kernel/tracepoint.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (C) 2008-2014 Mathieu Desnoyers
   4  */
   5 #include <linux/module.h>
   6 #include <linux/mutex.h>
   7 #include <linux/types.h>
   8 #include <linux/jhash.h>
   9 #include <linux/list.h>
  10 #include <linux/rcupdate.h>
  11 #include <linux/tracepoint.h>
  12 #include <linux/err.h>
  13 #include <linux/slab.h>
  14 #include <linux/sched/signal.h>
  15 #include <linux/sched/task.h>
  16 #include <linux/static_key.h>
  17
  18 extern tracepoint_ptr_t __start___tracepoints_ptrs[];
  19 extern tracepoint_ptr_t __stop___tracepoints_ptrs[];
  20
  21 DEFINE_SRCU(tracepoint_srcu);
  22 EXPORT_SYMBOL_GPL(tracepoint_srcu);
  23
  24 /* Set to 1 to enable tracepoint debug output */
  25 static const int tracepoint_debug;
  26
  27 #ifdef CONFIG_MODULES
  28 /*
  29  * Tracepoint module list mutex protects the local module list.
  30  */
  31 static DEFINE_MUTEX(tracepoint_module_list_mutex);
  32
  33 /* Local list of struct tp_module */
  34 static LIST_HEAD(tracepoint_module_list);
  35 #endif /* CONFIG_MODULES */
  36
  37 /*
  38  * tracepoints_mutex protects the builtin and module tracepoints.
  39  * tracepoints_mutex nests inside tracepoint_module_list_mutex.
  40  */
  41 static DEFINE_MUTEX(tracepoints_mutex);
  42
  43 static struct rcu_head *early_probes;
  44 static bool ok_to_free_tracepoints;
  45
  46 /*
  47  * Note about RCU :
  48  * It is used to delay the free of multiple probes array until a quiescent
  49  * state is reached.
  50  */
  51 struct tp_probes {
  52         struct rcu_head rcu;
  53         struct tracepoint_func probes[0];
  54 };
  55
  56 static inline void *allocate_probes(int count)
  57 {
  58         struct tp_probes *p  = kmalloc(struct_size(p, probes, count),
  59                                        GFP_KERNEL);
  60         return p == NULL ? NULL : p->probes;
  61 }
  62
  63 static void srcu_free_old_probes(struct rcu_head *head)
  64 {
  65         kfree(container_of(head, struct tp_probes, rcu));
  66 }
  67
  68 static void rcu_free_old_probes(struct rcu_head *head)
  69 {
  70         call_srcu(&tracepoint_srcu, head, srcu_free_old_probes);
  71 }
  72
  73 static __init int release_early_probes(void)
  74 {
  75         struct rcu_head *tmp;
  76
  77         ok_to_free_tracepoints = true;
  78
  79         while (early_probes) {
  80                 tmp = early_probes;
  81                 early_probes = tmp->next;
  82                 call_rcu(tmp, rcu_free_old_probes);
  83         }
  84
  85         return 0;
  86 }
  87
  88 /* SRCU is initialized at core_initcall */
  89 postcore_initcall(release_early_probes);
  90
  91 static inline void release_probes(struct tracepoint_func *old)
  92 {
  93         if (old) {
  94                 struct tp_probes *tp_probes = container_of(old,
  95                         struct tp_probes, probes[0]);
  96
  97                 /*
  98                  * We can't free probes if SRCU is not initialized yet.
  99                  * Postpone the freeing till after SRCU is initialized.
 100                  */
 101                 if (unlikely(!ok_to_free_tracepoints)) {
 102                         tp_probes->rcu.next = early_probes;
 103                         early_probes = &tp_probes->rcu;
 104                         return;
 105                 }
 106
 107                 /*
 108                  * Tracepoint probes are protected by both sched RCU and SRCU,
 109                  * by calling the SRCU callback in the sched RCU callback we
 110                  * cover both cases. So let us chain the SRCU and sched RCU
 111                  * callbacks to wait for both grace periods.
