summaryrefslogtreecommitdiff
path: root/kernel/bpf/trampoline.c
blob: e98de5e73ba59f756480cc5f962849be1859751b (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
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2019 Facebook */
#include <linux/hash.h>
#include <linux/bpf.h>
#include <linux/filter.h>
#include <linux/ftrace.h>
#include <linux/rbtree_latch.h>
#include <linux/perf_event.h>
#include <linux/btf.h>
#include <linux/rcupdate_trace.h>
#include <linux/rcupdate_wait.h>
#include <linux/module.h>
#include <linux/static_call.h>

/* dummy _ops. The verifier will operate on target program's ops. */
const struct bpf_verifier_ops bpf_extension_verifier_ops = {
};
const struct bpf_prog_ops bpf_extension_prog_ops = {
};

/* btf_vmlinux has ~22k attachable functions. 1k htab is enough. */
#define TRAMPOLINE_HASH_BITS 10
#define TRAMPOLINE_TABLE_SIZE (1 << TRAMPOLINE_HASH_BITS)

static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE];

/* serializes access to trampoline_table */
static DEFINE_MUTEX(trampoline_mutex);

void *bpf_jit_alloc_exec_page(void)
{
	void *image;

	image = bpf_jit_alloc_exec(PAGE_SIZE);
	if (!image)
		return NULL;

	set_vm_flush_reset_perms(image);
	/* Keep image as writeable. The alternative is to keep flipping ro/rw
	 * everytime new program is attached or detached.
	 */
	set_memory_x((long)image, 1);
	return image;
}

void bpf_image_ksym_add(void *data, struct bpf_ksym *ksym)
{
	ksym->start = (unsigned long) data;
	ksym->end = ksym->start + PAGE_SIZE;
	bpf_ksym_add(ksym);
	perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start,
			   PAGE_SIZE, false, ksym->name);
}

void bpf_image_ksym_del(struct bpf_ksym *ksym)
{
	bpf_ksym_del(ksym);
	perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start,
			   PAGE_SIZE, true, ksym->name);
}

static struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
{
	struct bpf_trampoline *tr;
	struct hlist_head *head;
	int i;

	mutex_lock(&trampoline_mutex);
	head = &trampoline_table[hash_64(key, TRAMPOLINE_HASH_BITS)];
	hlist_for_each_entry(tr, head, hlist) {
		if (tr->key == key) {
			refcount_inc(&tr->refcnt);
			goto out;
		}
	}
	tr = kzalloc(sizeof(*tr), GFP_KERNEL);
	if (!tr)
		goto out;

	tr->key = key;
	INIT_HLIST_NODE(&tr->hlist);
	hlist_add_head(&tr->hlist, head);
	refcount_set(&tr->refcnt, 1);
	mutex_init(&tr->mutex);
	for (i = 0; i < BPF_TRAMP_MAX; i++)
		INIT_HLIST_HEAD(&tr->progs_hlist[i]);
out:
	mutex_unlock(&trampoline_mutex);
	return tr;
}

static int bpf_trampoline_module_get(struct bpf_trampoline *tr)
{
	struct module *mod;
	int err = 0;

	preempt_disable();
	mod = __module_text_address((unsigned long) tr->func.addr);
	if (mod && !try_module_get(mod))
		err = -ENOENT;
	preempt_enable();
	tr->mod = mod;
	return err;
}

static void bpf_trampoline_module_put(struct bpf_trampoline *tr)
{
	module_put(tr->mod);
	tr->mod = NULL;
}

static int is_ftrace_location(void *ip)
{
	long addr;

	addr = ftrace_location((long)ip);
	if (!addr)
		return 0;
	if (WARN_ON_ONCE(addr != (long)ip))
		return -EFAULT;
	return 1;
}

static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
{
	void *ip = tr->func.addr;
	int ret;

	if (tr->func.ftrace_managed)
		ret = unregister_ftrace_direct((long)ip, (long)old_addr);
	else
		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL);

	if (!ret)
		bpf_trampoline_module_put(tr);
	return ret;
}

static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_addr)
{
	void *ip = tr->func.addr;
	int ret;

	if (tr->func.ftrace_managed)
		ret = modify_ftrace_direct((long)ip, (long)old_addr, (long)new_addr);
	else
		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, new_addr);
	return ret;
}

