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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 <pzijlstr@redhat.com>
  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, int enable);
 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_read(&key->enabled) == 0) {
 67                 if (!jump_label_get_branch_default(key))
 68                         jump_label_update(key, JUMP_LABEL_ENABLE);
 69                 else
 70                         jump_label_update(key, JUMP_LABEL_DISABLE);
 71         }
 72         atomic_inc(&key->enabled);
 73         jump_label_unlock();
 74 }
 75 EXPORT_SYMBOL_GPL(static_key_slow_inc);
 76 
 77 static void __static_key_slow_dec(struct static_key *key,
 78                 unsigned long rate_limit, struct delayed_work *work)
 79 {
 80         if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
 81                 WARN(atomic_read(&key->enabled) < 0,
 82                      "jump label: negative count!\n");
 83                 return;
 84         }
 85 
 86         if (rate_limit) {
 87                 atomic_inc(&key->enabled);
 88                 schedule_delayed_work(work, rate_limit);
 89         } else {
 90                 if (!jump_label_get_branch_default(key))
 91                         jump_label_update(key, JUMP_LABEL_DISABLE);
 92                 else
 93                         jump_label_update(key, JUMP_LABEL_ENABLE);
 94         }
 95         jump_label_unlock();
 96 }
 97 
 98 static void jump_label_update_timeout(struct work_struct *work)
 99 {
100         struct static_key_deferred *key =
101                 container_of(work, struct static_key_deferred, work.work);
102         __static_key_slow_dec(&key->key, 0, NULL);
103 }
104 
105 void static_key_slow_dec(struct static_key *key)
106 {
107         STATIC_KEY_CHECK_USE();
108         __static_key_slow_dec(key, 0, NULL);
109 }
110 EXPORT_SYMBOL_GPL(static_key_slow_dec);
111 
112 void static_key_slow_dec_deferred(struct static_key_deferred *key)
113 {
114         STATIC_KEY_CHECK_USE();
115         __static_key_slow_dec(&key->key, key->timeout, &key->work);
116 }
117 EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
118 
119 void static_key_deferred_flush(struct static_key_deferred *key)
120 {
121         STATIC_KEY_CHECK_USE();
122         flush_delayed_work(&key->work);
123 }
124 EXPORT_SYMBOL_GPL(static_key_deferred_flush);
125 
126 void jump_label_rate_limit(struct static_key_deferred *key,
127                 unsigned long rl)
128 {
129         STATIC_KEY_CHECK_USE();
130         key->timeout = rl;
131         INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
132 }
133 EXPORT_SYMBOL_GPL(jump_label_rate_limit);
134 
135 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
136 {
137         if (entry->code <= (unsigned long)end &&
138                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
139                 return 1;
140 
141         return 0;
142 }
143 
144 static int __jump_label_text_reserved(struct jump_entry *iter_start,
145                 struct jump_entry *iter_stop, void *start, void *end)
146 {
147         struct jump_entry *iter;
148 
149         iter = iter_start;
150         while (iter < iter_stop) {
151                 if (addr_conflict(iter, start, end))
152                         return 1;
153                 iter++;
154         }
155 
156         return 0;
157 }
158 
159 /* 
160  * Update code which is definitely not currently executing.
161  * Architectures which need heavyweight synchronization to modify
162  * running code can override this to make the non-live update case
163  * cheaper.
164  */
165 void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
166                                             enum jump_label_type type)
167 {
168         arch_jump_label_transform(entry, type); 
169 }
170 
171 static void __jump_label_update(struct static_key *key,
172                                 struct jump_entry *entry,
173                                 struct jump_entry *stop, int enable)
174 {
175         for (; (entry < stop) &&
176               (entry->key == (jump_label_t)(unsigned long)key);
177               entry++) {
178                 /*
179                  * entry->code set to 0 invalidates module init text sections
180                  * kernel_text_address() verifies we are not in core kernel
181                  * init code, see jump_label_invalidate_module_init().
