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 9 /* dummy _ops. The verifier will operate on target program's ops. */ 10 const struct bpf_verifier_ops bpf_extension_verifier_ops = { 11 }; 12 const struct bpf_prog_ops bpf_extension_prog_ops = { 13 }; 14 15 /* btf_vmlinux has ~22k attachable functions. 1k htab is enough. */ 16 #define TRAMPOLINE_HASH_BITS 10 17 #define TRAMPOLINE_TABLE_SIZE (1 << TRAMPOLINE_HASH_BITS) 18 19 static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE]; 20 static struct latch_tree_root image_tree __cacheline_aligned; 21 22 /* serializes access to trampoline_table and image_tree */ 23 static DEFINE_MUTEX(trampoline_mutex); 24 25 static 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 static __always_inline bool image_tree_less(struct latch_tree_node *a, 42 struct latch_tree_node *b) 43 { 44 struct bpf_image *ia = container_of(a, struct bpf_image, tnode); 45 struct bpf_image *ib = container_of(b, struct bpf_image, tnode); 46 47 return ia < ib; 48 } 49 50 static __always_inline int image_tree_comp(void *addr, struct latch_tree_node *n) 51 { 52 void *image = container_of(n, struct bpf_image, tnode); 53 54 if (addr < image) 55 return -1; 56 if (addr >= image + PAGE_SIZE) 57 return 1; 58 59 return 0; 60 } 61 62 static const struct latch_tree_ops image_tree_ops = { 63 .less = image_tree_less, 64 .comp = image_tree_comp, 65 }; 66 67 static void *__bpf_image_alloc(bool lock) 68 { 69 struct bpf_image *image; 70 71 image = bpf_jit_alloc_exec_page(); 72 if (!image) 73 return NULL; 74 75 if (lock) 76 mutex_lock(&trampoline_mutex); 77 latch_tree_insert(&image->tnode, &image_tree, &image_tree_ops); 78 if (lock) 79 mutex_unlock(&trampoline_mutex); 80 return image->data; 81 } 82 83 void *bpf_image_alloc(void) 84 { 85 return __bpf_image_alloc(true); 86 } 87 88 bool is_bpf_image_address(unsigned long addr) 89 { 90 bool ret; 91 92 rcu_read_lock(); 93 ret = latch_tree_find((void *) addr, &image_tree, &image_tree_ops) != NULL; 94 rcu_read_unlock(); 95 96 return ret; 97 } 98 99 struct bpf_trampoline *bpf_trampoline_lookup(u64 key) 100 { 101 struct bpf_trampoline *tr; 102 struct hlist_head *head; 103 void *image; 104 int i; 105 106 mutex_lock(&trampoline_mutex); 107 head = &trampoline_table[hash_64(key, TRAMPOLINE_HASH_BITS)]; 108 hlist_for_each_entry(tr, head, hlist) { 109 if (tr->key == key) { 110 refcount_inc(&tr->refcnt); 111 goto out; 112 } 113 } 114 tr = kzalloc(sizeof(*tr), GFP_KERNEL); 115 if (!tr) 116 goto out; 117 118 /* is_root was checked earlier. No need for bpf_jit_charge_modmem() */ 119 image = __bpf_image_alloc(false); 120 if (!image) { 121 kfree(tr); 122 tr = NULL; 123 goto out; 124 } 125 126 tr->key = key; 127 INIT_HLIST_NODE(&tr->hlist); 128 hlist_add_head(&tr->hlist, head); 129 refcount_set(&tr->refcnt, 1); 130 mutex_init(&tr->mutex); 131 for (i = 0; i < BPF_TRAMP_MAX; i++) 132 INIT_HLIST_HEAD(&tr->progs_hlist[i]); 133 tr->image = image; 134 out: 135 mutex_unlock(&trampoline_mutex); 136 return tr; 137 } 138 139 static int is_ftrace_location(void *ip) 140 { 141 long addr; 142 143 addr = ftrace_location((long)ip); 144 if (!addr) 145 return 0; 146 if (WARN_ON_ONCE(addr != (long)ip)) 147 return -EFAULT; 148 return 1; 149 } 150 151 static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr) 152 { 153 void *ip = tr->func.addr; 154 int ret; 155 156 if (tr->func.ftrace_managed) 157 ret = unregister_ftrace_direct((long)ip, (long)old_addr); 158 else 159 ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL); 160 return ret; 161 } 162 163 static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_addr) 164 { 165 void *ip = tr->func.addr; 166 int ret; 167 168 if (tr->func.ftrace_managed) 169 ret = modify_ftrace_direct((long)ip, (long)old_addr, (long)new_addr); 170 else 171 ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, new_addr); 172 return ret; 173 } 174 175 /* first time registering */ 176 static int register_fentry(struct bpf_trampoline *tr, void *new_addr) 177 { 178 void *ip = tr->func.addr; 179 int ret; 180 181 ret = is_ftrace_location(ip); 182 if (ret < 0) 183 return ret; 184 tr->func.ftrace_managed = ret; 185 186 if (tr->func.ftrace_managed) 187 ret = register_ftrace_direct((long)ip, (long)new_addr); 188 else 189 ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr); 190 return ret; 191 } 192 193 /* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50 194 * bytes on x86. Pick a number to fit into BPF_IMAGE_SIZE / 2 195 */ 196 #define BPF_MAX_TRAMP_PROGS 40 197 198 static int bpf_trampoline_update(struct bpf_trampoline *tr) 199 { 200 void *old_image = tr->image + ((tr->selector + 1) & 1) * BPF_IMAGE_SIZE/2; 201 void *new_image = tr->image + (tr->selector & 1) * BPF_IMAGE_SIZE/2; 202 struct bpf_prog *progs_to_run[BPF_MAX_TRAMP_PROGS]; 203 int fentry_cnt = tr->progs_cnt[BPF_TRAMP_FENTRY]; 204 int fexit_cnt = tr->progs_cnt[BPF_TRAMP_FEXIT]; 205 struct bpf_prog **progs, **fentry, **fexit; 206 u32 flags = BPF_TRAMP_F_RESTORE_REGS; 207 struct bpf_prog_aux *aux; 208 int err; 209 210 if (fentry_cnt + fexit_cnt == 0) { 211 err = unregister_fentry(tr, old_image); 212 tr->selector = 0; 213 goto out; 214 } 215 216 /* populate fentry progs */ 217 fentry = progs = progs_to_run; 218 hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FENTRY], tramp_hlist) 219 *progs++ = aux->prog; 220 221 /* populate fexit progs */ 222 fexit = progs; 223 hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FEXIT], tramp_hlist) 224 *progs++ = aux->prog; 225 226 if (fexit_cnt) 227 flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME; 228 229 /* Though the second half of trampoline page is unused a task could be 230 * preempted in the middle of the first half of trampoline and two 231 * updates to trampoline would change the code from underneath the 232 * preempted task. Hence wait for tasks to voluntarily schedule or go 233 * to userspace. 234 */ 235 synchronize_rcu_tasks(); 236 237 err = arch_prepare_bpf_trampoline(new_image, new_image + BPF_IMAGE_SIZE / 2, 238 &tr->func.model, flags, 239 fentry, fentry_cnt, 240 fexit, fexit_cnt, 241 tr->func.addr); 242 if (err < 0) 243 goto out; 244 245 if (tr->selector) 246 /* progs already running at this address */ 247 err = modify_fentry(tr, old_image, new_image); 248 else 249 /* first time registering */ 250 err = register_fentry(tr, new_image); 251 if (err) 252 goto out; 253 tr->selector++; 254 out: 255 return err; 256 } 257 258 static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(enum bpf_attach_type t) 259 { 260 switch (t) { 261 case BPF_TRACE_FENTRY: 262 return BPF_TRAMP_FENTRY; 263 case BPF_TRACE_FEXIT: 264 return BPF_TRAMP_FEXIT; 265 default: 266 return BPF_TRAMP_REPLACE; 267 } 268 } 269 270 int bpf_trampoline_link_prog(struct bpf_prog *prog) 271 { 272 enum bpf_tramp_prog_type kind; 273 struct bpf_trampoline *tr; 274 int err = 0; 275 int cnt; 276 277 tr = prog->aux->trampoline; 278 kind = bpf_attach_type_to_tramp(prog->expected_attach_type); 279 mutex_lock(&tr->mutex); 280 if (tr->extension_prog) { 281 /* cannot attach fentry/fexit if extension prog is attached. 282 * cannot overwrite extension prog either. 