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Linux/kernel/jump_label.c

  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         return (struct jump_entry *)((unsigned long)key->entries & ~JUMP_TYPE_MASK);
240 }
241 
242 static inline bool static_key_type(struct static_key *key)
243 {
244         return (unsigned long)key->entries & JUMP_TYPE_MASK;
245 }
246 
247 static inline struct static_key *jump_entry_key(struct jump_entry *entry)
248 {
249         return (struct static_key *)((unsigned long)entry->key & ~1UL);
250 }
251 
252 static bool jump_entry_branch(struct jump_entry *entry)
253 {
254         return (unsigned long)entry->key & 1UL;
255 }
256 
257 static enum jump_label_type jump_label_type(struct jump_entry *entry)
258 {
259         struct static_key *key = jump_entry_key(entry);
260         bool enabled = static_key_enabled(key);
261         bool branch = jump_entry_branch(entry);
262 
263         /* See the comment in linux/jump_label.h */
264         return enabled ^ branch;
265 }
266 
267 static void __jump_label_update(struct static_key *key,
268                                 struct jump_entry *entry,
269                                 struct jump_entry *stop)
270 {
271         for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) {
272                 /*
273                  * entry->code set to 0 invalidates module init text sections
274                  * kernel_text_address() verifies we are not in core kernel
275                  * init code, see jump_label_invalidate_module_init().
276                  */
277                 if (entry->code && kernel_text_address(entry->code))
278                         arch_jump_label_transform(entry, jump_label_type(entry));
279         }
280 }
281 
282 void __init jump_label_init(void)
283 {
284         struct jump_entry *iter_start = __start___jump_table;
285         struct jump_entry *iter_stop = __stop___jump_table;
286         struct static_key *key = NULL;
287         struct jump_entry *iter;
288 
289         /*
290          * Since we are initializing the static_key.enabled field with
291          * with the 'raw' int values (to avoid pulling in atomic.h) in
292          * jump_label.h, let's make sure that is safe. There are only two
293          * cases to check since we initialize to 0 or 1.
294          */
295         BUILD_BUG_ON((int)ATOMIC_INIT(0) != 0);
296         BUILD_BUG_ON((int)ATOMIC_INIT(1) != 1);
297 
298         if (static_key_initialized)
299                 return;
300 
301         jump_label_lock();
302         jump_label_sort_entries(iter_start, iter_stop);
303 
304         for (iter = iter_start; iter < iter_stop; iter++) {
305                 struct static_key *iterk;
306 
307                 /* rewrite NOPs */
308                 if (jump_label_type(iter) == JUMP_LABEL_NOP)
309                         arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
310 
311                 iterk = jump_entry_key(iter);
312                 if (iterk == key)
313                         continue;
314 
315                 key = iterk;
316                 /*
317                  * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
318                  */
319                 *((unsigned long *)&key->entries) += (unsigned long)iter;
320 #ifdef CONFIG_MODULES
321                 key->next = NULL;
322 #endif
323         }
324         static_key_initialized = true;
325         jump_label_unlock();
326 }
327 
328 #ifdef CONFIG_MODULES
329 
330 static enum jump_label_type jump_label_init_type(struct jump_entry *entry)
331 {
332         struct static_key *key = jump_entry_key(entry);
333         bool type = static_key_type(key);
334         bool branch = jump_entry_branch(entry);
335 
336         /* See the comment in linux/jump_label.h */
337         return type ^ branch;
338 }
339 
340 struct static_key_mod {
341         struct static_key_mod *next;
342         struct jump_entry *entries;
343         struct module *mod;
344 };
345 
346 static int __jump_label_mod_text_reserved(void *start, void *end)
347 {
348         struct module *mod;
349 
350         preempt_disable();
351         mod = __module_text_address((unsigned long)start);
352         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
353         preempt_enable();
354 
355         if (!mod)
356                 return 0;
357 
358 
359         return __jump_label_text_reserved(mod->jump_entries,
360                                 mod->jump_entries + mod->num_jump_entries,
361                                 start, end);
362 }
363 
364 static void __jump_label_mod_update(struct static_key *key)
365 {
366         struct static_key_mod *mod;
367 
368         for (mod = key->next; mod; mod = mod->next) {
369                 struct module *m = mod->mod;
370 
371                 __jump_label_update(key, mod->entries,
372                                     m->jump_entries + m->num_jump_entries);
373         }
374 }
375 
376 /***
377  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
378  * @mod: module to patch
379  *
380  * Allow for run-time selection of the optimal nops. Before the module
381  * loads patch these with arch_get_jump_label_nop(), which is specified by
382  * the arch specific jump label code.