182                  */
183                 if (entry->code && kernel_text_address(entry->code))
184                         arch_jump_label_transform(entry, enable);
185         }
186 }
187 
188 static enum jump_label_type jump_label_type(struct static_key *key)
189 {
190         bool true_branch = jump_label_get_branch_default(key);
191         bool state = static_key_enabled(key);
192 
193         if ((!true_branch && state) || (true_branch && !state))
194                 return JUMP_LABEL_ENABLE;
195 
196         return JUMP_LABEL_DISABLE;
197 }
198 
199 void __init jump_label_init(void)
200 {
201         struct jump_entry *iter_start = __start___jump_table;
202         struct jump_entry *iter_stop = __stop___jump_table;
203         struct static_key *key = NULL;
204         struct jump_entry *iter;
205 
206         jump_label_lock();
207         jump_label_sort_entries(iter_start, iter_stop);
208 
209         for (iter = iter_start; iter < iter_stop; iter++) {
210                 struct static_key *iterk;
211 
212                 iterk = (struct static_key *)(unsigned long)iter->key;
213                 arch_jump_label_transform_static(iter, jump_label_type(iterk));
214                 if (iterk == key)
215                         continue;
216 
217                 key = iterk;
218                 /*
219                  * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
220                  */
221                 *((unsigned long *)&key->entries) += (unsigned long)iter;
222 #ifdef CONFIG_MODULES
223                 key->next = NULL;
224 #endif
225         }
226         static_key_initialized = true;
227         jump_label_unlock();
228 }
229 
230 #ifdef CONFIG_MODULES
231 
232 struct static_key_mod {
233         struct static_key_mod *next;
234         struct jump_entry *entries;
235         struct module *mod;
236 };
237 
238 static int __jump_label_mod_text_reserved(void *start, void *end)
239 {
240         struct module *mod;
241 
242         mod = __module_text_address((unsigned long)start);
243         if (!mod)
244                 return 0;
245 
246         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
247 
248         return __jump_label_text_reserved(mod->jump_entries,
249                                 mod->jump_entries + mod->num_jump_entries,
250                                 start, end);
251 }
252 
253 static void __jump_label_mod_update(struct static_key *key, int enable)
254 {
255         struct static_key_mod *mod = key->next;
256 
257         while (mod) {
258                 struct module *m = mod->mod;
259 
260                 __jump_label_update(key, mod->entries,
261                                     m->jump_entries + m->num_jump_entries,
262                                     enable);
263                 mod = mod->next;
264         }
265 }
266 
267 /***
268  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
269  * @mod: module to patch
270  *
271  * Allow for run-time selection of the optimal nops. Before the module
272  * loads patch these with arch_get_jump_label_nop(), which is specified by
273  * the arch specific jump label code.
274  */
275 void jump_label_apply_nops(struct module *mod)
276 {
277         struct jump_entry *iter_start = mod->jump_entries;
278         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
279         struct jump_entry *iter;
280 
281         /* if the module doesn't have jump label entries, just return */
282         if (iter_start == iter_stop)
283                 return;
284 
285         for (iter = iter_start; iter < iter_stop; iter++) {
286                 arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
287         }
288 }
289 
290 static int jump_label_add_module(struct module *mod)
291 {
292         struct jump_entry *iter_start = mod->jump_entries;
293         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
294         struct jump_entry *iter;
295         struct static_key *key = NULL;
296         struct static_key_mod *jlm;
297 
298         /* if the module doesn't have jump label entries, just return */
299         if (iter_start == iter_stop)
300                 return 0;
301 
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                 iterk = (struct static_key *)(unsigned long)iter->key;
308                 if (iterk == key)
309                         continue;
310 
311                 key = iterk;
312                 if (__module_address(iter->key) == mod) {
313                         /*
314                          * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
315                          */
316                         *((unsigned long *)&key->entries) += (unsigned long)iter;
317                         key->next = NULL;
318                         continue;
319                 }
320                 jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
321                 if (!jlm)
