summaryrefslogtreecommitdiffstats
path: root/kernel/static_call.c
blob: dc5665b628140ee9b0a841011a4ae495d2c9eee8 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
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
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
// SPDX-License-Identifier: GPL-2.0
#include <linux/init.h>
#include <linux/static_call.h>
#include <linux/bug.h>
#include <linux/smp.h>
#include <linux/sort.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/cpu.h>
#include <linux/processor.h>
#include <asm/sections.h>

extern struct static_call_site __start_static_call_sites[],
			       __stop_static_call_sites[];
extern struct static_call_tramp_key __start_static_call_tramp_key[],
				    __stop_static_call_tramp_key[];

static bool static_call_initialized;

/* mutex to protect key modules/sites */
static DEFINE_MUTEX(static_call_mutex);

static void static_call_lock(void)
{
	mutex_lock(&static_call_mutex);
}

static void static_call_unlock(void)
{
	mutex_unlock(&static_call_mutex);
}

static inline void *static_call_addr(struct static_call_site *site)
{
	return (void *)((long)site->addr + (long)&site->addr);
}

static inline unsigned long __static_call_key(const struct static_call_site *site)
{
	return (long)site->key + (long)&site->key;
}

static inline struct static_call_key *static_call_key(const struct static_call_site *site)
{
	return (void *)(__static_call_key(site) & ~STATIC_CALL_SITE_FLAGS);
}

/* These assume the key is word-aligned. */
static inline bool static_call_is_init(struct static_call_site *site)
{
	return __static_call_key(site) & STATIC_CALL_SITE_INIT;
}

static inline bool static_call_is_tail(struct static_call_site *site)
{
	return __static_call_key(site) & STATIC_CALL_SITE_TAIL;
}

static inline void static_call_set_init(struct static_call_site *site)
{
	site->key = (__static_call_key(site) | STATIC_CALL_SITE_INIT) -
		    (long)&site->key;
}

static int static_call_site_cmp(const void *_a, const void *_b)
{
	const struct static_call_site *a = _a;
	const struct static_call_site *b = _b;
	const struct static_call_key *key_a = static_call_key(a);
	const struct static_call_key *key_b = static_call_key(b);

	if (key_a < key_b)
		return -1;

	if (key_a > key_b)
		return 1;

	return 0;
}

static void static_call_site_swap(void *_a, void *_b, int size)
{
	long delta = (unsigned long)_a - (unsigned long)_b;
	struct static_call_site *a = _a;
	struct static_call_site *b = _b;
	struct static_call_site tmp = *a;

	a->addr = b->addr  - delta;
	a->key  = b->key   - delta;

	b->addr = tmp.addr + delta;
	b->key  = tmp.key  + delta;
}

static inline void static_call_sort_entries(struct static_call_site *start,
					    struct static_call_site *stop)
{
	sort(start, stop - start, sizeof(struct static_call_site),
	     static_call_site_cmp, static_call_site_swap);
}

static inline bool static_call_key_has_mods(struct static_call_key *key)
{
	return !(key->type & 1);
}

static inline struct static_call_mod *static_call_key_next(struct static_call_key *key)
{
	if (!static_call_key_has_mods(key))
		return NULL;

	return key->mods;
}

static inline struct static_call_site *static_call_key_sites(struct static_call_key *key)
{
	if (static_call_key_has_mods(key))
		return NULL;

	return (struct static_call_site *)(key->type & ~1);
}

void __static_call_update(struct static_call_key *key, void *tramp, void *func)
{
	struct static_call_site *site, *stop;
	struct static_call_mod *site_mod, first;

	cpus_read_lock();
	static_call_lock();

	if (key->func == func)
		goto done;

	key->func = func;

	arch_static_call_transform(NULL, tramp, func, false);

	/*
	 * If uninitialized, we'll not update the callsites, but they still
	 * point to the trampoline and we just patched that.
	 */
	if (WARN_ON_ONCE(!static_call_initialized))
		goto done;

	first = (struct static_call_mod){
		.next = static_call_key_next(key),
		.mod = NULL,
		.sites = static_call_key_sites(key),
	};

	for (site_mod = &first; site_mod; site_mod = site_mod->next) {
		bool init = system_state < SYSTEM_RUNNING;
		struct module *mod = site_mod->mod;

		if (!site_mod->sites) {
			/*
			 * This can happen if the static call key is defined in
			 * a module which doesn't use it.
			 *
			 * It also happens in the has_mods case, where the
			 * 'first' entry has no sites associated with it.
			 */
			continue;
		}

		stop = __stop_static_call_sites;

