059202d5b77aa908bd8d3478f9c1edd7c45c7c07
[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,
109                                 struct jump_entry *stop, int enable)
110 {
111         for (; (entry < stop) &&
112               (entry->key == (jump_label_t)(unsigned long)key);
113               entry++) {
114                 /*
115                  * entry->code set to 0 invalidates module init text sections
116                  * kernel_text_address() verifies we are not in core kernel
117                  * init code, see jump_label_invalidate_module_init().
118                  */
119                 if (entry->code && kernel_text_address(entry->code))
120                         arch_jump_label_transform(entry, enable);
121         }
122 }
123
124 static __init int jump_label_init(void)
125 {
126         struct jump_entry *iter_start = __start___jump_table;
127         struct jump_entry *iter_stop = __stop___jump_table;
128         struct jump_label_key *key = NULL;
129         struct jump_entry *iter;
130
131         jump_label_lock();
132         jump_label_sort_entries(iter_start, iter_stop);
133
134         for (iter = iter_start; iter < iter_stop; iter++) {
135                 struct jump_label_key *iterk;
136
137                 iterk = (struct jump_label_key *)(unsigned long)iter->key;
138                 arch_jump_label_transform(iter, jump_label_enabled(iterk) ?
139                                           JUMP_LABEL_ENABLE : JUMP_LABEL_DISABLE);
140                 if (iterk == key)
141                         continue;
142
143                 key = iterk;
144                 key->entries = iter;
145 #ifdef CONFIG_MODULES
146                 key->next = NULL;
147 #endif
148         }
149         jump_label_unlock();
150
151         return 0;
152 }
153 early_initcall(jump_label_init);
154
155 #ifdef CONFIG_MODULES
156
157 struct jump_label_mod {
158         struct jump_label_mod *next;
159         struct jump_entry *entries;
160         struct module *mod;
161 };
162
163 static int __jump_label_mod_text_reserved(void *start, void *end)
164 {
165         struct module *mod;
166
167         mod = __module_text_address((unsigned long)start);
168         if (!mod)
169                 return 0;
170
171         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
172
173         return __jump_label_text_reserved(mod->jump_entries,
174                                 mod->jump_entries + mod->num_jump_entries,
175                                 start, end);
176 }
177
178 static void __jump_label_mod_update(struct jump_label_key *key, int enable)
179 {
180         struct jump_label_mod *mod = key->next;
181
182         while (mod) {
183                 struct module *m = mod->mod;
184
185                 __jump_label_update(key, mod->entries,
186                                     m->jump_entries + m->num_jump_entries,
187                                     enable);
188                 mod = mod->next;
189         }
190 }
191
192 /***
193  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
194  * @mod: module to patch
195  *
196  * Allow for run-time selection of the optimal nops. Before the module
197  * loads patch these with arch_get_jump_label_nop(), which is specified by
198  * the arch specific jump label code.
199  */
200 void jump_label_apply_nops(struct module *mod)
201 {
202         struct jump_entry *iter_start = mod->jump_entries;
203         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
204         struct jump_entry *iter;
205
206         /* if the module doesn't have jump label entries, just return */
207         if (iter_start == iter_stop)
208                 return;
209
210         for (iter = iter_start; iter < iter_stop; iter++)
211                 arch_jump_label_transform(iter, JUMP_LABEL_DISABLE);
212 }
213
214 static int jump_label_add_module(struct module *mod)
215 {
216         struct jump_entry *iter_start = mod->jump_entries;
217         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
218         struct jump_entry *iter;
219         struct jump_label_key *key = NULL;
220         struct jump_label_mod *jlm;
221
222         /* if the module doesn't have jump label entries, just return */
223         if (iter_start == iter_stop)
224                 return 0;
225
226         jump_label_sort_entries(iter_start, iter_stop);
227
228         for (iter = iter_start; iter < iter_stop; iter++) {
229                 if (iter->key == (jump_label_t)(unsigned long)key)
230                         continue;
231
232                 key = (struct jump_label_key *)(unsigned long)iter->key;
233
234                 if (__module_address(iter->key) == mod) {
235                         atomic_set(&key->enabled, 0);
236                         key->entries = iter;
237                         key->next = NULL;
238                         continue;
