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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 
 18 #ifdef HAVE_JUMP_LABEL
 19 
 20 /* mutex to protect coming/going of the the jump_label table */
 21 static DEFINE_MUTEX(jump_label_mutex);
 22 
 23 void jump_label_lock(void)
 24 {
 25         mutex_lock(&jump_label_mutex);
 26 }
 27 
 28 void jump_label_unlock(void)
 29 {
 30         mutex_unlock(&jump_label_mutex);
 31 }
 32 
 33 static int jump_label_cmp(const void *a, const void *b)
 34 {
 35         const struct jump_entry *jea = a;
 36         const struct jump_entry *jeb = b;
 37 
 38         if (jea->key < jeb->key)
 39                 return -1;
 40 
 41         if (jea->key > jeb->key)
 42                 return 1;
 43 
 44         return 0;
 45 }
 46 
 47 static void
 48 jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
 49 {
 50         unsigned long size;
 51 
 52         size = (((unsigned long)stop - (unsigned long)start)
 53                                         / sizeof(struct jump_entry));
 54         sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
 55 }
 56 
 57 static void jump_label_update(struct static_key *key);
 58 
 59 void static_key_slow_inc(struct static_key *key)
 60 {
 61         STATIC_KEY_CHECK_USE();
 62         if (atomic_inc_not_zero(&key->enabled))
 63                 return;
 64 
 65         jump_label_lock();
 66         if (atomic_inc_return(&key->enabled) == 1)
 67                 jump_label_update(key);
 68         jump_label_unlock();
 69 }
 70 EXPORT_SYMBOL_GPL(static_key_slow_inc);
 71 
 72 static void __static_key_slow_dec(struct static_key *key,
 73                 unsigned long rate_limit, struct delayed_work *work)
 74 {
 75         if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
 76                 WARN(atomic_read(&key->enabled) < 0,
 77                      "jump label: negative count!\n");
 78                 return;
 79         }
 80 
 81         if (rate_limit) {
 82                 atomic_inc(&key->enabled);
 83                 schedule_delayed_work(work, rate_limit);
 84         } else {
 85                 jump_label_update(key);
 86         }
 87         jump_label_unlock();
 88 }
 89 
 90 static void jump_label_update_timeout(struct work_struct *work)
 91 {
 92         struct static_key_deferred *key =
 93                 container_of(work, struct static_key_deferred, work.work);
 94         __static_key_slow_dec(&key->key, 0, NULL);
 95 }
 96 
 97 void static_key_slow_dec(struct static_key *key)
 98 {
 99         STATIC_KEY_CHECK_USE();
100         __static_key_slow_dec(key, 0, NULL);
101 }
102 EXPORT_SYMBOL_GPL(static_key_slow_dec);
103 
104 void static_key_slow_dec_deferred(struct static_key_deferred *key)
105 {
106         STATIC_KEY_CHECK_USE();
107         __static_key_slow_dec(&key->key, key->timeout, &key->work);
108 }
109 EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
110 
111 void jump_label_rate_limit(struct static_key_deferred *key,
112                 unsigned long rl)
113 {
114         STATIC_KEY_CHECK_USE();
115         key->timeout = rl;
116         INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
117 }
118 EXPORT_SYMBOL_GPL(jump_label_rate_limit);
119 
120 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
121 {
122         if (entry->code <= (unsigned long)end &&
123                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
124                 return 1;
125 
126         return 0;
127 }
128 
129 static int __jump_label_text_reserved(struct jump_entry *iter_start,
130                 struct jump_entry *iter_stop, void *start, void *end)
131 {
132         struct jump_entry *iter;
133 
134         iter = iter_start;
135         while (iter < iter_stop) {
136                 if (addr_conflict(iter, start, end))
137                         return 1;
138                 iter++;
139         }
140 
141         return 0;
142 }
143 
144 /*
145  * Update code which is definitely not currently executing.
146  * Architectures which need heavyweight synchronization to modify
147  * running code can override this to make the non-live update case
148  * cheaper.