383  */
384 void jump_label_apply_nops(struct module *mod)
385 {
386         struct jump_entry *iter_start = mod->jump_entries;
387         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
388         struct jump_entry *iter;
389 
390         /* if the module doesn't have jump label entries, just return */
391         if (iter_start == iter_stop)
392                 return;
393 
394         for (iter = iter_start; iter < iter_stop; iter++) {
395                 /* Only write NOPs for arch_branch_static(). */
396                 if (jump_label_init_type(iter) == JUMP_LABEL_NOP)
397                         arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
398         }
399 }
400 
401 static int jump_label_add_module(struct module *mod)
402 {
403         struct jump_entry *iter_start = mod->jump_entries;
404         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
405         struct jump_entry *iter;
406         struct static_key *key = NULL;
407         struct static_key_mod *jlm;
408 
409         /* if the module doesn't have jump label entries, just return */
410         if (iter_start == iter_stop)
411                 return 0;
412 
413         jump_label_sort_entries(iter_start, iter_stop);
414 
415         for (iter = iter_start; iter < iter_stop; iter++) {
416                 struct static_key *iterk;
417 
418                 iterk = jump_entry_key(iter);
419                 if (iterk == key)
420                         continue;
421 
422                 key = iterk;
423                 if (within_module(iter->key, mod)) {
424                         /*
425                          * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
426                          */
427                         *((unsigned long *)&key->entries) += (unsigned long)iter;
428                         key->next = NULL;
429                         continue;
430                 }
431                 jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
432                 if (!jlm)
433                         return -ENOMEM;
434                 jlm->mod = mod;
435                 jlm->entries = iter;
436                 jlm->next = key->next;
437                 key->next = jlm;
438 
439                 /* Only update if we've changed from our initial state */
440                 if (jump_label_type(iter) != jump_label_init_type(iter))
441                         __jump_label_update(key, iter, iter_stop);
442         }
443 
444         return 0;
445 }
446 
447 static void jump_label_del_module(struct module *mod)
448 {
449         struct jump_entry *iter_start = mod->jump_entries;
450         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
451         struct jump_entry *iter;
452         struct static_key *key = NULL;
453         struct static_key_mod *jlm, **prev;
454 
455         for (iter = iter_start; iter < iter_stop; iter++) {
456                 if (jump_entry_key(iter) == key)
457                         continue;
458 
459                 key = jump_entry_key(iter);
460 
461                 if (within_module(iter->key, mod))
462                         continue;
463 
464                 prev = &key->next;
465                 jlm = key->next;
466 
467                 while (jlm && jlm->mod != mod) {
468                         prev = &jlm->next;
469                         jlm = jlm->next;
470                 }
471 
472                 if (jlm) {
473                         *prev = jlm->next;
474                         kfree(jlm);
475                 }
476         }
477 }
478 
479 static void jump_label_invalidate_module_init(struct module *mod)
480 {
481         struct jump_entry *iter_start = mod->jump_entries;
482         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
483         struct jump_entry *iter;
484 
485         for (iter = iter_start; iter < iter_stop; iter++) {
486                 if (within_module_init(iter->code, mod))
487                         iter->code = 0;
488         }
489 }
490 
491 static int
492 jump_label_module_notify(struct notifier_block *self, unsigned long val,
493                          void *data)
494 {
495         struct module *mod = data;
496         int ret = 0;
497 
498         switch (val) {
