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fec56f58 AS |
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> | |
b91e014f | 6 | #include <linux/ftrace.h> |
fec56f58 AS |
7 | |
8 | /* btf_vmlinux has ~22k attachable functions. 1k htab is enough. */ | |
9 | #define TRAMPOLINE_HASH_BITS 10 | |
10 | #define TRAMPOLINE_TABLE_SIZE (1 << TRAMPOLINE_HASH_BITS) | |
11 | ||
12 | static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE]; | |
13 | ||
14 | /* serializes access to trampoline_table */ | |
15 | static DEFINE_MUTEX(trampoline_mutex); | |
16 | ||
17 | struct bpf_trampoline *bpf_trampoline_lookup(u64 key) | |
18 | { | |
19 | struct bpf_trampoline *tr; | |
20 | struct hlist_head *head; | |
21 | void *image; | |
22 | int i; | |
23 | ||
24 | mutex_lock(&trampoline_mutex); | |
25 | head = &trampoline_table[hash_64(key, TRAMPOLINE_HASH_BITS)]; | |
26 | hlist_for_each_entry(tr, head, hlist) { | |
27 | if (tr->key == key) { | |
28 | refcount_inc(&tr->refcnt); | |
29 | goto out; | |
30 | } | |
31 | } | |
32 | tr = kzalloc(sizeof(*tr), GFP_KERNEL); | |
33 | if (!tr) | |
34 | goto out; | |
35 | ||
36 | /* is_root was checked earlier. No need for bpf_jit_charge_modmem() */ | |
37 | image = bpf_jit_alloc_exec(PAGE_SIZE); | |
38 | if (!image) { | |
39 | kfree(tr); | |
40 | tr = NULL; | |
41 | goto out; | |
42 | } | |
43 | ||
44 | tr->key = key; | |
45 | INIT_HLIST_NODE(&tr->hlist); | |
46 | hlist_add_head(&tr->hlist, head); | |
47 | refcount_set(&tr->refcnt, 1); | |
48 | mutex_init(&tr->mutex); | |
49 | for (i = 0; i < BPF_TRAMP_MAX; i++) | |
50 | INIT_HLIST_HEAD(&tr->progs_hlist[i]); | |
51 | ||
52 | set_vm_flush_reset_perms(image); | |
53 | /* Keep image as writeable. The alternative is to keep flipping ro/rw | |
54 | * everytime new program is attached or detached. | |
55 | */ | |
56 | set_memory_x((long)image, 1); | |
57 | tr->image = image; | |
58 | out: | |
59 | mutex_unlock(&trampoline_mutex); | |
60 | return tr; | |
61 | } | |
62 | ||
b91e014f AS |
63 | static int is_ftrace_location(void *ip) |
64 | { | |
65 | long addr; | |
66 | ||
67 | addr = ftrace_location((long)ip); | |
68 | if (!addr) | |
69 | return 0; | |
70 | if (WARN_ON_ONCE(addr != (long)ip)) | |
71 | return -EFAULT; | |
72 | return 1; | |
73 | } | |
74 | ||
75 | static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr) | |
76 | { | |
77 | void *ip = tr->func.addr; | |
78 | int ret; | |
79 | ||
80 | if (tr->func.ftrace_managed) | |
81 | ret = unregister_ftrace_direct((long)ip, (long)old_addr); | |
82 | else | |
83 | ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL); | |
84 | return ret; | |
85 | } | |
86 | ||
87 | static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_addr) | |
88 | { | |
89 | void *ip = tr->func.addr; | |
90 | int ret; | |
91 | ||
92 | if (tr->func.ftrace_managed) | |
93 | ret = modify_ftrace_direct((long)ip, (long)old_addr, (long)new_addr); | |
94 | else | |
95 | ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, new_addr); | |
96 | return ret; | |
97 | } | |
98 | ||
99 | /* first time registering */ | |
100 | static int register_fentry(struct bpf_trampoline *tr, void *new_addr) | |
101 | { | |
102 | void *ip = tr->func.addr; | |
103 | int ret; | |
104 | ||
105 | ret = is_ftrace_location(ip); | |
106 | if (ret < 0) | |
107 | return ret; | |
108 | tr->func.ftrace_managed = ret; | |
109 | ||
