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1// SPDX-License-Identifier: GPL-2.0-only
2/* Copyright (c) 2019 Facebook */
3#include <linux/hash.h>
4#include <linux/bpf.h>
5#include <linux/filter.h>
6#include <linux/ftrace.h>
7#include <linux/rbtree_latch.h>
8#include <linux/perf_event.h>
9#include <linux/btf.h>
10#include <linux/rcupdate_trace.h>
11#include <linux/rcupdate_wait.h>
12#include <linux/module.h>
13
14/* dummy _ops. The verifier will operate on target program's ops. */
15const struct bpf_verifier_ops bpf_extension_verifier_ops = {
16};
17const struct bpf_prog_ops bpf_extension_prog_ops = {
18};
19
20/* btf_vmlinux has ~22k attachable functions. 1k htab is enough. */
21#define TRAMPOLINE_HASH_BITS 10
22#define TRAMPOLINE_TABLE_SIZE (1 << TRAMPOLINE_HASH_BITS)
23
24static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE];
25
26/* serializes access to trampoline_table */
27static DEFINE_MUTEX(trampoline_mutex);
28
29void *bpf_jit_alloc_exec_page(void)
30{
31 void *image;
32
33 image = bpf_jit_alloc_exec(PAGE_SIZE);
34 if (!image)
35 return NULL;
36
37 set_vm_flush_reset_perms(image);
38 /* Keep image as writeable. The alternative is to keep flipping ro/rw
39 * everytime new program is attached or detached.
40 */
41 set_memory_x((long)image, 1);
42 return image;
43}
44
45void bpf_image_ksym_add(void *data, struct bpf_ksym *ksym)
46{
47 ksym->start = (unsigned long) data;
48 ksym->end = ksym->start + PAGE_SIZE;
49 bpf_ksym_add(ksym);
50 perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start,
51 PAGE_SIZE, false, ksym->name);
52}
53
54void bpf_image_ksym_del(struct bpf_ksym *ksym)
55{
56 bpf_ksym_del(ksym);
57 perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start,
58 PAGE_SIZE, true, ksym->name);
59}
60
61static struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
62{
63 struct bpf_trampoline *tr;
64 struct hlist_head *head;
65 int i;
66
67 mutex_lock(&trampoline_mutex);
68 head = &trampoline_table[hash_64(key, TRAMPOLINE_HASH_BITS)];
69 hlist_for_each_entry(tr, head, hlist) {
70 if (tr->key == key) {
71 refcount_inc(&tr->refcnt);
72 goto out;
73 }
74 }
75 tr = kzalloc(sizeof(*tr), GFP_KERNEL);
76 if (!tr)
77 goto out;
78
79 tr->key = key;
80 INIT_HLIST_NODE(&tr->hlist);
81 hlist_add_head(&tr->hlist, head);
82 refcount_set(&tr->refcnt, 1);
83 mutex_init(&tr->mutex);
84 for (i = 0; i < BPF_TRAMP_MAX; i++)
85 INIT_HLIST_HEAD(&tr->progs_hlist[i]);
86out:
87 mutex_unlock(&trampoline_mutex);
88 return tr;
89}
90
91static int bpf_trampoline_module_get(struct bpf_trampoline *tr)
92{
93 struct module *mod;
94 int err = 0;
95
96 preempt_disable();
97 mod = __module_text_address((unsigned long) tr->func.addr);
98 if (mod && !try_module_get(mod))
99 err = -ENOENT;
100 preempt_enable();
101 tr->mod = mod;
102 return err;
103}
104
105static void bpf_trampoline_module_put(struct bpf_trampoline *tr)
106{
107 module_put(tr->mod);
108 tr->mod = NULL;
109}
110
111static int is_ftrace_location(void *ip)
112{
113 long addr;
114
115 addr = ftrace_location((long)ip);
116 if (!addr)
117 return 0;
118 if (WARN_ON_ONCE(addr != (long)ip))
119 return -EFAULT;
120 return 1;
121}
122
123static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
124{
125 void *ip = tr->func.addr;
126 int ret;
127
128 if (tr->func.ftrace_managed)
129 ret = unregister_ftrace_direct((long)ip, (long)old_addr);
130 else
131 ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL);
132
133 if (!ret)
134 bpf_trampoline_module_put(tr);
135 return ret;
136}
137
138static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_addr)
139{
140 void *ip = tr->func.addr;
141 int ret;
142
143 if (tr->func.ftrace_managed)
144 ret = modify_ftrace_direct((long)ip, (long)old_addr, (long)new_addr);
