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TOMOYO Linux Cross Reference
Linux/kernel/jump_label.c

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  1 /*
  2  * jump label support
  3  *
  4  * Copyright (C) 2009 Jason Baron <jbaron@redhat.com>
  5  * Copyright (C) 2011 Peter Zijlstra
  6  *
  7  */
  8 #include <linux/memory.h>
  9 #include <linux/uaccess.h>
 10 #include <linux/module.h>
 11 #include <linux/list.h>
 12 #include <linux/slab.h>
 13 #include <linux/sort.h>
 14 #include <linux/err.h>
 15 #include <linux/static_key.h>
 16 #include <linux/jump_label_ratelimit.h>
 17 #include <linux/bug.h>
 18 
 19 #ifdef HAVE_JUMP_LABEL
 20 
 21 /* mutex to protect coming/going of the the jump_label table */
 22 static DEFINE_MUTEX(jump_label_mutex);
 23 
 24 void jump_label_lock(void)
 25 {
 26         mutex_lock(&jump_label_mutex);
 27 }
 28 
 29 void jump_label_unlock(void)
 30 {
 31         mutex_unlock(&jump_label_mutex);
 32 }
 33 
 34 static int jump_label_cmp(const void *a, const void *b)
 35 {
 36         const struct jump_entry *jea = a;
 37         const struct jump_entry *jeb = b;
 38 
 39         if (jea->key < jeb->key)
 40                 return -1;
 41 
 42         if (jea->key > jeb->key)
 43                 return 1;
 44 
 45         return 0;
 46 }
 47 
 48 static void
 49 jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
 50 {
 51         unsigned long size;
 52 
 53         size = (((unsigned long)stop - (unsigned long)start)
 54                                         / sizeof(struct jump_entry));
 55         sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
 56 }
 57 
 58 static void jump_label_update(struct static_key *key);
 59 
 60 /*
 61  * There are similar definitions for the !HAVE_JUMP_LABEL case in jump_label.h.
 62  * The use of 'atomic_read()' requires atomic.h and its problematic for some
 63  * kernel headers such as kernel.h and others. Since static_key_count() is not
 64  * used in the branch statements as it is for the !HAVE_JUMP_LABEL case its ok
 65  * to have it be a function here. Similarly, for 'static_key_enable()' and
 66  * 'static_key_disable()', which require bug.h. This should allow jump_label.h
 67  * to be included from most/all places for HAVE_JUMP_LABEL.
 68  */
 69 int static_key_count(struct static_key *key)
 70 {
 71         /*
 72          * -1 means the first static_key_slow_inc() is in progress.
 73          *  static_key_enabled() must return true, so return 1 here.
 74          */
 75         int n = atomic_read(&key->enabled);
 76 
 77         return n >= 0 ? n : 1;
 78 }
 79 EXPORT_SYMBOL_GPL(static_key_count);
 80 
 81 void static_key_enable(struct static_key *key)
 82 {
 83         int count = static_key_count(key);
 84 
 85         WARN_ON_ONCE(count < 0 || count > 1);
 86 
 87         if (!count)
 88                 static_key_slow_inc(key);
 89 }
 90 EXPORT_SYMBOL_GPL(static_key_enable);
 91 
 92 void static_key_disable(struct static_key *key)
 93 {
 94         int count = static_key_count(key);
 95 
 96         WARN_ON_ONCE(count < 0 || count > 1);
 97 
 98         if (count)
 99                 static_key_slow_dec(key);
100 }
101 EXPORT_SYMBOL_GPL(static_key_disable);
102 
103 void static_key_slow_inc(struct static_key *key)
104 {
105         int v, v1;
106 
107         STATIC_KEY_CHECK_USE();
108 
109         /*
110          * Careful if we get concurrent static_key_slow_inc() calls;
111          * later calls must wait for the first one to _finish_ the
112          * jump_label_update() process.  At the same time, however,
113          * the jump_label_update() call below wants to see
114          * static_key_enabled(&key) for jumps to be updated properly.
