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![Song Liu](/assets/img/avatar_default.png)
BPF helpers bpf_task_storage_[get|delete] could hold two locks: bpf_local_storage_map_bucket->lock and bpf_local_storage->lock. Calling these helpers from fentry/fexit programs on functions in bpf_*_storage.c may cause deadlock on either locks. Prevent such deadlock with a per cpu counter, bpf_task_storage_busy. We need this counter to be global, because the two locks here belong to two different objects: bpf_local_storage_map and bpf_local_storage. If we pick one of them as the owner of the counter, it is still possible to trigger deadlock on the other lock. For example, if bpf_local_storage_map owns the counters, it cannot prevent deadlock on bpf_local_storage->lock when two maps are used. Signed-off-by: Song Liu <songliubraving@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Martin KaFai Lau <kafai@fb.com> Link: https://lore.kernel.org/bpf/20210225234319.336131-3-songliubraving@fb.com
608 lines
17 KiB
C
608 lines
17 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2019 Facebook */
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#include <linux/rculist.h>
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#include <linux/list.h>
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#include <linux/hash.h>
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#include <linux/types.h>
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#include <linux/spinlock.h>
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#include <linux/bpf.h>
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#include <linux/btf_ids.h>
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#include <linux/bpf_local_storage.h>
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#include <net/sock.h>
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#include <uapi/linux/sock_diag.h>
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#include <uapi/linux/btf.h>
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#define BPF_LOCAL_STORAGE_CREATE_FLAG_MASK (BPF_F_NO_PREALLOC | BPF_F_CLONE)
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static struct bpf_local_storage_map_bucket *
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select_bucket(struct bpf_local_storage_map *smap,
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struct bpf_local_storage_elem *selem)
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{
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return &smap->buckets[hash_ptr(selem, smap->bucket_log)];
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}
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static int mem_charge(struct bpf_local_storage_map *smap, void *owner, u32 size)
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{
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struct bpf_map *map = &smap->map;
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if (!map->ops->map_local_storage_charge)
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return 0;
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return map->ops->map_local_storage_charge(smap, owner, size);
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}
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static void mem_uncharge(struct bpf_local_storage_map *smap, void *owner,
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u32 size)
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{
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struct bpf_map *map = &smap->map;
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if (map->ops->map_local_storage_uncharge)
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map->ops->map_local_storage_uncharge(smap, owner, size);
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}
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static struct bpf_local_storage __rcu **
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owner_storage(struct bpf_local_storage_map *smap, void *owner)
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{
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struct bpf_map *map = &smap->map;
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return map->ops->map_owner_storage_ptr(owner);
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}
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static bool selem_linked_to_storage(const struct bpf_local_storage_elem *selem)
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{
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return !hlist_unhashed(&selem->snode);
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}
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static bool selem_linked_to_map(const struct bpf_local_storage_elem *selem)
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{
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return !hlist_unhashed(&selem->map_node);
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}
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struct bpf_local_storage_elem *
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bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner,
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void *value, bool charge_mem)
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{
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struct bpf_local_storage_elem *selem;
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if (charge_mem && mem_charge(smap, owner, smap->elem_size))
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return NULL;
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selem = bpf_map_kzalloc(&smap->map, smap->elem_size,
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GFP_ATOMIC | __GFP_NOWARN);
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if (selem) {
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if (value)
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memcpy(SDATA(selem)->data, value, smap->map.value_size);
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return selem;
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}
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if (charge_mem)
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mem_uncharge(smap, owner, smap->elem_size);
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return NULL;
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}
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/* local_storage->lock must be held and selem->local_storage == local_storage.
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* The caller must ensure selem->smap is still valid to be
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* dereferenced for its smap->elem_size and smap->cache_idx.
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*/
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bool bpf_selem_unlink_storage_nolock(struct bpf_local_storage *local_storage,
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struct bpf_local_storage_elem *selem,
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bool uncharge_mem)
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{
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struct bpf_local_storage_map *smap;
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bool free_local_storage;
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void *owner;
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smap = rcu_dereference(SDATA(selem)->smap);
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owner = local_storage->owner;
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/* All uncharging on the owner must be done first.
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* The owner may be freed once the last selem is unlinked
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* from local_storage.
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*/
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if (uncharge_mem)
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mem_uncharge(smap, owner, smap->elem_size);
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free_local_storage = hlist_is_singular_node(&selem->snode,
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&local_storage->list);
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if (free_local_storage) {
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mem_uncharge(smap, owner, sizeof(struct bpf_local_storage));
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local_storage->owner = NULL;
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/* After this RCU_INIT, owner may be freed and cannot be used */
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RCU_INIT_POINTER(*owner_storage(smap, owner), NULL);
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/* local_storage is not freed now. local_storage->lock is
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* still held and raw_spin_unlock_bh(&local_storage->lock)
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* will be done by the caller.