145 else
146 ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, new_addr);
147 return ret;
148}
149
150/* first time registering */
151static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
152{
153 void *ip = tr->func.addr;
154 int ret;
155
156 ret = is_ftrace_location(ip);
157 if (ret < 0)
158 return ret;
159 tr->func.ftrace_managed = ret;
160
161 if (bpf_trampoline_module_get(tr))
162 return -ENOENT;
163
164 if (tr->func.ftrace_managed)
165 ret = register_ftrace_direct((long)ip, (long)new_addr);
166 else
167 ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr);
168
169 if (ret)
170 bpf_trampoline_module_put(tr);
171 return ret;
172}
173
174static struct bpf_tramp_progs *
175bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total)
176{
177 const struct bpf_prog_aux *aux;
178 struct bpf_tramp_progs *tprogs;
179 struct bpf_prog **progs;
180 int kind;
181
182 *total = 0;
183 tprogs = kcalloc(BPF_TRAMP_MAX, sizeof(*tprogs), GFP_KERNEL);
184 if (!tprogs)
185 return ERR_PTR(-ENOMEM);
186
187 for (kind = 0; kind < BPF_TRAMP_MAX; kind++) {
188 tprogs[kind].nr_progs = tr->progs_cnt[kind];
189 *total += tr->progs_cnt[kind];
190 progs = tprogs[kind].progs;
191
192 hlist_for_each_entry(aux, &tr->progs_hlist[kind], tramp_hlist)
193 *progs++ = aux->prog;
194 }
195 return tprogs;
196}
197
198static void __bpf_tramp_image_put_deferred(struct work_struct *work)
199{
200 struct bpf_tramp_image *im;
201
202 im = container_of(work, struct bpf_tramp_image, work);
203 bpf_image_ksym_del(&im->ksym);
204 bpf_jit_free_exec(im->image);
205 bpf_jit_uncharge_modmem(1);
206 percpu_ref_exit(&im->pcref);
207 kfree_rcu(im, rcu);
208}
209
210/* callback, fexit step 3 or fentry step 2 */
211static void __bpf_tramp_image_put_rcu(struct rcu_head *rcu)
212{
213 struct bpf_tramp_image *im;
214
215 im = container_of(rcu, struct bpf_tramp_image, rcu);
216 INIT_WORK(&im->work, __bpf_tramp_image_put_deferred);
217 schedule_work(&im->work);
218}
219
220/* callback, fexit step 2. Called after percpu_ref_kill confirms. */
221static void __bpf_tramp_image_release(struct percpu_ref *pcref)
222{
223 struct bpf_tramp_image *im;
224
225 im = container_of(pcref, struct bpf_tramp_image, pcref);
226 call_rcu_tasks(&im->rcu, __bpf_tramp_image_put_rcu);
227}
228
229/* callback, fexit or fentry step 1 */
230static void __bpf_tramp_image_put_rcu_tasks(struct rcu_head *rcu)
231{
232 struct bpf_tramp_image *im;
233
234 im = container_of(rcu, struct bpf_tramp_image, rcu);
235 if (im->ip_after_call)
236 /* the case of fmod_ret/fexit trampoline and CONFIG_PREEMPTION=y */
237 percpu_ref_kill(&im->pcref);
238 else
239 /* the case of fentry trampoline */
240 call_rcu_tasks(&im->rcu, __bpf_tramp_image_put_rcu);
241}
242
243static void bpf_tramp_image_put(struct bpf_tramp_image *im)
244{
245 /* The trampoline image that calls original function is using:
246 * rcu_read_lock_trace to protect sleepable bpf progs
247 * rcu_read_lock to protect normal bpf progs
248 * percpu_ref to protect trampoline itself
249 * rcu tasks to protect trampoline asm not covered by percpu_ref
250 * (which are few asm insns before __bpf_tramp_enter and
251 * after __bpf_tramp_exit)
252 *
253 * The trampoline is unreachable before bpf_tramp_image_put().
254 *
255 * First, patch the trampoline to avoid calling into fexit progs.
256 * The progs will be freed even if the original function is still
257 * executing or sleeping.
258 * In case of CONFIG_PREEMPT=y use call_rcu_tasks() to wait on
259 * first few asm instructions to execute and call into
260 * __bpf_tramp_enter->percpu_ref_get.
261 * Then use percpu_ref_kill to wait for the trampoline and the original
262 * function to finish.
