![John Fastabend](/assets/img/avatar_default.png)
An integer overflow is possible in dev_map_bitmap_size() when calculating the BITS_TO_LONG logic which becomes, after macro replacement, (((n) + (d) - 1)/ (d)) where 'n' is a __u32 and 'd' is (8 * sizeof(long)). To avoid overflow cast to u64 before arithmetic. Reported-by: Richard Weinberger <richard@nod.at> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: John Fastabend <john.fastabend@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
416 lines
12 KiB
C
416 lines
12 KiB
C
/* Copyright (c) 2017 Covalent IO, Inc. http://covalent.io
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of version 2 of the GNU General Public
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* License as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*/
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/* Devmaps primary use is as a backend map for XDP BPF helper call
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* bpf_redirect_map(). Because XDP is mostly concerned with performance we
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* spent some effort to ensure the datapath with redirect maps does not use
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* any locking. This is a quick note on the details.
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*
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* We have three possible paths to get into the devmap control plane bpf
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* syscalls, bpf programs, and driver side xmit/flush operations. A bpf syscall
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* will invoke an update, delete, or lookup operation. To ensure updates and
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* deletes appear atomic from the datapath side xchg() is used to modify the
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* netdev_map array. Then because the datapath does a lookup into the netdev_map
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* array (read-only) from an RCU critical section we use call_rcu() to wait for
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* an rcu grace period before free'ing the old data structures. This ensures the
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* datapath always has a valid copy. However, the datapath does a "flush"
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* operation that pushes any pending packets in the driver outside the RCU
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* critical section. Each bpf_dtab_netdev tracks these pending operations using
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* an atomic per-cpu bitmap. The bpf_dtab_netdev object will not be destroyed
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* until all bits are cleared indicating outstanding flush operations have
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* completed.
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*
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* BPF syscalls may race with BPF program calls on any of the update, delete
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* or lookup operations. As noted above the xchg() operation also keep the
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* netdev_map consistent in this case. From the devmap side BPF programs
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* calling into these operations are the same as multiple user space threads
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* making system calls.
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*
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* Finally, any of the above may race with a netdev_unregister notifier. The
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* unregister notifier must search for net devices in the map structure that
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* contain a reference to the net device and remove them. This is a two step
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* process (a) dereference the bpf_dtab_netdev object in netdev_map and (b)
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* check to see if the ifindex is the same as the net_device being removed.
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* When removing the dev a cmpxchg() is used to ensure the correct dev is
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* removed, in the case of a concurrent update or delete operation it is
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* possible that the initially referenced dev is no longer in the map. As the
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* notifier hook walks the map we know that new dev references can not be
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* added by the user because core infrastructure ensures dev_get_by_index()
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* calls will fail at this point.
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*/
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#include <linux/bpf.h>
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#include <linux/filter.h>
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struct bpf_dtab_netdev {
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struct net_device *dev;
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struct bpf_dtab *dtab;
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unsigned int bit;
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struct rcu_head rcu;
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};
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struct bpf_dtab {
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struct bpf_map map;
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struct bpf_dtab_netdev **netdev_map;
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unsigned long __percpu *flush_needed;
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struct list_head list;
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};
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static DEFINE_SPINLOCK(dev_map_lock);
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static LIST_HEAD(dev_map_list);
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static u64 dev_map_bitmap_size(const union bpf_attr *attr)
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{
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return BITS_TO_LONGS((u64) attr->max_entries) * sizeof(unsigned long);
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}
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static struct bpf_map *dev_map_alloc(union bpf_attr *attr)
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{
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struct bpf_dtab *dtab;
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int err = -EINVAL;
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u64 cost;
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if (!capable(CAP_NET_ADMIN))
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return ERR_PTR(-EPERM);
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/* check sanity of attributes */
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if (attr->max_entries == 0 || attr->key_size != 4 ||
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attr->value_size != 4 || attr->map_flags & ~BPF_F_NUMA_NODE)
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return ERR_PTR(-EINVAL);
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dtab = kzalloc(sizeof(*dtab), GFP_USER);
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if (!dtab)
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return ERR_PTR(-ENOMEM);
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/* mandatory map attributes */
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dtab->map.map_type = attr->map_type;
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dtab->map.key_size = attr->key_size;
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dtab->map.value_size = attr->value_size;
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dtab->map.max_entries = attr->max_entries;
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dtab->map.map_flags = attr->map_flags;
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dtab->map.numa_node = bpf_map_attr_numa_node(attr);
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/* make sure page count doesn't overflow */
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cost = (u64) dtab->map.max_entries * sizeof(struct bpf_dtab_netdev *);
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cost += dev_map_bitmap_size(attr) * num_possible_cpus();
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if (cost >= U32_MAX - PAGE_SIZE)
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goto free_dtab;
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dtab->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;
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/* if map size is larger than memlock limit, reject it early */
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err = bpf_map_precharge_memlock(dtab->map.pages);
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if (err)
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goto free_dtab;
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err = -ENOMEM;
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/* A per cpu bitfield with a bit per possible net device */
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dtab->flush_needed = __alloc_percpu_gfp(dev_map_bitmap_size(attr),
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__alignof__(unsigned long),
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GFP_KERNEL | __GFP_NOWARN);
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if (!dtab->flush_needed)
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goto free_dtab;
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dtab->netdev_map = bpf_map_area_alloc(dtab->map.max_entries *
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sizeof(struct bpf_dtab_netdev *),
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dtab->map.numa_node);
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if (!dtab->netdev_map)
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goto free_dtab;
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spin_lock(&dev_map_lock);
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list_add_tail_rcu(&dtab->list, &dev_map_list);
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spin_unlock(&dev_map_lock);
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return &dtab->map;
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free_dtab:
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free_percpu(dtab->flush_needed);
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kfree(dtab);
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return ERR_PTR(err);
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}
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static void dev_map_free(struct bpf_map *map)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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int i, cpu;
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/* At this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
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* so the programs (can be more than one that used this map) were
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* disconnected from events. Wait for outstanding critical sections in
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* these programs to complete. The rcu critical section only guarantees
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* no further reads against netdev_map. It does __not__ ensure pending
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* flush operations (if any) are complete.
