kernel/bpf/trampoline.c

   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. */
  12 const struct bpf_verifier_ops bpf_extension_verifier_ops = {
  13 };
  14 const 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
  21 static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE];
  22
  23 /* serializes access to trampoline_table */
  24 static DEFINE_MUTEX(trampoline_mutex);
  25
  26 void *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
  42 void 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
  51 void 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
  58 static 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
  66 struct 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);
 103 out:
 104         mutex_unlock(&trampoline_mutex);
 105         return tr;
 106 }
 107
 108 static 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
 120 static 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
 132 static 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 */
 145 static 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
 162 static struct bpf_tramp_progs *
 163 bpf_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
 186 static 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++;
 232 out:
 233         kfree(tprogs);
 234         return err;
 235 }
 236
 237 static 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
 259 int 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         }
 304 out:
 305         mutex_unlock(&tr->mutex);
 306         return err;
 307 }
 308
 309 /* bpf_trampoline_unlink_prog() should never fail. */
 310 int 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);
 329 out:
 330         mutex_unlock(&tr->mutex);
 331         return err;
 332 }
 333
 334 void 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);
 352 out:
 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  */
 363 u64 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
 375 void 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
 397 int __weak
 398 arch_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
 406 static 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 }
 414 late_initcall(init_trampolines);