263 * Then use call_rcu_tasks() to make sure few asm insns in
264 * the trampoline epilogue are done as well.
265 *
266 * In !PREEMPT case the task that got interrupted in the first asm
267 * insns won't go through an RCU quiescent state which the
268 * percpu_ref_kill will be waiting for. Hence the first
269 * call_rcu_tasks() is not necessary.
270 */
271 if (im->ip_after_call) {
272 int err = bpf_arch_text_poke(im->ip_after_call, BPF_MOD_JUMP,
273 NULL, im->ip_epilogue);
274 WARN_ON(err);
275 if (IS_ENABLED(CONFIG_PREEMPTION))
276 call_rcu_tasks(&im->rcu, __bpf_tramp_image_put_rcu_tasks);
277 else
278 percpu_ref_kill(&im->pcref);
279 return;
280 }
281
282 /* The trampoline without fexit and fmod_ret progs doesn't call original
283 * function and doesn't use percpu_ref.
284 * Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
285 * Then use call_rcu_tasks() to wait for the rest of trampoline asm
286 * and normal progs.
287 */
288 call_rcu_tasks_trace(&im->rcu, __bpf_tramp_image_put_rcu_tasks);
289}
290
291static struct bpf_tramp_image *bpf_tramp_image_alloc(u64 key, u32 idx)
292{
293 struct bpf_tramp_image *im;
294 struct bpf_ksym *ksym;
295 void *image;
296 int err = -ENOMEM;
297
298 im = kzalloc(sizeof(*im), GFP_KERNEL);
299 if (!im)
300 goto out;
301
302 err = bpf_jit_charge_modmem(1);
303 if (err)
304 goto out_free_im;
305
306 err = -ENOMEM;
307 im->image = image = bpf_jit_alloc_exec_page();
308 if (!image)
309 goto out_uncharge;
310
311 err = percpu_ref_init(&im->pcref, __bpf_tramp_image_release, 0, GFP_KERNEL);
312 if (err)
313 goto out_free_image;
314
315 ksym = &im->ksym;
316 INIT_LIST_HEAD_RCU(&ksym->lnode);
317 snprintf(ksym->name, KSYM_NAME_LEN, "bpf_trampoline_%llu_%u", key, idx);
318 bpf_image_ksym_add(image, ksym);
319 return im;
320
321out_free_image:
322 bpf_jit_free_exec(im->image);
323out_uncharge:
324 bpf_jit_uncharge_modmem(1);
325out_free_im:
326 kfree(im);
327out:
328 return ERR_PTR(err);
329}
330
331static int bpf_trampoline_update(struct bpf_trampoline *tr)
332{
333 struct bpf_tramp_image *im;
334 struct bpf_tramp_progs *tprogs;
335 u32 flags = BPF_TRAMP_F_RESTORE_REGS;
336 int err, total;
337
338 tprogs = bpf_trampoline_get_progs(tr, &total);
339 if (IS_ERR(tprogs))
340 return PTR_ERR(tprogs);
341
342 if (total == 0) {
343 err = unregister_fentry(tr, tr->cur_image->image);
344 bpf_tramp_image_put(tr->cur_image);
345 tr->cur_image = NULL;
346 tr->selector = 0;
347 goto out;
348 }
349
350 im = bpf_tramp_image_alloc(tr->key, tr->selector);
351 if (IS_ERR(im)) {
352 err = PTR_ERR(im);
353 goto out;
354 }
355
356 if (tprogs[BPF_TRAMP_FEXIT].nr_progs ||
357 tprogs[BPF_TRAMP_MODIFY_RETURN].nr_progs)
358 flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;
359
360 err = arch_prepare_bpf_trampoline(im, im->image, im->image + PAGE_SIZE,
361 &tr->func.model, flags, tprogs,
362 tr->func.addr);
363 if (err < 0)
364 goto out;
365
366 WARN_ON(tr->cur_image && tr->selector == 0);
367 WARN_ON(!tr->cur_image && tr->selector);
368 if (tr->cur_image)
369 /* progs already running at this address */
370 err = modify_fentry(tr, tr->cur_image->image, im->image);
371 else
372 /* first time registering */
373 err = register_fentry(tr, im->image);
374 if (err)
375 goto out;
376 if (tr->cur_image)
377 bpf_tramp_image_put(tr->cur_image);
378 tr->cur_image = im;
379 tr->selector++;
380out:
381 kfree(tprogs);
382 return err;
383}
384
385static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
386{
387 switch (prog->expected_attach_type) {
388 case BPF_TRACE_FENTRY:
389 return BPF_TRAMP_FENTRY;
390 case BPF_MODIFY_RETURN:
391 return BPF_TRAMP_MODIFY_RETURN;
392 case BPF_TRACE_FEXIT:
393 return BPF_TRAMP_FEXIT;
394 case BPF_LSM_MAC:
395 if (!prog->aux->attach_func_proto->type)
396 /* The function returns void, we cannot modify its
397 * return value.
