jump_label.c 10.8 KB
Newer Older
1 2 3 4
/*
 * jump label support
 *
 * Copyright (C) 2009 Jason Baron <jbaron@redhat.com>
5
 * Copyright (C) 2011 Peter Zijlstra <pzijlstr@redhat.com>
6 7 8 9 10 11 12 13 14
 *
 */
#include <linux/memory.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/sort.h>
#include <linux/err.h>
15
#include <linux/static_key.h>
16 17 18 19 20 21

#ifdef HAVE_JUMP_LABEL

/* mutex to protect coming/going of the the jump_label table */
static DEFINE_MUTEX(jump_label_mutex);

22 23 24 25 26 27 28 29 30 31
void jump_label_lock(void)
{
	mutex_lock(&jump_label_mutex);
}

void jump_label_unlock(void)
{
	mutex_unlock(&jump_label_mutex);
}

32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
static int jump_label_cmp(const void *a, const void *b)
{
	const struct jump_entry *jea = a;
	const struct jump_entry *jeb = b;

	if (jea->key < jeb->key)
		return -1;

	if (jea->key > jeb->key)
		return 1;

	return 0;
}

static void
47
jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
48 49 50 51 52 53 54 55
{
	unsigned long size;

	size = (((unsigned long)stop - (unsigned long)start)
					/ sizeof(struct jump_entry));
	sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
}

56
static void jump_label_update(struct static_key *key, int enable);
57

58
void static_key_slow_inc(struct static_key *key)
59
{
60 61
	if (atomic_inc_not_zero(&key->enabled))
		return;
62

63
	jump_label_lock();
64 65 66 67 68 69
	if (atomic_read(&key->enabled) == 0) {
		if (!jump_label_get_branch_default(key))
			jump_label_update(key, JUMP_LABEL_ENABLE);
		else
			jump_label_update(key, JUMP_LABEL_DISABLE);
	}
70
	atomic_inc(&key->enabled);
71
	jump_label_unlock();
72
}
73
EXPORT_SYMBOL_GPL(static_key_slow_inc);
74

75
static void __static_key_slow_dec(struct static_key *key,
76
		unsigned long rate_limit, struct delayed_work *work)
77
{
78 79 80
	if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
		WARN(atomic_read(&key->enabled) < 0,
		     "jump label: negative count!\n");
81
		return;
82
	}
83

84 85 86
	if (rate_limit) {
		atomic_inc(&key->enabled);
		schedule_delayed_work(work, rate_limit);
87 88 89 90 91 92
	} else {
		if (!jump_label_get_branch_default(key))
			jump_label_update(key, JUMP_LABEL_DISABLE);
		else
			jump_label_update(key, JUMP_LABEL_ENABLE);
	}
93
	jump_label_unlock();
94 95
}

96 97
static void jump_label_update_timeout(struct work_struct *work)
{
98 99 100
	struct static_key_deferred *key =
		container_of(work, struct static_key_deferred, work.work);
	__static_key_slow_dec(&key->key, 0, NULL);
101 102
}

103
void static_key_slow_dec(struct static_key *key)
104
{
105
	__static_key_slow_dec(key, 0, NULL);
106
}
107
EXPORT_SYMBOL_GPL(static_key_slow_dec);
108

109
void static_key_slow_dec_deferred(struct static_key_deferred *key)
110
{
111
	__static_key_slow_dec(&key->key, key->timeout, &key->work);
112
}
113
EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
114

115
void jump_label_rate_limit(struct static_key_deferred *key,
116 117 118 119 120
		unsigned long rl)
{
	key->timeout = rl;
	INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
}
121
EXPORT_SYMBOL_GPL(jump_label_rate_limit);
122

123 124 125 126 127 128 129 130 131
static int addr_conflict(struct jump_entry *entry, void *start, void *end)
{
	if (entry->code <= (unsigned long)end &&
		entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
		return 1;

	return 0;
}

132 133
static int __jump_label_text_reserved(struct jump_entry *iter_start,
		struct jump_entry *iter_stop, void *start, void *end)
134 135 136 137 138
{
	struct jump_entry *iter;

	iter = iter_start;
	while (iter < iter_stop) {
139 140
		if (addr_conflict(iter, start, end))
			return 1;
141 142 143
		iter++;
	}