499         case MODULE_STATE_COMING:
500                 jump_label_lock();
501                 ret = jump_label_add_module(mod);
502                 if (ret)
503                         jump_label_del_module(mod);
504                 jump_label_unlock();
505                 break;
506         case MODULE_STATE_GOING:
507                 jump_label_lock();
508                 jump_label_del_module(mod);
509                 jump_label_unlock();
510                 break;
511         case MODULE_STATE_LIVE:
512                 jump_label_lock();
513                 jump_label_invalidate_module_init(mod);
514                 jump_label_unlock();
515                 break;
516         }
517 
518         return notifier_from_errno(ret);
519 }
520 
521 static struct notifier_block jump_label_module_nb = {
522         .notifier_call = jump_label_module_notify,
523         .priority = 1, /* higher than tracepoints */
524 };
525 
526 static __init int jump_label_init_module(void)
527 {
528         return register_module_notifier(&jump_label_module_nb);
529 }
530 early_initcall(jump_label_init_module);
531 
532 #endif /* CONFIG_MODULES */
533 
534 /***
535  * jump_label_text_reserved - check if addr range is reserved
536  * @start: start text addr
537  * @end: end text addr
538  *
539  * checks if the text addr located between @start and @end
540  * overlaps with any of the jump label patch addresses. Code
541  * that wants to modify kernel text should first verify that
542  * it does not overlap with any of the jump label addresses.
543  * Caller must hold jump_label_mutex.
544  *
545  * returns 1 if there is an overlap, 0 otherwise
546  */
547 int jump_label_text_reserved(void *start, void *end)
548 {
549         int ret = __jump_label_text_reserved(__start___jump_table,
550                         __stop___jump_table, start, end);
551 
552         if (ret)
553                 return ret;
554 
555 #ifdef CONFIG_MODULES
556         ret = __jump_label_mod_text_reserved(start, end);
557 #endif
558         return ret;
559 }
560 
561 static void jump_label_update(struct static_key *key)
562 {
563         struct jump_entry *stop = __stop___jump_table;
564         struct jump_entry *entry = static_key_entries(key);
565 #ifdef CONFIG_MODULES
566         struct module *mod;
567 
568         __jump_label_mod_update(key);
569 
570         preempt_disable();
571         mod = __module_address((unsigned long)key);
572         if (mod)
573                 stop = mod->jump_entries + mod->num_jump_entries;
574         preempt_enable();
575 #endif
576         /* if there are no users, entry can be NULL */
577         if (entry)
578                 __jump_label_update(key, entry, stop);
579 }
580 
581 #ifdef CONFIG_STATIC_KEYS_SELFTEST
582 static DEFINE_STATIC_KEY_TRUE(sk_true);
583 static DEFINE_STATIC_KEY_FALSE(sk_false);
584 
585 static __init int jump_label_test(void)
586 {
587         int i;
588 
589         for (i = 0; i < 2; i++) {
590                 WARN_ON(static_key_enabled(&sk_true.key) != true);
591                 WARN_ON(static_key_enabled(&sk_false.key) != false);
592 
593                 WARN_ON(!static_branch_likely(&sk_true));
594                 WARN_ON(!static_branch_unlikely(&sk_true));
595                 WARN_ON(static_branch_likely(&sk_false));
596                 WARN_ON(static_branch_unlikely(&sk_false));
597 
598                 static_branch_disable(&sk_true);
599                 static_branch_enable(&sk_false);
600 
601                 WARN_ON(static_key_enabled(&sk_true.key) == true);
602                 WARN_ON(static_key_enabled(&sk_false.key) == false);
603 
604                 WARN_ON(static_branch_likely(&sk_true));
605                 WARN_ON(static_branch_unlikely(&sk_true));
606                 WARN_ON(!static_branch_likely(&sk_false));
607                 WARN_ON(!static_branch_unlikely(&sk_false));
608 
609                 static_branch_enable(&sk_true);
610                 static_branch_disable(&sk_false);
611         }
612 
613         return 0;
614 }
615 late_initcall(jump_label_test);
616 #endif /* STATIC_KEYS_SELFTEST */
617 
618 #endif /* HAVE_JUMP_LABEL */
619 

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