398 */
399 return BPF_TRAMP_FEXIT;
400 else
401 return BPF_TRAMP_MODIFY_RETURN;
402 default:
403 return BPF_TRAMP_REPLACE;
404 }
405}
406
407int bpf_trampoline_link_prog(struct bpf_prog *prog, struct bpf_trampoline *tr)
408{
409 enum bpf_tramp_prog_type kind;
410 int err = 0;
411 int cnt;
412
413 kind = bpf_attach_type_to_tramp(prog);
414 mutex_lock(&tr->mutex);
415 if (tr->extension_prog) {
416 /* cannot attach fentry/fexit if extension prog is attached.
417 * cannot overwrite extension prog either.
418 */
419 err = -EBUSY;
420 goto out;
421 }
422 cnt = tr->progs_cnt[BPF_TRAMP_FENTRY] + tr->progs_cnt[BPF_TRAMP_FEXIT];
423 if (kind == BPF_TRAMP_REPLACE) {
424 /* Cannot attach extension if fentry/fexit are in use. */
425 if (cnt) {
426 err = -EBUSY;
427 goto out;
428 }
429 tr->extension_prog = prog;
430 err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP, NULL,
431 prog->bpf_func);
432 goto out;
433 }
434 if (cnt >= BPF_MAX_TRAMP_PROGS) {
435 err = -E2BIG;
436 goto out;
437 }
438 if (!hlist_unhashed(&prog->aux->tramp_hlist)) {
439 /* prog already linked */
440 err = -EBUSY;
441 goto out;
442 }
443 hlist_add_head(&prog->aux->tramp_hlist, &tr->progs_hlist[kind]);
444 tr->progs_cnt[kind]++;
445 err = bpf_trampoline_update(tr);
446 if (err) {
447 hlist_del_init(&prog->aux->tramp_hlist);
448 tr->progs_cnt[kind]--;
449 }
450out:
451 mutex_unlock(&tr->mutex);
452 return err;
453}
454
455/* bpf_trampoline_unlink_prog() should never fail. */
456int bpf_trampoline_unlink_prog(struct bpf_prog *prog, struct bpf_trampoline *tr)
457{
458 enum bpf_tramp_prog_type kind;
459 int err;
460
461 kind = bpf_attach_type_to_tramp(prog);
462 mutex_lock(&tr->mutex);
463 if (kind == BPF_TRAMP_REPLACE) {
464 WARN_ON_ONCE(!tr->extension_prog);
465 err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP,
466 tr->extension_prog->bpf_func, NULL);
467 tr->extension_prog = NULL;
468 goto out;
469 }
470 hlist_del_init(&prog->aux->tramp_hlist);
471 tr->progs_cnt[kind]--;
472 err = bpf_trampoline_update(tr);
473out:
474 mutex_unlock(&tr->mutex);
475 return err;
476}
477
478struct bpf_trampoline *bpf_trampoline_get(u64 key,
479 struct bpf_attach_target_info *tgt_info)
480{
481 struct bpf_trampoline *tr;
482
483 tr = bpf_trampoline_lookup(key);
484 if (!tr)
485 return NULL;
486
487 mutex_lock(&tr->mutex);
488 if (tr->func.addr)
489 goto out;
490
491 memcpy(&tr->func.model, &tgt_info->fmodel, sizeof(tgt_info->fmodel));
492 tr->func.addr = (void *)tgt_info->tgt_addr;
493out:
494 mutex_unlock(&tr->mutex);
495 return tr;
496}
497
498void bpf_trampoline_put(struct bpf_trampoline *tr)
499{
500 if (!tr)
501 return;
502 mutex_lock(&trampoline_mutex);
503 if (!refcount_dec_and_test(&tr->refcnt))
504 goto out;
505 WARN_ON_ONCE(mutex_is_locked(&tr->mutex));
506 if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FENTRY])))
507 goto out;
508 if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FEXIT])))
509 goto out;
510 /* This code will be executed even when the last bpf_tramp_image
511 * is alive. All progs are detached from the trampoline and the
512 * trampoline image is patched with jmp into epilogue to skip
513 * fexit progs. The fentry-only trampoline will be freed via
514 * multiple rcu callbacks.
