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/jump_label.h>
  16
  17#ifdef HAVE_JUMP_LABEL
  18
  19/* mutex to protect coming/going of the the jump_label table */
  20static DEFINE_MUTEX(jump_label_mutex);
  21
  22void jump_label_lock(void)
  23{
  24        mutex_lock(&jump_label_mutex);
  25}
  26
  27void jump_label_unlock(void)
  28{
  29        mutex_unlock(&jump_label_mutex);
  30}
  31
  32bool jump_label_enabled(struct jump_label_key *key)
  33{
  34        return !!atomic_read(&key->enabled);
  35}
  36
  37static 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
  51static void
  52jump_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
  61static void jump_label_update(struct jump_label_key *key, int enable);
  62
  63void 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_read(&key->enabled) == 0)
  70                jump_label_update(key, JUMP_LABEL_ENABLE);
  71        atomic_inc(&key->enabled);
  72        jump_label_unlock();
  73}
  74
  75void jump_label_dec(struct jump_label_key *key)
  76{
  77        if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex))
  78                return;
  79
  80        jump_label_update(key, JUMP_LABEL_DISABLE);
  81        jump_label_unlock();
  82}
  83
  84static int addr_conflict(struct jump_entry *entry, void *start, void *end)
  85{
  86        if (entry->code <= (unsigned long)end &&
  87                entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
  88                return 1;
  89
  90        return 0;
  91}
  92
  93static int __jump_label_text_reserved(struct jump_entry *iter_start,
  94                struct jump_entry *iter_stop, void *start, void *end)
  95{
  96        struct jump_entry *iter;
  97
  98        iter = iter_start;
  99        while (iter < iter_stop) {
 100                if (addr_conflict(iter, start, end))
 101                        return 1;
 102                iter++;
 103        }
 104
 105        return 0;
 106}
 107
 108static void __jump_label_update(struct jump_label_key *key,
 109                                struct jump_entry *entry,
 110                                struct jump_entry *stop, int enable)
 111{
 112        for (; (entry < stop) &&
 113              (entry->key == (jump_label_t)(unsigned long)key);
 114              entry++) {
 115                /*
 116                 * entry->code set to 0 invalidates module init text sections
 117                 * kernel_text_address() verifies we are not in core kernel
 118                 * init code, see jump_label_invalidate_module_init().
 119                 */
 120                if (entry->code && kernel_text_address(entry->code))
 121                        arch_jump_label_transform(entry, enable);
 122        }
 123}
 124
 125/*
 126 * Not all archs need this.
 127 */
 128void __weak arch_jump_label_text_poke_early(jump_label_t addr)
 129{
 130}
 131
 132static __init int jump_label_init(void)
 133{
 134        struct jump_entry *iter_start = __start___jump_table;
 135        struct jump_entry *iter_stop = __stop___jump_table;
 136        struct jump_label_key *key = NULL;
 137        struct jump_entry *iter;
 138
 139        jump_label_lock();
 140        jump_label_sort_entries(iter_start, iter_stop);
 141
 142        for (iter = iter_start; iter < iter_stop; iter++) {
 143                arch_jump_label_text_poke_early(iter->code);
 144                if (iter->key == (jump_label_t)(unsigned long)key)
 145                        continue;
 146
 147                key = (struct jump_label_key *)(unsigned long)iter->key;
 148                atomic_set(&key->enabled, 0);
 149                key->entries = iter;
 150#ifdef CONFIG_MODULES
 151                key->next = NULL;
 152#endif
 153        }
 154        jump_label_unlock();
 155
 156        return 0;
 157}
 158early_initcall(jump_label_init);
 159
 160#ifdef CONFIG_MODULES
 161
 162struct jump_label_mod {
 163        struct jump_label_mod *next;
 164        struct jump_entry *entries;
 165        struct module *mod;
 166};
 167
 168static int __jump_label_mod_text_reserved(void *start, void *end)
 169{
 170        struct module *mod;
 171
 172        mod = __module_text_address((unsigned long)start);
 173        if (!mod)
 174                return 0;
 175
 176        WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 177
 178        return __jump_label_text_reserved(mod->jump_entries,
 179                                mod->jump_entries + mod->num_jump_entries,
 180                                start, end);
 181}
 182
 183static void __jump_label_mod_update(struct jump_label_key *key, int enable)
 184{
 185        struct jump_label_mod *mod = key->next;
 186
 187        while (mod) {
 188                struct module *m = mod->mod;
 189
 190                __jump_label_update(key, mod->entries,
 191                                    m->jump_entries + m->num_jump_entries,
 192                                    enable);
 193                mod = mod->next;
 194        }
 195}
 196
 197/***
 198 * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 199 * @mod: module to patch
 200 *
 201 * Allow for run-time selection of the optimal nops. Before the module
 202 * loads patch these with arch_get_jump_label_nop(), which is specified by
 203 * the arch specific jump label code.