115          *
116          * So give a special meaning to negative key->enabled: it sends
117          * static_key_slow_inc() down the slow path, and it is non-zero
118          * so it counts as "enabled" in jump_label_update().  Note that
119          * atomic_inc_unless_negative() checks >= 0, so roll our own.
120          */
121         for (v = atomic_read(&key->enabled); v > 0; v = v1) {
122                 v1 = atomic_cmpxchg(&key->enabled, v, v + 1);
123                 if (likely(v1 == v))
124                         return;
125         }
126 
127         jump_label_lock();
128         if (atomic_read(&key->enabled) == 0) {
129                 atomic_set(&key->enabled, -1);
130                 jump_label_update(key);
131                 atomic_set(&key->enabled, 1);
132         } else {
133                 atomic_inc(&key->enabled);
134         }
135         jump_label_unlock();
136 }
137 EXPORT_SYMBOL_GPL(static_key_slow_inc);
138 
139 static void __static_key_slow_dec(struct static_key *key,
140                 unsigned long rate_limit, struct delayed_work *work)
141 {
142         /*
143          * The negative count check is valid even when a negative
144          * key->enabled is in use by static_key_slow_inc(); a
145          * __static_key_slow_dec() before the first static_key_slow_inc()
146          * returns is unbalanced, because all other static_key_slow_inc()
147          * instances block while the update is in progress.
148          */
149         if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
150                 WARN(atomic_read(&key->enabled) < 0,
151                      "jump label: negative count!\n");
152                 return;
153         }
154 
155         if (rate_limit) {
156                 atomic_inc(&key->enabled);
157                 schedule_delayed_work(work, rate_limit);
158         } else {
159                 jump_label_update(key);
160         }
161         jump_label_unlock();
162 }
163 
164 static void jump_label_update_timeout(struct work_struct *work)
165 {
166         struct static_key_deferred *key =
167                 container_of(work, struct static_key_deferred, work.work);
168         __static_key_slow_dec(&key->key, 0, NULL);
169 }
170 
171 void static_key_slow_dec(struct static_key *key)
172 {
173         STATIC_KEY_CHECK_USE();
174         __static_key_slow_dec(key, 0, NULL);
175 }
176 EXPORT_SYMBOL_GPL(static_key_slow_dec);
177 
178 void static_key_slow_dec_deferred(struct static_key_deferred *key)
179 {
180         STATIC_KEY_CHECK_USE();
181         __static_key_slow_dec(&key->key, key->timeout, &key->work);
182 }
183 EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
184 
185 void static_key_deferred_flush(struct static_key_deferred *key)
186 {
187         STATIC_KEY_CHECK_USE();
188         flush_delayed_work(&key->work);
189 }
190 EXPORT_SYMBOL_GPL(static_key_deferred_flush);
191 
192 void jump_label_rate_limit(struct static_key_deferred *key,
193                 unsigned long rl)
194 {
195         STATIC_KEY_CHECK_USE();
196         key->timeout = rl;
197         INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
198 }
199 EXPORT_SYMBOL_GPL(jump_label_rate_limit);
200 
201 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
202 {
203         if (entry->code <= (unsigned long)end &&
204                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
205                 return 1;
206 
207         return 0;
208 }
209 
210 static int __jump_label_text_reserved(struct jump_entry *iter_start,
211                 struct jump_entry *iter_stop, void *start, void *end)
212 {
213         struct jump_entry *iter;
214 
215         iter = iter_start;
216         while (iter < iter_stop) {
217                 if (addr_conflict(iter, start, end))
218                         return 1;
219                 iter++;
220         }
221 
222         return 0;
223 }
224 
225 /*
226  * Update code which is definitely not currently executing.
227  * Architectures which need heavyweight synchronization to modify
228  * running code can override this to make the non-live update case
229  * cheaper.
