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
  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
  32static int jump_label_cmp(const void *a, const void *b)
  33{
  34        const struct jump_entry *jea = a;
  35        const struct jump_entry *jeb = b;
  36
  37        if (jea->key < jeb->key)
  38                return -1;
  39
  40        if (jea->key > jeb->key)
  41                return 1;
  42
  43        return 0;
  44}
  45
  46static void
  47jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
  48{
  49        unsigned long size;
  50
  51        size = (((unsigned long)stop - (unsigned long)start)
  52                                        / sizeof(struct jump_entry));
  53        sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
  54}
  55
  56static void jump_label_update(struct static_key *key, int enable);
  57
  58void static_key_slow_inc(struct static_key *key)
  59{
  60        if (atomic_inc_not_zero(&key->enabled))
  61                return;
  62
  63        jump_label_lock();
  64        if (atomic_read(&key->enabled) == 0) {
  65                if (!jump_label_get_branch_default(key))
  66                        jump_label_update(key, JUMP_LABEL_ENABLE);
  67                else
  68                        jump_label_update(key, JUMP_LABEL_DISABLE);
  69        }
  70        atomic_inc(&key->enabled);
  71        jump_label_unlock();
  72}
  73EXPORT_SYMBOL_GPL(static_key_slow_inc);
  74
  75static void __static_key_slow_dec(struct static_key *key,
  76                unsigned long rate_limit, struct delayed_work *work)
  77{
  78        if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
  79                WARN(atomic_read(&key->enabled) < 0,
  80                     "jump label: negative count!\n");
  81                return;
  82        }
  83
  84        if (rate_limit) {
  85                atomic_inc(&key->enabled);
  86                schedule_delayed_work(work, rate_limit);
  87        } else {
  88                if (!jump_label_get_branch_default(key))
  89                        jump_label_update(key, JUMP_LABEL_DISABLE);
  90                else
  91                        jump_label_update(key, JUMP_LABEL_ENABLE);
  92        }
  93        jump_label_unlock();
  94}
  95
  96static void jump_label_update_timeout(struct work_struct *work)
  97{
  98        struct static_key_deferred *key =
  99                container_of(work, struct static_key_deferred, work.work);
 100        __static_key_slow_dec(&key->key, 0, NULL);
 101}
 102
 103void static_key_slow_dec(struct static_key *key)
 104{
 105        __static_key_slow_dec(key, 0, NULL);
 106}
 107EXPORT_SYMBOL_GPL(static_key_slow_dec);
 108
 109void static_key_slow_dec_deferred(struct static_key_deferred *key)
 110{
 111        __static_key_slow_dec(&key->key, key->timeout, &key->work);
 112}
 113EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
 114
 115void jump_label_rate_limit(struct static_key_deferred *key,
 116                unsigned long rl)
 117{
 118        key->timeout = rl;
 119        INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
 120}
 121EXPORT_SYMBOL_GPL(jump_label_rate_limit);
 122
 123static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 124{
 125        if (entry->code <= (unsigned long)end &&
 126                entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
 127                return 1;
 128
 129        return 0;
 130}
 131
 132static int __jump_label_text_reserved(struct jump_entry *iter_start,
 133                struct jump_entry *iter_stop, void *start, void *end)
 134{
 135        struct jump_entry *iter;
 136
 137        iter = iter_start;
 138        while (iter < iter_stop) {
 139                if (addr_conflict(iter, start, end))
 140                        return 1;
 141                iter++;
 142        }
 143
 144        return 0;
 145}
 146
 147/* 
 148 * Update code which is definitely not currently executing.
 149 * Architectures which need heavyweight synchronization to modify
 150 * running code can override this to make the non-live update case
 151 * cheaper.
 152 */
 153void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
 154                                            enum jump_label_type type)
 155{
 156        arch_jump_label_transform(entry, type); 
 157}
 158
 159static void __jump_label_update(struct static_key *key,
 160                                struct jump_entry *entry,
 161                                struct jump_entry *stop, int enable)
 162{
 163        for (; (entry < stop) &&
 164              (entry->key == (jump_label_t)(unsigned long)key);
 165              entry++) {
 166                /*
 167                 * entry->code set to 0 invalidates module init text sections
 168                 * kernel_text_address() verifies we are not in core kernel
 169                 * init code, see jump_label_invalidate_module_init().