 204 */
 205void jump_label_apply_nops(struct module *mod)
 206{
 207        struct jump_entry *iter_start = mod->jump_entries;
 208        struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 209        struct jump_entry *iter;
 210
 211        /* if the module doesn't have jump label entries, just return */
 212        if (iter_start == iter_stop)
 213                return;
 214
 215        for (iter = iter_start; iter < iter_stop; iter++)
 216                arch_jump_label_text_poke_early(iter->code);
 217}
 218
 219static int jump_label_add_module(struct module *mod)
 220{
 221        struct jump_entry *iter_start = mod->jump_entries;
 222        struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 223        struct jump_entry *iter;
 224        struct jump_label_key *key = NULL;
 225        struct jump_label_mod *jlm;
 226
 227        /* if the module doesn't have jump label entries, just return */
 228        if (iter_start == iter_stop)
 229                return 0;
 230
 231        jump_label_sort_entries(iter_start, iter_stop);
 232
 233        for (iter = iter_start; iter < iter_stop; iter++) {
 234                if (iter->key == (jump_label_t)(unsigned long)key)
 235                        continue;
 236
 237                key = (struct jump_label_key *)(unsigned long)iter->key;
 238
 239                if (__module_address(iter->key) == mod) {
 240                        atomic_set(&key->enabled, 0);
 241                        key->entries = iter;
 242                        key->next = NULL;
 243                        continue;
 244                }
 245
 246                jlm = kzalloc(sizeof(struct jump_label_mod), GFP_KERNEL);
 247                if (!jlm)
 248                        return -ENOMEM;
 249
 250                jlm->mod = mod;
 251                jlm->entries = iter;
 252                jlm->next = key->next;
 253                key->next = jlm;
 254
 255                if (jump_label_enabled(key))
 256                        __jump_label_update(key, iter, iter_stop,
 257                                            JUMP_LABEL_ENABLE);
 258        }
 259
 260        return 0;
 261}
 262
 263static void jump_label_del_module(struct module *mod)
 264{
 265        struct jump_entry *iter_start = mod->jump_entries;
 266        struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 267        struct jump_entry *iter;
 268        struct jump_label_key *key = NULL;
 269        struct jump_label_mod *jlm, **prev;
 270
 271        for (iter = iter_start; iter < iter_stop; iter++) {
 272                if (iter->key == (jump_label_t)(unsigned long)key)
 273                        continue;
 274
 275                key = (struct jump_label_key *)(unsigned long)iter->key;
 276
 277                if (__module_address(iter->key) == mod)
 278                        continue;
 279
 280                prev = &key->next;
 281                jlm = key->next;
 282
 283                while (jlm && jlm->mod != mod) {
 284                        prev = &jlm->next;
 285                        jlm = jlm->next;
 286                }
 287
 288                if (jlm) {
 289                        *prev = jlm->next;
 290                        kfree(jlm);
 291                }
 292        }
 293}
 294
 295static void jump_label_invalidate_module_init(struct module *mod)
 296{
 297        struct jump_entry *iter_start = mod->jump_entries;
 298        struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 299        struct jump_entry *iter;
 300
 301        for (iter = iter_start; iter < iter_stop; iter++) {
 302                if (within_module_init(iter->code, mod))
 303                        iter->code = 0;
 304        }
 305}
 306
 307static int
 308jump_label_module_notify(struct notifier_block *self, unsigned long val,
 309                         void *data)
 310{
 311        struct module *mod = data;
 312        int ret = 0;
 313
 314        switch (val) {
 315        case MODULE_STATE_COMING:
 316                jump_label_lock();
 317                ret = jump_label_add_module(mod);
 318                if (ret)
 319                        jump_label_del_module(mod);
 320                jump_label_unlock();
 321                break;
 322        case MODULE_STATE_GOING:
 323                jump_label_lock();
 324                jump_label_del_module(mod);
 325                jump_label_unlock();
 326                break;
 327        case MODULE_STATE_LIVE:
 328                jump_label_lock();
 329                jump_label_invalidate_module_init(mod);
 330                jump_label_unlock();
 331                break;
 332        }
 333
 334        return notifier_from_errno(ret);
 335}
 336
 337struct notifier_block jump_label_module_nb = {
 338        .notifier_call = jump_label_module_notify,
 339        .priority = 1, /* higher than tracepoints */
 340};
 341
 342static __init int jump_label_init_module(void)
 343{
 344        return register_module_notifier(&jump_label_module_nb);
 345}
 346early_initcall(jump_label_init_module);
 347
 348#endif /* CONFIG_MODULES */
 349
 350/***
 351 * jump_label_text_reserved - check if addr range is reserved
 352 * @start: start text addr
 353 * @end: end text addr
 354 *
 355 * checks if the text addr located between @start and @end
 356 * overlaps with any of the jump label patch addresses. Code
 357 * that wants to modify kernel text should first verify that
 358 * it does not overlap with any of the jump label addresses.
 359 * Caller must hold jump_label_mutex.
 360 *
 361 * returns 1 if there is an overlap, 0 otherwise
 362 */
 363int jump_label_text_reserved(void *start, void *end)
 364{
 365        int ret = __jump_label_text_reserved(__start___jump_table,
 366                        __stop___jump_table, start, end);
 367
 368        if (ret)
 369                return ret;
 370
 371#ifdef CONFIG_MODULES
 372        ret = __jump_label_mod_text_reserved(start, end);
 373#endif
 374        return ret;
 375}
 376
 377static void jump_label_update(struct jump_label_key *key, int enable)
 378{
 379        struct jump_entry *entry = key->entries, *stop = __stop___jump_table;
 380
 381#ifdef CONFIG_MODULES
 382        struct module *mod = __module_address((jump_label_t)key);
 383
 384        __jump_label_mod_update(key, enable);
 385
 386        if (mod)
 387                stop = mod->jump_entries + mod->num_jump_entries;
 388#endif
 389        /* if there are no users, entry can be NULL */
 390        if (entry)
 391                __jump_label_update(key, entry, stop, enable);
 392}
 393
 394#endif
 395
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