/* first time registering */
static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
{
	void *ip = tr->func.addr;
	int ret;

	ret = is_ftrace_location(ip);
	if (ret < 0)
		return ret;
	tr->func.ftrace_managed = ret;

	if (bpf_trampoline_module_get(tr))
		return -ENOENT;

	if (tr->func.ftrace_managed)
		ret = register_ftrace_direct((long)ip, (long)new_addr);
	else
		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr);

	if (ret)
		bpf_trampoline_module_put(tr);
	return ret;
}

static struct bpf_tramp_progs *
bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total, bool *ip_arg)
{
	const struct bpf_prog_aux *aux;
	struct bpf_tramp_progs *tprogs;
	struct bpf_prog **progs;
	int kind;

	*total = 0;
	tprogs = kcalloc(BPF_TRAMP_MAX, sizeof(*tprogs), GFP_KERNEL);
	if (!tprogs)
		return ERR_PTR(-ENOMEM);

	for (kind = 0; kind < BPF_TRAMP_MAX; kind++) {
		tprogs[kind].nr_progs = tr->progs_cnt[kind];
		*total += tr->progs_cnt[kind];
		progs = tprogs[kind].progs;

		hlist_for_each_entry(aux, &tr->progs_hlist[kind], tramp_hlist) {
			*ip_arg |= aux->prog->call_get_func_ip;
			*progs++ = aux->prog;
		}
	}
	return tprogs;
}

static void __bpf_tramp_image_put_deferred(struct work_struct *work)
{
	struct bpf_tramp_image *im;

	im = container_of(work, struct bpf_tramp_image, work);
	bpf_image_ksym_del(&im->ksym);
	bpf_jit_free_exec(im->image);
	bpf_jit_uncharge_modmem(1);
	percpu_ref_exit(&im->pcref);
	kfree_rcu(im, rcu);
}

/* callback, fexit step 3 or fentry step 2 */
static void __bpf_tramp_image_put_rcu(struct rcu_head *rcu)
{
	struct bpf_tramp_image *im;

	im = container_of(rcu, struct bpf_tramp_image, rcu);
	INIT_WORK(&im->work, __bpf_tramp_image_put_deferred);
	schedule_work(&im->work);
}

/* callback, fexit step 2. Called after percpu_ref_kill confirms. */
static void __bpf_tramp_image_release(struct percpu_ref *pcref)
{
	struct bpf_tramp_image *im;

	im = container_of(pcref, struct bpf_tramp_image, pcref);
	call_rcu_tasks(&im->rcu, __bpf_tramp_image_put_rcu);
}

/* callback, fexit or fentry step 1 */
static void __bpf_tramp_image_put_rcu_tasks(struct rcu_head *rcu)
{
	struct bpf_tramp_image *im;

	im = container_of(rcu, struct bpf_tramp_image, rcu);
	if (im->ip_after_call)
		/* the case of fmod_ret/fexit trampoline and CONFIG_PREEMPTION=y */
		percpu_ref_kill(&im->pcref);
	else
		/* the case of fentry trampoline */
		call_rcu_tasks(&im->rcu, __bpf_tramp_image_put_rcu);
}

static void bpf_tramp_image_put(struct bpf_tramp_image *im)
{
	/* The trampoline image that calls original function is using:
	 * rcu_read_lock_trace to protect sleepable bpf progs
	 * rcu_read_lock to protect normal bpf progs
	 * percpu_ref to protect trampoline itself
	 * rcu tasks to protect trampoline asm not covered by percpu_ref
	 * (which are few asm insns before __bpf_tramp_enter and
	 *  after __bpf_tramp_exit)
	 *
	 * The trampoline is unreachable before bpf_tramp_image_put().
	 *
	 * First, patch the trampoline to avoid calling into fexit progs.
	 * The progs will be freed even if the original function is still
	 * executing or sleeping.
	 * In case of CONFIG_PREEMPT=y use call_rcu_tasks() to wait on
	 * first few asm instructions to execute and call into
	 * __bpf_tramp_enter->percpu_ref_get.
	 * Then use percpu_ref_kill to wait for the trampoline and the original
	 * function to finish.
	 * Then use call_rcu_tasks() to make sure few asm insns in
	 * the trampoline epilogue are done as well.
	 *
	 * In !PREEMPT case the task that got interrupted in the first asm
	 * insns won't go through an RCU quiescent state which the
	 * percpu_ref_kill will be waiting for. Hence the first
	 * call_rcu_tasks() is not necessary.
	 */
	if (im->ip_after_call) {
		int err = bpf_arch_text_poke(im->ip_after_call, BPF_MOD_JUMP,
					     NULL, im->ip_epilogue);
		WARN_ON(err);
		if (IS_ENABLED(CONFIG_PREEMPTION))
			call_rcu_tasks(&im->rcu, __bpf_tramp_image_put_rcu_tasks);
		else
			percpu_ref_kill(&im->pcref);
		return;
	}