230  */
231 void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
232                                             enum jump_label_type type)
233 {
234         arch_jump_label_transform(entry, type);
235 }
236 
237 static inline struct jump_entry *static_key_entries(struct static_key *key)
238 {
239         WARN_ON_ONCE(key->type & JUMP_TYPE_LINKED);
240         return (struct jump_entry *)(key->type & ~JUMP_TYPE_MASK);
241 }
242 
243 static inline bool static_key_type(struct static_key *key)
244 {
245         return key->type & JUMP_TYPE_TRUE;
246 }
247 
248 static inline bool static_key_linked(struct static_key *key)
249 {
250         return key->type & JUMP_TYPE_LINKED;
251 }
252 
253 static inline void static_key_clear_linked(struct static_key *key)
254 {
255         key->type &= ~JUMP_TYPE_LINKED;
256 }
257 
258 static inline void static_key_set_linked(struct static_key *key)
259 {
260         key->type |= JUMP_TYPE_LINKED;
261 }
262 
263 static inline struct static_key *jump_entry_key(struct jump_entry *entry)
264 {
265         return (struct static_key *)((unsigned long)entry->key & ~1UL);
266 }
267 
268 static bool jump_entry_branch(struct jump_entry *entry)
269 {
270         return (unsigned long)entry->key & 1UL;
271 }
272 
273 /***
274  * A 'struct static_key' uses a union such that it either points directly
275  * to a table of 'struct jump_entry' or to a linked list of modules which in
276  * turn point to 'struct jump_entry' tables.
277  *
278  * The two lower bits of the pointer are used to keep track of which pointer
279  * type is in use and to store the initial branch direction, we use an access
280  * function which preserves these bits.
281  */
282 static void static_key_set_entries(struct static_key *key,
283                                    struct jump_entry *entries)
284 {
285         unsigned long type;
286 
287         WARN_ON_ONCE((unsigned long)entries & JUMP_TYPE_MASK);
288         type = key->type & JUMP_TYPE_MASK;
289         key->entries = entries;
290         key->type |= type;
291 }
292 
293 static enum jump_label_type jump_label_type(struct jump_entry *entry)
294 {
295         struct static_key *key = jump_entry_key(entry);
296         bool enabled = static_key_enabled(key);
297         bool branch = jump_entry_branch(entry);
298 
299         /* See the comment in linux/jump_label.h */
300         return enabled ^ branch;
301 }
302 
303 static void __jump_label_update(struct static_key *key,
304                                 struct jump_entry *entry,
305                                 struct jump_entry *stop)
306 {
307         for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) {
308                 /*
309                  * entry->code set to 0 invalidates module init text sections
310                  * kernel_text_address() verifies we are not in core kernel
311                  * init code, see jump_label_invalidate_module_init().
312                  */
313                 if (entry->code && kernel_text_address(entry->code))
314                         arch_jump_label_transform(entry, jump_label_type(entry));
315         }
316 }
317 
318 void __init jump_label_init(void)
319 {
320         struct jump_entry *iter_start = __start___jump_table;
321         struct jump_entry *iter_stop = __stop___jump_table;
322         struct static_key *key = NULL;
323         struct jump_entry *iter;
324 
325         /*
326          * Since we are initializing the static_key.enabled field with
327          * with the 'raw' int values (to avoid pulling in atomic.h) in
328          * jump_label.h, let's make sure that is safe. There are only two
329          * cases to check since we initialize to 0 or 1.