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*
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* Although the unlock will be done under
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* rcu_read_lock(), it is more intutivie to
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* read if kfree_rcu(local_storage, rcu) is done
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* after the raw_spin_unlock_bh(&local_storage->lock).
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*
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* Hence, a "bool free_local_storage" is returned
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* to the caller which then calls the kfree_rcu()
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* after unlock.
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*/
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}
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hlist_del_init_rcu(&selem->snode);
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if (rcu_access_pointer(local_storage->cache[smap->cache_idx]) ==
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SDATA(selem))
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RCU_INIT_POINTER(local_storage->cache[smap->cache_idx], NULL);
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kfree_rcu(selem, rcu);
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return free_local_storage;
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}
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static void __bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem)
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{
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struct bpf_local_storage *local_storage;
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bool free_local_storage = false;
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unsigned long flags;
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if (unlikely(!selem_linked_to_storage(selem)))
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/* selem has already been unlinked from sk */
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return;
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local_storage = rcu_dereference(selem->local_storage);
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raw_spin_lock_irqsave(&local_storage->lock, flags);
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if (likely(selem_linked_to_storage(selem)))
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free_local_storage = bpf_selem_unlink_storage_nolock(
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local_storage, selem, true);
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raw_spin_unlock_irqrestore(&local_storage->lock, flags);
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if (free_local_storage)
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kfree_rcu(local_storage, rcu);
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}
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void bpf_selem_link_storage_nolock(struct bpf_local_storage *local_storage,
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struct bpf_local_storage_elem *selem)
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{
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RCU_INIT_POINTER(selem->local_storage, local_storage);
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hlist_add_head_rcu(&selem->snode, &local_storage->list);
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}
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void bpf_selem_unlink_map(struct bpf_local_storage_elem *selem)
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{
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struct bpf_local_storage_map *smap;
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struct bpf_local_storage_map_bucket *b;
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unsigned long flags;
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if (unlikely(!selem_linked_to_map(selem)))
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/* selem has already be unlinked from smap */
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return;
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smap = rcu_dereference(SDATA(selem)->smap);
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b = select_bucket(smap, selem);
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raw_spin_lock_irqsave(&b->lock, flags);
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if (likely(selem_linked_to_map(selem)))
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hlist_del_init_rcu(&selem->map_node);
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raw_spin_unlock_irqrestore(&b->lock, flags);
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}
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void bpf_selem_link_map(struct bpf_local_storage_map *smap,
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struct bpf_local_storage_elem *selem)
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{
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struct bpf_local_storage_map_bucket *b = select_bucket(smap, selem);
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unsigned long flags;
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raw_spin_lock_irqsave(&b->lock, flags);
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RCU_INIT_POINTER(SDATA(selem)->smap, smap);
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hlist_add_head_rcu(&selem->map_node, &b->list);
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raw_spin_unlock_irqrestore(&b->lock, flags);
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}
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void bpf_selem_unlink(struct bpf_local_storage_elem *selem)
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{
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/* Always unlink from map before unlinking from local_storage
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* because selem will be freed after successfully unlinked from
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* the local_storage.
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*/
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bpf_selem_unlink_map(selem);
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__bpf_selem_unlink_storage(selem);
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}
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struct bpf_local_storage_data *
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bpf_local_storage_lookup(struct bpf_local_storage *local_storage,
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struct bpf_local_storage_map *smap,
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bool cacheit_lockit)
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{
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struct bpf_local_storage_data *sdata;
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struct bpf_local_storage_elem *selem;
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/* Fast path (cache hit) */
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sdata = rcu_dereference(local_storage->cache[smap->cache_idx]);
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if (sdata && rcu_access_pointer(sdata->smap) == smap)
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return sdata;
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/* Slow path (cache miss) */
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hlist_for_each_entry_rcu(selem, &local_storage->list, snode)
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if (rcu_access_pointer(SDATA(selem)->smap) == smap)
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break;
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if (!selem)
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return NULL;
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sdata = SDATA(selem);
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if (cacheit_lockit) {
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unsigned long flags;
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/* spinlock is needed to avoid racing with the
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* parallel delete. Otherwise, publishing an already
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* deleted sdata to the cache will become a use-after-free
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* problem in the next bpf_local_storage_lookup().