	/* The trampoline without fexit and fmod_ret progs doesn't call original
	 * function and doesn't use percpu_ref.
	 * Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
	 * Then use call_rcu_tasks() to wait for the rest of trampoline asm
	 * and normal progs.
	 */
	call_rcu_tasks_trace(&im->rcu, __bpf_tramp_image_put_rcu_tasks);
}

static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key, u32 idx)
{
	struct bpf_tramp_image *im;
	struct bpf_ksym *ksym;
	void *image;
	int err = -ENOMEM;

	im = kzalloc(sizeof(*im), GFP_KERNEL);
	if (!im)
		goto out;

	err = bpf_jit_charge_modmem(1);
	if (err)
		goto out_free_im;

	err = -ENOMEM;
	im->image = image = bpf_jit_alloc_exec_page();
	if (!image)
		goto out_uncharge;

	err = percpu_ref_init(&im->pcref, __bpf_tramp_image_release, 0, GFP_KERNEL);
	if (err)
		goto out_free_image;

	ksym = &im->ksym;
	INIT_LIST_HEAD_RCU(&ksym->lnode);
	snprintf(ksym->name, KSYM_NAME_LEN, "bpf_trampoline_%llu_%u", key, idx);
	bpf_image_ksym_add(image, ksym);
	return im;

out_free_image:
	bpf_jit_free_exec(im->image);
out_uncharge:
	bpf_jit_uncharge_modmem(1);
out_free_im:
	kfree(im);
out:
	return ERR_PTR(err);
}

static int bpf_trampoline_update(struct bpf_trampoline *tr)
{
	struct bpf_tramp_image *im;
	struct bpf_tramp_progs *tprogs;
	u32 flags = BPF_TRAMP_F_RESTORE_REGS;
	bool ip_arg = false;
	int err, total;

	tprogs = bpf_trampoline_get_progs(tr, &total, &ip_arg);
	if (IS_ERR(tprogs))
		return PTR_ERR(tprogs);

	if (total == 0) {
		err = unregister_fentry(tr, tr->cur_image->image);
		bpf_tramp_image_put(tr->cur_image);
		tr->cur_image = NULL;
		tr->selector = 0;
		goto out;
	}

	im = bpf_tramp_image_alloc(tr->key, tr->selector);
	if (IS_ERR(im)) {
		err = PTR_ERR(im);
		goto out;
	}

	if (tprogs[BPF_TRAMP_FEXIT].nr_progs ||
	    tprogs[BPF_TRAMP_MODIFY_RETURN].nr_progs)
		flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;

	if (ip_arg)
		flags |= BPF_TRAMP_F_IP_ARG;

	err = arch_prepare_bpf_trampoline(im, im->image, im->image + PAGE_SIZE,
					  &tr->func.model, flags, tprogs,
					  tr->func.addr);
	if (err < 0)
		goto out;

