SLUB_DEBUG */ @@ -6078,6 +6137,10 @@ static int slab_debugfs_show(struct seq_file *seq, v= oid *v) else seq_puts(seq, ""); =20 + if (l->waste) + seq_printf(seq, " waste=3D%lu/%lu", + l->count * l->waste, l->waste); + if (l->sum_time !=3D l->min_time) { seq_printf(seq, " age=3D%ld/%llu/%ld", l->min_time, div_u64(l->sum_time, l->count), --=20 2.27.0 From nobody Wed Apr 15 04:15:15 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9C0D0C04A68 for ; Wed, 27 Jul 2022 07:11:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230129AbiG0HLB (ORCPT ); Wed, 27 Jul 2022 03:11:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49346 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230014AbiG0HKt (ORCPT ); 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27 Jul 2022 00:10:46 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.93,195,1654585200"; d="scan'208";a="550737930" Received: from shbuild999.sh.intel.com ([10.239.146.138]) by orsmga003.jf.intel.com with ESMTP; 27 Jul 2022 00:10:42 -0700 From: Feng Tang To: Andrew Morton , Vlastimil Babka , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Dave Hansen , Robin Murphy , John Garry , Kefeng Wang , Feng Tang Subject: [PATCH v3 2/3] mm/slub: only zero the requested size of buffer for kzalloc Date: Wed, 27 Jul 2022 15:10:41 +0800 Message-Id: <20220727071042.8796-3-feng.tang@intel.com> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20220727071042.8796-1-feng.tang@intel.com> References: <20220727071042.8796-1-feng.tang@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" kzalloc/kmalloc will round up the request size to a fixed size (mostly power of 2), so the allocated memory could be more than requested. Currently kzalloc family APIs will zero all the allocated memory. To detect out-of-bound usage of the extra allocated memory, only zero the requested part, so that sanity check could be added to the extra space later. For kzalloc users who will call ksize() later and utilize this extra space, please be aware that the space is not zeroed any more. Signed-off-by: Feng Tang --- mm/slab.c | 8 ++++---- mm/slab.h | 9 +++++++-- mm/slub.c | 6 +++--- 3 files changed, 14 insertions(+), 9 deletions(-) diff --git a/mm/slab.c b/mm/slab.c index 5e73e2d80222..771f7c57d3ef 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -3236,7 +3236,7 @@ slab_alloc_node(struct kmem_cache *cachep, gfp_t flag= s, int nodeid, size_t orig_ init =3D slab_want_init_on_alloc(flags, cachep); =20 out_hooks: - slab_post_alloc_hook(cachep, objcg, flags, 1, &ptr, init); + slab_post_alloc_hook(cachep, objcg, flags, 1, &ptr, init, 0); return ptr; } =20 @@ -3299,7 +3299,7 @@ slab_alloc(struct kmem_cache *cachep, struct list_lru= *lru, gfp_t flags, init =3D slab_want_init_on_alloc(flags, cachep); =20 out: - slab_post_alloc_hook(cachep, objcg, flags, 1, &objp, init); + slab_post_alloc_hook(cachep, objcg, flags, 1, &objp, init, 0); return objp; } =20 @@ -3546,13 +3546,13 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp= _t flags, size_t size, * Done outside of the IRQ disabled section. */ slab_post_alloc_hook(s, objcg, flags, size, p, - slab_want_init_on_alloc(flags, s)); + slab_want_init_on_alloc(flags, s), 0); /* FIXME: Trace call missing. Christoph would like a bulk variant */ return size; error: local_irq_enable(); cache_alloc_debugcheck_after_bulk(s, flags, i, p, _RET_IP_); - slab_post_alloc_hook(s, objcg, flags, i, p, false); + slab_post_alloc_hook(s, objcg, flags, i, p, false, 0); kmem_cache_free_bulk(s, i, p); return 0; } diff --git a/mm/slab.h b/mm/slab.h index 4ec82bec15ec..7b53868efe6d 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -710,12 +710,17 @@ static inline struct kmem_cache *slab_pre_alloc_hook(= struct kmem_cache *s, =20 static inline void slab_post_alloc_hook(struct kmem_cache *s, struct obj_cgroup *objcg, gfp_t flags, - size_t size, void **p, bool init) + size_t size, void **p, bool init, + unsigned int orig_size) { size_t i; =20 flags &=3D gfp_allowed_mask; =20 + /* If original request size(kmalloc) is not set, use object_size */ + if (!orig_size) + orig_size =3D s->object_size; + /* * As memory initialization might be integrated into KASAN, * kasan_slab_alloc and initialization memset must be @@ -726,7 +731,7 @@ static inline void slab_post_alloc_hook(struct kmem_cac= he *s, for (i =3D 0; i < size; i++) { p[i] =3D kasan_slab_alloc(s, p[i], flags, init); if (p[i] && init && !kasan_has_integrated_init()) - memset(p[i], 0, s->object_size); + memset(p[i], 0, orig_size); kmemleak_alloc_recursive(p[i], s->object_size, 1, s->flags, flags); } diff --git a/mm/slub.c b/mm/slub.c index 2e046cc10b84..946919066a4b 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3285,7 +3285,7 @@ static __always_inline void *slab_alloc_node(struct k= mem_cache *s, struct list_l init =3D