linux/kernel/bpf/devmap.c

535 lines
15 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2017 Covalent IO, Inc. http://covalent.io
*/
/* 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
* a per-cpu flush list. The bpf_dtab_netdev object will not be destroyed until
* this list is empty, 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 <net/xdp.h>
#include <linux/filter.h>
#include <trace/events/xdp.h>
#define DEV_CREATE_FLAG_MASK \
(BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY)
#define DEV_MAP_BULK_SIZE 16
struct bpf_dtab_netdev;
struct xdp_bulk_queue {
struct xdp_frame *q[DEV_MAP_BULK_SIZE];
struct list_head flush_node;
struct net_device *dev_rx;
struct bpf_dtab_netdev *obj;
unsigned int count;
};
struct bpf_dtab_netdev {
struct net_device *dev; /* must be first member, due to tracepoint */
struct bpf_dtab *dtab;
unsigned int bit;
struct xdp_bulk_queue __percpu *bulkq;
struct rcu_head rcu;
};
struct bpf_dtab {
struct bpf_map map;
struct bpf_dtab_netdev **netdev_map;
struct list_head __percpu *flush_list;
struct list_head list;
};
static DEFINE_SPINLOCK(dev_map_lock);
static LIST_HEAD(dev_map_list);
static struct bpf_map *dev_map_alloc(union bpf_attr *attr)
{
struct bpf_dtab *dtab;
int err, cpu;
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 & ~DEV_CREATE_FLAG_MASK)
return ERR_PTR(-EINVAL);
/* Lookup returns a pointer straight to dev->ifindex, so make sure the
* verifier prevents writes from the BPF side
*/
attr->map_flags |= BPF_F_RDONLY_PROG;
dtab = kzalloc(sizeof(*dtab), GFP_USER);
if (!dtab)
return ERR_PTR(-ENOMEM);
bpf_map_init_from_attr(&dtab->map, attr);
/* make sure page count doesn't overflow */
cost = (u64) dtab->map.max_entries * sizeof(struct bpf_dtab_netdev *);
cost += sizeof(struct list_head) * num_possible_cpus();
/* if map size is larger than memlock limit, reject it */
err = bpf_map_charge_init(&dtab->map.memory, cost);
if (err)
goto free_dtab;
err = -ENOMEM;
dtab->flush_list = alloc_percpu(struct list_head);
if (!dtab->flush_list)
goto free_charge;
for_each_possible_cpu(cpu)
INIT_LIST_HEAD(per_cpu_ptr(dtab->flush_list, cpu));
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_percpu;
spin_lock(&dev_map_lock);
list_add_tail_rcu(&dtab->list, &dev_map_list);
spin_unlock(&dev_map_lock);
return &dtab->map;
free_percpu:
free_percpu(dtab->flush_list);
free_charge:
bpf_map_charge_finish(&dtab->map.memory);
free_dtab:
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);
bpf_clear_redirect_map(map);
synchronize_rcu();
/* Make sure prior __dev_map_entry_free() have completed. */
rcu_barrier();
/* To ensure all pending flush operations have completed wait for flush
* list to empty on _all_ cpus.
* Because the above synchronize_rcu() ensures the map is disconnected
* from the program we can assume no new items will be added.
*/
for_each_online_cpu(cpu) {
struct list_head *flush_list = per_cpu_ptr(dtab->flush_list, cpu);
while (!list_empty(flush_list))
cond_resched();
}
for (i = 0; i < dtab->map.max_entries; i++) {
struct bpf_dtab_netdev *dev;
dev = dtab->netdev_map[i];
if (!dev)
continue;
free_percpu(dev->bulkq);
dev_put(dev->dev);
kfree(dev);
}
free_percpu(dtab->flush_list);
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;
}
static int bq_xmit_all(struct xdp_bulk_queue *bq, u32 flags,
bool in_napi_ctx)
{
struct bpf_dtab_netdev *obj = bq->obj;
struct net_device *dev = obj->dev;
int sent = 0, drops = 0, err = 0;
int i;
if (unlikely(!bq->count))
return 0;
for (i = 0; i < bq->count; i++) {
struct xdp_frame *xdpf = bq->q[i];
prefetch(xdpf);
}
sent = dev->netdev_ops->ndo_xdp_xmit(dev, bq->count, bq->q, flags);
if (sent < 0) {
err = sent;
sent = 0;
goto error;
}
drops = bq->count - sent;
out:
bq->count = 0;
trace_xdp_devmap_xmit(&obj->dtab->map, obj->bit,
sent, drops, bq->dev_rx, dev, err);
bq->dev_rx = NULL;
__list_del_clearprev(&bq->flush_node);
return 0;
error:
/* If ndo_xdp_xmit fails with an errno, no frames have been
* xmit'ed and it's our responsibility to them free all.