144 145 146
	return 0;
}

147 148 149 150 151 152
/* 
 * Update code which is definitely not currently executing.
 * Architectures which need heavyweight synchronization to modify
 * running code can override this to make the non-live update case
 * cheaper.
 */
153
void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
154 155 156 157 158
					    enum jump_label_type type)
{
	arch_jump_label_transform(entry, type);	
}

159
static void __jump_label_update(struct static_key *key,
160 161
				struct jump_entry *entry,
				struct jump_entry *stop, int enable)
162
{
163 164 165
	for (; (entry < stop) &&
	      (entry->key == (jump_label_t)(unsigned long)key);
	      entry++) {
166 167 168 169 170 171 172 173
		/*
		 * entry->code set to 0 invalidates module init text sections
		 * kernel_text_address() verifies we are not in core kernel
		 * init code, see jump_label_invalidate_module_init().
		 */
		if (entry->code && kernel_text_address(entry->code))
			arch_jump_label_transform(entry, enable);
	}
174 175
}

176 177 178 179 180 181 182 183 184 185 186
static enum jump_label_type jump_label_type(struct static_key *key)
{
	bool true_branch = jump_label_get_branch_default(key);
	bool state = static_key_enabled(key);

	if ((!true_branch && state) || (true_branch && !state))
		return JUMP_LABEL_ENABLE;

	return JUMP_LABEL_DISABLE;
}

187
void __init jump_label_init(void)
188 189 190
{
	struct jump_entry *iter_start = __start___jump_table;
	struct jump_entry *iter_stop = __stop___jump_table;
191
	struct static_key *key = NULL;
192 193
	struct jump_entry *iter;

194
	jump_label_lock();
195 196 197
	jump_label_sort_entries(iter_start, iter_stop);

	for (iter = iter_start; iter < iter_stop; iter++) {
198
		struct static_key *iterk;
199

200 201
		iterk = (struct static_key *)(unsigned long)iter->key;
		arch_jump_label_transform_static(iter, jump_label_type(iterk));
202
		if (iterk == key)
203 204
			continue;

205
		key = iterk;
206 207 208 209
		/*
		 * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
		 */
		*((unsigned long *)&key->entries) += (unsigned long)iter;
210 211 212
#ifdef CONFIG_MODULES
		key->next = NULL;
#endif
213
	}
214
	jump_label_unlock();
215 216 217 218
}

#ifdef CONFIG_MODULES

219 220
struct static_key_mod {
	struct static_key_mod *next;
221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239
	struct jump_entry *entries;
	struct module *mod;
};

static int __jump_label_mod_text_reserved(void *start, void *end)
{
	struct module *mod;

	mod = __module_text_address((unsigned long)start);
	if (!mod)
		return 0;

	WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);

	return __jump_label_text_reserved(mod->jump_entries,
				mod->jump_entries + mod->num_jump_entries,
				start, end);
}

240
static void __jump_label_mod_update(struct static_key *key, int enable)
241
{
242
	struct static_key_mod *mod = key->next;
243 244

	while (mod) {
245 246 247 248 249
		struct module *m = mod->mod;

		__jump_label_update(key, mod->entries,
				    m->jump_entries + m->num_jump_entries,
				    enable);
250 251 252 253 254 255 256 257 258 259 260 261 262
		mod = mod->next;
	}
}

/***
 * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 * @mod: module to patch
 *
 * Allow for run-time selection of the optimal nops. Before the module
 * loads patch these with arch_get_jump_label_nop(), which is specified by
 * the arch specific jump label code.
 */
void jump_label_apply_nops(struct module *mod)
263
{
264 265 266 267 268 269 270 271
	struct jump_entry *iter_start = mod->jump_entries;
	struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
	struct jump_entry *iter;

	/* if the module doesn't have jump label entries, just return */
	if (iter_start == iter_stop)
		return;

272
	for (iter = iter_start; iter < iter_stop; iter++) {
273
		arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
274
	}
275 276
}

277
static int jump_label_add_module(struct module *mod)
278
{
279 280 281
	struct jump_entry *iter_start = mod->jump_entries;
	struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
	struct jump_entry *iter;
282 283
	struct static_key *key = NULL;
	struct static_key_mod *jlm;
284 285