515 */
516 hlist_del(&tr->hlist);
517 kfree(tr);
518out:
519 mutex_unlock(&trampoline_mutex);
520}
521
522#define NO_START_TIME 1
523static u64 notrace bpf_prog_start_time(void)
524{
525 u64 start = NO_START_TIME;
526
527 if (static_branch_unlikely(&bpf_stats_enabled_key)) {
528 start = sched_clock();
529 if (unlikely(!start))
530 start = NO_START_TIME;
531 }
532 return start;
533}
534
535static void notrace inc_misses_counter(struct bpf_prog *prog)
536{
537 struct bpf_prog_stats *stats;
538
539 stats = this_cpu_ptr(prog->stats);
540 u64_stats_update_begin(&stats->syncp);
541 stats->misses++;
542 u64_stats_update_end(&stats->syncp);
543}
544
545/* The logic is similar to BPF_PROG_RUN, but with an explicit
546 * rcu_read_lock() and migrate_disable() which are required
547 * for the trampoline. The macro is split into
548 * call __bpf_prog_enter
549 * call prog->bpf_func
550 * call __bpf_prog_exit
551 *
552 * __bpf_prog_enter returns:
553 * 0 - skip execution of the bpf prog
554 * 1 - execute bpf prog
555 * [2..MAX_U64] - execute bpf prog and record execution time.
556 * This is start time.
557 */
558u64 notrace __bpf_prog_enter(struct bpf_prog *prog)
559 __acquires(RCU)
560{
561 rcu_read_lock();
562 migrate_disable();
563 if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) {
564 inc_misses_counter(prog);
565 return 0;
566 }
567 return bpf_prog_start_time();
568}
569
570static void notrace update_prog_stats(struct bpf_prog *prog,
571 u64 start)
572{
573 struct bpf_prog_stats *stats;
574
575 if (static_branch_unlikely(&bpf_stats_enabled_key) &&
576 /* static_key could be enabled in __bpf_prog_enter*
577 * and disabled in __bpf_prog_exit*.
578 * And vice versa.
579 * Hence check that 'start' is valid.
580 */
581 start > NO_START_TIME) {
582 stats = this_cpu_ptr(prog->stats);
583 u64_stats_update_begin(&stats->syncp);
584 stats->cnt++;
585 stats->nsecs += sched_clock() - start;
586 u64_stats_update_end(&stats->syncp);
587 }
588}
589
590void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start)
591 __releases(RCU)
592{
593 update_prog_stats(prog, start);
594 __this_cpu_dec(*(prog->active));
595 migrate_enable();
596 rcu_read_unlock();
597}
598
599u64 notrace __bpf_prog_enter_sleepable(struct bpf_prog *prog)
600{
601 rcu_read_lock_trace();
602 migrate_disable();
603 might_fault();
604 if (unlikely(__this_cpu_inc_return(*(prog->active)) != 1)) {
605 inc_misses_counter(prog);
606 return 0;
607 }
608 return bpf_prog_start_time();
609}
610
611void notrace __bpf_prog_exit_sleepable(struct bpf_prog *prog, u64 start)
612{
613 update_prog_stats(prog, start);
614 __this_cpu_dec(*(prog->active));
615 migrate_enable();
616 rcu_read_unlock_trace();
617}
618
619void notrace __bpf_tramp_enter(struct bpf_tramp_image *tr)
620{
621 percpu_ref_get(&tr->pcref);
622}
623
624void notrace __bpf_tramp_exit(struct bpf_tramp_image *tr)
625{
626 percpu_ref_put(&tr->pcref);
627}
628
629int __weak
630arch_prepare_bpf_trampoline(struct bpf_tramp_image *tr, void *image, void *image_end,
631 const struct btf_func_model *m, u32 flags,
632 struct bpf_tramp_progs *tprogs,
633 void *orig_call)
634{
635 return -ENOTSUPP;
636}
637
638static int __init init_trampolines(void)
639{
640 int i;
641
642 for (i = 0; i < TRAMPOLINE_TABLE_SIZE; i++)
643 INIT_HLIST_HEAD(&trampoline_table[i]);
644 return 0;
645}
646late_initcall(init_trampolines);