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