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
 11/* dummy _ops. The verifier will operate on target program's ops. */
 12const struct bpf_verifier_ops bpf_extension_verifier_ops = {
 13};
 14const struct bpf_prog_ops bpf_extension_prog_ops = {
 15};
 16
 17/* btf_vmlinux has ~22k attachable functions. 1k htab is enough. */
 18#define TRAMPOLINE_HASH_BITS 10
 19#define TRAMPOLINE_TABLE_SIZE (1 << TRAMPOLINE_HASH_BITS)
 20
 21static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE];
 22
 23/* serializes access to trampoline_table */
 24static DEFINE_MUTEX(trampoline_mutex);
 25
 26void *bpf_jit_alloc_exec_page(void)
 27{
 28	void *image;
 29
 30	image = bpf_jit_alloc_exec(PAGE_SIZE);
 31	if (!image)
 32		return NULL;
 33
 34	set_vm_flush_reset_perms(image);
 35	/* Keep image as writeable. The alternative is to keep flipping ro/rw
 36	 * everytime new program is attached or detached.
 37	 */
 38	set_memory_x((long)image, 1);
 39	return image;
 40}
 41
 42void bpf_image_ksym_add(void *data, struct bpf_ksym *ksym)
 43{
 44	ksym->start = (unsigned long) data;
 45	ksym->end = ksym->start + PAGE_SIZE;
 46	bpf_ksym_add(ksym);
 47	perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start,
 48			   PAGE_SIZE, false, ksym->name);
 49}
 50
 51void bpf_image_ksym_del(struct bpf_ksym *ksym)
 52{
 53	bpf_ksym_del(ksym);
 54	perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start,
 55			   PAGE_SIZE, true, ksym->name);
 56}
 57
 58static void bpf_trampoline_ksym_add(struct bpf_trampoline *tr)
 59{
 60	struct bpf_ksym *ksym = &tr->ksym;
 61
 62	snprintf(ksym->name, KSYM_NAME_LEN, "bpf_trampoline_%llu", tr->key);
 63	bpf_image_ksym_add(tr->image, ksym);
 64}
 65
 66struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
 67{
 68	struct bpf_trampoline *tr;
 69	struct hlist_head *head;
 70	void *image;
 71	int i;
 72
 73	mutex_lock(&trampoline_mutex);
 74	head = &trampoline_table[hash_64(key, TRAMPOLINE_HASH_BITS)];
 75	hlist_for_each_entry(tr, head, hlist) {
 76		if (tr->key == key) {
 77			refcount_inc(&tr->refcnt);
 78			goto out;
 79		}
 80	}
 81	tr = kzalloc(sizeof(*tr), GFP_KERNEL);
 82	if (!tr)
 83		goto out;
 84
 85	/* is_root was checked earlier. No need for bpf_jit_charge_modmem() */
 86	image = bpf_jit_alloc_exec_page();
 87	if (!image) {
 88		kfree(tr);
 89		tr = NULL;
 90		goto out;
 91	}
 92
 93	tr->key = key;
 94	INIT_HLIST_NODE(&tr->hlist);
 95	hlist_add_head(&tr->hlist, head);
 96	refcount_set(&tr->refcnt, 1);
 97	mutex_init(&tr->mutex);
 98	for (i = 0; i < BPF_TRAMP_MAX; i++)
 99		INIT_HLIST_HEAD(&tr->progs_hlist[i]);
100	tr->image = image;
101	INIT_LIST_HEAD_RCU(&tr->ksym.lnode);
102	bpf_trampoline_ksym_add(tr);
103out:
104	mutex_unlock(&trampoline_mutex);
105	return tr;
106}
107
108static int is_ftrace_location(void *ip)
109{
110	long addr;
111
112	addr = ftrace_location((long)ip);
113	if (!addr)
114		return 0;
115	if (WARN_ON_ONCE(addr != (long)ip))
116		return -EFAULT;
117	return 1;
118}
119
120static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
121{
122	void *ip = tr->func.addr;
123	int ret;
124
125	if (tr->func.ftrace_managed)
126		ret = unregister_ftrace_direct((long)ip, (long)old_addr);
127	else
128		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL);
129	return ret;
130}
131
132static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_addr)
133{
134	void *ip = tr->func.addr;
135	int ret;
136
137	if (tr->func.ftrace_managed)
138		ret = modify_ftrace_direct((long)ip, (long)old_addr, (long)new_addr);
139	else
140		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, new_addr);
141	return ret;
142}
143