		if (mod) {
#ifdef CONFIG_MODULES
			stop = mod->static_call_sites +
			       mod->num_static_call_sites;
			init = mod->state == MODULE_STATE_COMING;
#endif
		}

		for (site = site_mod->sites;
		     site < stop && static_call_key(site) == key; site++) {
			void *site_addr = static_call_addr(site);

			if (!init && static_call_is_init(site))
				continue;

			if (!kernel_text_address((unsigned long)site_addr)) {
				/*
				 * This skips patching built-in __exit, which
				 * is part of init_section_contains() but is
				 * not part of kernel_text_address().
				 *
				 * Skipping built-in __exit is fine since it
				 * will never be executed.
				 */
				WARN_ONCE(!static_call_is_init(site),
					  "can't patch static call site at %pS",
					  site_addr);
				continue;
			}

			arch_static_call_transform(site_addr, NULL, func,
						   static_call_is_tail(site));
		}
	}

done:
	static_call_unlock();
	cpus_read_unlock();
}
EXPORT_SYMBOL_GPL(__static_call_update);

static int __static_call_init(struct module *mod,
			      struct static_call_site *start,
			      struct static_call_site *stop)
{
	struct static_call_site *site;
	struct static_call_key *key, *prev_key = NULL;
	struct static_call_mod *site_mod;

	if (start == stop)
		return 0;

	static_call_sort_entries(start, stop);

	for (site = start; site < stop; site++) {
		void *site_addr = static_call_addr(site);

		if ((mod && within_module_init((unsigned long)site_addr, mod)) ||
		    (!mod && init_section_contains(site_addr, 1)))
			static_call_set_init(site);

		key = static_call_key(site);
		if (key != prev_key) {
			prev_key = key;

			/*
			 * For vmlinux (!mod) avoid the allocation by storing
			 * the sites pointer in the key itself. Also see
			 * __static_call_update()'s @first.
			 *
			 * This allows architectures (eg. x86) to call
			 * static_call_init() before memory allocation works.
			 */
			if (!mod) {
				key->sites = site;
				key->type |= 1;
				goto do_transform;
			}

			site_mod = kzalloc(sizeof(*site_mod), GFP_KERNEL);
			if (!site_mod)
				return -ENOMEM;

			/*
			 * When the key has a direct sites pointer, extract
			 * that into an explicit struct static_call_mod, so we
			 * can have a list of modules.
			 */
			if (static_call_key_sites(key)) {
				site_mod->mod = NULL;
				site_mod->next = NULL;
				site_mod->sites = static_call_key_sites(key);

				key->mods = site_mod;

				site_mod = kzalloc(sizeof(*site_mod), GFP_KERNEL);
				if (!site_mod)
					return -ENOMEM;
			}

			site_mod->mod = mod;
			site_mod->sites = site;
			site_mod->next = static_call_key_next(key);
			key->mods = site_mod;
		}

do_transform:
		arch_static_call_transform(site_addr, NULL, key->func,
				static_call_is_tail(site));
	}

	return 0;
}

static int addr_conflict(struct static_call_site *site, void *start, void *end)
{
	unsigned long addr = (unsigned long)static_call_addr(site);

	if (addr <= (unsigned long)end &&
	    addr + CALL_INSN_SIZE > (unsigned long)start)
		return 1;

	return 0;
}

static int __static_call_text_reserved(struct static_call_site *iter_start,
				       struct static_call_site *iter_stop,
				       void *start, void *end, bool init)
{
	struct static_call_site *iter = iter_start;

	while (iter < iter_stop) {
		if (init || !static_call_is_init(iter)) {
			if (addr_conflict(iter, start, end))
				return 1;
		}
		iter++;
	}

	return 0;
}

#ifdef CONFIG_MODULES

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

	preempt_disable();
	mod = __module_text_address((unsigned long)start);
	WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
	if (!try_module_get(mod))
		mod = NULL;
	preempt_enable();

	if (!mod)
		return 0;

	ret = __static_call_text_reserved(mod->static_call_sites,
			mod->static_call_sites + mod->num_static_call_sites,
			start, end, mod->state == MODULE_STATE_COMING);

	module_put(mod);

	return ret;
}

static unsigned long tramp_key_lookup(unsigned long addr)
{
	struct static_call_tramp_key *start = __start_static_call_tramp_key;
	struct static_call_tramp_key *stop = __stop_static_call_tramp_key;
	struct static_call_tramp_key *tramp_key;

	for (tramp_key = start; tramp_key != stop; tramp_key++) {
		unsigned long tramp;

		tramp = (long)tramp_key->tramp + (long)&tramp_key->tramp;
		if (tramp == addr)
			return (long)tramp_key->key + (long)&tramp_key->key;
	}

	return 0;
}

static int static_call_add_module(struct module *mod)
{
	struct static_call_site *start = mod->static_call_sites;
	struct static_call_site *stop = start + mod->num_static_call_sites;
	struct static_call_site *site;

	for (site = start; site != stop; site++) {
		unsigned long s_key = __static_call_key(site);
		unsigned long addr = s_key & ~STATIC_CALL_SITE_FLAGS;
		unsigned long key;