 170                 */
 171                if (entry->code && kernel_text_address(entry->code))
 172                        arch_jump_label_transform(entry, enable);
 173        }
 174}
 175
 176static enum jump_label_type jump_label_type(struct static_key *key)
 177{
 178        bool true_branch = jump_label_get_branch_default(key);
 179        bool state = static_key_enabled(key);
 180
 181        if ((!true_branch && state) || (true_branch && !state))
 182                return JUMP_LABEL_ENABLE;
 183
 184        return JUMP_LABEL_DISABLE;
 185}
 186
 187void __init jump_label_init(void)
 188{
 189        struct jump_entry *iter_start = __start___jump_table;
 190        struct jump_entry *iter_stop = __stop___jump_table;
 191        struct static_key *key = NULL;
 192        struct jump_entry *iter;
 193
 194        jump_label_lock();
 195        jump_label_sort_entries(iter_start, iter_stop);
 196
 197        for (iter = iter_start; iter < iter_stop; iter++) {
 198                struct static_key *iterk;
 199
 200                iterk = (struct static_key *)(unsigned long)iter->key;
 201                arch_jump_label_transform_static(iter, jump_label_type(iterk));
 202                if (iterk == key)
 203                        continue;
 204
 205                key = iterk;
 206                /*
 207                 * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 208                 */
 209                *((unsigned long *)&key->entries) += (unsigned long)iter;
 210#ifdef CONFIG_MODULES
 211                key->next = NULL;
 212#endif
 213        }
 214        jump_label_unlock();
 215}
 216
 217#ifdef CONFIG_MODULES
 218
 219struct static_key_mod {
 220        struct static_key_mod *next;
 221        struct jump_entry *entries;
 222        struct module *mod;
 223};
 224
 225static int __jump_label_mod_text_reserved(void *start, void *end)
 226{
 227        struct module *mod;
 228
 229        mod = __module_text_address((unsigned long)start);
 230        if (!mod)
 231                return 0;
 232
 233        WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 234
 235        return __jump_label_text_reserved(mod->jump_entries,
 236                                mod->jump_entries + mod->num_jump_entries,
 237                                start, end);
 238}
 239
 240static void __jump_label_mod_update(struct static_key *key, int enable)
 241{
 242        struct static_key_mod *mod = key->next;
 243
 244        while (mod) {
 245                struct module *m = mod->mod;
 246
 247                __jump_label_update(key, mod->entries,
 248                                    m->jump_entries + m->num_jump_entries,
 249                                    enable);
 250                mod = mod->next;
 251        }
 252}
 253
 254/***
 255 * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 256 * @mod: module to patch
 257 *
 258 * Allow for run-time selection of the optimal nops. Before the module
 259 * loads patch these with arch_get_jump_label_nop(), which is specified by
 260 * the arch specific jump label code.
 261 */
 262void jump_label_apply_nops(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
 268        /* if the module doesn't have jump label entries, just return */
 269        if (iter_start == iter_stop)
 270                return;
 271
 272        for (iter = iter_start; iter < iter_stop; iter++) {
 273                arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
 274        }
 275}
 276
 277static int jump_label_add_module(struct module *mod)
 278{
 279        struct jump_entry *iter_start = mod->jump_entries;
 280        struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 281        struct jump_entry *iter;
 282        struct static_key *key = NULL;
 283        struct static_key_mod *jlm;
 284
 285        /* if the module doesn't have jump label entries, just return */
 286        if (iter_start == iter_stop)
 287                return 0;
 288
 289        jump_label_sort_entries(iter_start, iter_stop);
 290
 291        for (iter = iter_start; iter < iter_stop; iter++) {
 292                struct static_key *iterk;
 293
 294                iterk = (struct static_key *)(unsigned long)iter->key;
 295                if (iterk == key)
 296                        continue;
 297
 298                key = iterk;
 299                if (__module_address(iter->key) == mod) {
 300                        /*
 301                         * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 302                         */
 303                        *((unsigned long *)&key->entries) += (unsigned long)iter;
 304                        key->next = NULL;
 305                        continue;
 306                }
 307                jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
 308                if (!jlm)
 309                        return -ENOMEM;
