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 /*
 125  * Not all archs need this.
 126  */
 127 void __weak arch_jump_label_text_poke_early(jump_label_t addr)
 128 {
 129 }
 130
 131 static __init int jump_label_init(void)
 132 {
 133         struct jump_entry *iter_start = __start___jump_table;
 134         struct jump_entry *iter_stop = __stop___jump_table;
 135         struct jump_label_key *key = NULL;
 136         struct jump_entry *iter;
 137
 138         jump_label_lock();
 139         jump_label_sort_entries(iter_start, iter_stop);
 140
 141         for (iter = iter_start; iter < iter_stop; iter++) {
 142                 arch_jump_label_text_poke_early(iter->code);
 143                 if (iter->key == (jump_label_t)(unsigned long)key)
 144                         continue;
 145
 146                 key = (struct jump_label_key *)(unsigned long)iter->key;
 147                 atomic_set(&key->enabled, 0);
 148                 key->entries = iter;
 149 #ifdef CONFIG_MODULES
 150                 key->next = NULL;
 151 #endif
 152         }
 153         jump_label_unlock();
 154
 155         return 0;
 156 }
 157 early_initcall(jump_label_init);
 158
 159 #ifdef CONFIG_MODULES
 160
 161 struct jump_label_mod {
 162         struct jump_label_mod *next;
 163         struct jump_entry *entries;
 164         struct module *mod;
 165 };
 166
 167 static int __jump_label_mod_text_reserved(void *start, void *end)
 168 {
 169         struct module *mod;
 170
 171         mod = __module_text_address((unsigned long)start);
 172         if (!mod)
 173                 return 0;
 174
 175         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 176
 177         return __jump_label_text_reserved(mod->jump_entries,
 178                                 mod->jump_entries + mod->num_jump_entries,
 179                                 start, end);
 180 }
 181
 182 static void __jump_label_mod_update(struct jump_label_key *key, int enable)
 183 {
 184         struct jump_label_mod *mod = key->next;
 185
 186         while (mod) {
 187                 struct module *m = mod->mod;
 188
 189                 __jump_label_update(key, mod->entries,
 190                                     m->jump_entries + m->num_jump_entries,
 191                                     enable);
 192                 mod = mod->next;
 193         }
 194 }
 195
 196 /***
 197  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 198  * @mod: module to patch
 199  *
 200  * Allow for run-time selection of the optimal nops. Before the module
 201  * loads patch these with arch_get_jump_label_nop(), which is specified by
 202  * the arch specific jump label code.
 203  */
 204 void jump_label_apply_nops(struct module *mod)
 205 {
 206         struct jump_entry *iter_start = mod->jump_entries;
 207         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 208         struct jump_entry *iter;
 209
 210         /* if the module doesn't have jump label entries, just return */
 211         if (iter_start == iter_stop)
 212                 return;
 213
 214         for (iter = iter_start; iter < iter_stop; iter++)
 215                 arch_jump_label_text_poke_early(iter->code);
 216 }
 217
 218 static int jump_label_add_module(struct module *mod)
 219 {
 220         struct jump_entry *iter_start = mod->jump_entries;
 221         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 222         struct jump_entry *iter;
 223         struct jump_label_key *key = NULL;
 224         struct jump_label_mod *jlm;
 225
 226         /* if the module doesn't have jump label entries, just return */
 227         if (iter_start == iter_stop)
 228                 return 0;
 229
 230         jump_label_sort_entries(iter_start, iter_stop);
 231
 232         for (iter = iter_start; iter < iter_stop; iter++) {
 233                 if (iter->key == (jump_label_t)(unsigned long)key)
 234                         continue;
 235
 236                 key = (struct jump_label_key *)(unsigned long)iter->key;
 237
 238                 if (__module_address(iter->key) == mod) {
 239                         atomic_set(&key->enabled, 0);
 240                         key->entries = iter;
 241                         key->next = NULL;
 242                         continue;
 243                 }
 244
 245                 jlm = kzalloc(sizeof(struct jump_label_mod), GFP_KERNEL);
 246                 if (!jlm)
 247                         return -ENOMEM;
 248
 249                 jlm->mod = mod;
 250                 jlm->entries = iter;
 251                 jlm->next = key->next;