		/*
		 * Is the key is exported, 'addr' points to the key, which
		 * means modules are allowed to call static_call_update() on
		 * it.
		 *
		 * Otherwise, the key isn't exported, and 'addr' points to the
		 * trampoline so we need to lookup the key.
		 *
		 * We go through this dance to prevent crazy modules from
		 * abusing sensitive static calls.
		 */
		if (!kernel_text_address(addr))
			continue;

		key = tramp_key_lookup(addr);
		if (!key) {
			pr_warn("Failed to fixup __raw_static_call() usage at: %ps\n",
				static_call_addr(site));
			return -EINVAL;
		}

		key |= s_key & STATIC_CALL_SITE_FLAGS;
		site->key = key - (long)&site->key;
	}

	return __static_call_init(mod, start, stop);
}

static void static_call_del_module(struct module *mod)
{
	struct static_call_site *start = mod->static_call_sites;
	struct static_call_site *stop = mod->static_call_sites +
					mod->num_static_call_sites;
	struct static_call_key *key, *prev_key = NULL;
	struct static_call_mod *site_mod, **prev;
	struct static_call_site *site;

	for (site = start; site < stop; site++) {
		key = static_call_key(site);
		if (key == prev_key)
			continue;

		prev_key = key;

		for (prev = &key->mods, site_mod = key->mods;
		     site_mod && site_mod->mod != mod;
		     prev = &site_mod->next, site_mod = site_mod->next)
			;

		if (!site_mod)
			continue;

		*prev = site_mod->next;
		kfree(site_mod);
	}
}

static int static_call_module_notify(struct notifier_block *nb,
				     unsigned long val, void *data)
{
	struct module *mod = data;
	int ret = 0;

	cpus_read_lock();
	static_call_lock();

	switch (val) {
	case MODULE_STATE_COMING:
		ret = static_call_add_module(mod);
		if (ret) {
			WARN(1, "Failed to allocate memory for static calls");
			static_call_del_module(mod);
		}
		break;
	case MODULE_STATE_GOING:
		static_call_del_module(mod);
		break;
	}

	static_call_unlock();
	cpus_read_unlock();

	return notifier_from_errno(ret);
}

static struct notifier_block static_call_module_nb = {
	.notifier_call = static_call_module_notify,
};

#else

static inline int __static_call_mod_text_reserved(void *start, void *end)
{
	return 0;
}

#endif /* CONFIG_MODULES */

int static_call_text_reserved(void *start, void *end)
{
	bool init = system_state < SYSTEM_RUNNING;
	int ret = __static_call_text_reserved(__start_static_call_sites,
			__stop_static_call_sites, start, end, init);

	if (ret)
		return ret;

	return __static_call_mod_text_reserved(start, end);
}

int __init static_call_init(void)
{
	int ret;

	if (static_call_initialized)
		return 0;

	cpus_read_lock();
	static_call_lock();
	ret = __static_call_init(NULL, __start_static_call_sites,
				 __stop_static_call_sites);
	static_call_unlock();
	cpus_read_unlock();

	if (ret) {
		pr_err("Failed to allocate memory for static_call!\n");
		BUG();
	}

	static_call_initialized = true;

#ifdef CONFIG_MODULES
	register_module_notifier(&static_call_module_nb);
#endif
	return 0;
}
early_initcall(static_call_init);

#ifdef CONFIG_STATIC_CALL_SELFTEST

static int func_a(int x)
{
	return x+1;
}

static int func_b(int x)
{
	return x+2;
}

DEFINE_STATIC_CALL(sc_selftest, func_a);

static struct static_call_data {
      int (*func)(int);
      int val;
      int expect;
} static_call_data [] __initdata = {
      { NULL,   2, 3 },
      { func_b, 2, 4 },
      { func_a, 2, 3 }
};

static int __init test_static_call_init(void)
{
      int i;

      for (i = 0; i < ARRAY_SIZE(static_call_data); i++ ) {
	      struct static_call_data *scd = &static_call_data[i];

              if (scd->func)
                      static_call_update(sc_selftest, scd->func);

              WARN_ON(static_call(sc_selftest)(scd->val) != scd->expect);
      }

      return 0;
}
early_initcall(test_static_call_init);

#endif /* CONFIG_STATIC_CALL_SELFTEST */