144/* first time registering */
145static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
146{
147	void *ip = tr->func.addr;
148	int ret;
149
150	ret = is_ftrace_location(ip);
151	if (ret < 0)
152		return ret;
153	tr->func.ftrace_managed = ret;
154
155	if (tr->func.ftrace_managed)
156		ret = register_ftrace_direct((long)ip, (long)new_addr);
157	else
158		ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr);
159	return ret;
160}
161
162static struct bpf_tramp_progs *
163bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total)
164{
165	const struct bpf_prog_aux *aux;
166	struct bpf_tramp_progs *tprogs;
167	struct bpf_prog **progs;
168	int kind;
169
170	*total = 0;
171	tprogs = kcalloc(BPF_TRAMP_MAX, sizeof(*tprogs), GFP_KERNEL);
172	if (!tprogs)
173		return ERR_PTR(-ENOMEM);
174
175	for (kind = 0; kind < BPF_TRAMP_MAX; kind++) {
176		tprogs[kind].nr_progs = tr->progs_cnt[kind];
177		*total += tr->progs_cnt[kind];
178		progs = tprogs[kind].progs;
179
180		hlist_for_each_entry(aux, &tr->progs_hlist[kind], tramp_hlist)
181			*progs++ = aux->prog;
182	}
183	return tprogs;
184}
185
186static int bpf_trampoline_update(struct bpf_trampoline *tr)
187{
188	void *old_image = tr->image + ((tr->selector + 1) & 1) * PAGE_SIZE/2;
189	void *new_image = tr->image + (tr->selector & 1) * PAGE_SIZE/2;
190	struct bpf_tramp_progs *tprogs;
191	u32 flags = BPF_TRAMP_F_RESTORE_REGS;
192	int err, total;
193
194	tprogs = bpf_trampoline_get_progs(tr, &total);
195	if (IS_ERR(tprogs))
196		return PTR_ERR(tprogs);
197
198	if (total == 0) {
199		err = unregister_fentry(tr, old_image);
200		tr->selector = 0;
201		goto out;
202	}
203
204	if (tprogs[BPF_TRAMP_FEXIT].nr_progs ||
205	    tprogs[BPF_TRAMP_MODIFY_RETURN].nr_progs)
206		flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;
207
208	/* Though the second half of trampoline page is unused a task could be
209	 * preempted in the middle of the first half of trampoline and two
210	 * updates to trampoline would change the code from underneath the
211	 * preempted task. Hence wait for tasks to voluntarily schedule or go
212	 * to userspace.
213	 */
214
215	synchronize_rcu_tasks();
216
217	err = arch_prepare_bpf_trampoline(new_image, new_image + PAGE_SIZE / 2,
218					  &tr->func.model, flags, tprogs,
219					  tr->func.addr);
220	if (err < 0)
221		goto out;
222
223	if (tr->selector)
224		/* progs already running at this address */
225		err = modify_fentry(tr, old_image, new_image);
226	else
227		/* first time registering */
228		err = register_fentry(tr, new_image);
229	if (err)
230		goto out;
231	tr->selector++;
232out:
233	kfree(tprogs);
234	return err;
235}
236
237static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
238{
239	switch (prog->expected_attach_type) {
240	case BPF_TRACE_FENTRY:
241		return BPF_TRAMP_FENTRY;
242	case BPF_MODIFY_RETURN:
243		return BPF_TRAMP_MODIFY_RETURN;
244	case BPF_TRACE_FEXIT:
245		return BPF_TRAMP_FEXIT;
246	case BPF_LSM_MAC:
247		if (!prog->aux->attach_func_proto->type)
248			/* The function returns void, we cannot modify its
249			 * return value.
250			 */
251			return BPF_TRAMP_FEXIT;
252		else
253			return BPF_TRAMP_MODIFY_RETURN;
254	default:
255		return BPF_TRAMP_REPLACE;
256	}
257}
258
259int bpf_trampoline_link_prog(struct bpf_prog *prog)
260{
261	enum bpf_tramp_prog_type kind;
262	struct bpf_trampoline *tr;
263	int err = 0;
264	int cnt;
265
266	tr = prog->aux->trampoline;
267	kind = bpf_attach_type_to_tramp(prog);
268	mutex_lock(&tr->mutex);
269	if (tr->extension_prog) {
270		/* cannot attach fentry/fexit if extension prog is attached.
271		 * cannot overwrite extension prog either.