 112                  */
 113                 call_rcu(&tp_probes->rcu, rcu_free_old_probes);
 114         }
 115 }
 116
 117 static void debug_print_probes(struct tracepoint_func *funcs)
 118 {
 119         int i;
 120
 121         if (!tracepoint_debug || !funcs)
 122                 return;
 123
 124         for (i = 0; funcs[i].func; i++)
 125                 printk(KERN_DEBUG "Probe %d : %p\n", i, funcs[i].func);
 126 }
 127
 128 static struct tracepoint_func *
 129 func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,
 130          int prio)
 131 {
 132         struct tracepoint_func *old, *new;
 133         int nr_probes = 0;
 134         int pos = -1;
 135
 136         if (WARN_ON(!tp_func->func))
 137                 return ERR_PTR(-EINVAL);
 138
 139         debug_print_probes(*funcs);
 140         old = *funcs;
 141         if (old) {
 142                 /* (N -> N+1), (N != 0, 1) probes */
 143                 for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
 144                         /* Insert before probes of lower priority */
 145                         if (pos < 0 && old[nr_probes].prio < prio)
 146                                 pos = nr_probes;
 147                         if (old[nr_probes].func == tp_func->func &&
 148                             old[nr_probes].data == tp_func->data)
 149                                 return ERR_PTR(-EEXIST);
 150                 }
 151         }
 152         /* + 2 : one for new probe, one for NULL func */
 153         new = allocate_probes(nr_probes + 2);
 154         if (new == NULL)
 155                 return ERR_PTR(-ENOMEM);
 156         if (old) {
 157                 if (pos < 0) {
 158                         pos = nr_probes;
 159                         memcpy(new, old, nr_probes * sizeof(struct tracepoint_func));
 160                 } else {
 161                         /* Copy higher priority probes ahead of the new probe */
 162                         memcpy(new, old, pos * sizeof(struct tracepoint_func));
 163                         /* Copy the rest after it. */
 164                         memcpy(new + pos + 1, old + pos,
 165                                (nr_probes - pos) * sizeof(struct tracepoint_func));
 166                 }
 167         } else
 168                 pos = 0;
 169         new[pos] = *tp_func;
 170         new[nr_probes + 1].func = NULL;
 171         *funcs = new;
 172         debug_print_probes(*funcs);
 173         return old;
 174 }
 175
 176 static void *func_remove(struct tracepoint_func **funcs,
 177                 struct tracepoint_func *tp_func)
 178 {
 179         int nr_probes = 0, nr_del = 0, i;
 180         struct tracepoint_func *old, *new;
 181
 182         old = *funcs;
 183
 184         if (!old)
 185                 return ERR_PTR(-ENOENT);
 186
 187         debug_print_probes(*funcs);
 188         /* (N -> M), (N > 1, M >= 0) probes */
 189         if (tp_func->func) {
 190                 for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
 191                         if (old[nr_probes].func == tp_func->func &&
 192                              old[nr_probes].data == tp_func->data)
 193                                 nr_del++;
 194                 }
 195         }
 196
 197         /*
 198          * If probe is NULL, then nr_probes = nr_del = 0, and then the
 199          * entire entry will be removed.
 200          */
 201         if (nr_probes - nr_del == 0) {
 202                 /* N -> 0, (N > 1) */
 203                 *funcs = NULL;
 204                 debug_print_probes(*funcs);
 205                 return old;
 206         } else {
 207                 int j = 0;
 208                 /* N -> M, (N > 1, M > 0) */
 209                 /* + 1 for NULL */
 210                 new = allocate_probes(nr_probes - nr_del + 1);
 211                 if (new == NULL)
 212                         return ERR_PTR(-ENOMEM);
 213                 for (i = 0; old[i].func; i++)
 214                         if (old[i].func != tp_func->func
 215                                         || old[i].data != tp_func->data)
 216                                 new[j++] = old[i];
 217                 new[nr_probes - nr_del].func = NULL;
 218                 *funcs = new;
 219         }
 220         debug_print_probes(*funcs);
 221         return old;
 222 }
 223
 224 /*
 225  * Add the probe function to a tracepoint.
 226  */
 227 static int tracepoint_add_func(struct tracepoint *tp,
 228                                struct tracepoint_func *func, int prio)
 229 {
 230         struct tracepoint_func *old, *tp_funcs;
 231         int ret;
 232
 233         if (tp->regfunc && !static_key_enabled(&tp->key)) {
 234                 ret = tp->regfunc();
 235                 if (ret < 0)
 236                         return ret;
 237         }
 238
 239         tp_funcs = rcu_dereference_protected(tp->funcs,
 240                         lockdep_is_held(&tracepoints_mutex));
 241         old = func_add(&tp_funcs, func, prio);
 242         if (IS_ERR(old)) {
 243                 WARN_ON_ONCE(PTR_ERR(old) != -ENOMEM);
 244                 return PTR_ERR(old);
 245         }
 246
 247         /*
 248          * rcu_assign_pointer has as smp_store_release() which makes sure
 249          * that the new probe callbacks array is consistent before setting
 250          * a pointer to it.  This array is referenced by __DO_TRACE from
 251          * include/linux/tracepoint.h using rcu_dereference_sched().
