aboutsummaryrefslogtreecommitdiff
path: root/arch/x86/kernel/alternative.c
blob: 1a160d5d44d0bd0f47b0b88b9e6a98f4b9b7f2b3 (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
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/mutex.h>
#include <linux/list.h>
#include <linux/stringify.h>
#include <linux/kprobes.h>
#include <linux/mm.h>
#include <linux/vmalloc.h>
#include <linux/memory.h>
#include <linux/stop_machine.h>
#include <linux/slab.h>
#include <asm/alternative.h>
#include <asm/sections.h>
#include <asm/pgtable.h>
#include <asm/mce.h>
#include <asm/nmi.h>
#include <asm/vsyscall.h>
#include <asm/cacheflush.h>
#include <asm/tlbflush.h>
#include <asm/io.h>
#include <asm/fixmap.h>

#define MAX_PATCH_LEN (255-1)

#ifdef CONFIG_HOTPLUG_CPU
static int smp_alt_once;

static int __init bootonly(char *str)
{
	smp_alt_once = 1;
	return 1;
}
__setup("smp-alt-boot", bootonly);
#else
#define smp_alt_once 1
#endif

static int __initdata_or_module debug_alternative;

static int __init debug_alt(char *str)
{
	debug_alternative = 1;
	return 1;
}
__setup("debug-alternative", debug_alt);

static int noreplace_smp;

static int __init setup_noreplace_smp(char *str)
{
	noreplace_smp = 1;
	return 1;
}
__setup("noreplace-smp", setup_noreplace_smp);

#ifdef CONFIG_PARAVIRT
static int __initdata_or_module noreplace_paravirt = 0;

static int __init setup_noreplace_paravirt(char *str)
{
	noreplace_paravirt = 1;
	return 1;
}
__setup("noreplace-paravirt", setup_noreplace_paravirt);
#endif

#define DPRINTK(fmt, args...) if (debug_alternative) \
	printk(KERN_DEBUG fmt, args)

#if defined(GENERIC_NOP1) && !defined(CONFIG_X86_64)
/* Use inline assembly to define this because the nops are defined
   as inline assembly strings in the include files and we cannot
   get them easily into strings. */
asm("\t" __stringify(__INITRODATA_OR_MODULE) "\nintelnops: "
	GENERIC_NOP1 GENERIC_NOP2 GENERIC_NOP3 GENERIC_NOP4 GENERIC_NOP5 GENERIC_NOP6
	GENERIC_NOP7 GENERIC_NOP8
    "\t.previous");
extern const unsigned char intelnops[];
static const unsigned char *const __initconst_or_module
intel_nops[ASM_NOP_MAX+1] = {
	NULL,
	intelnops,
	intelnops + 1,
	intelnops + 1 + 2,
	intelnops + 1 + 2 + 3,
	intelnops + 1 + 2 + 3 + 4,
	intelnops + 1 + 2 + 3 + 4 + 5,
	intelnops + 1 + 2 + 3 + 4 + 5 + 6,
	intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
};
#endif

#ifdef K8_NOP1
asm("\t" __stringify(__INITRODATA_OR_MODULE) "\nk8nops: "
	K8_NOP1 K8_NOP2 K8_NOP3 K8_NOP4 K8_NOP5 K8_NOP6
	K8_NOP7 K8_NOP8
    "\t.previous");
extern const unsigned char k8nops[];
static const unsigned char *const __initconst_or_module
k8_nops[ASM_NOP_MAX+1] = {
	NULL,
	k8nops,
	k8nops + 1,
	k8nops + 1 + 2,
	k8nops + 1 + 2 + 3,
	k8nops + 1 + 2 + 3 + 4,
	k8nops + 1 + 2 + 3 + 4 + 5,
	k8nops + 1 + 2 + 3 + 4 + 5 + 6,
	k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
};
#endif