*/
for (i = 0; i < bq->count; i++) {
struct xdp_frame *xdpf = bq->q[i];
/* RX path under NAPI protection, can return frames faster */
if (likely(in_napi_ctx))
xdp_return_frame_rx_napi(xdpf);
else
xdp_return_frame(xdpf);
drops++;
}
goto out;
}
/* __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 flush list
* is empty 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);
struct list_head *flush_list = this_cpu_ptr(dtab->flush_list);
struct xdp_bulk_queue *bq, *tmp;
rcu_read_lock();
list_for_each_entry_safe(bq, tmp, flush_list, flush_node)
bq_xmit_all(bq, XDP_XMIT_FLUSH, true);
rcu_read_unlock();
}
/* 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 bpf_dtab_netdev *__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 *obj;
if (key >= map->max_entries)
return NULL;
obj = READ_ONCE(dtab->netdev_map[key]);
return obj;
}
/* Runs under RCU-read-side, plus in softirq under NAPI protection.
* Thus, safe percpu variable access.
*/
static int bq_enqueue(struct bpf_dtab_netdev *obj, struct xdp_frame *xdpf,
struct net_device *dev_rx)
{
struct list_head *flush_list = this_cpu_ptr(obj->dtab->flush_list);
struct xdp_bulk_queue *bq = this_cpu_ptr(obj->bulkq);
if (unlikely(bq->count == DEV_MAP_BULK_SIZE))
bq_xmit_all(bq, 0, true);
/* Ingress dev_rx will be the same for all xdp_frame's in
* bulk_queue, because bq stored per-CPU and must be flushed
* from net_device drivers NAPI func end.
*/
if (!bq->dev_rx)
bq->dev_rx = dev_rx;
bq->q[bq->count++] = xdpf;
if (!bq->flush_node.prev)
list_add(&bq->flush_node, flush_list);
return 0;
}
int dev_map_enqueue(struct bpf_dtab_netdev *dst, struct xdp_buff *xdp,
struct net_device *dev_rx)
{
struct net_device *dev = dst->dev;
struct xdp_frame *xdpf;
int err;
if (!dev->netdev_ops->ndo_xdp_xmit)
return -EOPNOTSUPP;
err = xdp_ok_fwd_dev(dev, xdp->data_end - xdp->data);
if (unlikely(err))
return err;
xdpf = convert_to_xdp_frame(xdp);
if (unlikely(!xdpf))
return -EOVERFLOW;
return bq_enqueue(dst, xdpf, dev_rx);
}
int dev_map_generic_redirect(struct bpf_dtab_netdev *dst, struct sk_buff *skb,
struct bpf_prog *xdp_prog)
{
int err;
err = xdp_ok_fwd_dev(dst->dev, skb->len);
if (unlikely(err))
return err;
skb->dev = dst->dev;
generic_xdp_tx(skb, xdp_prog);
return 0;
}
static void *dev_map_lookup_elem(struct bpf_map *map, void *key)
{
struct bpf_dtab_netdev *obj = __dev_map_lookup_elem(map, *(u32 *)key);
struct net_device *dev = obj ? obj->dev : NULL;
return dev ? &dev->ifindex : NULL;
}
static void dev_map_flush_old(struct bpf_dtab_netdev *dev)
{
if (dev->dev->netdev_ops->ndo_xdp_xmit) {
struct xdp_bulk_queue *bq;
int cpu;
rcu_read_lock();
for_each_online_cpu(cpu) {
bq = per_cpu_ptr(dev->bulkq, cpu);
bq_xmit_all(bq, XDP_XMIT_FLUSH, false);
}
rcu_read_unlock();
}
}
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);
free_percpu(dev->bulkq);
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;
gfp_t gfp = GFP_ATOMIC | __GFP_NOWARN;
struct bpf_dtab_netdev *dev, *old_dev;
u32 ifindex = *(u32 *)value;
struct xdp_bulk_queue *bq;
u32 i = *(u32 *)key;
int cpu;
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, map->numa_node);
if (!dev)
return -ENOMEM;
dev->bulkq = __alloc_percpu_gfp(sizeof(*dev->bulkq),
sizeof(void *), gfp);
if (!dev->bulkq) {
kfree(dev);
return -ENOMEM;
}
for_each_possible_cpu(cpu) {
bq = per_cpu_ptr(dev->bulkq, cpu);
bq->obj = dev;
}
dev->dev = dev_get_by_index(net, ifindex);
if (!dev->dev) {
free_percpu(dev->bulkq);
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,
.map_check_btf = map_check_no_btf,
};
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 || netdev != dev->dev)
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)
{
/* Assure tracepoint shadow struct _bpf_dtab_netdev is in sync */
BUILD_BUG_ON(offsetof(struct bpf_dtab_netdev, dev) !=
offsetof(struct _bpf_dtab_netdev, dev));
register_netdevice_notifier(&dev_map_notifier);
return 0;
}
subsys_initcall(dev_map_init);