322                         return -ENOMEM;
323                 jlm->mod = mod;
324                 jlm->entries = iter;
325                 jlm->next = key->next;
326                 key->next = jlm;
327 
328                 if (jump_label_type(key) == JUMP_LABEL_ENABLE)
329                         __jump_label_update(key, iter, iter_stop, JUMP_LABEL_ENABLE);
330         }
331 
332         return 0;
333 }
334 
335 static void jump_label_del_module(struct module *mod)
336 {
337         struct jump_entry *iter_start = mod->jump_entries;
338         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
339         struct jump_entry *iter;
340         struct static_key *key = NULL;
341         struct static_key_mod *jlm, **prev;
342 
343         for (iter = iter_start; iter < iter_stop; iter++) {
344                 if (iter->key == (jump_label_t)(unsigned long)key)
345                         continue;
346 
347                 key = (struct static_key *)(unsigned long)iter->key;
348 
349                 if (__module_address(iter->key) == mod)
350                         continue;
351 
352                 prev = &key->next;
353                 jlm = key->next;
354 
355                 while (jlm && jlm->mod != mod) {
356                         prev = &jlm->next;
357                         jlm = jlm->next;
358                 }
359 
360                 if (jlm) {
361                         *prev = jlm->next;
362                         kfree(jlm);
363                 }
364         }
365 }
366 
367 static void jump_label_invalidate_module_init(struct module *mod)
368 {
369         struct jump_entry *iter_start = mod->jump_entries;
370         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
371         struct jump_entry *iter;
372 
373         for (iter = iter_start; iter < iter_stop; iter++) {
374                 if (within_module_init(iter->code, mod))
375                         iter->code = 0;
376         }
377 }
378 
379 static int
380 jump_label_module_notify(struct notifier_block *self, unsigned long val,
381                          void *data)
382 {
383         struct module *mod = data;
384         int ret = 0;
385 
386         switch (val) {
387         case MODULE_STATE_COMING:
388                 jump_label_lock();
389                 ret = jump_label_add_module(mod);
390                 if (ret)
391                         jump_label_del_module(mod);
392                 jump_label_unlock();
393                 break;
394         case MODULE_STATE_GOING:
395                 jump_label_lock();
396                 jump_label_del_module(mod);
397                 jump_label_unlock();
398                 break;
399         case MODULE_STATE_LIVE:
400                 jump_label_lock();
401                 jump_label_invalidate_module_init(mod);
402                 jump_label_unlock();
403                 break;
404         }
405 
406         return notifier_from_errno(ret);
407 }
408 
409 struct notifier_block jump_label_module_nb = {
410         .notifier_call = jump_label_module_notify,
411         .priority = 1, /* higher than tracepoints */
412 };
413 
414 static __init int jump_label_init_module(void)
415 {
416         return register_module_notifier(&jump_label_module_nb);
417 }
418 early_initcall(jump_label_init_module);
419 
420 #endif /* CONFIG_MODULES */
421 
422 /***
423  * jump_label_text_reserved - check if addr range is reserved
424  * @start: start text addr
425  * @end: end text addr
426  *
427  * checks if the text addr located between @start and @end
428  * overlaps with any of the jump label patch addresses. Code
429  * that wants to modify kernel text should first verify that
430  * it does not overlap with any of the jump label addresses.
431  * Caller must hold jump_label_mutex.
432  *
433  * returns 1 if there is an overlap, 0 otherwise
434  */
435 int jump_label_text_reserved(void *start, void *end)
436 {
437         int ret = __jump_label_text_reserved(__start___jump_table,
438                         __stop___jump_table, start, end);
439 
440         if (ret)
441                 return ret;
442 
443 #ifdef CONFIG_MODULES
444         ret = __jump_label_mod_text_reserved(start, end);
445 #endif
446         return ret;
447 }
448 
449 static void jump_label_update(struct static_key *key, int enable)
450 {
451         struct jump_entry *stop = __stop___jump_table;
452         struct jump_entry *entry = jump_label_get_entries(key);
453 
454 #ifdef CONFIG_MODULES
455         struct module *mod = __module_address((unsigned long)key);
456 
457         __jump_label_mod_update(key, enable);
458 
459         if (mod)
460                 stop = mod->jump_entries + mod->num_jump_entries;
461 #endif
462         /* if there are no users, entry can be NULL */
463         if (entry)
464                 __jump_label_update(key, entry, stop, enable);
465 }
466 
467 #endif
468 

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