From patchwork Sun Nov 17 06:50:31 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrii Nakryiko X-Patchwork-Id: 1196307 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Original-To: incoming-bpf@patchwork.ozlabs.org Delivered-To: patchwork-incoming-bpf@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=none (no SPF record) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=bpf-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=pass (p=none dis=none) header.from=fb.com Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=fb.com header.i=@fb.com header.b="Hesi6yHW"; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 47G2m851Zyz9sP6 for ; Sun, 17 Nov 2019 17:50:48 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725901AbfKQGuq (ORCPT ); Sun, 17 Nov 2019 01:50:46 -0500 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:7688 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725867AbfKQGuq (ORCPT ); Sun, 17 Nov 2019 01:50:46 -0500 Received: from pps.filterd (m0109331.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id xAH6nQGE002542 for ; Sat, 16 Nov 2019 22:50:43 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-type; s=facebook; bh=63+8qd7O0ydfR/0T3LG2muosFp4njM6pnyZpTOJtrkI=; b=Hesi6yHWf2SBGsZCssmtDTwQbqt6JfelouC/8NifIOdEWIJ0KheglxCryb1UFqiiCA+0 bpNfnd8AjdckGESWd57cBYugj8Rhj5ZjiZFtW4t7mkF3fNqwcfuXVWiTXyp2aii5+guC tItsfk/7zyC3qkf+QdA0rLENKcOFaPMgcD8= Received: from mail.thefacebook.com (mailout.thefacebook.com [199.201.64.23]) by mx0a-00082601.pphosted.com with ESMTP id 2waftjsek4-5 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-SHA384 bits=256 verify=NOT) for ; Sat, 16 Nov 2019 22:50:43 -0800 Received: from 2401:db00:12:909f:face:0:3:0 (2620:10d:c081:10::13) by mail.thefacebook.com (2620:10d:c081:35::127) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA) id 15.1.1713.5; Sat, 16 Nov 2019 22:50:41 -0800 Received: by devbig012.ftw2.facebook.com (Postfix, from userid 137359) id 96D432EC18AA; Sat, 16 Nov 2019 22:50:40 -0800 (PST) Smtp-Origin-Hostprefix: devbig From: Andrii Nakryiko Smtp-Origin-Hostname: devbig012.ftw2.facebook.com To: , , , CC: , , Andrii Nakryiko Smtp-Origin-Cluster: ftw2c04 Subject: [PATCH v5 bpf-next 1/5] bpf: switch bpf_map ref counter to atomic64_t so bpf_map_inc() never fails Date: Sat, 16 Nov 2019 22:50:31 -0800 Message-ID: <20191117065035.202462-2-andriin@fb.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20191117065035.202462-1-andriin@fb.com> References: <20191117065035.202462-1-andriin@fb.com> X-FB-Internal: Safe MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95, 18.0.572 definitions=2019-11-17_01:2019-11-15, 2019-11-16 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 lowpriorityscore=0 malwarescore=0 adultscore=0 phishscore=0 bulkscore=0 priorityscore=1501 mlxlogscore=999 clxscore=1015 mlxscore=0 spamscore=0 impostorscore=0 suspectscore=25 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1910280000 definitions=main-1911170063 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org 92117d8443bc ("bpf: fix refcnt overflow") turned refcounting of bpf_map into potentially failing operation, when refcount reaches BPF_MAX_REFCNT limit (32k). Due to using 32-bit counter, it's possible in practice to overflow refcounter and make it wrap around to 0, causing erroneous map free, while there are still references to it, causing use-after-free problems. But having a failing refcounting operations are problematic in some cases. One example is mmap() interface. After establishing initial memory-mapping, user is allowed to arbitrarily map/remap/unmap parts of mapped memory, arbitrarily splitting it into multiple non-contiguous regions. All this happening without any control from the users of mmap subsystem. Rather mmap subsystem sends notifications to original