	/* if the module doesn't have jump label entries, just return */
286
	if (iter_start == iter_stop)
287 288
		return 0;

289 290 291
	jump_label_sort_entries(iter_start, iter_stop);

	for (iter = iter_start; iter < iter_stop; iter++) {
292
		struct static_key *iterk;
293

294 295 296
		iterk = (struct static_key *)(unsigned long)iter->key;
		if (iterk == key)
			continue;
297

298
		key = iterk;
299
		if (__module_address(iter->key) == mod) {
300 301 302 303
			/*
			 * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
			 */
			*((unsigned long *)&key->entries) += (unsigned long)iter;
304 305
			key->next = NULL;
			continue;
306
		}
307
		jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
308 309 310 311 312 313 314
		if (!jlm)
			return -ENOMEM;
		jlm->mod = mod;
		jlm->entries = iter;
		jlm->next = key->next;
		key->next = jlm;

315
		if (jump_label_type(key) == JUMP_LABEL_ENABLE)
316
			__jump_label_update(key, iter, iter_stop, JUMP_LABEL_ENABLE);
317
	}
318

319 320 321
	return 0;
}

322
static void jump_label_del_module(struct module *mod)
323
{
324 325 326
	struct jump_entry *iter_start = mod->jump_entries;
	struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
	struct jump_entry *iter;
327 328
	struct static_key *key = NULL;
	struct static_key_mod *jlm, **prev;
329

330 331 332 333
	for (iter = iter_start; iter < iter_stop; iter++) {
		if (iter->key == (jump_label_t)(unsigned long)key)
			continue;

334
		key = (struct static_key *)(unsigned long)iter->key;
335 336 337 338 339 340

		if (__module_address(iter->key) == mod)
			continue;

		prev = &key->next;
		jlm = key->next;
341

342 343 344 345 346 347 348 349
		while (jlm && jlm->mod != mod) {
			prev = &jlm->next;
			jlm = jlm->next;
		}

		if (jlm) {
			*prev = jlm->next;
			kfree(jlm);
350 351 352 353
		}
	}
}

354
static void jump_label_invalidate_module_init(struct module *mod)
355
{
356 357
	struct jump_entry *iter_start = mod->jump_entries;
	struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
358 359
	struct jump_entry *iter;

360 361 362
	for (iter = iter_start; iter < iter_stop; iter++) {
		if (within_module_init(iter->code, mod))
			iter->code = 0;
363 364 365
	}
}

366 367 368 369 370 371 372 373 374
static int
jump_label_module_notify(struct notifier_block *self, unsigned long val,
			 void *data)
{
	struct module *mod = data;
	int ret = 0;

	switch (val) {
	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();
380 381
		break;
	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);
394 395 396 397
}

struct notifier_block jump_label_module_nb = {
	.notifier_call = jump_label_module_notify,
398
	.priority = 1, /* higher than tracepoints */
399 400
};

401
static __init int jump_label_init_module(void)
402 403 404
{
	return register_module_notifier(&jump_label_module_nb);
}
405
early_initcall(jump_label_init_module);
406 407 408

#endif /* CONFIG_MODULES */

409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435
/***
 * jump_label_text_reserved - check if addr range is reserved
 * @start: start text addr
 * @end: end text addr
 *
 * checks if the text addr located between @start and @end
 * overlaps with any of the jump label patch addresses. Code
 * that wants to modify kernel text should first verify that
 * it does not overlap with any of the jump label addresses.
 * Caller must hold jump_label_mutex.
 *
 * returns 1 if there is an overlap, 0 otherwise
 */
int jump_label_text_reserved(void *start, void *end)
{
	int ret = __jump_label_text_reserved(__start___jump_table,
			__stop___jump_table, start, end);

	if (ret)
		return ret;

#ifdef CONFIG_MODULES
	ret = __jump_label_mod_text_reserved(start, end);
#endif
	return ret;
}

436
static void jump_label_update(struct static_key *key, int enable)
437
{
438 439
	struct jump_entry *stop = __stop___jump_table;
	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);
445 446 447

	if (mod)
		stop = mod->jump_entries + mod->num_jump_entries;
448
#endif
449 450 451
	/* if there are no users, entry can be NULL */
	if (entry)
		__jump_label_update(key, entry, stop, enable);
452 453
}

454
#endif