aboutsummaryrefslogtreecommitdiffstats
path: root/kernel/bpf/devmap.c
blob: fc500ca464d008a8e2a65b07b8a3c2e49b630a84 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
/* 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 <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 xdp_bulk_queue {
	struct xdp_frame *q[DEV_MAP_BULK_SIZE];
	struct net_device *dev_rx;
	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;
	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 & ~DEV_CREATE_FLAG_MASK)
		return ERR_PTR(-EINVAL);

	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 += 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);

	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
	 * 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;

		free_percpu(dev->bulkq);
		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);
}

static int bq_xmit_all(struct bpf_dtab_netdev *obj,
		       struct xdp_bulk_queue *bq, u32 flags,
		       bool in_napi_ctx)
{
	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;
	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 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;

	rcu_read_lock();
	for_each_set_bit(bit, bitmap, map->max_entries) {
		struct bpf_dtab_netdev *dev = READ_ONCE(dtab->netdev_map[bit]);
		struct xdp_bulk_queue *bq;

		/* This is possible if the dev entry is removed by user space
		 * between xdp redirect and flush op.
		 */
		if (unlikely(!dev))
			continue;

		bq = this_cpu_ptr(dev->bulkq);
		bq_xmit_all(dev, bq, XDP_XMIT_FLUSH, true);

		__clear_bit(bit, bitmap);
	}
	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 xdp_bulk_queue *bq = this_cpu_ptr(obj->bulkq);

	if (unlikely(bq->count == DEV_MAP_BULK_SIZE))
		bq_xmit_all(obj, 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;
	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;
		unsigned long *bitmap;

		int cpu;

		rcu_read_lock();
		for_each_online_cpu(cpu) {
			bitmap = per_cpu_ptr(dev->dtab->flush_needed, cpu);
			__clear_bit(dev->bit, bitmap);

			bq = per_cpu_ptr(dev->bulkq, cpu);
			bq_xmit_all(dev, 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 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, 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;
		}

		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 ||
				    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)
{
	/* 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);