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*/
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spin_lock(&dev_map_lock);
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list_del_rcu(&dtab->list);
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spin_unlock(&dev_map_lock);
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synchronize_rcu();
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/* To ensure all pending flush operations have completed wait for flush
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* bitmap to indicate all flush_needed bits to be zero on _all_ cpus.
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* Because the above synchronize_rcu() ensures the map is disconnected
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* from the program we can assume no new bits will be set.
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*/
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for_each_online_cpu(cpu) {
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unsigned long *bitmap = per_cpu_ptr(dtab->flush_needed, cpu);
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while (!bitmap_empty(bitmap, dtab->map.max_entries))
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cond_resched();
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}
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for (i = 0; i < dtab->map.max_entries; i++) {
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struct bpf_dtab_netdev *dev;
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dev = dtab->netdev_map[i];
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if (!dev)
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continue;
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dev_put(dev->dev);
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kfree(dev);
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}
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free_percpu(dtab->flush_needed);
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bpf_map_area_free(dtab->netdev_map);
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kfree(dtab);
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}
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static int dev_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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u32 index = key ? *(u32 *)key : U32_MAX;
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u32 *next = next_key;
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if (index >= dtab->map.max_entries) {
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*next = 0;
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return 0;
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}
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if (index == dtab->map.max_entries - 1)
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return -ENOENT;
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*next = index + 1;
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return 0;
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}
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void __dev_map_insert_ctx(struct bpf_map *map, u32 bit)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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unsigned long *bitmap = this_cpu_ptr(dtab->flush_needed);
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__set_bit(bit, bitmap);
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}
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/* __dev_map_flush is called from xdp_do_flush_map() which _must_ be signaled
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* from the driver before returning from its napi->poll() routine. The poll()
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* routine is called either from busy_poll context or net_rx_action signaled
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* from NET_RX_SOFTIRQ. Either way the poll routine must complete before the
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* net device can be torn down. On devmap tear down we ensure the ctx bitmap
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* is zeroed before completing to ensure all flush operations have completed.
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*/
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void __dev_map_flush(struct bpf_map *map)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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unsigned long *bitmap = this_cpu_ptr(dtab->flush_needed);
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u32 bit;
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for_each_set_bit(bit, bitmap, map->max_entries) {
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struct bpf_dtab_netdev *dev = READ_ONCE(dtab->netdev_map[bit]);
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struct net_device *netdev;
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/* This is possible if the dev entry is removed by user space
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* between xdp redirect and flush op.
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*/
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if (unlikely(!dev))
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continue;
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__clear_bit(bit, bitmap);
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netdev = dev->dev;
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if (likely(netdev->netdev_ops->ndo_xdp_flush))
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netdev->netdev_ops->ndo_xdp_flush(netdev);
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}
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}
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/* rcu_read_lock (from syscall and BPF contexts) ensures that if a delete and/or
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* update happens in parallel here a dev_put wont happen until after reading the
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* ifindex.