#if defined(K7_NOP1) && !defined(CONFIG_X86_64)
asm("\t" __stringify(__INITRODATA_OR_MODULE) "\nk7nops: "
	K7_NOP1 K7_NOP2 K7_NOP3 K7_NOP4 K7_NOP5 K7_NOP6
	K7_NOP7 K7_NOP8
    "\t.previous");
extern const unsigned char k7nops[];
static const unsigned char *const __initconst_or_module
k7_nops[ASM_NOP_MAX+1] = {
	NULL,
	k7nops,
	k7nops + 1,
	k7nops + 1 + 2,
	k7nops + 1 + 2 + 3,
	k7nops + 1 + 2 + 3 + 4,
	k7nops + 1 + 2 + 3 + 4 + 5,
	k7nops + 1 + 2 + 3 + 4 + 5 + 6,
	k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
};
#endif

#ifdef P6_NOP1
asm("\t" __stringify(__INITRODATA_OR_MODULE) "\np6nops: "
	P6_NOP1 P6_NOP2 P6_NOP3 P6_NOP4 P6_NOP5 P6_NOP6
	P6_NOP7 P6_NOP8
    "\t.previous");
extern const unsigned char p6nops[];
static const unsigned char *const __initconst_or_module
p6_nops[ASM_NOP_MAX+1] = {
	NULL,
	p6nops,
	p6nops + 1,
	p6nops + 1 + 2,
	p6nops + 1 + 2 + 3,
	p6nops + 1 + 2 + 3 + 4,
	p6nops + 1 + 2 + 3 + 4 + 5,
	p6nops + 1 + 2 + 3 + 4 + 5 + 6,
	p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
};
#endif

#ifdef CONFIG_X86_64

extern char __vsyscall_0;
static const unsigned char *const *__init_or_module find_nop_table(void)
{
	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
	    boot_cpu_has(X86_FEATURE_NOPL))
		return p6_nops;
	else
		return k8_nops;
}

#else /* CONFIG_X86_64 */

static const unsigned char *const *__init_or_module find_nop_table(void)
{
	if (boot_cpu_has(X86_FEATURE_K8))
		return k8_nops;
	else if (boot_cpu_has(X86_FEATURE_K7))
		return k7_nops;
	else if (boot_cpu_has(X86_FEATURE_NOPL))
		return p6_nops;
	else
		return intel_nops;
}

#endif /* CONFIG_X86_64 */

/* Use this to add nops to a buffer, then text_poke the whole buffer. */
static void __init_or_module add_nops(void *insns, unsigned int len)
{
	const unsigned char *const *noptable = find_nop_table();

	while (len > 0) {
		unsigned int noplen = len;
		if (noplen > ASM_NOP_MAX)
			noplen = ASM_NOP_MAX;
		memcpy(insns, noptable[noplen], noplen);
		insns += noplen;
		len -= noplen;
	}
}

extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
extern u8 *__smp_locks[], *__smp_locks_end[];
static void *text_poke_early(void *addr, const void *opcode, size_t len);

/* Replace instructions with better alternatives for this CPU type.
   This runs before SMP is initialized to avoid SMP problems with
   self modifying code. This implies that assymetric systems where
   APs have less capabilities than the boot processor are not handled.
   Tough. Make sure you disable such features by hand. */

void __init_or_module apply_alternatives(struct alt_instr *start,
					 struct alt_instr *end)
{
	struct alt_instr *a;
	u8 insnbuf[MAX_PATCH_LEN];

	DPRINTK("%s: alt table %p -> %p\n", __func__, start, end);
	for (a = start; a < end; a++) {
		u8 *instr = a->instr;
		BUG_ON(a->replacementlen > a->instrlen);
		BUG_ON(a->instrlen > sizeof(insnbuf));
		if (!boot_cpu_has(a->cpuid))
			continue;
#ifdef CONFIG_X86_64
		/* vsyscall code is not mapped yet. resolve it manually. */
		if (instr >= (u8 *)VSYSCALL_START && instr < (u8*)VSYSCALL_END) {
			instr = __va(instr - (u8*)VSYSCALL_START + (u8*)__pa_symbol(&__vsyscall_0));
			DPRINTK("%s: vsyscall fixup: %p => %p\n",
				__func__, a->instr, instr);
		}
#endif
		memcpy(insnbuf, a->replacement, a->replacementlen);
		if (*insnbuf == 0xe8 && a->replacementlen == 5)
		    *(s32 *)(insnbuf + 1) += a->replacement - a->instr;
		add_nops(insnbuf + a->replacementlen,
			 a->instrlen - a->replacementlen);
		text_poke_early(instr, insnbuf, a->instrlen);
	}
}