272		 */
273		err = -EBUSY;
274		goto out;
275	}
276	cnt = tr->progs_cnt[BPF_TRAMP_FENTRY] + tr->progs_cnt[BPF_TRAMP_FEXIT];
277	if (kind == BPF_TRAMP_REPLACE) {
278		/* Cannot attach extension if fentry/fexit are in use. */
279		if (cnt) {
280			err = -EBUSY;
281			goto out;
282		}
283		tr->extension_prog = prog;
284		err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP, NULL,
285					 prog->bpf_func);
286		goto out;
287	}
288	if (cnt >= BPF_MAX_TRAMP_PROGS) {
289		err = -E2BIG;
290		goto out;
291	}
292	if (!hlist_unhashed(&prog->aux->tramp_hlist)) {
293		/* prog already linked */
294		err = -EBUSY;
295		goto out;
296	}
297	hlist_add_head(&prog->aux->tramp_hlist, &tr->progs_hlist[kind]);
298	tr->progs_cnt[kind]++;
299	err = bpf_trampoline_update(prog->aux->trampoline);
300	if (err) {
301		hlist_del(&prog->aux->tramp_hlist);
302		tr->progs_cnt[kind]--;
303	}
304out:
305	mutex_unlock(&tr->mutex);
306	return err;
307}
308
309/* bpf_trampoline_unlink_prog() should never fail. */
310int bpf_trampoline_unlink_prog(struct bpf_prog *prog)
311{
312	enum bpf_tramp_prog_type kind;
313	struct bpf_trampoline *tr;
314	int err;
315
316	tr = prog->aux->trampoline;
317	kind = bpf_attach_type_to_tramp(prog);
318	mutex_lock(&tr->mutex);
319	if (kind == BPF_TRAMP_REPLACE) {
320		WARN_ON_ONCE(!tr->extension_prog);
321		err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP,
322					 tr->extension_prog->bpf_func, NULL);
323		tr->extension_prog = NULL;
324		goto out;
325	}
326	hlist_del(&prog->aux->tramp_hlist);
327	tr->progs_cnt[kind]--;
328	err = bpf_trampoline_update(prog->aux->trampoline);
329out:
330	mutex_unlock(&tr->mutex);
331	return err;
332}
333
334void bpf_trampoline_put(struct bpf_trampoline *tr)
335{
336	if (!tr)
337		return;
338	mutex_lock(&trampoline_mutex);
339	if (!refcount_dec_and_test(&tr->refcnt))
340		goto out;
341	WARN_ON_ONCE(mutex_is_locked(&tr->mutex));
342	if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FENTRY])))
343		goto out;
344	if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FEXIT])))
345		goto out;
346	bpf_image_ksym_del(&tr->ksym);
347	/* wait for tasks to get out of trampoline before freeing it */
348	synchronize_rcu_tasks();
349	bpf_jit_free_exec(tr->image);
350	hlist_del(&tr->hlist);
351	kfree(tr);
352out:
353	mutex_unlock(&trampoline_mutex);
354}
355
356/* The logic is similar to BPF_PROG_RUN, but with an explicit
357 * rcu_read_lock() and migrate_disable() which are required
358 * for the trampoline. The macro is split into
359 * call _bpf_prog_enter
360 * call prog->bpf_func
361 * call __bpf_prog_exit
362 */
363u64 notrace __bpf_prog_enter(void)
364	__acquires(RCU)
365{
366	u64 start = 0;
367
368	rcu_read_lock();
369	migrate_disable();
370	if (static_branch_unlikely(&bpf_stats_enabled_key))
371		start = sched_clock();
372	return start;
373}
374
375void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start)
376	__releases(RCU)
377{
378	struct bpf_prog_stats *stats;
379
380	if (static_branch_unlikely(&bpf_stats_enabled_key) &&
381	    /* static_key could be enabled in __bpf_prog_enter
382	     * and disabled in __bpf_prog_exit.
383	     * And vice versa.
384	     * Hence check that 'start' is not zero.
385	     */
386	    start) {
387		stats = this_cpu_ptr(prog->aux->stats);
388		u64_stats_update_begin(&stats->syncp);
389		stats->cnt++;
390		stats->nsecs += sched_clock() - start;
391		u64_stats_update_end(&stats->syncp);
392	}
393	migrate_enable();
394	rcu_read_unlock();
395}
396
397int __weak
398arch_prepare_bpf_trampoline(void *image, void *image_end,
399			    const struct btf_func_model *m, u32 flags,
400			    struct bpf_tramp_progs *tprogs,
401			    void *orig_call)
402{
403	return -ENOTSUPP;
404}
405
406static int __init init_trampolines(void)
407{
408	int i;
409
410	for (i = 0; i < TRAMPOLINE_TABLE_SIZE; i++)
411		INIT_HLIST_HEAD(&trampoline_table[i]);
412	return 0;
413}
414late_initcall(init_trampolines);