jump label: Introduce static_branch() interface
[linux-2.6.git] / 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 <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/jump_label.h>
16
17 #ifdef HAVE_JUMP_LABEL
18
19 /* mutex to protect coming/going of the the jump_label table */
20 static DEFINE_MUTEX(jump_label_mutex);
21
22 void jump_label_lock(void)
23 {
24         mutex_lock(&jump_label_mutex);
25 }
26
27 void jump_label_unlock(void)
28 {
29         mutex_unlock(&jump_label_mutex);
30 }
31
32 bool jump_label_enabled(struct jump_label_key *key)
33 {
34         return !!atomic_read(&key->enabled);
35 }
36
37 static int jump_label_cmp(const void *a, const void *b)
38 {
39         const struct jump_entry *jea = a;
40         const struct jump_entry *jeb = b;
41
42         if (jea->key < jeb->key)
43                 return -1;
44
45         if (jea->key > jeb->key)
46                 return 1;
47
48         return 0;
49 }
50
51 static void
52 jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
53 {
54         unsigned long size;
55
56         size = (((unsigned long)stop - (unsigned long)start)
57                                         / sizeof(struct jump_entry));
58         sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
59 }
60
61 static void jump_label_update(struct jump_label_key *key, int enable);
62
63 void jump_label_inc(struct jump_label_key *key)
64 {
65         if (atomic_inc_not_zero(&key->enabled))
66                 return;
67
68         jump_label_lock();
69         if (atomic_add_return(1, &key->enabled) == 1)
70                 jump_label_update(key, JUMP_LABEL_ENABLE);
71         jump_label_unlock();
72 }
73
74 void jump_label_dec(struct jump_label_key *key)
75 {
76         if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex))
77                 return;
78
79         jump_label_update(key, JUMP_LABEL_DISABLE);
80         jump_label_unlock();
81 }
82
83 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
84 {
85         if (entry->code <= (unsigned long)end &&
86                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
87                 return 1;
88
89         return 0;
90 }
91
92 static int __jump_label_text_reserved(struct jump_entry *iter_start,
93                 struct jump_entry *iter_stop, void *start, void *end)
94 {
95         struct jump_entry *iter;
96
97         iter = iter_start;
98         while (iter < iter_stop) {
99                 if (addr_conflict(iter, start, end))
100                         return 1;
101                 iter++;
102         }
103
104         return 0;
105 }
106
107 static void __jump_label_update(struct jump_label_key *key,
108                 struct jump_entry *entry, int enable)
109 {
110         for (; entry->key == (jump_label_t)(unsigned long)key; entry++) {
111                 /*
112                  * entry->code set to 0 invalidates module init text sections
113                  * kernel_text_address() verifies we are not in core kernel
114                  * init code, see jump_label_invalidate_module_init().
115                  */
116                 if (entry->code && kernel_text_address(entry->code))
117                         arch_jump_label_transform(entry, enable);
118         }
119 }
120
121 /*
122  * Not all archs need this.
123  */
124 void __weak arch_jump_label_text_poke_early(jump_label_t addr)
125 {
126 }
127
128 static __init int jump_label_init(void)
129 {
130         struct jump_entry *iter_start = __start___jump_table;
131         struct jump_entry *iter_stop = __stop___jump_table;
132         struct jump_label_key *key = NULL;
133         struct jump_entry *iter;
134
135         jump_label_lock();
136         jump_label_sort_entries(iter_start, iter_stop);
137
138         for (iter = iter_start; iter < iter_stop; iter++) {
139                 arch_jump_label_text_poke_early(iter->code);
140                 if (iter->key == (jump_label_t)(unsigned long)key)
141                         continue;
142
143                 key = (struct jump_label_key *)(unsigned long)iter->key;
144                 atomic_set(&key->enabled, 0);
145                 key->entries = iter;
146 #ifdef CONFIG_MODULES
147                 key->next = NULL;
148 #endif
149         }
150         jump_label_unlock();
151
152         return 0;
153 }
154 early_initcall(jump_label_init);
155
156 #ifdef CONFIG_MODULES
157
158 struct jump_label_mod {
159         struct jump_label_mod *next;
160         struct jump_entry *entries;
161         struct module *mod;
162 };
163
164 static int __jump_label_mod_text_reserved(void *start, void *end)
165 {
166         struct module *mod;
167
168         mod = __module_text_address((unsigned long)start);
169         if (!mod)
170                 return 0;
171
172         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
173
174         return __jump_label_text_reserved(mod->jump_entries,
175                                 mod->jump_entries + mod->num_jump_entries,
176                                 start, end);
177 }
178
179 static void __jump_label_mod_update(struct jump_label_key *key, int enable)
180 {
181         struct jump_label_mod *mod = key->next;
182
183         while (mod) {
184                 __jump_label_update(key, mod->entries, enable);
185                 mod = mod->next;
186         }
187 }
188
189 /***
190  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
191  * @mod: module to patch
192  *
193  * Allow for run-time selection of the optimal nops. Before the module
194  * loads patch these with arch_get_jump_label_nop(), which is specified by
195  * the arch specific jump label code.