 252          */
 253         rcu_assign_pointer(tp->funcs, tp_funcs);
 254         if (!static_key_enabled(&tp->key))
 255                 static_key_slow_inc(&tp->key);
 256         release_probes(old);
 257         return 0;
 258 }
 259
 260 /*
 261  * Remove a probe function from a tracepoint.
 262  * Note: only waiting an RCU period after setting elem->call to the empty
 263  * function insures that the original callback is not used anymore. This insured
 264  * by preempt_disable around the call site.
 265  */
 266 static int tracepoint_remove_func(struct tracepoint *tp,
 267                 struct tracepoint_func *func)
 268 {
 269         struct tracepoint_func *old, *tp_funcs;
 270
 271         tp_funcs = rcu_dereference_protected(tp->funcs,
 272                         lockdep_is_held(&tracepoints_mutex));
 273         old = func_remove(&tp_funcs, func);
 274         if (IS_ERR(old)) {
 275                 WARN_ON_ONCE(PTR_ERR(old) != -ENOMEM);
 276                 return PTR_ERR(old);
 277         }
 278
 279         if (!tp_funcs) {
 280                 /* Removed last function */
 281                 if (tp->unregfunc && static_key_enabled(&tp->key))
 282                         tp->unregfunc();
 283
 284                 if (static_key_enabled(&tp->key))
 285                         static_key_slow_dec(&tp->key);
 286         }
 287         rcu_assign_pointer(tp->funcs, tp_funcs);
 288         release_probes(old);
 289         return 0;
 290 }
 291
 292 /**
 293  * tracepoint_probe_register_prio -  Connect a probe to a tracepoint with priority
 294  * @tp: tracepoint
 295  * @probe: probe handler
 296  * @data: tracepoint data
 297  * @prio: priority of this function over other registered functions
 298  *
 299  * Returns 0 if ok, error value on error.
 300  * Note: if @tp is within a module, the caller is responsible for
 301  * unregistering the probe before the module is gone. This can be
 302  * performed either with a tracepoint module going notifier, or from
 303  * within module exit functions.
 304  */
 305 int tracepoint_probe_register_prio(struct tracepoint *tp, void *probe,
 306                                    void *data, int prio)
 307 {
 308         struct tracepoint_func tp_func;
 309         int ret;
 310
 311         mutex_lock(&tracepoints_mutex);
 312         tp_func.func = probe;
 313         tp_func.data = data;
 314         tp_func.prio = prio;
 315         ret = tracepoint_add_func(tp, &tp_func, prio);
 316         mutex_unlock(&tracepoints_mutex);
 317         return ret;
 318 }
 319 EXPORT_SYMBOL_GPL(tracepoint_probe_register_prio);
 320
 321 /**
 322  * tracepoint_probe_register -  Connect a probe to a tracepoint
 323  * @tp: tracepoint
 324  * @probe: probe handler
 325  * @data: tracepoint data
 326  *
 327  * Returns 0 if ok, error value on error.
 328  * Note: if @tp is within a module, the caller is responsible for
 329  * unregistering the probe before the module is gone. This can be
 330  * performed either with a tracepoint module going notifier, or from
 331  * within module exit functions.
 332  */
 333 int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data)
 334 {
 335         return tracepoint_probe_register_prio(tp, probe, data, TRACEPOINT_DEFAULT_PRIO);
 336 }
 337 EXPORT_SYMBOL_GPL(tracepoint_probe_register);
 338
 339 /**
 340  * tracepoint_probe_unregister -  Disconnect a probe from a tracepoint
 341  * @tp: tracepoint
 342  * @probe: probe function pointer
 343  * @data: tracepoint data
 344  *
 345  * Returns 0 if ok, error value on error.