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*/
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raw_spin_lock_irqsave(&local_storage->lock, flags);
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if (selem_linked_to_storage(selem))
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rcu_assign_pointer(local_storage->cache[smap->cache_idx],
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sdata);
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raw_spin_unlock_irqrestore(&local_storage->lock, flags);
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}
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return sdata;
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}
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static int check_flags(const struct bpf_local_storage_data *old_sdata,
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u64 map_flags)
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{
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if (old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_NOEXIST)
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/* elem already exists */
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return -EEXIST;
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if (!old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_EXIST)
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/* elem doesn't exist, cannot update it */
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return -ENOENT;
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return 0;
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}
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int bpf_local_storage_alloc(void *owner,
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struct bpf_local_storage_map *smap,
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struct bpf_local_storage_elem *first_selem)
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{
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struct bpf_local_storage *prev_storage, *storage;
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struct bpf_local_storage **owner_storage_ptr;
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int err;
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err = mem_charge(smap, owner, sizeof(*storage));
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if (err)
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return err;
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storage = bpf_map_kzalloc(&smap->map, sizeof(*storage),
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GFP_ATOMIC | __GFP_NOWARN);
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if (!storage) {
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err = -ENOMEM;
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goto uncharge;
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}
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INIT_HLIST_HEAD(&storage->list);
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raw_spin_lock_init(&storage->lock);
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storage->owner = owner;
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bpf_selem_link_storage_nolock(storage, first_selem);
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bpf_selem_link_map(smap, first_selem);
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owner_storage_ptr =
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(struct bpf_local_storage **)owner_storage(smap, owner);
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/* Publish storage to the owner.
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* Instead of using any lock of the kernel object (i.e. owner),
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* cmpxchg will work with any kernel object regardless what
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* the running context is, bh, irq...etc.
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*
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* From now on, the owner->storage pointer (e.g. sk->sk_bpf_storage)
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* is protected by the storage->lock. Hence, when freeing
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* the owner->storage, the storage->lock must be held before
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* setting owner->storage ptr to NULL.
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*/
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prev_storage = cmpxchg(owner_storage_ptr, NULL, storage);
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if (unlikely(prev_storage)) {
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bpf_selem_unlink_map(first_selem);
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err = -EAGAIN;
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goto uncharge;
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/* Note that even first_selem was linked to smap's
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* bucket->list, first_selem can be freed immediately
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* (instead of kfree_rcu) because
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* bpf_local_storage_map_free() does a
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* synchronize_rcu() before walking the bucket->list.
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* Hence, no one is accessing selem from the
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* bucket->list under rcu_read_lock().
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*/
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}
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return 0;
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uncharge:
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kfree(storage);
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mem_uncharge(smap, owner, sizeof(*storage));
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return err;
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}
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/* sk cannot be going away because it is linking new elem
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* to sk->sk_bpf_storage. (i.e. sk->sk_refcnt cannot be 0).
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* Otherwise, it will become a leak (and other memory issues
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* during map destruction).
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*/
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struct bpf_local_storage_data *
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bpf_local_storage_update(void *owner, struct bpf_local_storage_map *smap,
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void *value, u64 map_flags)
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{
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struct bpf_local_storage_data *old_sdata = NULL;
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struct bpf_local_storage_elem *selem;
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struct bpf_local_storage *local_storage;
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unsigned long flags;
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int err;
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/* BPF_EXIST and BPF_NOEXIST cannot be both set */
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if (unlikely((map_flags & ~BPF_F_LOCK) > BPF_EXIST) ||
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/* BPF_F_LOCK can only be used in a value with spin_lock */
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unlikely((map_flags & BPF_F_LOCK) &&
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!map_value_has_spin_lock(&smap->map)))
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return ERR_PTR(-EINVAL);
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local_storage = rcu_dereference(*owner_storage(smap, owner));
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if (!local_storage || hlist_empty(&local_storage->list)) {
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/* Very first elem for the owner */
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err = check_flags(NULL, map_flags);
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if (err)
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return ERR_PTR(err);
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selem = bpf_selem_alloc(smap, owner, value, true);
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if (!selem)
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return ERR_PTR(-ENOMEM);
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err = bpf_local_storage_alloc(owner, smap, selem);
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if (err) {
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kfree(selem);
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mem_uncharge(smap, owner, smap->elem_size);
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return ERR_PTR(err);
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}
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return SDATA(selem);
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}
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if ((map_flags & BPF_F_LOCK) && !(map_flags & BPF_NOEXIST)) {
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/* Hoping to find an old_sdata to do inline update
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* such that it can avoid taking the local_storage->lock
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* and changing the lists.