creator of memory mapping through open/close callbacks, which are optionally specified during initial memory mapping creation. These callbacks are used to maintain accurate refcount for bpf_map (see next patch in this series). The problem is that open() callback is not supposed to fail, because memory-mapped resource is set up and properly referenced. This is posing a problem for using memory-mapping with BPF maps. One solution to this is to maintain separate refcount for just memory-mappings and do single bpf_map_inc/bpf_map_put when it goes from/to zero, respectively. There are similar use cases in current work on tcp-bpf, necessitating extra counter as well. This seems like a rather unfortunate and ugly solution that doesn't scale well to various new use cases. Another approach to solve this is to use non-failing refcount_t type, which uses 32-bit counter internally, but, once reaching overflow state at UINT_MAX, stays there. This utlimately causes memory leak, but prevents use after free. But given refcounting is not the most performance-critical operation with BPF maps (it's not used from running BPF program code), we can also just switch to 64-bit counter that can't overflow in practice, potentially disadvantaging 32-bit platforms a tiny bit. This simplifies semantics and allows above described scenarios to not worry about failing refcount increment operation. In terms of struct bpf_map size, we are still good and use the same amount of space: BEFORE (3 cache lines, 8 bytes of padding at the end): struct bpf_map { const struct bpf_map_ops * ops __attribute__((__aligned__(64))); /* 0 8 */ struct bpf_map * inner_map_meta; /* 8 8 */ void * security; /* 16 8 */ enum bpf_map_type map_type; /* 24 4 */ u32 key_size; /* 28 4 */ u32 value_size; /* 32 4 */ u32 max_entries; /* 36 4 */ u32 map_flags; /* 40 4 */ int spin_lock_off; /* 44 4 */ u32 id; /* 48 4 */ int numa_node; /* 52 4 */ u32 btf_key_type_id; /* 56 4 */ u32 btf_value_type_id; /* 60 4 */ /* --- cacheline 1 boundary (64 bytes) --- */ struct btf * btf; /* 64 8 */ struct bpf_map_memory memory; /* 72 16 */ bool unpriv_array; /* 88 1 */ bool frozen; /* 89 1 */ /* XXX 38 bytes hole, try to pack */ /* --- cacheline 2 boundary (128 bytes) --- */ atomic_t refcnt __attribute__((__aligned__(64))); /* 128 4 */ atomic_t usercnt; /* 132 4 */ struct work_struct work; /* 136 32 */ char name[16]; /* 168 16 */ /* size: 192, cachelines: 3, members: 21 */ /* sum members: 146, holes: 1, sum holes: 38 */ /* padding: 8 */ /* forced alignments: 2, forced holes: 1, sum forced holes: 38 */ } __attribute__((__aligned__(64))); AFTER (same 3 cache lines, no extra padding now): struct bpf_map { const struct bpf_map_ops * ops __attribute__((__aligned__(64))); /* 0 8 */ struct bpf_map * inner_map_meta; /* 8 8 */ void * security; /* 16 8 */ enum bpf_map_type map_type; /* 24 4 */ u32 key_size; /* 28 4 */ u32 value_size; /* 32 4 */ u32 max_entries; /* 36 4 */ u32 map_flags; /* 40 4 */ int spin_lock_off; /* 44 4 */ u32 id; /* 48 4 */ int numa_node; /* 52 4 */ u32 btf_key_type_id; /* 56 4 */ u32 btf_value_type_id; /* 60 4 */ /* --- cacheline 1 boundary (64 bytes) --- */ struct btf * btf; /* 64 8 */ struct bpf_map_memory memory; /* 72 16 */ bool unpriv_array; /* 88 1 */ bool frozen; /* 89 1 */ /* XXX 38 bytes hole, try to pack */ /* --- cacheline 2 boundary (128 bytes) --- */ atomic64_t refcnt __attribute__((__aligned__(64))); /* 128 8 */ atomic64_t usercnt; /* 136 8 */ struct work_struct work; /* 144 32 */ char name[16]; /* 176 16 */ /* size: 192, cachelines: 3, members: 21 */ /* sum members: 154, holes: 1, sum holes: 38 */ /* forced alignments: 2, forced holes: 1, sum forced holes: 38 */ } __attribute__((__aligned__(64))); This patch, while modifying all users of bpf_map_inc, also cleans up its interface to match