 252                 key->next = jlm;
 253
 254                 if (jump_label_enabled(key))
 255                         __jump_label_update(key, iter, iter_stop,
 256                                             JUMP_LABEL_ENABLE);
 257         }
 258
 259         return 0;
 260 }
 261
 262 static void jump_label_del_module(struct module *mod)
 263 {
 264         struct jump_entry *iter_start = mod->jump_entries;
 265         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 266         struct jump_entry *iter;
 267         struct jump_label_key *key = NULL;
 268         struct jump_label_mod *jlm, **prev;
 269
 270         for (iter = iter_start; iter < iter_stop; iter++) {
 271                 if (iter->key == (jump_label_t)(unsigned long)key)
 272                         continue;
 273
 274                 key = (struct jump_label_key *)(unsigned long)iter->key;
 275
 276                 if (__module_address(iter->key) == mod)
 277                         continue;
 278
 279                 prev = &key->next;
 280                 jlm = key->next;
 281
 282                 while (jlm && jlm->mod != mod) {
 283                         prev = &jlm->next;
 284                         jlm = jlm->next;
 285                 }
 286
 287                 if (jlm) {
 288                         *prev = jlm->next;
 289                         kfree(jlm);
 290                 }
 291         }
 292 }
 293
 294 static void jump_label_invalidate_module_init(struct module *mod)
 295 {
 296         struct jump_entry *iter_start = mod->jump_entries;
 297         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 298         struct jump_entry *iter;
 299
 300         for (iter = iter_start; iter < iter_stop; iter++) {
 301                 if (within_module_init(iter->code, mod))
 302                         iter->code = 0;
 303         }
 304 }
 305
 306 static int
 307 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 308                          void *data)
 309 {
 310         struct module *mod = data;
 311         int ret = 0;
 312
 313         switch (val) {
 314         case MODULE_STATE_COMING:
 315                 jump_label_lock();
 316                 ret = jump_label_add_module(mod);
 317                 if (ret)
 318                         jump_label_del_module(mod);
 319                 jump_label_unlock();
 320                 break;
 321         case MODULE_STATE_GOING:
 322                 jump_label_lock();
 323                 jump_label_del_module(mod);
 324                 jump_label_unlock();
 325                 break;
 326         case MODULE_STATE_LIVE:
 327                 jump_label_lock();
 328                 jump_label_invalidate_module_init(mod);
 329                 jump_label_unlock();
 330                 break;
 331         }
 332
 333         return notifier_from_errno(ret);
 334 }
 335
 336 struct notifier_block jump_label_module_nb = {
 337         .notifier_call = jump_label_module_notify,
 338         .priority = 1, /* higher than tracepoints */
 339 };
 340
 341 static __init int jump_label_init_module(void)
 342 {
 343         return register_module_notifier(&jump_label_module_nb);
 344 }
 345 early_initcall(jump_label_init_module);
 346
 347 #endif /* CONFIG_MODULES */
 348
 349 /***
 350  * jump_label_text_reserved - check if addr range is reserved
 351  * @start: start text addr
 352  * @end: end text addr
 353  *
 354  * checks if the text addr located between @start and @end
 355  * overlaps with any of the jump label patch addresses. Code
 356  * that wants to modify kernel text should first verify that
 357  * it does not overlap with any of the jump label addresses.
 358  * Caller must hold jump_label_mutex.
 359  *
 360  * returns 1 if there is an overlap, 0 otherwise
 361  */
 362 int jump_label_text_reserved(void *start, void *end)
 363 {
 364         int ret = __jump_label_text_reserved(__start___jump_table,
 365                         __stop___jump_table, start, end);
 366
 367         if (ret)
 368                 return ret;
 369
 370 #ifdef CONFIG_MODULES
 371         ret = __jump_label_mod_text_reserved(start, end);
 372 #endif
 373         return ret;
 374 }
 375
 376 static void jump_label_update(struct jump_label_key *key, int enable)
 377 {
 378         struct jump_entry *entry = key->entries;
 379
 380         /* if there are no users, entry can be NULL */
 381         if (entry)
 382                 __jump_label_update(key, entry, __stop___jump_table, enable);
 383
 384 #ifdef CONFIG_MODULES
 385         __jump_label_mod_update(key, enable);
 386 #endif
 387 }
 388
 389 #endif