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*/
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old_sdata =
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bpf_local_storage_lookup(local_storage, smap, false);
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err = check_flags(old_sdata, map_flags);
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if (err)
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return ERR_PTR(err);
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if (old_sdata && selem_linked_to_storage(SELEM(old_sdata))) {
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copy_map_value_locked(&smap->map, old_sdata->data,
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value, false);
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return old_sdata;
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}
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}
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raw_spin_lock_irqsave(&local_storage->lock, flags);
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/* Recheck local_storage->list under local_storage->lock */
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if (unlikely(hlist_empty(&local_storage->list))) {
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/* A parallel del is happening and local_storage is going
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* away. It has just been checked before, so very
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* unlikely. Return instead of retry to keep things
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* simple.
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*/
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err = -EAGAIN;
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goto unlock_err;
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}
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old_sdata = bpf_local_storage_lookup(local_storage, smap, false);
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err = check_flags(old_sdata, map_flags);
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if (err)
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goto unlock_err;
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if (old_sdata && (map_flags & BPF_F_LOCK)) {
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copy_map_value_locked(&smap->map, old_sdata->data, value,
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false);
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selem = SELEM(old_sdata);
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goto unlock;
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}
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/* local_storage->lock is held. Hence, we are sure
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* we can unlink and uncharge the old_sdata successfully
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* later. Hence, instead of charging the new selem now
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* and then uncharge the old selem later (which may cause
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* a potential but unnecessary charge failure), avoid taking
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* a charge at all here (the "!old_sdata" check) and the
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* old_sdata will not be uncharged later during
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* bpf_selem_unlink_storage_nolock().
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*/
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selem = bpf_selem_alloc(smap, owner, value, !old_sdata);
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if (!selem) {
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err = -ENOMEM;
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goto unlock_err;
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}
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/* First, link the new selem to the map */
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bpf_selem_link_map(smap, selem);
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/* Second, link (and publish) the new selem to local_storage */
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bpf_selem_link_storage_nolock(local_storage, selem);
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/* Third, remove old selem, SELEM(old_sdata) */
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if (old_sdata) {
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bpf_selem_unlink_map(SELEM(old_sdata));
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bpf_selem_unlink_storage_nolock(local_storage, SELEM(old_sdata),
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false);
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}
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unlock:
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raw_spin_unlock_irqrestore(&local_storage->lock, flags);
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return SDATA(selem);
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unlock_err:
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raw_spin_unlock_irqrestore(&local_storage->lock, flags);
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return ERR_PTR(err);
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}
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u16 bpf_local_storage_cache_idx_get(struct bpf_local_storage_cache *cache)
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{
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u64 min_usage = U64_MAX;
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u16 i, res = 0;
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spin_lock(&cache->idx_lock);
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for (i = 0; i < BPF_LOCAL_STORAGE_CACHE_SIZE; i++) {
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if (cache->idx_usage_counts[i] < min_usage) {
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min_usage = cache->idx_usage_counts[i];
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res = i;
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/* Found a free cache_idx */
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if (!min_usage)
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break;
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}
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}
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cache->idx_usage_counts[res]++;
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spin_unlock(&cache->idx_lock);
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return res;
|
|
}
|
|
|
|
void bpf_local_storage_cache_idx_free(struct bpf_local_storage_cache *cache,
|
|
u16 idx)
|
|
{
|
|
spin_lock(&cache->idx_lock);
|
|
cache->idx_usage_counts[idx]--;
|
|
spin_unlock(&cache->idx_lock);
|
|
}
|
|
|
|
void bpf_local_storage_map_free(struct bpf_local_storage_map *smap,
|
|
int __percpu *busy_counter)
|
|
{
|
|
struct bpf_local_storage_elem *selem;
|
|
struct bpf_local_storage_map_bucket *b;
|
|
unsigned int i;
|
|
|
|
/* Note that this map might be concurrently cloned from
|
|
* bpf_sk_storage_clone. Wait for any existing bpf_sk_storage_clone
|
|
* RCU read section to finish before proceeding. New RCU
|
|
* read sections should be prevented via bpf_map_inc_not_zero.
|
|
*/
|
|
synchronize_rcu();
|
|
|
|
/* bpf prog and the userspace can no longer access this map
|
|
* now. No new selem (of this map) can be added
|
|
* to the owner->storage or to the map bucket's list.
|
|
*
|
|
* The elem of this map can be cleaned up here
|
|
* or when the storage is freed e.g.
|
|
* by bpf_sk_storage_free() during __sk_destruct().
