4 * Copyright (C) 2009 Jason Baron <jbaron@redhat.com>
5 * Copyright (C) 2011 Peter Zijlstra
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 #include <linux/bug.h>
19 #ifdef HAVE_JUMP_LABEL
21 /* mutex to protect coming/going of the the jump_label table */
22 static DEFINE_MUTEX(jump_label_mutex);
24 void jump_label_lock(void)
26 mutex_lock(&jump_label_mutex);
29 void jump_label_unlock(void)
31 mutex_unlock(&jump_label_mutex);
34 static int jump_label_cmp(const void *a, const void *b)
36 const struct jump_entry *jea = a;
37 const struct jump_entry *jeb = b;
39 if (jea->key < jeb->key)
42 if (jea->key > jeb->key)
49 jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
53 size = (((unsigned long)stop - (unsigned long)start)
54 / sizeof(struct jump_entry));
55 sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
58 static void jump_label_update(struct static_key *key);
61 * There are similar definitions for the !HAVE_JUMP_LABEL case in jump_label.h.
62 * The use of 'atomic_read()' requires atomic.h and its problematic for some
63 * kernel headers such as kernel.h and others. Since static_key_count() is not
64 * used in the branch statements as it is for the !HAVE_JUMP_LABEL case its ok
65 * to have it be a function here. Similarly, for 'static_key_enable()' and
66 * 'static_key_disable()', which require bug.h. This should allow jump_label.h
67 * to be included from most/all places for HAVE_JUMP_LABEL.
69 int static_key_count(struct static_key *key)
72 * -1 means the first static_key_slow_inc() is in progress.
73 * static_key_enabled() must return true, so return 1 here.
75 int n = atomic_read(&key->enabled);
77 return n >= 0 ? n : 1;
79 EXPORT_SYMBOL_GPL(static_key_count);
81 void static_key_enable(struct static_key *key)
83 int count = static_key_count(key);
85 WARN_ON_ONCE(count < 0 || count > 1);
88 static_key_slow_inc(key);
90 EXPORT_SYMBOL_GPL(static_key_enable);
92 void static_key_disable(struct static_key *key)
94 int count = static_key_count(key);
96 WARN_ON_ONCE(count < 0 || count > 1);
99 static_key_slow_dec(key);
101 EXPORT_SYMBOL_GPL(static_key_disable);
103 void static_key_slow_inc(struct static_key *key)
107 STATIC_KEY_CHECK_USE();
110 * Careful if we get concurrent static_key_slow_inc() calls;
111 * later calls must wait for the first one to _finish_ the
112 * jump_label_update() process. At the same time, however,
113 * the jump_label_update() call below wants to see
114 * static_key_enabled(&key) for jumps to be updated properly.
116 * So give a special meaning to negative key->enabled: it sends
117 * static_key_slow_inc() down the slow path, and it is non-zero
118 * so it counts as "enabled" in jump_label_update(). Note that
119 * atomic_inc_unless_negative() checks >= 0, so roll our own.
121 for (v = atomic_read(&key->enabled); v > 0; v = v1) {
122 v1 = atomic_cmpxchg(&key->enabled, v, v + 1);
128 if (atomic_read(&key->enabled) == 0) {
129 atomic_set(&key->enabled, -1);
130 jump_label_update(key);
131 atomic_set(&key->enabled, 1);
133 atomic_inc(&key->enabled);
137 EXPORT_SYMBOL_GPL(static_key_slow_inc);
139 static void __static_key_slow_dec(struct static_key *key,
140 unsigned long rate_limit, struct delayed_work *work)
143 * The negative count check is valid even when a negative
144 * key->enabled is in use by static_key_slow_inc(); a
145 * __static_key_slow_dec() before the first static_key_slow_inc()
146 * returns is unbalanced, because all other static_key_slow_inc()
147 * instances block while the update is in progress.