149  */
150 void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
151                                             enum jump_label_type type)
152 {
153         arch_jump_label_transform(entry, type);
154 }
155 
156 static inline struct jump_entry *static_key_entries(struct static_key *key)
157 {
158         return (struct jump_entry *)((unsigned long)key->entries & ~JUMP_TYPE_MASK);
159 }
160 
161 static inline bool static_key_type(struct static_key *key)
162 {
163         return (unsigned long)key->entries & JUMP_TYPE_MASK;
164 }
165 
166 static inline struct static_key *jump_entry_key(struct jump_entry *entry)
167 {
168         return (struct static_key *)((unsigned long)entry->key & ~1UL);
169 }
170 
171 static bool jump_entry_branch(struct jump_entry *entry)
172 {
173         return (unsigned long)entry->key & 1UL;
174 }
175 
176 static enum jump_label_type jump_label_type(struct jump_entry *entry)
177 {
178         struct static_key *key = jump_entry_key(entry);
179         bool enabled = static_key_enabled(key);
180         bool branch = jump_entry_branch(entry);
181 
182         /* See the comment in linux/jump_label.h */
183         return enabled ^ branch;
184 }
185 
186 static void __jump_label_update(struct static_key *key,
187                                 struct jump_entry *entry,
188                                 struct jump_entry *stop)
189 {
190         for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) {
191                 /*
192                  * entry->code set to 0 invalidates module init text sections
193                  * kernel_text_address() verifies we are not in core kernel
194                  * init code, see jump_label_invalidate_module_init().
195                  */
196                 if (entry->code && kernel_text_address(entry->code))
197                         arch_jump_label_transform(entry, jump_label_type(entry));
198         }
199 }
200 
201 void __init jump_label_init(void)
202 {
203         struct jump_entry *iter_start = __start___jump_table;
204         struct jump_entry *iter_stop = __stop___jump_table;
205         struct static_key *key = NULL;
206         struct jump_entry *iter;
207 
208         jump_label_lock();
209         jump_label_sort_entries(iter_start, iter_stop);
210 
211         for (iter = iter_start; iter < iter_stop; iter++) {
212                 struct static_key *iterk;
213 
214                 /* rewrite NOPs */
215                 if (jump_label_type(iter) == JUMP_LABEL_NOP)
216                         arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
217 
218                 iterk = jump_entry_key(iter);
219                 if (iterk == key)
220                         continue;
221 
222                 key = iterk;
223                 /*
224                  * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
225                  */
226                 *((unsigned long *)&key->entries) += (unsigned long)iter;
227 #ifdef CONFIG_MODULES
228                 key->next = NULL;
229 #endif
230         }
231         static_key_initialized = true;
232         jump_label_unlock();
233 }
234 
235 #ifdef CONFIG_MODULES
236 
237 static enum jump_label_type jump_label_init_type(struct jump_entry *entry)
238 {
239         struct static_key *key = jump_entry_key(entry);
240         bool type = static_key_type(key);
241         bool branch = jump_entry_branch(entry);
242 
243         /* See the comment in linux/jump_label.h */
244         return type ^ branch;
245 }
246 
247 struct static_key_mod {
248         struct static_key_mod *next;
249         struct jump_entry *entries;
250         struct module *mod;
251 };
252 
253 static int __jump_label_mod_text_reserved(void *start, void *end)
254 {
255         struct module *mod;
256 
257         mod = __module_text_address((unsigned long)start);
258         if (!mod)
259                 return 0;
260 
261         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
262 
263         return __jump_label_text_reserved(mod->jump_entries,
264                                 mod->jump_entries + mod->num_jump_entries,
265                                 start, end);
266 }
267 
268 static void __jump_label_mod_update(struct static_key *key)
269 {
270         struct static_key_mod *mod;
271 
272         for (mod = key->next; mod; mod = mod->next) {
273                 struct module *m = mod->mod;
274 
275                 __jump_label_update(key, mod->entries,
276                                     m->jump_entries + m->num_jump_entries);
277         }
278 }
279 
280 /***
281  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
282  * @mod: module to patch
283  *
284  * Allow for run-time selection of the optimal nops. Before the module
285  * loads patch these with arch_get_jump_label_nop(), which is specified by
286  * the arch specific jump label code.