 346  */
 347 int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data)
 348 {
 349         struct tracepoint_func tp_func;
 350         int ret;
 351
 352         mutex_lock(&tracepoints_mutex);
 353         tp_func.func = probe;
 354         tp_func.data = data;
 355         ret = tracepoint_remove_func(tp, &tp_func);
 356         mutex_unlock(&tracepoints_mutex);
 357         return ret;
 358 }
 359 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
 360
 361 static void for_each_tracepoint_range(
 362                 tracepoint_ptr_t *begin, tracepoint_ptr_t *end,
 363                 void (*fct)(struct tracepoint *tp, void *priv),
 364                 void *priv)
 365 {
 366         tracepoint_ptr_t *iter;
 367
 368         if (!begin)
 369                 return;
 370         for (iter = begin; iter < end; iter++)
 371                 fct(tracepoint_ptr_deref(iter), priv);
 372 }
 373
 374 #ifdef CONFIG_MODULES
 375 bool trace_module_has_bad_taint(struct module *mod)
 376 {
 377         return mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP) |
 378                                (1 << TAINT_UNSIGNED_MODULE));
 379 }
 380
 381 static BLOCKING_NOTIFIER_HEAD(tracepoint_notify_list);
 382
 383 /**
 384  * register_tracepoint_notifier - register tracepoint coming/going notifier
 385  * @nb: notifier block
 386  *
 387  * Notifiers registered with this function are called on module
 388  * coming/going with the tracepoint_module_list_mutex held.
 389  * The notifier block callback should expect a "struct tp_module" data
 390  * pointer.
 391  */
 392 int register_tracepoint_module_notifier(struct notifier_block *nb)
 393 {
 394         struct tp_module *tp_mod;
 395         int ret;
 396
 397         mutex_lock(&tracepoint_module_list_mutex);
 398         ret = blocking_notifier_chain_register(&tracepoint_notify_list, nb);
 399         if (ret)
 400                 goto end;
 401         list_for_each_entry(tp_mod, &tracepoint_module_list, list)
 402                 (void) nb->notifier_call(nb, MODULE_STATE_COMING, tp_mod);
 403 end:
 404         mutex_unlock(&tracepoint_module_list_mutex);
 405         return ret;
 406 }
 407 EXPORT_SYMBOL_GPL(register_tracepoint_module_notifier);
 408
 409 /**
 410  * unregister_tracepoint_notifier - unregister tracepoint coming/going notifier
 411  * @nb: notifier block
 412  *
 413  * The notifier block callback should expect a "struct tp_module" data
 414  * pointer.
 415  */
 416 int unregister_tracepoint_module_notifier(struct notifier_block *nb)
 417 {
 418         struct tp_module *tp_mod;
 419         int ret;
 420
 421         mutex_lock(&tracepoint_module_list_mutex);
 422         ret = blocking_notifier_chain_unregister(&tracepoint_notify_list, nb);
 423         if (ret)
 424                 goto end;
 425         list_for_each_entry(tp_mod, &tracepoint_module_list, list)
 426                 (void) nb->notifier_call(nb, MODULE_STATE_GOING, tp_mod);
 427 end:
 428         mutex_unlock(&tracepoint_module_list_mutex);
 429         return ret;
 430
 431 }
 432 EXPORT_SYMBOL_GPL(unregister_tracepoint_module_notifier);
 433
 434 /*
 435  * Ensure the tracer unregistered the module's probes before the module
 436  * teardown is performed. Prevents leaks of probe and data pointers.
 437  */
 438 static void tp_module_going_check_quiescent(struct tracepoint *tp, void *priv)
 439 {
 440         WARN_ON_ONCE(tp->funcs);
 441 }
 442
 443 static int tracepoint_module_coming(struct module *mod)
 444 {
 445         struct tp_module *tp_mod;
 446         int ret = 0;
 447
 448         if (!mod->num_tracepoints)
 449                 return 0;
 450
 451         /*
 452          * We skip modules that taint the kernel, especially those with different
 453          * module headers (for forced load), to make sure we don't cause a crash.
 454          * Staging, out-of-tree, and unsigned GPL modules are fine.
