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 */
  21static DEFINE_MUTEX(jump_label_mutex);
  22
  23void jump_label_lock(void)
  24{
  25        mutex_lock(&jump_label_mutex);
  26}
  27
  28void jump_label_unlock(void)
  29{
  30        mutex_unlock(&jump_label_mutex);
  31}
  32
  33static 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
  47static void
  48jump_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
  57static void jump_label_update(struct static_key *key, int enable);
  58
  59void static_key_slow_inc(struct static_key *key)
  60{
  61        if (atomic_inc_not_zero(&key->enabled))
  62                return;
  63
  64        jump_label_lock();
  65        if (atomic_read(&key->enabled) == 0) {
  66                if (!jump_label_get_branch_default(key))
  67                        jump_label_update(key, JUMP_LABEL_ENABLE);
  68                else
  69                        jump_label_update(key, JUMP_LABEL_DISABLE);
  70        }
  71        atomic_inc(&key->enabled);
  72        jump_label_unlock();
  73}
  74EXPORT_SYMBOL_GPL(static_key_slow_inc);
  75
  76static void __static_key_slow_dec(struct static_key *key,
  77                unsigned long rate_limit, struct delayed_work *work)
  78{
  79        if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
  80                WARN(atomic_read(&key->enabled) < 0,
  81                     "jump label: negative count!\n");
  82                return;
  83        }
  84
  85        if (rate_limit) {
  86                atomic_inc(&key->enabled);
  87                schedule_delayed_work(work, rate_limit);
  88        } else {
  89                if (!jump_label_get_branch_default(key))
  90                        jump_label_update(key, JUMP_LABEL_DISABLE);
  91                else
  92                        jump_label_update(key, JUMP_LABEL_ENABLE);
  93        }
  94        jump_label_unlock();
  95}
  96
  97static void jump_label_update_timeout(struct work_struct *work)
  98{
  99        struct static_key_deferred *key =
 100                container_of(work, struct static_key_deferred, work.work);
 101        __static_key_slow_dec(&key->key, 0, NULL);
 102}
 103
 104void static_key_slow_dec(struct static_key *key)
 105{
 106        __static_key_slow_dec(key, 0, NULL);
 107}
 108EXPORT_SYMBOL_GPL(static_key_slow_dec);
 109
 110void static_key_slow_dec_deferred(struct static_key_deferred *key)
 111{
 112        __static_key_slow_dec(&key->key, key->timeout, &key->work);
 113}
 114EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
 115
 116void jump_label_rate_limit(struct static_key_deferred *key,
 117                unsigned long rl)
 118{
 119        key->timeout = rl;
 120        INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
 121}
 122EXPORT_SYMBOL_GPL(jump_label_rate_limit);
 123
 124static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 125{
 126        if (entry->code <= (unsigned long)end &&
 127                entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
 128                return 1;
 129
 130        return 0;
 131}
 132
 133static int __jump_label_text_reserved(struct jump_entry *iter_start,
 134                struct jump_entry *iter_stop, void *start, void *end)
 135{
 136        struct jump_entry *iter;
 137
 138        iter = iter_start;
 139        while (iter < iter_stop) {
 140                if (addr_conflict(iter, start, end))
 141                        return 1;
 142                iter++;
 143        }
 144
 145        return 0;
 146}
 147
 148/* 
 149 * Update code which is definitely not currently executing.
 150 * Architectures which need heavyweight synchronization to modify
 151 * running code can override this to make the non-live update case
 152 * cheaper.
 153 */
 154void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
 155                                            enum jump_label_type type)
 156{
 157        arch_jump_label_transform(entry, type); 
 158}
 159
 160static void __jump_label_update(struct static_key *key,
 161                                struct jump_entry *entry,
 162                                struct jump_entry *stop, int enable)
 163{
 164        for (; (entry < stop) &&
 165              (entry->key == (jump_label_t)(unsigned long)key);
 166              entry++) {
 167                /*
 168                 * entry->code set to 0 invalidates module init text sections
 169                 * kernel_text_address() verifies we are not in core kernel
 170                 * init code, see jump_label_invalidate_module_init().