bpf_map_put with separate operations for bpf_map_inc and bpf_map_inc_with_uref (to match bpf_map_put and bpf_map_put_with_uref, respectively). Also, given there are no users of bpf_map_inc_not_zero specifying uref=true, remove uref flag and default to uref=false internally. Acked-by: Song Liu Signed-off-by: Andrii Nakryiko --- .../net/ethernet/netronome/nfp/bpf/offload.c | 4 +- include/linux/bpf.h | 10 ++-- kernel/bpf/inode.c | 2 +- kernel/bpf/map_in_map.c | 2 +- kernel/bpf/syscall.c | 51 ++++++++----------- kernel/bpf/verifier.c | 6 +-- kernel/bpf/xskmap.c | 6 +-- net/core/bpf_sk_storage.c | 2 +- 8 files changed, 34 insertions(+), 49 deletions(-) diff --git a/drivers/net/ethernet/netronome/nfp/bpf/offload.c b/drivers/net/ethernet/netronome/nfp/bpf/offload.c index 88fab6a82acf..06927ba5a3ae 100644 --- a/drivers/net/ethernet/netronome/nfp/bpf/offload.c +++ b/drivers/net/ethernet/netronome/nfp/bpf/offload.c @@ -46,9 +46,7 @@ nfp_map_ptr_record(struct nfp_app_bpf *bpf, struct nfp_prog *nfp_prog, /* Grab a single ref to the map for our record. The prog destroy ndo * happens after free_used_maps(). */ - map = bpf_map_inc(map, false); - if (IS_ERR(map)) - return PTR_ERR(map); + bpf_map_inc(map); record = kmalloc(sizeof(*record), GFP_KERNEL); if (!record) { diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 5b81cde47314..34a34445c009 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -103,8 +103,8 @@ struct bpf_map { /* The 3rd and 4th cacheline with misc members to avoid false sharing * particularly with refcounting. */ - atomic_t refcnt ____cacheline_aligned; - atomic_t usercnt; + atomic64_t refcnt ____cacheline_aligned; + atomic64_t usercnt; struct work_struct work; char name[BPF_OBJ_NAME_LEN]; }; @@ -783,9 +783,9 @@ void bpf_map_free_id(struct bpf_map *map, bool do_idr_lock); struct bpf_map *bpf_map_get_with_uref(u32 ufd); struct bpf_map *__bpf_map_get(struct fd f); -struct bpf_map * __must_check bpf_map_inc(struct bpf_map *map, bool uref); -struct bpf_map * __must_check bpf_map_inc_not_zero(struct bpf_map *map, - bool uref); +void bpf_map_inc(struct bpf_map *map); +void bpf_map_inc_with_uref(struct bpf_map *map); +struct bpf_map * __must_check bpf_map_inc_not_zero(struct bpf_map *map); void bpf_map_put_with_uref(struct bpf_map *map); void bpf_map_put(struct bpf_map *map); int bpf_map_charge_memlock(struct bpf_map *map, u32 pages); diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c index a70f7209cda3..2f17f24258dc 100644 --- a/kernel/bpf/inode.c +++ b/kernel/bpf/inode.c @@ -34,7 +34,7 @@ static void *bpf_any_get(void *raw, enum bpf_type type) raw = bpf_prog_inc(raw); break; case BPF_TYPE_MAP: - raw = bpf_map_inc(raw, true); + bpf_map_inc_with_uref(raw); break; default: WARN_ON_ONCE(1); diff --git a/kernel/bpf/map_in_map.c b/kernel/bpf/map_in_map.c index fab4fb134547..4cbe987be35b 100644 --- a/kernel/bpf/map_in_map.c +++ b/kernel/bpf/map_in_map.c @@ -98,7 +98,7 @@ void *bpf_map_fd_get_ptr(struct bpf_map *map, return inner_map; if (bpf_map_meta_equal(map->inner_map_meta, inner_map)) - inner_map = bpf_map_inc(inner_map, false); + bpf_map_inc(inner_map); else inner_map = ERR_PTR(-EINVAL); diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index c88c815c2154..20030751b7a2 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -311,7 +311,7 @@ static void bpf_map_free_deferred(struct work_struct *work) static void bpf_map_put_uref(struct bpf_map *map) { - if (atomic_dec_and_test(&map->usercnt)) { + if (atomic64_dec_and_test(&map->usercnt)) { if (map->ops->map_release_uref) map->ops->map_release_uref(map); } @@ -322,7 +322,7 @@ static void bpf_map_put_uref(struct bpf_map *map) */ static void __bpf_map_put(struct bpf_map *map, bool do_idr_lock) { - if (atomic_dec_and_test(&map->refcnt)) { + if (atomic64_dec_and_test(&map->refcnt)) { /* bpf_map_free_id() must