 455          */
 456         if (trace_module_has_bad_taint(mod))
 457                 return 0;
 458         mutex_lock(&tracepoint_module_list_mutex);
 459         tp_mod = kmalloc(sizeof(struct tp_module), GFP_KERNEL);
 460         if (!tp_mod) {
 461                 ret = -ENOMEM;
 462                 goto end;
 463         }
 464         tp_mod->mod = mod;
 465         list_add_tail(&tp_mod->list, &tracepoint_module_list);
 466         blocking_notifier_call_chain(&tracepoint_notify_list,
 467                         MODULE_STATE_COMING, tp_mod);
 468 end:
 469         mutex_unlock(&tracepoint_module_list_mutex);
 470         return ret;
 471 }
 472
 473 static void tracepoint_module_going(struct module *mod)
 474 {
 475         struct tp_module *tp_mod;
 476
 477         if (!mod->num_tracepoints)
 478                 return;
 479
 480         mutex_lock(&tracepoint_module_list_mutex);
 481         list_for_each_entry(tp_mod, &tracepoint_module_list, list) {
 482                 if (tp_mod->mod == mod) {
 483                         blocking_notifier_call_chain(&tracepoint_notify_list,
 484                                         MODULE_STATE_GOING, tp_mod);
 485                         list_del(&tp_mod->list);
 486                         kfree(tp_mod);
 487                         /*
 488                          * Called the going notifier before checking for
 489                          * quiescence.
 490                          */
 491                         for_each_tracepoint_range(mod->tracepoints_ptrs,
 492                                 mod->tracepoints_ptrs + mod->num_tracepoints,
 493                                 tp_module_going_check_quiescent, NULL);
 494                         break;
 495                 }
 496         }
 497         /*
 498          * In the case of modules that were tainted at "coming", we'll simply
 499          * walk through the list without finding it. We cannot use the "tainted"
 500          * flag on "going", in case a module taints the kernel only after being
 501          * loaded.
 502          */
 503         mutex_unlock(&tracepoint_module_list_mutex);
 504 }
 505
 506 static int tracepoint_module_notify(struct notifier_block *self,
 507                 unsigned long val, void *data)
 508 {
 509         struct module *mod = data;
 510         int ret = 0;
 511
 512         switch (val) {
 513         case MODULE_STATE_COMING:
 514                 ret = tracepoint_module_coming(mod);
 515                 break;
 516         case MODULE_STATE_LIVE:
 517                 break;
 518         case MODULE_STATE_GOING:
 519                 tracepoint_module_going(mod);
 520                 break;
 521         case MODULE_STATE_UNFORMED:
 522                 break;
 523         }
 524         return ret;
 525 }
 526
 527 static struct notifier_block tracepoint_module_nb = {
 528         .notifier_call = tracepoint_module_notify,
 529         .priority = 0,
 530 };
 531
 532 static __init int init_tracepoints(void)
 533 {
 534         int ret;
 535
 536         ret = register_module_notifier(&tracepoint_module_nb);
 537         if (ret)
 538                 pr_warn("Failed to register tracepoint module enter notifier\n");
 539
 540         return ret;
 541 }
 542 __initcall(init_tracepoints);
 543 #endif /* CONFIG_MODULES */
 544
 545 /**
 546  * for_each_kernel_tracepoint - iteration on all kernel tracepoints
 547  * @fct: callback
 548  * @priv: private data
 549  */
 550 void for_each_kernel_tracepoint(void (*fct)(struct tracepoint *tp, void *priv),
 551                 void *priv)
 552 {
 553         for_each_tracepoint_range(__start___tracepoints_ptrs,
 554                 __stop___tracepoints_ptrs, fct, priv);
 555 }
 556 EXPORT_SYMBOL_GPL(for_each_kernel_tracepoint);
 557
 558 #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
 559
 560 /* NB: reg/unreg are called while guarded with the tracepoints_mutex */
 561 static int sys_tracepoint_refcount;
 562
 563 int syscall_regfunc(void)
 564 {
 565         struct task_struct *p, *t;
 566
 567         if (!sys_tracepoint_refcount) {
 568                 read_lock(&tasklist_lock);
 569                 for_each_process_thread(p, t) {
 570                         set_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
 571                 }
 572                 read_unlock(&tasklist_lock);
 573         }
 574         sys_tracepoint_refcount++;
 575
 576         return 0;
 577 }
 578
 579 void syscall_unregfunc(void)
 580 {
 581         struct task_struct *p, *t;
 582
 583         sys_tracepoint_refcount--;
 584         if (!sys_tracepoint_refcount) {
 585                 read_lock(&tasklist_lock);
 586                 for_each_process_thread(p, t) {
 587                         clear_tsk_thread_flag(t, TIF_SYSCALL_TRACEPOINT);
 588                 }
 589                 read_unlock(&tasklist_lock);
 590         }
 591 }
 592 #endif