149 if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
150 WARN(atomic_read(&key->enabled) < 0,
151 "jump label: negative count!\n");
156 atomic_inc(&key->enabled);
157 schedule_delayed_work(work, rate_limit);
159 jump_label_update(key);
164 static void jump_label_update_timeout(struct work_struct *work)
166 struct static_key_deferred *key =
167 container_of(work, struct static_key_deferred, work.work);
168 __static_key_slow_dec(&key->key, 0, NULL);
171 void static_key_slow_dec(struct static_key *key)
173 STATIC_KEY_CHECK_USE();
174 __static_key_slow_dec(key, 0, NULL);
176 EXPORT_SYMBOL_GPL(static_key_slow_dec);
178 void static_key_slow_dec_deferred(struct static_key_deferred *key)
180 STATIC_KEY_CHECK_USE();
181 __static_key_slow_dec(&key->key, key->timeout, &key->work);
183 EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
185 void jump_label_rate_limit(struct static_key_deferred *key,
188 STATIC_KEY_CHECK_USE();
190 INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
192 EXPORT_SYMBOL_GPL(jump_label_rate_limit);
194 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
196 if (entry->code <= (unsigned long)end &&
197 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
203 static int __jump_label_text_reserved(struct jump_entry *iter_start,
204 struct jump_entry *iter_stop, void *start, void *end)
206 struct jump_entry *iter;
209 while (iter < iter_stop) {
210 if (addr_conflict(iter, start, end))
219 * Update code which is definitely not currently executing.
220 * Architectures which need heavyweight synchronization to modify
221 * running code can override this to make the non-live update case
224 void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
225 enum jump_label_type type)
227 arch_jump_label_transform(entry, type);
230 static inline struct jump_entry *static_key_entries(struct static_key *key)
232 WARN_ON_ONCE(key->type & JUMP_TYPE_LINKED);
233 return (struct jump_entry *)(key->type & ~JUMP_TYPE_MASK);
236 static inline bool static_key_type(struct static_key *key)
238 return key->type & JUMP_TYPE_TRUE;
241 static inline bool static_key_linked(struct static_key *key)
243 return key->type & JUMP_TYPE_LINKED;
246 static inline void static_key_clear_linked(struct static_key *key)
248 key->type &= ~JUMP_TYPE_LINKED;
251 static inline void static_key_set_linked(struct static_key *key)
253 key->type |= JUMP_TYPE_LINKED;
256 static inline struct static_key *jump_entry_key(struct jump_entry *entry)
258 return (struct static_key *)((unsigned long)entry->key & ~1UL);
261 static bool jump_entry_branch(struct jump_entry *entry)
263 return (unsigned long)entry->key & 1UL;
267 * A 'struct static_key' uses a union such that it either points directly
268 * to a table of 'struct jump_entry' or to a linked list of modules which in
269 * turn point to 'struct jump_entry' tables.
271 * The two lower bits of the pointer are used to keep track of which pointer
272 * type is in use and to store the initial branch direction, we use an access
273 * function which preserves these bits.
275 static void static_key_set_entries(struct static_key *key,
276 struct jump_entry *entries)
280 WARN_ON_ONCE((unsigned long)entries & JUMP_TYPE_MASK);
281 type = key->type & JUMP_TYPE_MASK;
282 key->entries = entries;
286 static enum jump_label_type jump_label_type(struct jump_entry *entry)
288 struct static_key *key = jump_entry_key(entry);
289 bool enabled = static_key_enabled(key);
290 bool branch = jump_entry_branch(entry);
292 /* See the comment in linux/jump_label.h */
293 return enabled ^ branch;
296 static void __jump_label_update(struct static_key *key,
297 struct jump_entry *entry,
298 struct jump_entry *stop)
300 for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) {
302 * entry->code set to 0 invalidates module init text sections
303 * kernel_text_address() verifies we are not in core kernel
304 * init code, see jump_label_invalidate_module_init().
306 if (entry->code && kernel_text_address(entry->code))
307 arch_jump_label_transform(entry, jump_label_type(entry));
311 void __init jump_label_init(void)
313 struct jump_entry *iter_start = __start___jump_table;
314 struct jump_entry *iter_stop = __stop___jump_table;
315 struct static_key *key = NULL;
316 struct jump_entry *iter;
319 * Since we are initializing the static_key.enabled field with
320 * with the 'raw' int values (to avoid pulling in atomic.h) in
321 * jump_label.h, let's make sure that is safe. There are only two
322 * cases to check since we initialize to 0 or 1.