110 | if (tr->func.ftrace_managed) | |
111 | ret = register_ftrace_direct((long)ip, (long)new_addr); | |
112 | else | |
113 | ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr); | |
114 | return ret; | |
115 | } | |
116 | ||
fec56f58 AS |
117 | /* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50 |
118 | * bytes on x86. Pick a number to fit into PAGE_SIZE / 2 | |
119 | */ | |
120 | #define BPF_MAX_TRAMP_PROGS 40 | |
121 | ||
122 | static int bpf_trampoline_update(struct bpf_trampoline *tr) | |
123 | { | |
124 | void *old_image = tr->image + ((tr->selector + 1) & 1) * PAGE_SIZE/2; | |
125 | void *new_image = tr->image + (tr->selector & 1) * PAGE_SIZE/2; | |
126 | struct bpf_prog *progs_to_run[BPF_MAX_TRAMP_PROGS]; | |
127 | int fentry_cnt = tr->progs_cnt[BPF_TRAMP_FENTRY]; | |
128 | int fexit_cnt = tr->progs_cnt[BPF_TRAMP_FEXIT]; | |
129 | struct bpf_prog **progs, **fentry, **fexit; | |
130 | u32 flags = BPF_TRAMP_F_RESTORE_REGS; | |
131 | struct bpf_prog_aux *aux; | |
132 | int err; | |
133 | ||
134 | if (fentry_cnt + fexit_cnt == 0) { | |
b91e014f | 135 | err = unregister_fentry(tr, old_image); |
fec56f58 AS |
136 | tr->selector = 0; |
137 | goto out; | |
138 | } | |
139 | ||
140 | /* populate fentry progs */ | |
141 | fentry = progs = progs_to_run; | |
142 | hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FENTRY], tramp_hlist) | |
143 | *progs++ = aux->prog; | |
144 | ||
145 | /* populate fexit progs */ | |
146 | fexit = progs; | |
147 | hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FEXIT], tramp_hlist) | |
148 | *progs++ = aux->prog; | |
149 | ||
150 | if (fexit_cnt) | |
151 | flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME; | |
152 | ||
153 | err = arch_prepare_bpf_trampoline(new_image, &tr->func.model, flags, | |
154 | fentry, fentry_cnt, | |
155 | fexit, fexit_cnt, | |
156 | tr->func.addr); | |
157 | if (err) | |
158 | goto out; | |
159 | ||
160 | if (tr->selector) | |
161 | /* progs already running at this address */ | |
b91e014f | 162 | err = modify_fentry(tr, old_image, new_image); |
fec56f58 AS |
163 | else |
164 | /* first time registering */ | |
b91e014f | 165 | err = register_fentry(tr, new_image); |
fec56f58 AS |
166 | if (err) |
167 | goto out; | |
168 | tr->selector++; | |
169 | out: | |
170 | return err; | |
171 | } | |
172 | ||
173 | static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(enum bpf_attach_type t) | |
174 | { | |
175 | switch (t) { | |
176 | case BPF_TRACE_FENTRY: | |
177 | return BPF_TRAMP_FENTRY; | |
178 | default: | |
179 | return BPF_TRAMP_FEXIT; | |
180 | } | |
181 | } | |
182 | ||
183 | int bpf_trampoline_link_prog(struct bpf_prog *prog) | |
184 | { | |
185 | enum bpf_tramp_prog_type kind; | |
186 | struct bpf_trampoline *tr; | |
187 | int err = 0; | |
188 | ||
189 | tr = prog->aux->trampoline; | |
190 | kind = bpf_attach_type_to_tramp(prog->expected_attach_type); | |
191 | mutex_lock(&tr->mutex); | |
192 | if (tr->progs_cnt[BPF_TRAMP_FENTRY] + tr->progs_cnt[BPF_TRAMP_FEXIT] | |
193 | >= BPF_MAX_TRAMP_PROGS) { | |
194 | err = -E2BIG; | |
195 | goto out; | |
196 | } | |
197 | if (!hlist_unhashed(&prog->aux->tramp_hlist)) { | |
198 | /* prog already linked */ | |
199 | err = -EBUSY; | |
200 | goto out; | |
201 | } | |
202 | hlist_add_head(&prog->aux->tramp_hlist, &tr->progs_hlist[kind]); | |
203 | tr->progs_cnt[kind]++; | |