#ifdef CONFIG_SMP

static void alternatives_smp_lock(u8 **start, u8 **end, u8 *text, u8 *text_end)
{
	u8 **ptr;

	mutex_lock(&text_mutex);
	for (ptr = start; ptr < end; ptr++) {
		if (*ptr < text)
			continue;
		if (*ptr > text_end)
			continue;
		/* turn DS segment override prefix into lock prefix */
		text_poke(*ptr, ((unsigned char []){0xf0}), 1);
	};
	mutex_unlock(&text_mutex);
}

static void alternatives_smp_unlock(u8 **start, u8 **end, u8 *text, u8 *text_end)
{
	u8 **ptr;

	if (noreplace_smp)
		return;

	mutex_lock(&text_mutex);
	for (ptr = start; ptr < end; ptr++) {
		if (*ptr < text)
			continue;
		if (*ptr > text_end)
			continue;
		/* turn lock prefix into DS segment override prefix */
		text_poke(*ptr, ((unsigned char []){0x3E}), 1);
	};
	mutex_unlock(&text_mutex);
}

struct smp_alt_module {
	/* what is this ??? */
	struct module	*mod;
	char		*name;

	/* ptrs to lock prefixes */
	u8		**locks;
	u8		**locks_end;

	/* .text segment, needed to avoid patching init code ;) */
	u8		*text;
	u8		*text_end;

	struct list_head next;
};
static LIST_HEAD(smp_alt_modules);
static DEFINE_MUTEX(smp_alt);
static int smp_mode = 1;	/* protected by smp_alt */

void __init_or_module alternatives_smp_module_add(struct module *mod,
						  char *name,
						  void *locks, void *locks_end,
						  void *text,  void *text_end)
{
	struct smp_alt_module *smp;

	if (noreplace_smp)
		return;

	if (smp_alt_once) {
		if (boot_cpu_has(X86_FEATURE_UP))
			alternatives_smp_unlock(locks, locks_end,
						text, text_end);
		return;
	}

	smp = kzalloc(sizeof(*smp), GFP_KERNEL);
	if (NULL == smp)
		return; /* we'll run the (safe but slow) SMP code then ... */

	smp->mod	= mod;
	smp->name	= name;
	smp->locks	= locks;
	smp->locks_end	= locks_end;
	smp->text	= text;
	smp->text_end	= text_end;
	DPRINTK("%s: locks %p -> %p, text %p -> %p, name %s\n",
		__func__, smp->locks, smp->locks_end,
		smp->text, smp->text_end, smp->name);

	mutex_lock(&smp_alt);
	list_add_tail(&smp->next, &smp_alt_modules);
	if (boot_cpu_has(X86_FEATURE_UP))
		alternatives_smp_unlock(smp->locks, smp->locks_end,
					smp->text, smp->text_end);
	mutex_unlock(&smp_alt);
}

void __init_or_module alternatives_smp_module_del(struct module *mod)
{
	struct smp_alt_module *item;

	if (smp_alt_once || noreplace_smp)
		return;

	mutex_lock(&smp_alt);
	list_for_each_entry(item, &smp_alt_modules, next) {
		if (mod != item->mod)
			continue;
		list_del(&item->next);
		mutex_unlock(&smp_alt);
		DPRINTK("%s: %s\n", __func__, item->name);
		kfree(item);
		return;
	}
	mutex_unlock(&smp_alt);
}

void alternatives_smp_switch(int smp)
{
	struct smp_alt_module *mod;

#ifdef CONFIG_LOCKDEP
	/*
	 * Older binutils section handling bug prevented
	 * alternatives-replacement from working reliably.
	 *
	 * If this still occurs then you should see a hang
	 * or crash shortly after this line:
	 */
	printk("lockdep: fixing up alternatives.\n");
#endif

	if (noreplace_smp || smp_alt_once)
		return;
	BUG_ON(!smp && (num_online_cpus() > 1));

	mutex_lock(&smp_alt);