324 BUILD_BUG_ON((int)ATOMIC_INIT(0) != 0);
325 BUILD_BUG_ON((int)ATOMIC_INIT(1) != 1);
327 if (static_key_initialized)
331 jump_label_sort_entries(iter_start, iter_stop);
333 for (iter = iter_start; iter < iter_stop; iter++) {
334 struct static_key *iterk;
337 if (jump_label_type(iter) == JUMP_LABEL_NOP)
338 arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
340 iterk = jump_entry_key(iter);
345 static_key_set_entries(key, iter);
347 static_key_initialized = true;
351 #ifdef CONFIG_MODULES
353 static enum jump_label_type jump_label_init_type(struct jump_entry *entry)
355 struct static_key *key = jump_entry_key(entry);
356 bool type = static_key_type(key);
357 bool branch = jump_entry_branch(entry);
359 /* See the comment in linux/jump_label.h */
360 return type ^ branch;
363 struct static_key_mod {
364 struct static_key_mod *next;
365 struct jump_entry *entries;
369 static inline struct static_key_mod *static_key_mod(struct static_key *key)
371 WARN_ON_ONCE(!(key->type & JUMP_TYPE_LINKED));
372 return (struct static_key_mod *)(key->type & ~JUMP_TYPE_MASK);
376 * key->type and key->next are the same via union.
377 * This sets key->next and preserves the type bits.
379 * See additional comments above static_key_set_entries().
381 static void static_key_set_mod(struct static_key *key,
382 struct static_key_mod *mod)
386 WARN_ON_ONCE((unsigned long)mod & JUMP_TYPE_MASK);
387 type = key->type & JUMP_TYPE_MASK;
392 static int __jump_label_mod_text_reserved(void *start, void *end)
397 mod = __module_text_address((unsigned long)start);
398 WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
405 return __jump_label_text_reserved(mod->jump_entries,
406 mod->jump_entries + mod->num_jump_entries,
410 static void __jump_label_mod_update(struct static_key *key)
412 struct static_key_mod *mod;
414 for (mod = static_key_mod(key); mod; mod = mod->next) {
415 struct jump_entry *stop;
419 * NULL if the static_key is defined in a module
420 * that does not use it
427 stop = __stop___jump_table;
429 stop = m->jump_entries + m->num_jump_entries;
430 __jump_label_update(key, mod->entries, stop);
435 * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
436 * @mod: module to patch
438 * Allow for run-time selection of the optimal nops. Before the module
439 * loads patch these with arch_get_jump_label_nop(), which is specified by
440 * the arch specific jump label code.
442 void jump_label_apply_nops(struct module *mod)
444 struct jump_entry *iter_start = mod->jump_entries;
445 struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
446 struct jump_entry *iter;
448 /* if the module doesn't have jump label entries, just return */
449 if (iter_start == iter_stop)
452 for (iter = iter_start; iter < iter_stop; iter++) {
453 /* Only write NOPs for arch_branch_static(). */
454 if (jump_label_init_type(iter) == JUMP_LABEL_NOP)
455 arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
459 static int jump_label_add_module(struct module *mod)
461 struct jump_entry *iter_start = mod->jump_entries;
462 struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
463 struct jump_entry *iter;
464 struct static_key *key = NULL;
465 struct static_key_mod *jlm, *jlm2;
467 /* if the module doesn't have jump label entries, just return */
468 if (iter_start == iter_stop)
471 jump_label_sort_entries(iter_start, iter_stop);
473 for (iter = iter_start; iter < iter_stop; iter++) {
474 struct static_key *iterk;
476 iterk = jump_entry_key(iter);
481 if (within_module(iter->key, mod)) {
482 static_key_set_entries(key, iter);
485 jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
488 if (!static_key_linked(key)) {
489 jlm2 = kzalloc(sizeof(struct static_key_mod),
496 jlm2->mod = __module_address((unsigned long)key);
498 jlm2->entries = static_key_entries(key);
500 static_key_set_mod(key, jlm2);
501 static_key_set_linked(key);
505 jlm->next = static_key_mod(key);
506 static_key_set_mod(key, jlm);
507 static_key_set_linked(key);
509 /* Only update if we've changed from our initial state */
510 if (jump_label_type(iter) != jump_label_init_type(iter))
511 __jump_label_update(key, iter, iter_stop);
517 static void jump_label_del_module(struct module *mod)
