summaryrefslogtreecommitdiff
path: root/kernel/bpf/trampoline.c
blob: 7e89f1f49d7712d6f530bba2c6572b57ae702b1f (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
// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2019 Facebook */
#include <linux/hash.h>
#include <linux/bpf.h>
#include <linux/filter.h>

/* 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);

struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
{
	struct bpf_trampoline *tr;
	struct hlist_head *head;
	void *image;
	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;

	/* is_root was checked earlier. No need for bpf_jit_charge_modmem() */
	image = bpf_jit_alloc_exec(PAGE_SIZE);
	if (!image) {
		kfree(tr);
		tr = NULL;
		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]);

	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);
	tr->image = image;
out:
	mutex_unlock(&trampoline_mutex);
	return tr;
}

/* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50
 * bytes on x86.  Pick a number to fit into PAGE_SIZE / 2
 */
#define BPF_MAX_TRAMP_PROGS 40

static int bpf_trampoline_update(struct bpf_trampoline *tr)
{
	void *old_image = tr->image + ((tr->selector + 1) & 1) * PAGE_SIZE/2;
	void *new_image = tr->image + (tr->selector & 1) * PAGE_SIZE/2;
	struct bpf_prog *progs_to_run[BPF_MAX_TRAMP_PROGS];
	int fentry_cnt = tr->progs_cnt[BPF_TRAMP_FENTRY];
	int fexit_cnt = tr->progs_cnt[BPF_TRAMP_FEXIT];
	struct bpf_prog **progs, **fentry, **fexit;
	u32 flags = BPF_TRAMP_F_RESTORE_REGS;
	struct bpf_prog_aux *aux;
	int err;

	if (fentry_cnt + fexit_cnt == 0) {
		err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_CALL,
					 old_image, NULL);
		tr->selector = 0;
		goto out;
	}

	/* populate fentry progs */
	fentry = progs = progs_to_run;
	hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FENTRY], tramp_hlist)
		*progs++ = aux->prog;

	/* populate fexit progs */
	fexit = progs;
	hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FEXIT], tramp_hlist)
		*progs++ = aux->prog;

	if (fexit_cnt)
		flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;

	err = arch_prepare_bpf_trampoline(new_image, &tr->func.model, flags,
					  fentry, fentry_cnt,
					  fexit, fexit_cnt,
					  tr->func.addr);
	if (err)
		goto out;

	if (tr->selector)
		/* progs already running at this address */
		err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_CALL,
					 old_image, new_image);
	else
		/* first time registering */
		err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_CALL, NULL,
					 new_image);
	if (err)
		goto out;
	tr->selector++;
out:
	return err;
}

static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(enum bpf_attach_type t)
{
	switch (t) {
	case BPF_TRACE_FENTRY:
		return BPF_TRAMP_FENTRY;
	default:
		return BPF_TRAMP_FEXIT;
	}
}

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

	tr = prog->aux->trampoline;
	kind = bpf_attach_type_to_tramp(prog->expected_attach_type);
	mutex_lock(&tr->mutex);
	if (tr->progs_cnt[BPF_TRAMP_FENTRY] + tr->progs_cnt[BPF_TRAMP_FEXIT]
	    >= 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(prog->aux->trampoline);
	if (err) {
		hlist_del(&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)
{
	enum bpf_tramp_prog_type kind;
	struct bpf_trampoline *tr;
	int err;

	tr = prog->aux->trampoline;
	kind = bpf_attach_type_to_tramp(prog->expected_attach_type);
	mutex_lock(&tr->mutex);
	hlist_del(&prog->aux->tramp_hlist);
	tr->progs_cnt[kind]--;
	err = bpf_trampoline_update(prog->aux->trampoline);
	mutex_unlock(&tr->mutex);
	return err;
}

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;
	bpf_jit_free_exec(tr->image);
	hlist_del(&tr->hlist);
	kfree(tr);
out:
	mutex_unlock(&trampoline_mutex);
}

/* The logic is similar to BPF_PROG_RUN, but with explicit rcu and preempt that
 * are needed for trampoline. The macro is split into
 * call _bpf_prog_enter
 * call prog->bpf_func
 * call __bpf_prog_exit
 */
u64 notrace __bpf_prog_enter(void)
{
	u64 start = 0;

	rcu_read_lock();
	preempt_disable();
	if (static_branch_unlikely(&bpf_stats_enabled_key))
		start = sched_clock();
	return start;
}

void notrace __bpf_prog_exit(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 not zero.
	     */
	    start) {
		stats = this_cpu_ptr(prog->aux->stats);
		u64_stats_update_begin(&stats->syncp);
		stats->cnt++;
		stats->nsecs += sched_clock() - start;
		u64_stats_update_end(&stats->syncp);
	}
	preempt_enable();
	rcu_read_unlock();
}

int __weak
arch_prepare_bpf_trampoline(void *image, struct btf_func_model *m, u32 flags,
			    struct bpf_prog **fentry_progs, int fentry_cnt,
			    struct bpf_prog **fexit_progs, int fexit_cnt,
			    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);