 171                 */
 172                if (entry->code && kernel_text_address(entry->code))
 173                        arch_jump_label_transform(entry, enable);
 174        }
 175}
 176
 177static enum jump_label_type jump_label_type(struct static_key *key)
 178{
 179        bool true_branch = jump_label_get_branch_default(key);
 180        bool state = static_key_enabled(key);
 181
 182        if ((!true_branch && state) || (true_branch && !state))
 183                return JUMP_LABEL_ENABLE;
 184
 185        return JUMP_LABEL_DISABLE;
 186}
 187
 188void __init jump_label_init(void)
 189{
 190        struct jump_entry *iter_start = __start___jump_table;
 191        struct jump_entry *iter_stop = __stop___jump_table;
 192        struct static_key *key = NULL;
 193        struct jump_entry *iter;
 194
 195        jump_label_lock();
 196        jump_label_sort_entries(iter_start, iter_stop);
 197
 198        for (iter = iter_start; iter < iter_stop; iter++) {
 199                struct static_key *iterk;
 200
 201                iterk = (struct static_key *)(unsigned long)iter->key;
 202                arch_jump_label_transform_static(iter, jump_label_type(iterk));
 203                if (iterk == key)
 204                        continue;
 205
 206                key = iterk;
 207                /*
 208                 * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 209                 */
 210                *((unsigned long *)&key->entries) += (unsigned long)iter;
 211#ifdef CONFIG_MODULES
 212                key->next = NULL;
 213#endif
 214        }
 215        jump_label_unlock();
 216}
 217
 218#ifdef CONFIG_MODULES
 219
 220struct static_key_mod {
 221        struct static_key_mod *next;
 222        struct jump_entry *entries;
 223        struct module *mod;
 224};
 225
 226static int __jump_label_mod_text_reserved(void *start, void *end)
 227{
 228        struct module *mod;
 229
 230        mod = __module_text_address((unsigned long)start);
 231        if (!mod)
 232                return 0;
 233
 234        WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 235
 236        return __jump_label_text_reserved(mod->jump_entries,
 237                                mod->jump_entries + mod->num_jump_entries,
 238                                start, end);
 239}
 240
 241static void __jump_label_mod_update(struct static_key *key, int enable)
 242{
 243        struct static_key_mod *mod = key->next;
 244
 245        while (mod) {
 246                struct module *m = mod->mod;
 247
 248                __jump_label_update(key, mod->entries,
 249                                    m->jump_entries + m->num_jump_entries,
 250                                    enable);
 251                mod = mod->next;
 252        }
 253}
 254
 255/***
 256 * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 257 * @mod: module to patch
 258 *
 259 * Allow for run-time selection of the optimal nops. Before the module
 260 * loads patch these with arch_get_jump_label_nop(), which is specified by
 261 * the arch specific jump label code.
 262 */
 263void jump_label_apply_nops(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
 269        /* if the module doesn't have jump label entries, just return */
 270        if (iter_start == iter_stop)
 271                return;
 272
 273        for (iter = iter_start; iter < iter_stop; iter++) {
 274                arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
 275        }
 276}
 277
 278static int jump_label_add_module(struct module *mod)
 279{
 280        struct jump_entry *iter_start = mod->jump_entries;
 281        struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 282        struct jump_entry *iter;
 283        struct static_key *key = NULL;
 284        struct static_key_mod *jlm;
 285
 286        /* if the module doesn't have jump label entries, just return */
 287        if (iter_start == iter_stop)
 288                return 0;
 289
 290        jump_label_sort_entries(iter_start, iter_stop);
 291
 292        for (iter = iter_start; iter < iter_stop; iter++) {
 293                struct static_key *iterk;
 294
 295                iterk = (struct static_key *)(unsigned long)iter->key;
 296                if (iterk == key)
 297                        continue;
 298
 299                key = iterk;
 300                if (__module_address(iter->key) == mod) {
 301                        /*
 302                         * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 303                         */
 304                        *((unsigned long *)&key->entries) += (unsigned long)iter;
 305                        key->next = NULL;
 306                        continue;
 307                }
 308                jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
 309                if (!jlm)
 310                        return -ENOMEM;