	WARN_ON(tr->cur_image && tr->selector == 0);
	WARN_ON(!tr->cur_image && tr->selector);
	if (tr->cur_image)
		/* progs already running at this address */
		err = modify_fentry(tr, tr->cur_image->image, im->image);
	else
		/* first time registering */
		err = register_fentry(tr, im->image);
	if (err)
		goto out;
	if (tr->cur_image)
		bpf_tramp_image_put(tr->cur_image);
	tr->cur_image = im;
	tr->selector++;
out:
	kfree(tprogs);
	return err;
}

static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
{
	switch (prog->expected_attach_type) {
	case BPF_TRACE_FENTRY:
		return BPF_TRAMP_FENTRY;
	case BPF_MODIFY_RETURN:
		return BPF_TRAMP_MODIFY_RETURN;
	case BPF_TRACE_FEXIT:
		return BPF_TRAMP_FEXIT;
	case BPF_LSM_MAC:
		if (!prog->aux->attach_func_proto->type)
			/* The function returns void, we cannot modify its
			 * return value.
			 */
			return BPF_TRAMP_FEXIT;
		else
			return BPF_TRAMP_MODIFY_RETURN;
	default:
		return BPF_TRAMP_REPLACE;
	}
}

int bpf_trampoline_link_prog(struct bpf_prog *prog, struct bpf_trampoline *tr)
{
	enum bpf_tramp_prog_type kind;
	int err = 0;
	int cnt;

	kind = bpf_attach_type_to_tramp(prog);
	mutex_lock(&tr->mutex);
	if (tr->extension_prog) {
		/* cannot attach fentry/fexit if extension prog is attached.
		 * cannot overwrite extension prog either.
		 */
		err = -EBUSY;
		goto out;
	}
	cnt = tr->progs_cnt[BPF_TRAMP_FENTRY] + tr->progs_cnt[BPF_TRAMP_FEXIT];
	if (kind == BPF_TRAMP_REPLACE) {
		/* Cannot attach extension if fentry/fexit are in use. */
		if (cnt) {
			err = -EBUSY;
			goto out;
		}
		tr->extension_prog = prog;
		err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP, NULL,
					 prog->bpf_func);
		goto out;
	}
	if (cnt >= BPF_MAX_TRAMP_PROGS) {
		err = -E2BIG;
		goto out;
	}
	if (!hlist_unhashed(&prog->aux->tramp_hlist)) {
		/* prog already linked */
		err = -EBUSY;
		goto out;
	}
	hlist_add_head(&prog->aux->tramp_hlist, &tr->progs_hlist[kind]);
	tr->progs_cnt[kind]++;
	err = bpf_trampoline_update(tr);
	if (err) {
		hlist_del_init(&prog->aux->tramp_hlist);
		tr->progs_cnt[kind]--;
	}
out:
	mutex_unlock(&tr->mutex);
	return err;
}

/* bpf_trampoline_unlink_prog() should never fail. */
int bpf_trampoline_unlink_prog(struct bpf_prog *prog, struct bpf_trampoline *tr)
{
	enum bpf_tramp_prog_type kind;
	int err;

	kind = bpf_attach_type_to_tramp(prog);
	mutex_lock(&tr->mutex);
	if (kind == BPF_TRAMP_REPLACE) {
		WARN_ON_ONCE(!tr->extension_prog);
		err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP,
					 tr->extension_prog->bpf_func, NULL);
		tr->extension_prog = NULL;
		goto out;
	}
	hlist_del_init(&prog->aux->tramp_hlist);
	tr->progs_cnt[kind]--;
	err = bpf_trampoline_update(tr);
out:
	mutex_unlock(&tr->mutex);
	return err;
}

struct bpf_trampoline *bpf_trampoline_get(u64 key,
					  struct bpf_attach_target_info *tgt_info)
{
	struct bpf_trampoline *tr;

	tr = bpf_trampoline_lookup(key);
	if (!tr)
		return NULL;

	mutex_lock(&tr->mutex);
	if (tr->func.addr)
		goto out;

	memcpy(&tr->func.model, &tgt_info->fmodel, sizeof(tgt_info->fmodel));
	tr->func.addr = (void *)tgt_info->tgt_addr;
out:
	mutex_unlock(&tr->mutex);
	return tr;
}

void bpf_trampoline_put(struct bpf_trampoline *tr)
{
	if (!tr)
		return;
	mutex_lock(&trampoline_mutex);
	if (!refcount_dec_and_test(&tr->refcnt))
		goto out;
	WARN_ON_ONCE(mutex_is_locked(&tr->mutex));
	if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FENTRY])))
		goto out;
	if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FEXIT])))
		goto out;
	/* This code will be executed even when the last bpf_tramp_image
	 * is alive. All progs are detached from the trampoline and the
	 * trampoline image is patched with jmp into epilogue to skip
	 * fexit progs. The fentry-only trampoline will be freed via
	 * multiple rcu callbacks.
	 */
	hlist_del(&tr->hlist);
	kfree(tr);
out:
	mutex_unlock(&trampoline_mutex);
}