330          */
331         BUILD_BUG_ON((int)ATOMIC_INIT(0) != 0);
332         BUILD_BUG_ON((int)ATOMIC_INIT(1) != 1);
333 
334         if (static_key_initialized)
335                 return;
336 
337         jump_label_lock();
338         jump_label_sort_entries(iter_start, iter_stop);
339 
340         for (iter = iter_start; iter < iter_stop; iter++) {
341                 struct static_key *iterk;
342 
343                 /* rewrite NOPs */
344                 if (jump_label_type(iter) == JUMP_LABEL_NOP)
345                         arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
346 
347                 iterk = jump_entry_key(iter);
348                 if (iterk == key)
349                         continue;
350 
351                 key = iterk;
352                 static_key_set_entries(key, iter);
353         }
354         static_key_initialized = true;
355         jump_label_unlock();
356 }
357 
358 #ifdef CONFIG_MODULES
359 
360 static enum jump_label_type jump_label_init_type(struct jump_entry *entry)
361 {
362         struct static_key *key = jump_entry_key(entry);
363         bool type = static_key_type(key);
364         bool branch = jump_entry_branch(entry);
365 
366         /* See the comment in linux/jump_label.h */
367         return type ^ branch;
368 }
369 
370 struct static_key_mod {
371         struct static_key_mod *next;
372         struct jump_entry *entries;
373         struct module *mod;
374 };
375 
376 static inline struct static_key_mod *static_key_mod(struct static_key *key)
377 {
378         WARN_ON_ONCE(!(key->type & JUMP_TYPE_LINKED));
379         return (struct static_key_mod *)(key->type & ~JUMP_TYPE_MASK);
380 }
381 
382 /***
383  * key->type and key->next are the same via union.
384  * This sets key->next and preserves the type bits.
385  *
386  * See additional comments above static_key_set_entries().
387  */
388 static void static_key_set_mod(struct static_key *key,
389                                struct static_key_mod *mod)
390 {
391         unsigned long type;
392 
393         WARN_ON_ONCE((unsigned long)mod & JUMP_TYPE_MASK);
394         type = key->type & JUMP_TYPE_MASK;
395         key->next = mod;
396         key->type |= type;
397 }
398 
399 static int __jump_label_mod_text_reserved(void *start, void *end)
400 {
401         struct module *mod;
402 
403         preempt_disable();
404         mod = __module_text_address((unsigned long)start);
405         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
406         preempt_enable();
407 
408         if (!mod)
409                 return 0;
410 
411 
412         return __jump_label_text_reserved(mod->jump_entries,
413                                 mod->jump_entries + mod->num_jump_entries,
414                                 start, end);
415 }
416 
417 static void __jump_label_mod_update(struct static_key *key)
418 {
419         struct static_key_mod *mod;
420 
421         for (mod = static_key_mod(key); mod; mod = mod->next) {
422                 struct jump_entry *stop;
423                 struct module *m;
424 
425                 /*
426                  * NULL if the static_key is defined in a module
427                  * that does not use it
428                  */
429                 if (!mod->entries)
430                         continue;
431 
432                 m = mod->mod;
433                 if (!m)
434                         stop = __stop___jump_table;
435                 else
436                         stop = m->jump_entries + m->num_jump_entries;
437                 __jump_label_update(key, mod->entries, stop);
438         }
439 }
440 
441 /***
442  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
443  * @mod: module to patch
444  *
445  * Allow for run-time selection of the optimal nops. Before the module
446  * loads patch these with arch_get_jump_label_nop(), which is specified by
447  * the arch specific jump label code.