|
|
*/
|
|
for (i = 0; i < (1U << smap->bucket_log); i++) {
|
|
b = &smap->buckets[i];
|
|
|
|
rcu_read_lock();
|
|
/* No one is adding to b->list now */
|
|
while ((selem = hlist_entry_safe(
|
|
rcu_dereference_raw(hlist_first_rcu(&b->list)),
|
|
struct bpf_local_storage_elem, map_node))) {
|
|
if (busy_counter) {
|
|
migrate_disable();
|
|
__this_cpu_inc(*busy_counter);
|
|
}
|
|
bpf_selem_unlink(selem);
|
|
if (busy_counter) {
|
|
__this_cpu_dec(*busy_counter);
|
|
migrate_enable();
|
|
}
|
|
cond_resched_rcu();
|
|
}
|
|
rcu_read_unlock();
|
|
}
|
|
|
|
/* While freeing the storage we may still need to access the map.
|
|
*
|
|
* e.g. when bpf_sk_storage_free() has unlinked selem from the map
|
|
* which then made the above while((selem = ...)) loop
|
|
* exit immediately.
|
|
*
|
|
* However, while freeing the storage one still needs to access the
|
|
* smap->elem_size to do the uncharging in
|
|
* bpf_selem_unlink_storage_nolock().
|
|
*
|
|
* Hence, wait another rcu grace period for the storage to be freed.
|
|
*/
|
|
synchronize_rcu();
|
|
|
|
kvfree(smap->buckets);
|
|
kfree(smap);
|
|
}
|
|
|
|
int bpf_local_storage_map_alloc_check(union bpf_attr *attr)
|
|
{
|
|
if (attr->map_flags & ~BPF_LOCAL_STORAGE_CREATE_FLAG_MASK ||
|
|
!(attr->map_flags & BPF_F_NO_PREALLOC) ||
|
|
attr->max_entries ||
|
|
attr->key_size != sizeof(int) || !attr->value_size ||
|
|
/* Enforce BTF for userspace sk dumping */
|
|
!attr->btf_key_type_id || !attr->btf_value_type_id)
|
|
return -EINVAL;
|
|
|
|
if (!bpf_capable())
|
|
return -EPERM;
|
|
|
|
if (attr->value_size > BPF_LOCAL_STORAGE_MAX_VALUE_SIZE)
|
|
return -E2BIG;
|
|
|
|
return 0;
|
|
}
|
|
|
|
struct bpf_local_storage_map *bpf_local_storage_map_alloc(union bpf_attr *attr)
|
|
{
|
|
struct bpf_local_storage_map *smap;
|
|
unsigned int i;
|
|
u32 nbuckets;
|
|
|
|
smap = kzalloc(sizeof(*smap), GFP_USER | __GFP_NOWARN | __GFP_ACCOUNT);
|
|
if (!smap)
|
|
return ERR_PTR(-ENOMEM);
|
|
bpf_map_init_from_attr(&smap->map, attr);
|
|
|
|
nbuckets = roundup_pow_of_two(num_possible_cpus());
|
|
/* Use at least 2 buckets, select_bucket() is undefined behavior with 1 bucket */
|
|
nbuckets = max_t(u32, 2, nbuckets);
|
|
smap->bucket_log = ilog2(nbuckets);
|
|
|
|
smap->buckets = kvcalloc(sizeof(*smap->buckets), nbuckets,
|
|
GFP_USER | __GFP_NOWARN | __GFP_ACCOUNT);
|
|
if (!smap->buckets) {
|
|
kfree(smap);
|
|
return ERR_PTR(-ENOMEM);
|
|
}
|
|
|
|
for (i = 0; i < nbuckets; i++) {
|
|
INIT_HLIST_HEAD(&smap->buckets[i].list);
|
|
raw_spin_lock_init(&smap->buckets[i].lock);
|
|
}
|
|
|
|
smap->elem_size =
|
|
sizeof(struct bpf_local_storage_elem) + attr->value_size;
|
|
|
|
return smap;
|
|
}
|
|
|
|
int bpf_local_storage_map_check_btf(const struct bpf_map *map,
|
|
const struct btf *btf,
|
|
const struct btf_type *key_type,
|
|
const struct btf_type *value_type)
|
|
{
|
|
u32 int_data;
|
|
|
|
if (BTF_INFO_KIND(key_type->info) != BTF_KIND_INT)
|
|
return -EINVAL;
|
|
|
|
int_data = *(u32 *)(key_type + 1);
|
|
if (BTF_INT_BITS(int_data) != 32 || BTF_INT_OFFSET(int_data))
|
|
return -EINVAL;
|
|
|
|
return 0;
|
|
}
|