204 | err = bpf_trampoline_update(prog->aux->trampoline); | |
205 | if (err) { | |
206 | hlist_del(&prog->aux->tramp_hlist); | |
207 | tr->progs_cnt[kind]--; | |
208 | } | |
209 | out: | |
210 | mutex_unlock(&tr->mutex); | |
211 | return err; | |
212 | } | |
213 | ||
214 | /* bpf_trampoline_unlink_prog() should never fail. */ | |
215 | int bpf_trampoline_unlink_prog(struct bpf_prog *prog) | |
216 | { | |
217 | enum bpf_tramp_prog_type kind; | |
218 | struct bpf_trampoline *tr; | |
219 | int err; | |
220 | ||
221 | tr = prog->aux->trampoline; | |
222 | kind = bpf_attach_type_to_tramp(prog->expected_attach_type); | |
223 | mutex_lock(&tr->mutex); | |
224 | hlist_del(&prog->aux->tramp_hlist); | |
225 | tr->progs_cnt[kind]--; | |
226 | err = bpf_trampoline_update(prog->aux->trampoline); | |
227 | mutex_unlock(&tr->mutex); | |
228 | return err; | |
229 | } | |
230 | ||
231 | void bpf_trampoline_put(struct bpf_trampoline *tr) | |
232 | { | |
233 | if (!tr) | |
234 | return; | |
235 | mutex_lock(&trampoline_mutex); | |
236 | if (!refcount_dec_and_test(&tr->refcnt)) | |
237 | goto out; | |
238 | WARN_ON_ONCE(mutex_is_locked(&tr->mutex)); | |
239 | if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FENTRY]))) | |
240 | goto out; | |
241 | if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FEXIT]))) | |
242 | goto out; | |
243 | bpf_jit_free_exec(tr->image); | |
244 | hlist_del(&tr->hlist); | |
245 | kfree(tr); | |
246 | out: | |
247 | mutex_unlock(&trampoline_mutex); | |
248 | } | |
249 | ||
250 | /* The logic is similar to BPF_PROG_RUN, but with explicit rcu and preempt that | |
251 | * are needed for trampoline. The macro is split into | |
252 | * call _bpf_prog_enter | |
253 | * call prog->bpf_func | |
254 | * call __bpf_prog_exit | |
255 | */ | |
256 | u64 notrace __bpf_prog_enter(void) | |
257 | { | |
258 | u64 start = 0; | |
259 | ||
260 | rcu_read_lock(); | |
261 | preempt_disable(); | |
262 | if (static_branch_unlikely(&bpf_stats_enabled_key)) | |
263 | start = sched_clock(); | |
264 | return start; | |
265 | } | |
266 | ||
267 | void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start) | |
268 | { | |
269 | struct bpf_prog_stats *stats; | |
270 | ||
271 | if (static_branch_unlikely(&bpf_stats_enabled_key) && | |
272 | /* static_key could be enabled in __bpf_prog_enter | |
273 | * and disabled in __bpf_prog_exit. | |
274 | * And vice versa. | |
275 | * Hence check that 'start' is not zero. | |
276 | */ | |
277 | start) { | |
278 | stats = this_cpu_ptr(prog->aux->stats); | |
279 | u64_stats_update_begin(&stats->syncp); | |
280 | stats->cnt++; | |
281 | stats->nsecs += sched_clock() - start; | |
282 | u64_stats_update_end(&stats->syncp); | |
283 | } | |
284 | preempt_enable(); | |
285 | rcu_read_unlock(); | |
286 | } | |
287 | ||
288 | int __weak | |
289 | arch_prepare_bpf_trampoline(void *image, struct btf_func_model *m, u32 flags, | |
290 | struct bpf_prog **fentry_progs, int fentry_cnt, | |
291 | struct bpf_prog **fexit_progs, int fexit_cnt, | |
292 | void *orig_call) | |
293 | { | |
294 | return -ENOTSUPP; | |
295 | } | |
296 | ||
297 | static int __init init_trampolines(void) | |
298 | { | |
299 | int i; | |
300 | ||
301 | for (i = 0; i < TRAMPOLINE_TABLE_SIZE; i++) | |
302 | INIT_HLIST_HEAD(&trampoline_table[i]); | |
303 | return 0; | |
304 | } | |
305 | late_initcall(init_trampolines); |