519 struct jump_entry *iter_start = mod->jump_entries;
520 struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
521 struct jump_entry *iter;
522 struct static_key *key = NULL;
523 struct static_key_mod *jlm, **prev;
525 for (iter = iter_start; iter < iter_stop; iter++) {
526 if (jump_entry_key(iter) == key)
529 key = jump_entry_key(iter);
531 if (within_module(iter->key, mod))
534 /* No memory during module load */
535 if (WARN_ON(!static_key_linked(key)))
539 jlm = static_key_mod(key);
541 while (jlm && jlm->mod != mod) {
546 /* No memory during module load */
550 if (prev == &key->next)
551 static_key_set_mod(key, jlm->next);
557 jlm = static_key_mod(key);
558 /* if only one etry is left, fold it back into the static_key */
559 if (jlm->next == NULL) {
560 static_key_set_entries(key, jlm->entries);
561 static_key_clear_linked(key);
567 static void jump_label_invalidate_module_init(struct module *mod)
569 struct jump_entry *iter_start = mod->jump_entries;
570 struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
571 struct jump_entry *iter;
573 for (iter = iter_start; iter < iter_stop; iter++) {
574 if (within_module_init(iter->code, mod))
580 jump_label_module_notify(struct notifier_block *self, unsigned long val,
583 struct module *mod = data;
587 case MODULE_STATE_COMING:
589 ret = jump_label_add_module(mod);
591 WARN(1, "Failed to allocatote memory: jump_label may not work properly.\n");
592 jump_label_del_module(mod);
596 case MODULE_STATE_GOING:
598 jump_label_del_module(mod);
601 case MODULE_STATE_LIVE:
603 jump_label_invalidate_module_init(mod);
608 return notifier_from_errno(ret);
611 static struct notifier_block jump_label_module_nb = {
612 .notifier_call = jump_label_module_notify,
613 .priority = 1, /* higher than tracepoints */
616 static __init int jump_label_init_module(void)
618 return register_module_notifier(&jump_label_module_nb);
620 early_initcall(jump_label_init_module);
622 #endif /* CONFIG_MODULES */
625 * jump_label_text_reserved - check if addr range is reserved
626 * @start: start text addr
627 * @end: end text addr
629 * checks if the text addr located between @start and @end
630 * overlaps with any of the jump label patch addresses. Code
631 * that wants to modify kernel text should first verify that
632 * it does not overlap with any of the jump label addresses.
633 * Caller must hold jump_label_mutex.
635 * returns 1 if there is an overlap, 0 otherwise
637 int jump_label_text_reserved(void *start, void *end)
639 int ret = __jump_label_text_reserved(__start___jump_table,
640 __stop___jump_table, start, end);
645 #ifdef CONFIG_MODULES
646 ret = __jump_label_mod_text_reserved(start, end);
651 static void jump_label_update(struct static_key *key)
653 struct jump_entry *stop = __stop___jump_table;
654 struct jump_entry *entry;
655 #ifdef CONFIG_MODULES
658 if (static_key_linked(key)) {
659 __jump_label_mod_update(key);
664 mod = __module_address((unsigned long)key);
666 stop = mod->jump_entries + mod->num_jump_entries;
669 entry = static_key_entries(key);
670 /* if there are no users, entry can be NULL */
672 __jump_label_update(key, entry, stop);
675 #ifdef CONFIG_STATIC_KEYS_SELFTEST
676 static DEFINE_STATIC_KEY_TRUE(sk_true);
677 static DEFINE_STATIC_KEY_FALSE(sk_false);
679 static __init int jump_label_test(void)
683 for (i = 0; i < 2; i++) {
684 WARN_ON(static_key_enabled(&sk_true.key) != true);
685 WARN_ON(static_key_enabled(&sk_false.key) != false);
687 WARN_ON(!static_branch_likely(&sk_true));
688 WARN_ON(!static_branch_unlikely(&sk_true));
689 WARN_ON(static_branch_likely(&sk_false));
690 WARN_ON(static_branch_unlikely(&sk_false));
692 static_branch_disable(&sk_true);
693 static_branch_enable(&sk_false);
695 WARN_ON(static_key_enabled(&sk_true.key) == true);
696 WARN_ON(static_key_enabled(&sk_false.key) == false);
698 WARN_ON(static_branch_likely(&sk_true));
699 WARN_ON(static_branch_unlikely(&sk_true));
700 WARN_ON(!static_branch_likely(&sk_false));
701 WARN_ON(!static_branch_unlikely(&sk_false));
703 static_branch_enable(&sk_true);
704 static_branch_disable(&sk_false);
709 late_initcall(jump_label_test);
710 #endif /* STATIC_KEYS_SELFTEST */
712 #endif /* HAVE_JUMP_LABEL */