283 */ 284 err = -EBUSY; 285 goto out; 286 } 287 cnt = tr->progs_cnt[BPF_TRAMP_FENTRY] + tr->progs_cnt[BPF_TRAMP_FEXIT]; 288 if (kind == BPF_TRAMP_REPLACE) { 289 /* Cannot attach extension if fentry/fexit are in use. */ 290 if (cnt) { 291 err = -EBUSY; 292 goto out; 293 } 294 tr->extension_prog = prog; 295 err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP, NULL, 296 prog->bpf_func); 297 goto out; 298 } 299 if (cnt >= BPF_MAX_TRAMP_PROGS) { 300 err = -E2BIG; 301 goto out; 302 } 303 if (!hlist_unhashed(&prog->aux->tramp_hlist)) { 304 /* prog already linked */ 305 err = -EBUSY; 306 goto out; 307 } 308 hlist_add_head(&prog->aux->tramp_hlist, &tr->progs_hlist[kind]); 309 tr->progs_cnt[kind]++; 310 err = bpf_trampoline_update(prog->aux->trampoline); 311 if (err) { 312 hlist_del(&prog->aux->tramp_hlist); 313 tr->progs_cnt[kind]--; 314 } 315 out: 316 mutex_unlock(&tr->mutex); 317 return err; 318 } 319 320 /* bpf_trampoline_unlink_prog() should never fail. */ 321 int bpf_trampoline_unlink_prog(struct bpf_prog *prog) 322 { 323 enum bpf_tramp_prog_type kind; 324 struct bpf_trampoline *tr; 325 int err; 326 327 tr = prog->aux->trampoline; 328 kind = bpf_attach_type_to_tramp(prog->expected_attach_type); 329 mutex_lock(&tr->mutex); 330 if (kind == BPF_TRAMP_REPLACE) { 331 WARN_ON_ONCE(!tr->extension_prog); 332 err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP, 333 tr->extension_prog->bpf_func, NULL); 334 tr->extension_prog = NULL; 335 goto out; 336 } 337 hlist_del(&prog->aux->tramp_hlist); 338 tr->progs_cnt[kind]--; 339 err = bpf_trampoline_update(prog->aux->trampoline); 340 out: 341 mutex_unlock(&tr->mutex); 342 return err; 343 } 344 345 void bpf_trampoline_put(struct bpf_trampoline *tr) 346 { 347 struct bpf_image *image; 348 349 if (!tr) 350 return; 351 mutex_lock(&trampoline_mutex); 352 if (!refcount_dec_and_test(&tr->refcnt)) 353 goto out; 354 WARN_ON_ONCE(mutex_is_locked(&tr->mutex)); 355 if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FENTRY]))) 356 goto out; 357 if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FEXIT]))) 358 goto out; 359 image = container_of(tr->image, struct bpf_image, data); 360 latch_tree_erase(&image->tnode, &image_tree, &image_tree_ops); 361 /* wait for tasks to get out of trampoline before freeing it */ 362 synchronize_rcu_tasks(); 363 bpf_jit_free_exec(image); 364 hlist_del(&tr->hlist); 365 kfree(tr); 366 out: 367 mutex_unlock(&trampoline_mutex); 368 } 369 370 /* The logic is similar to BPF_PROG_RUN, but with explicit rcu and preempt that 371 * are needed for trampoline. The macro is split into 372 * call _bpf_prog_enter 373 * call prog->bpf_func 374 * call __bpf_prog_exit 375 */ 376 u64 notrace __bpf_prog_enter(void) 377 { 378 u64 start = 0; 379 380 rcu_read_lock(); 381 preempt_disable(); 382 if (static_branch_unlikely(&bpf_stats_enabled_key)) 383 start = sched_clock(); 384 return start; 385 } 386 387 void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start) 388 { 389 struct bpf_prog_stats *stats; 390 391 if (static_branch_unlikely(&bpf_stats_enabled_key) && 392 /* static_key could be enabled in __bpf_prog_enter 393 * and disabled in __bpf_prog_exit. 394 * And vice versa. 395 * Hence check that 'start' is not zero. 396 */ 397 start) { 398 stats = this_cpu_ptr(prog->aux->stats); 399 u64_stats_update_begin(&stats->syncp); 400 stats->cnt++; 401 stats->nsecs += sched_clock() - start; 402 u64_stats_update_end(&stats->syncp); 403 } 404 preempt_enable(); 405 rcu_read_unlock(); 406 } 407 408 int __weak 409 arch_prepare_bpf_trampoline(void *image, void *image_end, 410 const struct btf_func_model *m, u32 flags, 411 struct bpf_prog **fentry_progs, int fentry_cnt, 412 struct bpf_prog **fexit_progs, int fexit_cnt, 413 void *orig_call) 414 { 415 return -ENOTSUPP; 416 } 417 418 static int __init init_trampolines(void) 419 { 420 int i; 421 422 for (i = 0; i < TRAMPOLINE_TABLE_SIZE; i++) 423 INIT_HLIST_HEAD(&trampoline_table[i]); 424 return 0; 425 } 426 late_initcall(init_trampolines); 427