287  */
288 void jump_label_apply_nops(struct module *mod)
289 {
290         struct jump_entry *iter_start = mod->jump_entries;
291         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
292         struct jump_entry *iter;
293 
294         /* if the module doesn't have jump label entries, just return */
295         if (iter_start == iter_stop)
296                 return;
297 
298         for (iter = iter_start; iter < iter_stop; iter++) {
299                 /* Only write NOPs for arch_branch_static(). */
300                 if (jump_label_init_type(iter) == JUMP_LABEL_NOP)
301                         arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
302         }
303 }
304 
305 static int jump_label_add_module(struct module *mod)
306 {
307         struct jump_entry *iter_start = mod->jump_entries;
308         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
309         struct jump_entry *iter;
310         struct static_key *key = NULL;
311         struct static_key_mod *jlm;
312 
313         /* if the module doesn't have jump label entries, just return */
314         if (iter_start == iter_stop)
315                 return 0;
316 
317         jump_label_sort_entries(iter_start, iter_stop);
318 
319         for (iter = iter_start; iter < iter_stop; iter++) {
320                 struct static_key *iterk;
321 
322                 iterk = jump_entry_key(iter);
323                 if (iterk == key)
324                         continue;
325 
326                 key = iterk;
327                 if (within_module(iter->key, mod)) {
328                         /*
329                          * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
330                          */
331                         *((unsigned long *)&key->entries) += (unsigned long)iter;
332                         key->next = NULL;
333                         continue;
334                 }
335                 jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
336                 if (!jlm)
337                         return -ENOMEM;
338                 jlm->mod = mod;
339                 jlm->entries = iter;
340                 jlm->next = key->next;
341                 key->next = jlm;
342 
343                 /* Only update if we've changed from our initial state */
344                 if (jump_label_type(iter) != jump_label_init_type(iter))
345                         __jump_label_update(key, iter, iter_stop);
346         }
347 
348         return 0;
349 }
350 
351 static void jump_label_del_module(struct module *mod)
352 {
353         struct jump_entry *iter_start = mod->jump_entries;
354         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
355         struct jump_entry *iter;
356         struct static_key *key = NULL;
357         struct static_key_mod *jlm, **prev;
358 
359         for (iter = iter_start; iter < iter_stop; iter++) {
360                 if (jump_entry_key(iter) == key)
361                         continue;
362 
363                 key = jump_entry_key(iter);
364 
365                 if (within_module(iter->key, mod))
366                         continue;
367 
368                 prev = &key->next;
369                 jlm = key->next;
370 
371                 while (jlm && jlm->mod != mod) {
372                         prev = &jlm->next;
373                         jlm = jlm->next;
374                 }
375 
376                 if (jlm) {
377                         *prev = jlm->next;
378                         kfree(jlm);
379                 }
380         }
381 }
382 
383 static void jump_label_invalidate_module_init(struct module *mod)
384 {
385         struct jump_entry *iter_start = mod->jump_entries;
386         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
387         struct jump_entry *iter;
388 
389         for (iter = iter_start; iter < iter_stop; iter++) {
390                 if (within_module_init(iter->code, mod))
391                         iter->code = 0;
392         }
393 }
394 
395 static int
396 jump_label_module_notify(struct notifier_block *self, unsigned long val,
397                          void *data)
398 {
399         struct module *mod = data;
400         int ret = 0;
401 
402         switch (val) {
403         case MODULE_STATE_COMING:
404                 jump_label_lock();
405                 ret = jump_label_add_module(mod);
406                 if (ret)
407                         jump_label_del_module(mod);
408                 jump_label_unlock();
409                 break;
410         case MODULE_STATE_GOING:
411                 jump_label_lock();
412                 jump_label_del_module(mod);
413                 jump_label_unlock();
414                 break;
415         case MODULE_STATE_LIVE:
416                 jump_label_lock();
417                 jump_label_invalidate_module_init(mod);
418                 jump_label_unlock();
419                 break;
420         }
421 
422         return notifier_from_errno(ret);
423 }
424 
425 struct notifier_block jump_label_module_nb = {
426         .notifier_call = jump_label_module_notify,
427         .priority = 1, /* higher than tracepoints */
428 };
429 
430 static __init int jump_label_init_module(void)
431 {
432         return register_module_notifier(&jump_label_module_nb);
433 }
434 early_initcall(jump_label_init_module);
435 
436 #endif /* CONFIG_MODULES */
437 
438 /***
439  * jump_label_text_reserved - check if addr range is reserved
440  * @start: start text addr
441  * @end: end text addr
442  *
443  * checks if the text addr located between @start and @end
444  * overlaps with any of the jump label patch addresses. Code
445  * that wants to modify kernel text should first verify that
446  * it does not overlap with any of the jump label addresses.