slab_want_init_on_alloc(gfpflags, s); =20 out: - slab_post_alloc_hook(s, objcg, gfpflags, 1, &object, init); + slab_post_alloc_hook(s, objcg, gfpflags, 1, &object, init, orig_size); =20 return object; } @@ -3778,11 +3778,11 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp= _t flags, size_t size, * Done outside of the IRQ disabled fastpath loop. */ slab_post_alloc_hook(s, objcg, flags, size, p, - slab_want_init_on_alloc(flags, s)); + slab_want_init_on_alloc(flags, s), 0); return i; error: slub_put_cpu_ptr(s->cpu_slab); 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27 Jul 2022 00:10:46 -0700 From: Feng Tang To: Andrew Morton , Vlastimil Babka , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Dave Hansen , Robin Murphy , John Garry , Kefeng Wang , Feng Tang Subject: [PATCH v3 3/3] mm/slub: extend redzone check to cover extra allocated kmalloc space than requested Date: Wed, 27 Jul 2022 15:10:42 +0800 Message-Id: <20220727071042.8796-4-feng.tang@intel.com> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20220727071042.8796-1-feng.tang@intel.com> References: <20220727071042.8796-1-feng.tang@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" kmalloc will round up the request size to a fixed size (mostly power of 2), so there could be a extra space than what is requested, whose size is the actual buffer size minus original request size. To better detect out of bound access or abuse of this space, add redzone sanity check for it. And in current kernel, some kmalloc user already knows the existence of the space and utilizes it after calling 'ksize()' to know the real size of the allocated buffer. So we skip the sanity check for objects which have been called with ksize(), as treating them as legitimate users. Suggested-by: Vlastimil Babka Signed-off-by: Feng Tang Acked-by: Dmitry Vyukov Reported-by: kernel test robot --- mm/slub.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 49 insertions(+), 3 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 946919066a4b..added2653bb0 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -836,6 +836,11 @@ static inline void set_orig_size(struct kmem_cache *s, *(unsigned int *)p =3D orig_size; } =20 +static inline void skip_orig_size_check(struct kmem_cache *s, const void *= object) +{ + set_orig_size(s, (void *)object, s->object_size); +} + static unsigned int get_orig_size(struct kmem_cache *s, void *object) { void *p =3D kasan_reset_tag(object); @@ -967,13 +972,35 @@ static __printf(3, 4) void slab_err(struct kmem_cache= *s, struct slab *slab, static void init_object(struct kmem_cache *s, void *object, u8 val) { u8 *p =3D kasan_reset_tag(object); + unsigned int orig_size =3D s->object_size; =20 - if (s->flags & SLAB_RED_ZONE) + if (s->flags & SLAB_RED_ZONE) { memset(p - s->red_left_pad, val, s->red_left_pad); =20 + if (slub_debug_orig_size(s) && val =3D=3D SLUB_RED_ACTIVE) { + unsigned int zone_start; + + orig_size =3D get_orig_size(s, object); + zone_start =3D orig_size; + + if (!freeptr_outside_object(s)) + zone_start =3D max_t(unsigned int, orig_size, + s->offset + sizeof(void *)); + + /* + * Redzone the extra allocated space by kmalloc + * than requested. + */ + if (zone_start < s->object_size) + memset(p + zone_start, val, + s->object_size - zone_start); + } + + } + if (s->flags & __OBJECT_POISON) { - memset(p, POISON_FREE, s->object_size - 1); - p[s->object_size - 1] =3D POISON_END; + memset(p, POISON_FREE, orig_size - 1); + p[orig_size - 1] =3D POISON_END; } =20 if (s->flags & SLAB_RED_ZONE) @@ -1120,6 +1147,7 @@ static int check_object(struct kmem_cache *s, struct = slab *slab, { u8 *p =3D object; u8 *endobject =3D object + s->object_size; + unsigned int orig_size; =20 if (s->flags & SLAB_RED_ZONE) { if (!check_bytes_and_report(s, slab, object, "Left Redzone", @@ -1129,6 +1157,20 @@ static int check_object(struct kmem_cache *s, struct= slab *slab, if (!check_bytes_and_report(s, slab, object, "Right Redzone", endobject, val, s->inuse - s->object_size)) return 0; + + if (slub_debug_orig_size(s) && val =3D=3D SLUB_RED_ACTIVE) { + orig_size =3D get_orig_size(s, object); + + if (!freeptr_outside_object(s)) + orig_size =3D max_t(unsigned int, orig_size, + s->offset + sizeof(void *)); + if (s->object_size > orig_size && + !check_bytes_and_report(s, slab, object, + "kmalloc Redzone", p + orig_size, + val, s->object_size - orig_size)) { + return 0; + } + } } else { if ((s->flags & SLAB_POISON) && s->object_size < s->inuse) { check_bytes_and_report(s, slab, p, "Alignment padding", @@ -4588,6 +4630,10 @@ size_t __ksize(const void *object) if (unlikely(!folio_test_slab(folio))) return folio_size(folio); =20 +#ifdef CONFIG_SLUB_DEBUG + skip_orig_size_check(folio_slab(folio)->slab_cache, object); +#endif + return slab_ksize(folio_slab(folio)->slab_cache); } EXPORT_SYMBOL(__ksize); --=20 2.27.0