 310                jlm->mod = mod;
 311                jlm->entries = iter;
 312                jlm->next = key->next;
 313                key->next = jlm;
 314
 315                if (jump_label_type(key) == JUMP_LABEL_ENABLE)
 316                        __jump_label_update(key, iter, iter_stop, JUMP_LABEL_ENABLE);
 317        }
 318
 319        return 0;
 320}
 321
 322static void jump_label_del_module(struct module *mod)
 323{
 324        struct jump_entry *iter_start = mod->jump_entries;
 325        struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 326        struct jump_entry *iter;
 327        struct static_key *key = NULL;
 328        struct static_key_mod *jlm, **prev;
 329
 330        for (iter = iter_start; iter < iter_stop; iter++) {
 331                if (iter->key == (jump_label_t)(unsigned long)key)
 332                        continue;
 333
 334                key = (struct static_key *)(unsigned long)iter->key;
 335
 336                if (__module_address(iter->key) == mod)
 337                        continue;
 338
 339                prev = &key->next;
 340                jlm = key->next;
 341
 342                while (jlm && jlm->mod != mod) {
 343                        prev = &jlm->next;
 344                        jlm = jlm->next;
 345                }
 346
 347                if (jlm) {
 348                        *prev = jlm->next;
 349                        kfree(jlm);
 350                }
 351        }
 352}
 353
 354static void jump_label_invalidate_module_init(struct module *mod)
 355{
 356        struct jump_entry *iter_start = mod->jump_entries;
 357        struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 358        struct jump_entry *iter;
 359
 360        for (iter = iter_start; iter < iter_stop; iter++) {
 361                if (within_module_init(iter->code, mod))
 362                        iter->code = 0;
 363        }
 364}
 365
 366static int
 367jump_label_module_notify(struct notifier_block *self, unsigned long val,
 368                         void *data)
 369{
 370        struct module *mod = data;
 371        int ret = 0;
 372
 373        switch (val) {
 374        case MODULE_STATE_COMING:
 375                jump_label_lock();
 376                ret = jump_label_add_module(mod);
 377                if (ret)
 378                        jump_label_del_module(mod);
 379                jump_label_unlock();
 380                break;
 381        case MODULE_STATE_GOING:
 382                jump_label_lock();
 383                jump_label_del_module(mod);
 384                jump_label_unlock();
 385                break;
 386        case MODULE_STATE_LIVE:
 387                jump_label_lock();
 388                jump_label_invalidate_module_init(mod);
 389                jump_label_unlock();
 390                break;
 391        }
 392
 393        return notifier_from_errno(ret);
 394}
 395
 396struct notifier_block jump_label_module_nb = {
 397        .notifier_call = jump_label_module_notify,
 398        .priority = 1, /* higher than tracepoints */
 399};
 400
 401static __init int jump_label_init_module(void)
 402{
 403        return register_module_notifier(&jump_label_module_nb);
 404}
 405early_initcall(jump_label_init_module);
 406
 407#endif /* CONFIG_MODULES */
 408
 409/***
 410 * jump_label_text_reserved - check if addr range is reserved
 411 * @start: start text addr
 412 * @end: end text addr
 413 *
 414 * checks if the text addr located between @start and @end
 415 * overlaps with any of the jump label patch addresses. Code
 416 * that wants to modify kernel text should first verify that
 417 * it does not overlap with any of the jump label addresses.
 418 * Caller must hold jump_label_mutex.
 419 *
 420 * returns 1 if there is an overlap, 0 otherwise
 421 */
 422int jump_label_text_reserved(void *start, void *end)
 423{
 424        int ret = __jump_label_text_reserved(__start___jump_table,
 425                        __stop___jump_table, start, end);
 426
 427        if (ret)
 428                return ret;
 429
 430#ifdef CONFIG_MODULES
 431        ret = __jump_label_mod_text_reserved(start, end);
 432#endif
 433        return ret;
 434}
 435
 436static void jump_label_update(struct static_key *key, int enable)
 437{
 438        struct jump_entry *stop = __stop___jump_table;
 439        struct jump_entry *entry = jump_label_get_entries(key);
 440
 441#ifdef CONFIG_MODULES
 442        struct module *mod = __module_address((unsigned long)key);
 443
 444        __jump_label_mod_update(key, enable);
 445
 446        if (mod)
 447                stop = mod->jump_entries + mod->num_jump_entries;
 448#endif
 449        /* if there are no users, entry can be NULL */
 450        if (entry)
 451                __jump_label_update(key, entry, stop, enable);
 452}
 453
 454#endif
 455
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