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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 jump_label_rate_limit(struct static_key_deferred *key,
120                 unsigned long rl)
121 {
122         STATIC_KEY_CHECK_USE();
123         key->timeout = rl;
124         INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
125 }
126 EXPORT_SYMBOL_GPL(jump_label_rate_limit);
127 
128 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
129 {
130         if (entry->code <= (unsigned long)end &&
131                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
132                 return 1;
133 
134         return 0;
135 }
136 
137 static int __jump_label_text_reserved(struct jump_entry *iter_start,
138                 struct jump_entry *iter_stop, void *start, void *end)
139 {
140         struct jump_entry *iter;
141 
142         iter = iter_start;
143         while (iter < iter_stop) {
144                 if (addr_conflict(iter, start, end))
145                         return 1;
146                 iter++;
147         }
148 
149         return 0;
150 }
151 
152 /* 
153  * Update code which is definitely not currently executing.
154  * Architectures which need heavyweight synchronization to modify
155  * running code can override this to make the non-live update case
156  * cheaper.
157  */
158 void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
159                                             enum jump_label_type type)
160 {
161         arch_jump_label_transform(entry, type); 
162 }
163 
164 static void __jump_label_update(struct static_key *key,
165                                 struct jump_entry *entry,
166                                 struct jump_entry *stop, int enable)
167 {
168         for (; (entry < stop) &&
169               (entry->key == (jump_label_t)(unsigned long)key);
170               entry++) {
171                 /*
172                  * entry->code set to 0 invalidates module init text sections
173                  * kernel_text_address() verifies we are not in core kernel
174                  * init code, see jump_label_invalidate_module_init().
175                  */
176                 if (entry->code && kernel_text_address(entry->code))
177                         arch_jump_label_transform(entry, enable);
178         }
179 }
180 
181 static enum jump_label_type jump_label_type(struct static_key *key)
182 {
183         bool true_branch = jump_label_get_branch_default(key);
184         bool state = static_key_enabled(key);
185 
186         if ((!true_branch && state) || (true_branch && !state))
187                 return JUMP_LABEL_ENABLE;
188 
189         return JUMP_LABEL_DISABLE;
190 }
191 
192 void __init jump_label_init(void)
193 {
194         struct jump_entry *iter_start = __start___jump_table;
195         struct jump_entry *iter_stop = __stop___jump_table;
196         struct static_key *key = NULL;
197         struct jump_entry *iter;
198 
199         jump_label_lock();
200         jump_label_sort_entries(iter_start, iter_stop);
201 
202         for (iter = iter_start; iter < iter_stop; iter++) {
203                 struct static_key *iterk;
204 
205                 iterk = (struct static_key *)(unsigned long)iter->key;
206                 arch_jump_label_transform_static(iter, jump_label_type(iterk));
207                 if (iterk == key)
208                         continue;
209 
210                 key = iterk;
211                 /*
212                  * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
213                  */
214                 *((unsigned long *)&key->entries) += (unsigned long)iter;
215 #ifdef CONFIG_MODULES
216                 key->next = NULL;
217 #endif
218         }
219         static_key_initialized = true;
220         jump_label_unlock();
221 }
222 
223 #ifdef CONFIG_MODULES
224 
225 struct static_key_mod {
226         struct static_key_mod *next;
227         struct jump_entry *entries;
228         struct module *mod;
229 };
230 
231 static int __jump_label_mod_text_reserved(void *start, void *end)
232 {
233         struct module *mod;
234 
235         mod = __module_text_address((unsigned long)start);
236         if (!mod)
237                 return 0;
238 
239         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
240 
241         return __jump_label_text_reserved(mod->jump_entries,
242                                 mod->jump_entries + mod->num_jump_entries,
243                                 start, end);
244 }
245 
246 static void __jump_label_mod_update(struct static_key *key, int enable)
247 {
248         struct static_key_mod *mod = key->next;
249 
250         while (mod) {
251                 struct module *m = mod->mod;
252 
253                 __jump_label_update(key, mod->entries,
254                                     m->jump_entries + m->num_jump_entries,
255                                     enable);
256                 mod = mod->next;
257         }
258 }
259 
260 /***
261  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
262  * @mod: module to patch
263  *
264  * Allow for run-time selection of the optimal nops. Before the module
265  * loads patch these with arch_get_jump_label_nop(), which is specified by
266  * the arch specific jump label code.