239                 }
240
241                 jlm = kzalloc(sizeof(struct jump_label_mod), GFP_KERNEL);
242                 if (!jlm)
243                         return -ENOMEM;
244
245                 jlm->mod = mod;
246                 jlm->entries = iter;
247                 jlm->next = key->next;
248                 key->next = jlm;
249
250                 if (jump_label_enabled(key))
251                         __jump_label_update(key, iter, iter_stop,
252                                             JUMP_LABEL_ENABLE);
253         }
254
255         return 0;
256 }
257
258 static void jump_label_del_module(struct module *mod)
259 {
260         struct jump_entry *iter_start = mod->jump_entries;
261         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
262         struct jump_entry *iter;
263         struct jump_label_key *key = NULL;
264         struct jump_label_mod *jlm, **prev;
265
266         for (iter = iter_start; iter < iter_stop; iter++) {
267                 if (iter->key == (jump_label_t)(unsigned long)key)
268                         continue;
269
270                 key = (struct jump_label_key *)(unsigned long)iter->key;
271
272                 if (__module_address(iter->key) == mod)
273                         continue;
274
275                 prev = &key->next;
276                 jlm = key->next;
277
278                 while (jlm && jlm->mod != mod) {
279                         prev = &jlm->next;
280                         jlm = jlm->next;
281                 }
282
283                 if (jlm) {
284                         *prev = jlm->next;
285                         kfree(jlm);
286                 }
287         }
288 }
289
290 static void jump_label_invalidate_module_init(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
296         for (iter = iter_start; iter < iter_stop; iter++) {
297                 if (within_module_init(iter->code, mod))
298                         iter->code = 0;
299         }
300 }
301
302 static int
303 jump_label_module_notify(struct notifier_block *self, unsigned long val,
304                          void *data)
305 {
306         struct module *mod = data;
307         int ret = 0;
308
309         switch (val) {
310         case MODULE_STATE_COMING:
311                 jump_label_lock();
312                 ret = jump_label_add_module(mod);
313                 if (ret)
314                         jump_label_del_module(mod);
315                 jump_label_unlock();
316                 break;
317         case MODULE_STATE_GOING:
318                 jump_label_lock();
319                 jump_label_del_module(mod);
320                 jump_label_unlock();
321                 break;
322         case MODULE_STATE_LIVE:
323                 jump_label_lock();
324                 jump_label_invalidate_module_init(mod);
325                 jump_label_unlock();
326                 break;
327         }
328
329         return notifier_from_errno(ret);
330 }
331
332 struct notifier_block jump_label_module_nb = {
333         .notifier_call = jump_label_module_notify,
334         .priority = 1, /* higher than tracepoints */
335 };
336
337 static __init int jump_label_init_module(void)
338 {
339         return register_module_notifier(&jump_label_module_nb);
340 }
341 early_initcall(jump_label_init_module);
342
343 #endif /* CONFIG_MODULES */
344
345 /***
346  * jump_label_text_reserved - check if addr range is reserved
347  * @start: start text addr
348  * @end: end text addr
349  *
350  * checks if the text addr located between @start and @end
351  * overlaps with any of the jump label patch addresses. Code
352  * that wants to modify kernel text should first verify that
353  * it does not overlap with any of the jump label addresses.
354  * Caller must hold jump_label_mutex.
355  *
356  * returns 1 if there is an overlap, 0 otherwise
357  */
358 int jump_label_text_reserved(void *start, void *end)
359 {
360         int ret = __jump_label_text_reserved(__start___jump_table,
361                         __stop___jump_table, start, end);
362
363         if (ret)
364                 return ret;
365
366 #ifdef CONFIG_MODULES
367         ret = __jump_label_mod_text_reserved(start, end);
368 #endif
369         return ret;
370 }
371
372 static void jump_label_update(struct jump_label_key *key, int enable)
373 {
374         struct jump_entry *entry = key->entries, *stop = __stop___jump_table;
375
376 #ifdef CONFIG_MODULES
377         struct module *mod = __module_address((jump_label_t)key);
378
379         __jump_label_mod_update(key, enable);
380
381         if (mod)
382                 stop = mod->jump_entries + mod->num_jump_entries;
383 #endif
384         /* if there are no users, entry can be NULL */
385         if (entry)
386                 __jump_label_update(key, entry, stop, enable);
387 }
388
389 #endif