	/*
	 * Avoid unnecessary switches because it forces JIT based VMs to
	 * throw away all cached translations, which can be quite costly.
	 */
	if (smp == smp_mode) {
		/* nothing */
	} else if (smp) {
		printk(KERN_INFO "SMP alternatives: switching to SMP code\n");
		clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
		clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
		list_for_each_entry(mod, &smp_alt_modules, next)
			alternatives_smp_lock(mod->locks, mod->locks_end,
					      mod->text, mod->text_end);
	} else {
		printk(KERN_INFO "SMP alternatives: switching to UP code\n");
		set_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
		set_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
		list_for_each_entry(mod, &smp_alt_modules, next)
			alternatives_smp_unlock(mod->locks, mod->locks_end,
						mod->text, mod->text_end);
	}
	smp_mode = smp;
	mutex_unlock(&smp_alt);
}

/* Return 1 if the address range is reserved for smp-alternatives */
int alternatives_text_reserved(void *start, void *end)
{
	struct smp_alt_module *mod;
	u8 **ptr;
	u8 *text_start = start;
	u8 *text_end = end;

	list_for_each_entry(mod, &smp_alt_modules, next) {
		if (mod->text > text_end || mod->text_end < text_start)
			continue;
		for (ptr = mod->locks; ptr < mod->locks_end; ptr++)
			if (text_start <= *ptr && text_end >= *ptr)
				return 1;
	}

	return 0;
}
#endif

#ifdef CONFIG_PARAVIRT
void __init_or_module apply_paravirt(struct paravirt_patch_site *start,
				     struct paravirt_patch_site *end)
{
	struct paravirt_patch_site *p;
	char insnbuf[MAX_PATCH_LEN];

	if (noreplace_paravirt)
		return;

	for (p = start; p < end; p++) {
		unsigned int used;

		BUG_ON(p->len > MAX_PATCH_LEN);
		/* prep the buffer with the original instructions */
		memcpy(insnbuf, p->instr, p->len);
		used = pv_init_ops.patch(p->instrtype, p->clobbers, insnbuf,
					 (unsigned long)p->instr, p->len);

		BUG_ON(used > p->len);

		/* Pad the rest with nops */
		add_nops(insnbuf + used, p->len - used);
		text_poke_early(p->instr, insnbuf, p->len);
	}
}
extern struct paravirt_patch_site __start_parainstructions[],
	__stop_parainstructions[];
#endif	/* CONFIG_PARAVIRT */

void __init alternative_instructions(void)
{
	/* The patching is not fully atomic, so try to avoid local interruptions
	   that might execute the to be patched code.
	   Other CPUs are not running. */
	stop_nmi();

	/*
	 * Don't stop machine check exceptions while patching.
	 * MCEs only happen when something got corrupted and in this
	 * case we must do something about the corruption.
	 * Ignoring it is worse than a unlikely patching race.
	 * Also machine checks tend to be broadcast and if one CPU
	 * goes into machine check the others follow quickly, so we don't
	 * expect a machine check to cause undue problems during to code
	 * patching.
	 */

	apply_alternatives(__alt_instructions, __alt_instructions_end);

	/* switch to patch-once-at-boottime-only mode and free the
	 * tables in case we know the number of CPUs will never ever
	 * change */
#ifdef CONFIG_HOTPLUG_CPU
	if (num_possible_cpus() < 2)
		smp_alt_once = 1;
#endif

#ifdef CONFIG_SMP
	if (smp_alt_once) {
		if (1 == num_possible_cpus()) {
			printk(KERN_INFO "SMP alternatives: switching to UP code\n");
			set_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
			set_cpu_cap(&cpu_data(0), X86_FEATURE_UP);

			alternatives_smp_unlock(__smp_locks, __smp_locks_end,
						_text, _etext);
		}
	} else {
		alternatives_smp_module_add(NULL, "core kernel",
					    __smp_locks, __smp_locks_end,
					    _text, _etext);