267  */
268 void jump_label_apply_nops(struct module *mod)
269 {
270         struct jump_entry *iter_start = mod->jump_entries;
271         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
272         struct jump_entry *iter;
273 
274         /* if the module doesn't have jump label entries, just return */
275         if (iter_start == iter_stop)
276                 return;
277 
278         for (iter = iter_start; iter < iter_stop; iter++) {
279                 arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
280         }
281 }
282 
283 static int jump_label_add_module(struct module *mod)
284 {
285         struct jump_entry *iter_start = mod->jump_entries;
286         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
287         struct jump_entry *iter;
288         struct static_key *key = NULL;
289         struct static_key_mod *jlm;
290 
291         /* if the module doesn't have jump label entries, just return */
292         if (iter_start == iter_stop)
293                 return 0;
294 
295         jump_label_sort_entries(iter_start, iter_stop);
296 
297         for (iter = iter_start; iter < iter_stop; iter++) {
298                 struct static_key *iterk;
299 
300                 iterk = (struct static_key *)(unsigned long)iter->key;
301                 if (iterk == key)
302                         continue;
303 
304                 key = iterk;
305                 if (__module_address(iter->key) == mod) {
306                         /*
307                          * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
308                          */
309                         *((unsigned long *)&key->entries) += (unsigned long)iter;
310                         key->next = NULL;
311                         continue;
312                 }
313                 jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
314                 if (!jlm)
315                         return -ENOMEM;
316                 jlm->mod = mod;
317                 jlm->entries = iter;
318                 jlm->next = key->next;
319                 key->next = jlm;
320 
321                 if (jump_label_type(key) == JUMP_LABEL_ENABLE)
322                         __jump_label_update(key, iter, iter_stop, JUMP_LABEL_ENABLE);
323         }
324 
325         return 0;
326 }
327 
328 static void jump_label_del_module(struct module *mod)
329 {
330         struct jump_entry *iter_start = mod->jump_entries;
331         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
332         struct jump_entry *iter;
333         struct static_key *key = NULL;
334         struct static_key_mod *jlm, **prev;
335 
336         for (iter = iter_start; iter < iter_stop; iter++) {
337                 if (iter->key == (jump_label_t)(unsigned long)key)
338                         continue;
339 
340                 key = (struct static_key *)(unsigned long)iter->key;
341 
342                 if (__module_address(iter->key) == mod)
343                         continue;
344 
345                 prev = &key->next;
346                 jlm = key->next;
347 
348                 while (jlm && jlm->mod != mod) {
349                         prev = &jlm->next;
350                         jlm = jlm->next;
351                 }
352 
353                 if (jlm) {
354                         *prev = jlm->next;
355                         kfree(jlm);
356                 }
357         }
358 }
359 
360 static void jump_label_invalidate_module_init(struct module *mod)
361 {
362         struct jump_entry *iter_start = mod->jump_entries;
363         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
364         struct jump_entry *iter;
365 
366         for (iter = iter_start; iter < iter_stop; iter++) {
367                 if (within_module_init(iter->code, mod))
368                         iter->code = 0;
369         }
370 }
371 
372 static int
373 jump_label_module_notify(struct notifier_block *self, unsigned long val,
374                          void *data)
375 {
376         struct module *mod = data;
377         int ret = 0;
378 
379         switch (val) {
380         case MODULE_STATE_COMING:
381                 jump_label_lock();
382                 ret = jump_label_add_module(mod);
383                 if (ret)
384                         jump_label_del_module(mod);
385                 jump_label_unlock();
386                 break;
387         case MODULE_STATE_GOING:
388                 jump_label_lock();
389                 jump_label_del_module(mod);
390                 jump_label_unlock();
391                 break;
392         case MODULE_STATE_LIVE:
393                 jump_label_lock();
394                 jump_label_invalidate_module_init(mod);
395                 jump_label_unlock();
396                 break;
397         }
398 
399         return notifier_from_errno(ret);
400 }
401 
402 struct notifier_block jump_label_module_nb = {
403         .notifier_call = jump_label_module_notify,
404         .priority = 1, /* higher than tracepoints */
405 };
406 
407 static __init int jump_label_init_module(void)
408 {
409         return register_module_notifier(&jump_label_module_nb);
410 }
411 early_initcall(jump_label_init_module);
412 
413 #endif /* CONFIG_MODULES */
414 
415 /***
416  * jump_label_text_reserved - check if addr range is reserved
417  * @start: start text addr
418  * @end: end text addr
419  *
420  * checks if the text addr located between @start and @end
421  * overlaps with any of the jump label patch addresses. Code
422  * that wants to modify kernel text should first verify that
423  * it does not overlap with any of the jump label addresses.
424  * Caller must hold jump_label_mutex.
425  *
426  * returns 1 if there is an overlap, 0 otherwise
427  */
428 int jump_label_text_reserved(void *start, void *end)
429 {
430         int ret = __jump_label_text_reserved(__start___jump_table,
431                         __stop___jump_table, start, end);
432 
433         if (ret)
434                 return ret;
435 
436 #ifdef CONFIG_MODULES
437         ret = __jump_label_mod_text_reserved(start, end);
438 #endif
439         return ret;
440 }
441 
442 static void jump_label_update(struct static_key *key, int enable)
443 {
444         struct jump_entry *stop = __stop___jump_table;
445         struct jump_entry *entry = jump_label_get_entries(key);
446 
447 #ifdef CONFIG_MODULES
448         struct module *mod = __module_address((unsigned long)key);
449 
450         __jump_label_mod_update(key, enable);
451 
452         if (mod)
453                 stop = mod->jump_entries + mod->num_jump_entries;
454 #endif
455         /* if there are no users, entry can be NULL */
456         if (entry)
457                 __jump_label_update(key, entry, stop, enable);
458 }
459 
460 #endif
461 

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