448  */
449 void jump_label_apply_nops(struct module *mod)
450 {
451         struct jump_entry *iter_start = mod->jump_entries;
452         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
453         struct jump_entry *iter;
454 
455         /* if the module doesn't have jump label entries, just return */
456         if (iter_start == iter_stop)
457                 return;
458 
459         for (iter = iter_start; iter < iter_stop; iter++) {
460                 /* Only write NOPs for arch_branch_static(). */
461                 if (jump_label_init_type(iter) == JUMP_LABEL_NOP)
462                         arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
463         }
464 }
465 
466 static int jump_label_add_module(struct module *mod)
467 {
468         struct jump_entry *iter_start = mod->jump_entries;
469         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
470         struct jump_entry *iter;
471         struct static_key *key = NULL;
472         struct static_key_mod *jlm, *jlm2;
473 
474         /* if the module doesn't have jump label entries, just return */
475         if (iter_start == iter_stop)
476                 return 0;
477 
478         jump_label_sort_entries(iter_start, iter_stop);
479 
480         for (iter = iter_start; iter < iter_stop; iter++) {
481                 struct static_key *iterk;
482 
483                 iterk = jump_entry_key(iter);
484                 if (iterk == key)
485                         continue;
486 
487                 key = iterk;
488                 if (within_module(iter->key, mod)) {
489                         static_key_set_entries(key, iter);
490                         continue;
491                 }
492                 jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
493                 if (!jlm)
494                         return -ENOMEM;
495                 if (!static_key_linked(key)) {
496                         jlm2 = kzalloc(sizeof(struct static_key_mod),
497                                        GFP_KERNEL);
498                         if (!jlm2) {
499                                 kfree(jlm);
500                                 return -ENOMEM;
501                         }
502                         preempt_disable();
503                         jlm2->mod = __module_address((unsigned long)key);
504                         preempt_enable();
505                         jlm2->entries = static_key_entries(key);
506                         jlm2->next = NULL;
507                         static_key_set_mod(key, jlm2);
508                         static_key_set_linked(key);
509                 }
510                 jlm->mod = mod;
511                 jlm->entries = iter;
512                 jlm->next = static_key_mod(key);
513                 static_key_set_mod(key, jlm);
514                 static_key_set_linked(key);
515 
516                 /* Only update if we've changed from our initial state */
517                 if (jump_label_type(iter) != jump_label_init_type(iter))
518                         __jump_label_update(key, iter, iter_stop);
519         }
520 
521         return 0;
522 }
523 
524 static void jump_label_del_module(struct module *mod)
525 {
526         struct jump_entry *iter_start = mod->jump_entries;
527         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
528         struct jump_entry *iter;
529         struct static_key *key = NULL;
530         struct static_key_mod *jlm, **prev;
531 
532         for (iter = iter_start; iter < iter_stop; iter++) {
533                 if (jump_entry_key(iter) == key)
534                         continue;
535 
536                 key = jump_entry_key(iter);
537 
538                 if (within_module(iter->key, mod))
539                         continue;
540 
541                 /* No memory during module load */
542                 if (WARN_ON(!static_key_linked(key)))
543                         continue;
544 
545                 prev = &key->next;
546                 jlm = static_key_mod(key);
547 
548                 while (jlm && jlm->mod != mod) {
549                         prev = &jlm->next;
550                         jlm = jlm->next;
551                 }
552 
553                 /* No memory during module load */
554                 if (WARN_ON(!jlm))
555                         continue;
556 
557                 if (prev == &key->next)
558                         static_key_set_mod(key, jlm->next);
559                 else
560                         *prev = jlm->next;
561 
562                 kfree(jlm);
563 
564                 jlm = static_key_mod(key);
565                 /* if only one etry is left, fold it back into the static_key */
566                 if (jlm->next == NULL) {
567                         static_key_set_entries(key, jlm->entries);
568                         static_key_clear_linked(key);
569                         kfree(jlm);
570                 }
571         }
572 }
573 
574 static void jump_label_invalidate_module_init(struct module *mod)
575 {
576         struct jump_entry *iter_start = mod->jump_entries;
577         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
578         struct jump_entry *iter;
579 
580         for (iter = iter_start; iter < iter_stop; iter++) {
581                 if (within_module_init(iter->code, mod))
582                         iter->code = 0;
583         }
584 }
585 
586 static int
587 jump_label_module_notify(struct notifier_block *self, unsigned long val,
588                          void *data)
589 {
590         struct module *mod = data;
591         int ret = 0;
592 
593         switch (val) {
594         case MODULE_STATE_COMING:
595                 jump_label_lock();
596                 ret = jump_label_add_module(mod);
597                 if (ret) {
598                         WARN(1, "Failed to allocatote memory: jump_label may not work properly.\n");
599                         jump_label_del_module(mod);
600                 }
601                 jump_label_unlock();
602                 break;
603         case MODULE_STATE_GOING:
604                 jump_label_lock();
605                 jump_label_del_module(mod);
606                 jump_label_unlock();
607                 break;
608         case MODULE_STATE_LIVE:
609                 jump_label_lock();
610                 jump_label_invalidate_module_init(mod);
611                 jump_label_unlock();
612                 break;
613         }
614 
615         return notifier_from_errno(ret);
616 }
617 
618 static struct notifier_block jump_label_module_nb = {
619         .notifier_call = jump_label_module_notify,
620         .priority = 1, /* higher than tracepoints */
621 };
622 
623 static __init int jump_label_init_module(void)
624 {
625         return register_module_notifier(&jump_label_module_nb);
626 }
627 early_initcall(jump_label_init_module);
628 
629 #endif /* CONFIG_MODULES */
630 
631 /***
632  * jump_label_text_reserved - check if addr range is reserved
633  * @start: start text addr
634  * @end: end text addr
635  *
636  * checks if the text addr located between @start and @end
637  * overlaps with any of the jump label patch addresses. Code
638  * that wants to modify kernel text should first verify that
639  * it does not overlap with any of the jump label addresses.