 311                jlm->mod = mod;
 312                jlm->entries = iter;
 313                jlm->next = key->next;
 314                key->next = jlm;
 315
 316                if (jump_label_type(key) == JUMP_LABEL_ENABLE)
 317                        __jump_label_update(key, iter, iter_stop, JUMP_LABEL_ENABLE);
 318        }
 319
 320        return 0;
 321}
 322
 323static void jump_label_del_module(struct module *mod)
 324{
 325        struct jump_entry *iter_start = mod->jump_entries;
 326        struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 327        struct jump_entry *iter;
 328        struct static_key *key = NULL;
 329        struct static_key_mod *jlm, **prev;
 330
 331        for (iter = iter_start; iter < iter_stop; iter++) {
 332                if (iter->key == (jump_label_t)(unsigned long)key)
 333                        continue;
 334
 335                key = (struct static_key *)(unsigned long)iter->key;
 336
 337                if (__module_address(iter->key) == mod)
 338                        continue;
 339
 340                prev = &key->next;
 341                jlm = key->next;
 342
 343                while (jlm && jlm->mod != mod) {
 344                        prev = &jlm->next;
 345                        jlm = jlm->next;
 346                }
 347
 348                if (jlm) {
 349                        *prev = jlm->next;
 350                        kfree(jlm);
 351                }
 352        }
 353}
 354
 355static void jump_label_invalidate_module_init(struct module *mod)
 356{
 357        struct jump_entry *iter_start = mod->jump_entries;
 358        struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 359        struct jump_entry *iter;
 360
 361        for (iter = iter_start; iter < iter_stop; iter++) {
 362                if (within_module_init(iter->code, mod))
 363                        iter->code = 0;
 364        }
 365}
 366
 367static int
 368jump_label_module_notify(struct notifier_block *self, unsigned long val,
 369                         void *data)
 370{
 371        struct module *mod = data;
 372        int ret = 0;
 373
 374        switch (val) {
 375        case MODULE_STATE_COMING:
 376                jump_label_lock();
 377                ret = jump_label_add_module(mod);
 378                if (ret)
 379                        jump_label_del_module(mod);
 380                jump_label_unlock();
 381                break;
 382        case MODULE_STATE_GOING:
 383                jump_label_lock();
 384                jump_label_del_module(mod);
 385                jump_label_unlock();
 386                break;
 387        case MODULE_STATE_LIVE:
 388                jump_label_lock();
 389                jump_label_invalidate_module_init(mod);
 390                jump_label_unlock();
 391                break;
 392        }
 393
 394        return notifier_from_errno(ret);
 395}
 396
 397struct notifier_block jump_label_module_nb = {
 398        .notifier_call = jump_label_module_notify,
 399        .priority = 1, /* higher than tracepoints */
 400};
 401
 402static __init int jump_label_init_module(void)
 403{
 404        return register_module_notifier(&jump_label_module_nb);
 405}
 406early_initcall(jump_label_init_module);
 407
 408#endif /* CONFIG_MODULES */
 409
 410/***
 411 * jump_label_text_reserved - check if addr range is reserved
 412 * @start: start text addr
 413 * @end: end text addr
 414 *
 415 * checks if the text addr located between @start and @end
 416 * overlaps with any of the jump label patch addresses. Code
 417 * that wants to modify kernel text should first verify that
 418 * it does not overlap with any of the jump label addresses.
 419 * Caller must hold jump_label_mutex.
 420 *
 421 * returns 1 if there is an overlap, 0 otherwise
 422 */
 423int jump_label_text_reserved(void *start, void *end)
 424{
 425        int ret = __jump_label_text_reserved(__start___jump_table,
 426                        __stop___jump_table, start, end);
 427
 428        if (ret)
 429                return ret;
 430
 431#ifdef CONFIG_MODULES
 432        ret = __jump_label_mod_text_reserved(start, end);
 433#endif
 434        return ret;
 435}
 436
 437static void jump_label_update(struct static_key *key, int enable)
 438{
 439        struct jump_entry *stop = __stop___jump_table;
 440        struct jump_entry *entry = jump_label_get_entries(key);
 441
 442#ifdef CONFIG_MODULES
 443        struct module *mod = __module_address((unsigned long)key);
 444
 445        __jump_label_mod_update(key, enable);
 446
 447        if (mod)
 448                stop = mod->jump_entries + mod->num_jump_entries;
 449#endif
 450        /* if there are no users, entry can be NULL */
 451        if (entry)
 452                __jump_label_update(key, entry, stop, enable);
 453}
 454
 455#endif
 456
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