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