be called first */ bpf_map_free_id(map, do_idr_lock); btf_put(map->btf); @@ -575,8 +575,8 @@ static int map_create(union bpf_attr *attr) if (err) goto free_map; - atomic_set(&map->refcnt, 1); - atomic_set(&map->usercnt, 1); + atomic64_set(&map->refcnt, 1); + atomic64_set(&map->usercnt, 1); if (attr->btf_key_type_id || attr->btf_value_type_id) { struct btf *btf; @@ -653,21 +653,19 @@ struct bpf_map *__bpf_map_get(struct fd f) return f.file->private_data; } -/* prog's and map's refcnt limit */ -#define BPF_MAX_REFCNT 32768 - -struct bpf_map *bpf_map_inc(struct bpf_map *map, bool uref) +void bpf_map_inc(struct bpf_map *map) { - if (atomic_inc_return(&map->refcnt) > BPF_MAX_REFCNT) { - atomic_dec(&map->refcnt); - return ERR_PTR(-EBUSY); - } - if (uref) - atomic_inc(&map->usercnt); - return map; + atomic64_inc(&map->refcnt); } EXPORT_SYMBOL_GPL(bpf_map_inc); +void bpf_map_inc_with_uref(struct bpf_map *map) +{ + atomic64_inc(&map->refcnt); + atomic64_inc(&map->usercnt); +} +EXPORT_SYMBOL_GPL(bpf_map_inc_with_uref); + struct bpf_map *bpf_map_get_with_uref(u32 ufd) { struct fd f = fdget(ufd); @@ -677,38 +675,30 @@ struct bpf_map *bpf_map_get_with_uref(u32 ufd) if (IS_ERR(map)) return map; - map = bpf_map_inc(map, true); + bpf_map_inc_with_uref(map); fdput(f); return map; } /* map_idr_lock should have been held */ -static struct bpf_map *__bpf_map_inc_not_zero(struct bpf_map *map, - bool uref) +static struct bpf_map *__bpf_map_inc_not_zero(struct bpf_map *map, bool uref) { int refold; - refold = atomic_fetch_add_unless(&map->refcnt, 1, 0); - - if (refold >= BPF_MAX_REFCNT) { - __bpf_map_put(map, false); - return ERR_PTR(-EBUSY); - } - + refold = atomic64_fetch_add_unless(&map->refcnt, 1, 0); if (!refold) return ERR_PTR(-ENOENT); - if (uref) - atomic_inc(&map->usercnt); + atomic64_inc(&map->usercnt); return map; } -struct bpf_map *bpf_map_inc_not_zero(struct bpf_map *map, bool uref) +struct bpf_map *bpf_map_inc_not_zero(struct bpf_map *map) { spin_lock_bh(&map_idr_lock); - map = __bpf_map_inc_not_zero(map, uref); + map = __bpf_map_inc_not_zero(map, false); spin_unlock_bh(&map_idr_lock); return map; @@ -1455,6 +1445,9 @@ static struct bpf_prog *____bpf_prog_get(struct fd f) return f.file->private_data; } +/* prog's refcnt limit */ +#define BPF_MAX_REFCNT 32768 + struct bpf_prog *bpf_prog_add(struct bpf_prog *prog, int i) { if (atomic_add_return(i, &prog->aux->refcnt) > BPF_MAX_REFCNT) { diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index e9dc95a18d44..9f59f7a19dd0 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -8179,11 +8179,7 @@ static int replace_map_fd_with_map_ptr(struct bpf_verifier_env *env) * will be used by the valid program until it's unloaded * and all maps are released in free_used_maps() */ - map = bpf_map_inc(map, false); - if (IS_ERR(map)) { - fdput(f); - return PTR_ERR(map); - } + bpf_map_inc(map); aux->map_index = env->used_map_cnt; env->used_maps[env->used_map_cnt++] = map; diff --git a/kernel/bpf/xskmap.c b/kernel/bpf/xskmap.c index da16c30868f3..90c4fce1c981 100644 --- a/kernel/bpf/xskmap.c +++ b/kernel/bpf/xskmap.c @@ -11,10 +11,8 @@ int xsk_map_inc(struct xsk_map *map) { - struct bpf_map *m = &map->map; - - m = bpf_map_inc(m, false); - return PTR_ERR_OR_ZERO(m); + bpf_map_inc(&map->map); + return 0; } void xsk_map_put(struct xsk_map *map) diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c index da5639a5bd3b..458be6b3eda9 100644 --- a/net/core/bpf_sk_storage.c +++ b/net/core/bpf_sk_storage.c @@ -798,7 +798,7 @@ int bpf_sk_storage_clone(const struct sock *sk, struct sock *newsk) * Try to grab map refcnt to make sure that it's still * alive and prevent concurrent removal. */ - map = bpf_map_inc_not_zero(&smap->map, false); + map = bpf_map_inc_not_zero(&smap->map); if (IS_ERR(map)) continue;