#define NO_START_TIME 1
static __always_inline u64 notrace bpf_prog_start_time(void)
{
	u64 start = NO_START_TIME;

	if (static_branch_unlikely(&bpf_stats_enabled_key)) {
		start = sched_clock();
		if (unlikely(!start))
			start = NO_START_TIME;
	}
	return start;
}

static void notrace inc_misses_counter(struct bpf_prog *prog)
{
	struct bpf_prog_stats *stats;

	stats = this_cpu_ptr(prog->stats);
	u64_stats_update_begin(&stats->syncp);
	u64_stats_inc(&stats->misses);
	u64_stats_update_end(&stats->syncp);
}

/* The logic is similar to bpf_prog_run(), but with an explicit
 * rcu_read_lock() and migrate_disable() which are required
 * for the trampoline. The macro is split into
 * call __bpf_prog_enter
 * call prog->bpf_func
 * call __bpf_prog_exit
 *
 * __bpf_prog_enter returns:
 * 0 - skip execution of the bpf prog
 * 1 - execute bpf prog
 * [2..MAX_U64] - execute bpf prog and record execution time.
 *     This is start time.
 */
u64 notrace __bpf_prog_enter(struct bpf_prog *prog)
	__acquires(RCU)
{
	rcu_read_lock();
	migrate_disable();
	if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) {
		inc_misses_counter(prog);
		return 0;
	}
	return bpf_prog_start_time();
}

static void notrace update_prog_stats(struct bpf_prog *prog,
				      u64 start)
{
	struct bpf_prog_stats *stats;

	if (static_branch_unlikely(&bpf_stats_enabled_key) &&
	    /* static_key could be enabled in __bpf_prog_enter*
	     * and disabled in __bpf_prog_exit*.
	     * And vice versa.
	     * Hence check that 'start' is valid.
	     */
	    start > NO_START_TIME) {
		unsigned long flags;

		stats = this_cpu_ptr(prog->stats);
		flags = u64_stats_update_begin_irqsave(&stats->syncp);
		u64_stats_inc(&stats->cnt);
		u64_stats_add(&stats->nsecs, sched_clock() - start);
		u64_stats_update_end_irqrestore(&stats->syncp, flags);
	}
}

void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start)
	__releases(RCU)
{
	update_prog_stats(prog, start);
	__this_cpu_dec(*(prog->active));
	migrate_enable();
	rcu_read_unlock();
}

u64 notrace __bpf_prog_enter_sleepable(struct bpf_prog *prog)
{
	rcu_read_lock_trace();
	migrate_disable();
	might_fault();
	if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) {
		inc_misses_counter(prog);
		return 0;
	}
	return bpf_prog_start_time();
}

void notrace __bpf_prog_exit_sleepable(struct bpf_prog *prog, u64 start)
{
	update_prog_stats(prog, start);
	__this_cpu_dec(*(prog->active));
	migrate_enable();
	rcu_read_unlock_trace();
}

void notrace __bpf_tramp_enter(struct bpf_tramp_image *tr)
{
	percpu_ref_get(&tr->pcref);
}

void notrace __bpf_tramp_exit(struct bpf_tramp_image *tr)
{
	percpu_ref_put(&tr->pcref);
}

int __weak
arch_prepare_bpf_trampoline(struct bpf_tramp_image *tr, void *image, void *image_end,
			    const struct btf_func_model *m, u32 flags,
			    struct bpf_tramp_progs *tprogs,
			    void *orig_call)
{
	return -ENOTSUPP;
}

static int __init init_trampolines(void)
{
	int i;

	for (i = 0; i < TRAMPOLINE_TABLE_SIZE; i++)
		INIT_HLIST_HEAD(&trampoline_table[i]);
	return 0;
}
late_initcall(init_trampolines);