447  * Caller must hold jump_label_mutex.
448  *
449  * returns 1 if there is an overlap, 0 otherwise
450  */
451 int jump_label_text_reserved(void *start, void *end)
452 {
453         int ret = __jump_label_text_reserved(__start___jump_table,
454                         __stop___jump_table, start, end);
455 
456         if (ret)
457                 return ret;
458 
459 #ifdef CONFIG_MODULES
460         ret = __jump_label_mod_text_reserved(start, end);
461 #endif
462         return ret;
463 }
464 
465 static void jump_label_update(struct static_key *key)
466 {
467         struct jump_entry *stop = __stop___jump_table;
468         struct jump_entry *entry = static_key_entries(key);
469 #ifdef CONFIG_MODULES
470         struct module *mod;
471 
472         __jump_label_mod_update(key);
473 
474         preempt_disable();
475         mod = __module_address((unsigned long)key);
476         if (mod)
477                 stop = mod->jump_entries + mod->num_jump_entries;
478         preempt_enable();
479 #endif
480         /* if there are no users, entry can be NULL */
481         if (entry)
482                 __jump_label_update(key, entry, stop);
483 }
484 
485 #ifdef CONFIG_STATIC_KEYS_SELFTEST
486 static DEFINE_STATIC_KEY_TRUE(sk_true);
487 static DEFINE_STATIC_KEY_FALSE(sk_false);
488 
489 static __init int jump_label_test(void)
490 {
491         int i;
492 
493         for (i = 0; i < 2; i++) {
494                 WARN_ON(static_key_enabled(&sk_true.key) != true);
495                 WARN_ON(static_key_enabled(&sk_false.key) != false);
496 
497                 WARN_ON(!static_branch_likely(&sk_true));
498                 WARN_ON(!static_branch_unlikely(&sk_true));
499                 WARN_ON(static_branch_likely(&sk_false));
500                 WARN_ON(static_branch_unlikely(&sk_false));
501 
502                 static_branch_disable(&sk_true);
503                 static_branch_enable(&sk_false);
504 
505                 WARN_ON(static_key_enabled(&sk_true.key) == true);
506                 WARN_ON(static_key_enabled(&sk_false.key) == false);
507 
508                 WARN_ON(static_branch_likely(&sk_true));
509                 WARN_ON(static_branch_unlikely(&sk_true));
510                 WARN_ON(!static_branch_likely(&sk_false));
511                 WARN_ON(!static_branch_unlikely(&sk_false));
512 
513                 static_branch_enable(&sk_true);
514                 static_branch_disable(&sk_false);
515         }
516 
517         return 0;
518 }
519 late_initcall(jump_label_test);
520 #endif /* STATIC_KEYS_SELFTEST */
521 
522 #endif /* HAVE_JUMP_LABEL */
523 

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