		/* Only switch to UP mode if we don't immediately boot others */
		if (num_present_cpus() == 1 || setup_max_cpus <= 1)
			alternatives_smp_switch(0);
	}
#endif
 	apply_paravirt(__parainstructions, __parainstructions_end);

	if (smp_alt_once)
		free_init_pages("SMP alternatives",
				(unsigned long)__smp_locks,
				(unsigned long)__smp_locks_end);

	restart_nmi();
}

/**
 * text_poke_early - Update instructions on a live kernel at boot time
 * @addr: address to modify
 * @opcode: source of the copy
 * @len: length to copy
 *
 * When you use this code to patch more than one byte of an instruction
 * you need to make sure that other CPUs cannot execute this code in parallel.
 * Also no thread must be currently preempted in the middle of these
 * instructions. And on the local CPU you need to be protected again NMI or MCE
 * handlers seeing an inconsistent instruction while you patch.
 */
static void *__init_or_module text_poke_early(void *addr, const void *opcode,
					      size_t len)
{
	unsigned long flags;
	local_irq_save(flags);
	memcpy(addr, opcode, len);
	sync_core();
	local_irq_restore(flags);
	/* Could also do a CLFLUSH here to speed up CPU recovery; but
	   that causes hangs on some VIA CPUs. */
	return addr;
}

/**
 * text_poke - Update instructions on a live kernel
 * @addr: address to modify
 * @opcode: source of the copy
 * @len: length to copy
 *
 * Only atomic text poke/set should be allowed when not doing early patching.
 * It means the size must be writable atomically and the address must be aligned
 * in a way that permits an atomic write. It also makes sure we fit on a single
 * page.
 *
 * Note: Must be called under text_mutex.
 */
void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
{
	unsigned long flags;
	char *vaddr;
	struct page *pages[2];
	int i;

	if (!core_kernel_text((unsigned long)addr)) {
		pages[0] = vmalloc_to_page(addr);
		pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
	} else {
		pages[0] = virt_to_page(addr);
		WARN_ON(!PageReserved(pages[0]));
		pages[1] = virt_to_page(addr + PAGE_SIZE);
	}
	BUG_ON(!pages[0]);
	local_irq_save(flags);
	set_fixmap(FIX_TEXT_POKE0, page_to_phys(pages[0]));
	if (pages[1])
		set_fixmap(FIX_TEXT_POKE1, page_to_phys(pages[1]));
	vaddr = (char *)fix_to_virt(FIX_TEXT_POKE0);
	memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
	clear_fixmap(FIX_TEXT_POKE0);
	if (pages[1])
		clear_fixmap(FIX_TEXT_POKE1);
	local_flush_tlb();
	sync_core();
	/* Could also do a CLFLUSH here to speed up CPU recovery; but
	   that causes hangs on some VIA CPUs. */
	for (i = 0; i < len; i++)
		BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);
	local_irq_restore(flags);
	return addr;
}

/*
 * Cross-modifying kernel text with stop_machine().
 * This code originally comes from immediate value.
 */
static atomic_t stop_machine_first;
static int wrote_text;

struct text_poke_params {
	void *addr;
	const void *opcode;
	size_t len;
};

static int __kprobes stop_machine_text_poke(void *data)
{
	struct text_poke_params *tpp = data;

	if (atomic_dec_and_test(&stop_machine_first)) {
		text_poke(tpp->addr, tpp->opcode, tpp->len);
		smp_wmb();	/* Make sure other cpus see that this has run */
		wrote_text = 1;
	} else {
		while (!wrote_text)
			cpu_relax();
		smp_mb();	/* Load wrote_text before following execution */
	}

	flush_icache_range((unsigned long)tpp->addr,
			   (unsigned long)tpp->addr + tpp->len);
	return 0;
}

/**
 * text_poke_smp - Update instructions on a live kernel on SMP
 * @addr: address to modify
 * @opcode: source of the copy
 * @len: length to copy
 *
 * Modify multi-byte instruction by using stop_machine() on SMP. This allows
 * user to poke/set multi-byte text on SMP. Only non-NMI/MCE code modifying
 * should be allowed, since stop_machine() does _not_ protect code against
 * NMI and MCE.
 *
 * Note: Must be called under get_online_cpus() and text_mutex.
 */
void *__kprobes text_poke_smp(void *addr, const void *opcode, size_t len)
{
	struct text_poke_params tpp;

	tpp.addr = addr;
	tpp.opcode = opcode;
	tpp.len = len;
	atomic_set(&stop_machine_first, 1);
	wrote_text = 0;
	stop_machine(stop_machine_text_poke, (void *)&tpp, NULL);
	return addr;
}