196  */
197 void jump_label_apply_nops(struct module *mod)
198 {
199         struct jump_entry *iter_start = mod->jump_entries;
200         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
201         struct jump_entry *iter;
202
203         /* if the module doesn't have jump label entries, just return */
204         if (iter_start == iter_stop)
205                 return;
206
207         for (iter = iter_start; iter < iter_stop; iter++)
208                 arch_jump_label_text_poke_early(iter->code);
209 }
210
211 static int jump_label_add_module(struct module *mod)
212 {
213         struct jump_entry *iter_start = mod->jump_entries;
214         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
215         struct jump_entry *iter;
216         struct jump_label_key *key = NULL;
217         struct jump_label_mod *jlm;
218
219         /* if the module doesn't have jump label entries, just return */
220         if (iter_start == iter_stop)
221                 return 0;
222
223         jump_label_sort_entries(iter_start, iter_stop);
224
225         for (iter = iter_start; iter < iter_stop; iter++) {
226                 if (iter->key == (jump_label_t)(unsigned long)key)
227                         continue;
228
229                 key = (struct jump_label_key *)(unsigned long)iter->key;
230
231                 if (__module_address(iter->key) == mod) {
232                         atomic_set(&key->enabled, 0);
233                         key->entries = iter;
234                         key->next = NULL;
235                         continue;
236                 }
237
238                 jlm = kzalloc(sizeof(struct jump_label_mod), GFP_KERNEL);
239                 if (!jlm)
240                         return -ENOMEM;
241
242                 jlm->mod = mod;
243                 jlm->entries = iter;
244                 jlm->next = key->next;
245                 key->next = jlm;
246
247                 if (jump_label_enabled(key))
248                         __jump_label_update(key, iter, JUMP_LABEL_ENABLE);
249         }
250
251         return 0;
252 }
253
254 static void jump_label_del_module(struct module *mod)
255 {
256         struct jump_entry *iter_start = mod->jump_entries;
257         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
258         struct jump_entry *iter;
259         struct jump_label_key *key = NULL;
260         struct jump_label_mod *jlm, **prev;
261
262         for (iter = iter_start; iter < iter_stop; iter++) {
263                 if (iter->key == (jump_label_t)(unsigned long)key)
264                         continue;
265
266                 key = (struct jump_label_key *)(unsigned long)iter->key;
267
268                 if (__module_address(iter->key) == mod)
269                         continue;
270
271                 prev = &key->next;
272                 jlm = key->next;
273
274                 while (jlm && jlm->mod != mod) {
275                         prev = &jlm->next;
276                         jlm = jlm->next;
277                 }
278
279                 if (jlm) {
280                         *prev = jlm->next;
281                         kfree(jlm);
282                 }
283         }
284 }
285
286 static void jump_label_invalidate_module_init(struct module *mod)
287 {
288         struct jump_entry *iter_start = mod->jump_entries;
289         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
290         struct jump_entry *iter;
291
292         for (iter = iter_start; iter < iter_stop; iter++) {
293                 if (within_module_init(iter->code, mod))
294                         iter->code = 0;
295         }
296 }
297
298 static int
299 jump_label_module_notify(struct notifier_block *self, unsigned long val,
300                          void *data)
301 {
302         struct module *mod = data;
303         int ret = 0;
304
305         switch (val) {
306         case MODULE_STATE_COMING:
307                 jump_label_lock();
308                 ret = jump_label_add_module(mod);
309                 if (ret)
310                         jump_label_del_module(mod);
311                 jump_label_unlock();
312                 break;
313         case MODULE_STATE_GOING:
314                 jump_label_lock();
315                 jump_label_del_module(mod);
316                 jump_label_unlock();
317                 break;
318         case MODULE_STATE_LIVE:
319                 jump_label_lock();
320                 jump_label_invalidate_module_init(mod);
321                 jump_label_unlock();
322                 break;
323         }
324
325         return notifier_from_errno(ret);
326 }
327
328 struct notifier_block jump_label_module_nb = {
329         .notifier_call = jump_label_module_notify,
330         .priority = 1, /* higher than tracepoints */
331 };
332
333 static __init int jump_label_init_module(void)
334 {
335         return register_module_notifier(&jump_label_module_nb);
336 }
337 early_initcall(jump_label_init_module);
338
339 #endif /* CONFIG_MODULES */
340
341 /***
342  * jump_label_text_reserved - check if addr range is reserved
343  * @start: start text addr
344  * @end: end text addr
345  *
346  * checks if the text addr located between @start and @end
347  * overlaps with any of the jump label patch addresses. Code
348  * that wants to modify kernel text should first verify that
349  * it does not overlap with any of the jump label addresses.
350  * Caller must hold jump_label_mutex.
351  *
352  * returns 1 if there is an overlap, 0 otherwise
353  */
354 int jump_label_text_reserved(void *start, void *end)
355 {
356         int ret = __jump_label_text_reserved(__start___jump_table,
357                         __stop___jump_table, start, end);
358
359         if (ret)
360                 return ret;
361
362 #ifdef CONFIG_MODULES
363         ret = __jump_label_mod_text_reserved(start, end);
364 #endif
365         return ret;
366 }
367
368 static void jump_label_update(struct jump_label_key *key, int enable)
369 {
370         struct jump_entry *entry = key->entries;
371
372         /* if there are no users, entry can be NULL */
373         if (entry)
374                 __jump_label_update(key, entry, enable);
375
376 #ifdef CONFIG_MODULES
377         __jump_label_mod_update(key, enable);
378 #endif
379 }
380
381 #endif