640  * Caller must hold jump_label_mutex.
641  *
642  * returns 1 if there is an overlap, 0 otherwise
643  */
644 int jump_label_text_reserved(void *start, void *end)
645 {
646         int ret = __jump_label_text_reserved(__start___jump_table,
647                         __stop___jump_table, start, end);
648 
649         if (ret)
650                 return ret;
651 
652 #ifdef CONFIG_MODULES
653         ret = __jump_label_mod_text_reserved(start, end);
654 #endif
655         return ret;
656 }
657 
658 static void jump_label_update(struct static_key *key)
659 {
660         struct jump_entry *stop = __stop___jump_table;
661         struct jump_entry *entry;
662 #ifdef CONFIG_MODULES
663         struct module *mod;
664 
665         if (static_key_linked(key)) {
666                 __jump_label_mod_update(key);
667                 return;
668         }
669 
670         preempt_disable();
671         mod = __module_address((unsigned long)key);
672         if (mod)
673                 stop = mod->jump_entries + mod->num_jump_entries;
674         preempt_enable();
675 #endif
676         entry = static_key_entries(key);
677         /* if there are no users, entry can be NULL */
678         if (entry)
679                 __jump_label_update(key, entry, stop);
680 }
681 
682 #ifdef CONFIG_STATIC_KEYS_SELFTEST
683 static DEFINE_STATIC_KEY_TRUE(sk_true);
684 static DEFINE_STATIC_KEY_FALSE(sk_false);
685 
686 static __init int jump_label_test(void)
687 {
688         int i;
689 
690         for (i = 0; i < 2; i++) {
691                 WARN_ON(static_key_enabled(&sk_true.key) != true);
692                 WARN_ON(static_key_enabled(&sk_false.key) != false);
693 
694                 WARN_ON(!static_branch_likely(&sk_true));
695                 WARN_ON(!static_branch_unlikely(&sk_true));
696                 WARN_ON(static_branch_likely(&sk_false));
697                 WARN_ON(static_branch_unlikely(&sk_false));
698 
699                 static_branch_disable(&sk_true);
700                 static_branch_enable(&sk_false);
701 
702                 WARN_ON(static_key_enabled(&sk_true.key) == true);
703                 WARN_ON(static_key_enabled(&sk_false.key) == false);
704 
705                 WARN_ON(static_branch_likely(&sk_true));
706                 WARN_ON(static_branch_unlikely(&sk_true));
707                 WARN_ON(!static_branch_likely(&sk_false));
708                 WARN_ON(!static_branch_unlikely(&sk_false));
709 
710                 static_branch_enable(&sk_true);
711                 static_branch_disable(&sk_false);
712         }
713 
714         return 0;
715 }
716 late_initcall(jump_label_test);
717 #endif /* STATIC_KEYS_SELFTEST */
718 
719 #endif /* HAVE_JUMP_LABEL */
720 

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