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*/
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struct net_device *__dev_map_lookup_elem(struct bpf_map *map, u32 key)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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struct bpf_dtab_netdev *dev;
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if (key >= map->max_entries)
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return NULL;
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dev = READ_ONCE(dtab->netdev_map[key]);
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return dev ? dev->dev : NULL;
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}
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static void *dev_map_lookup_elem(struct bpf_map *map, void *key)
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{
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struct net_device *dev = __dev_map_lookup_elem(map, *(u32 *)key);
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return dev ? &dev->ifindex : NULL;
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}
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static void dev_map_flush_old(struct bpf_dtab_netdev *dev)
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{
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if (dev->dev->netdev_ops->ndo_xdp_flush) {
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struct net_device *fl = dev->dev;
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unsigned long *bitmap;
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int cpu;
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for_each_online_cpu(cpu) {
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bitmap = per_cpu_ptr(dev->dtab->flush_needed, cpu);
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__clear_bit(dev->bit, bitmap);
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fl->netdev_ops->ndo_xdp_flush(dev->dev);
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}
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}
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}
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static void __dev_map_entry_free(struct rcu_head *rcu)
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{
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struct bpf_dtab_netdev *dev;
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dev = container_of(rcu, struct bpf_dtab_netdev, rcu);
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dev_map_flush_old(dev);
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dev_put(dev->dev);
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kfree(dev);
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}
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static int dev_map_delete_elem(struct bpf_map *map, void *key)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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struct bpf_dtab_netdev *old_dev;
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int k = *(u32 *)key;
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if (k >= map->max_entries)
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return -EINVAL;
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/* Use call_rcu() here to ensure any rcu critical sections have
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* completed, but this does not guarantee a flush has happened
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* yet. Because driver side rcu_read_lock/unlock only protects the
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* running XDP program. However, for pending flush operations the
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* dev and ctx are stored in another per cpu map. And additionally,
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* the driver tear down ensures all soft irqs are complete before
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* removing the net device in the case of dev_put equals zero.
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*/
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old_dev = xchg(&dtab->netdev_map[k], NULL);
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if (old_dev)
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call_rcu(&old_dev->rcu, __dev_map_entry_free);
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return 0;
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}
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static int dev_map_update_elem(struct bpf_map *map, void *key, void *value,
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u64 map_flags)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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struct net *net = current->nsproxy->net_ns;
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struct bpf_dtab_netdev *dev, *old_dev;
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u32 i = *(u32 *)key;
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u32 ifindex = *(u32 *)value;
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if (unlikely(map_flags > BPF_EXIST))
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return -EINVAL;
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if (unlikely(i >= dtab->map.max_entries))
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return -E2BIG;
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if (unlikely(map_flags == BPF_NOEXIST))
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return -EEXIST;
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if (!ifindex) {
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dev = NULL;
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} else {
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dev = kmalloc_node(sizeof(*dev), GFP_ATOMIC | __GFP_NOWARN,
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map->numa_node);
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if (!dev)
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return -ENOMEM;
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dev->dev = dev_get_by_index(net, ifindex);
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if (!dev->dev) {
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kfree(dev);
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return -EINVAL;
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}
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dev->bit = i;
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dev->dtab = dtab;
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}
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/* Use call_rcu() here to ensure rcu critical sections have completed
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* Remembering the driver side flush operation will happen before the
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* net device is removed.
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*/
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old_dev = xchg(&dtab->netdev_map[i], dev);
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if (old_dev)
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call_rcu(&old_dev->rcu, __dev_map_entry_free);
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return 0;
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}
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const struct bpf_map_ops dev_map_ops = {
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.map_alloc = dev_map_alloc,
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.map_free = dev_map_free,
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.map_get_next_key = dev_map_get_next_key,
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.map_lookup_elem = dev_map_lookup_elem,
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.map_update_elem = dev_map_update_elem,
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.map_delete_elem = dev_map_delete_elem,
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};
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static int dev_map_notification(struct notifier_block *notifier,
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ulong event, void *ptr)
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{
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struct net_device *netdev = netdev_notifier_info_to_dev(ptr);
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struct bpf_dtab *dtab;
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int i;
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switch (event) {
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case NETDEV_UNREGISTER:
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/* This rcu_read_lock/unlock pair is needed because
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* dev_map_list is an RCU list AND to ensure a delete
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* operation does not free a netdev_map entry while we
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* are comparing it against the netdev being unregistered.
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*/
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rcu_read_lock();
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list_for_each_entry_rcu(dtab, &dev_map_list, list) {
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for (i = 0; i < dtab->map.max_entries; i++) {
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struct bpf_dtab_netdev *dev, *odev;
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dev = READ_ONCE(dtab->netdev_map[i]);
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if (!dev ||
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dev->dev->ifindex != netdev->ifindex)
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continue;
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odev = cmpxchg(&dtab->netdev_map[i], dev, NULL);
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if (dev == odev)
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call_rcu(&dev->rcu,
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__dev_map_entry_free);
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}
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}
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rcu_read_unlock();
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break;
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default:
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break;
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}
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return NOTIFY_OK;
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}
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static struct notifier_block dev_map_notifier = {
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.notifier_call = dev_map_notification,
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};
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static int __init dev_map_init(void)
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{
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register_netdevice_notifier(&dev_map_notifier);
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return 0;
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}
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subsys_initcall(dev_map_init);
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