summaryrefslogtreecommitdiff
path: root/arch/x86/mm/kmemcheck/kmemcheck.c
blob: 2c55ed098654f3815586973a52446b83c3db5228 (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
636
637
638
639
640
/**
 * kmemcheck - a heavyweight memory checker for the linux kernel
 * Copyright (C) 2007, 2008  Vegard Nossum <vegardno@ifi.uio.no>
 * (With a lot of help from Ingo Molnar and Pekka Enberg.)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License (version 2) as
 * published by the Free Software Foundation.
 */

#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kallsyms.h>
#include <linux/kernel.h>
#include <linux/kmemcheck.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/page-flags.h>
#include <linux/percpu.h>
#include <linux/ptrace.h>
#include <linux/string.h>
#include <linux/types.h>

#include <asm/cacheflush.h>
#include <asm/kmemcheck.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>

#include "error.h"
#include "opcode.h"
#include "pte.h"
#include "selftest.h"
#include "shadow.h"


#ifdef CONFIG_KMEMCHECK_DISABLED_BY_DEFAULT
#  define KMEMCHECK_ENABLED 0
#endif

#ifdef CONFIG_KMEMCHECK_ENABLED_BY_DEFAULT
#  define KMEMCHECK_ENABLED 1
#endif

#ifdef CONFIG_KMEMCHECK_ONESHOT_BY_DEFAULT
#  define KMEMCHECK_ENABLED 2
#endif

int kmemcheck_enabled = KMEMCHECK_ENABLED;

int __init kmemcheck_init(void)
{
#ifdef CONFIG_SMP
	/*
	 * Limit SMP to use a single CPU. We rely on the fact that this code
	 * runs before SMP is set up.
	 */
	if (setup_max_cpus > 1) {
		printk(KERN_INFO
			"kmemcheck: Limiting number of CPUs to 1.\n");
		setup_max_cpus = 1;
	}
#endif

	if (!kmemcheck_selftest()) {
		printk(KERN_INFO "kmemcheck: self-tests failed; disabling\n");
		kmemcheck_enabled = 0;
		return -EINVAL;
	}

	printk(KERN_INFO "kmemcheck: Initialized\n");
	return 0;
}

early_initcall(kmemcheck_init);

/*
 * We need to parse the kmemcheck= option before any memory is allocated.
 */
static int __init param_kmemcheck(char *str)
{
	if (!str)
		return -EINVAL;

	sscanf(str, "%d", &kmemcheck_enabled);
	return 0;
}

early_param("kmemcheck", param_kmemcheck);

int kmemcheck_show_addr(unsigned long address)
{
	pte_t *pte;

	pte = kmemcheck_pte_lookup(address);
	if (!pte)
		return 0;

	set_pte(pte, __pte(pte_val(*pte) | _PAGE_PRESENT));
	__flush_tlb_one(address);
	return 1;
}

int kmemcheck_hide_addr(unsigned long address)
{
	pte_t *pte;

	pte = kmemcheck_pte_lookup(address);
	if (!pte)
		return 0;

	set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_PRESENT));
	__flush_tlb_one(address);
	return 1;
}

struct kmemcheck_context {
	bool busy;
	int balance;

	/*
	 * There can be at most two memory operands to an instruction, but
	 * each address can cross a page boundary -- so we may need up to
	 * four addresses that must be hidden/revealed for each fault.
	 */
	unsigned long addr[4];
	unsigned long n_addrs;
	unsigned long flags;

	/* Data size of the instruction that caused a fault. */
	unsigned int size;
};

static DEFINE_PER_CPU(struct kmemcheck_context, kmemcheck_context);

bool kmemcheck_active(struct pt_regs *regs)
{
	struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);

	return data->balance > 0;
}

/* Save an address that needs to be shown/hidden */
static void kmemcheck_save_addr(unsigned long addr)
{
	struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);

	BUG_ON(data->n_addrs >= ARRAY_SIZE(data->addr));
	data->addr[data->n_addrs++] = addr;
}

static unsigned int kmemcheck_show_all(void)
{
	struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);
	unsigned int i;
	unsigned int n;

	n = 0;
	for (i = 0; i < data->n_addrs; ++i)
		n += kmemcheck_show_addr(data->addr[i]);

	return n;
}

static unsigned int kmemcheck_hide_all(void)
{
	struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);
	unsigned int i;
	unsigned int n;

	n = 0;
	for (i = 0; i < data->n_addrs; ++i)
		n += kmemcheck_hide_addr(data->addr[i]);

	return n;
}

/*
 * Called from the #PF handler.
 */
void kmemcheck_show(struct pt_regs *regs)
{
	struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);

	BUG_ON(!irqs_disabled());

	if (unlikely(data->balance != 0)) {
		kmemcheck_show_all();
		kmemcheck_error_save_bug(regs);
		data->balance = 0;
		return;
	}

	/*
	 * None of the addresses actually belonged to kmemcheck. Note that
	 * this is not an error.
	 */
	if (kmemcheck_show_all() == 0)
		return;

	++data->balance;

	/*
	 * The IF needs to be cleared as well, so that the faulting
	 * instruction can run "uninterrupted". Otherwise, we might take
	 * an interrupt and start executing that before we've had a chance
	 * to hide the page again.
	 *
	 * NOTE: In the rare case of multiple faults, we must not override
	 * the original flags:
	 */
	if (!(regs->flags & X86_EFLAGS_TF))
		data->flags = regs->flags;

	regs->flags |= X86_EFLAGS_TF;
	regs->flags &= ~X86_EFLAGS_IF;
}

/*
 * Called from the #DB handler.
 */
void kmemcheck_hide(struct pt_regs *regs)
{
	struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);
	int n;

	BUG_ON(!irqs_disabled());

	if (data->balance == 0)
		return;

	if (unlikely(data->balance != 1)) {
		kmemcheck_show_all();
		kmemcheck_error_save_bug(regs);
		data->n_addrs = 0;
		data->balance = 0;

		if (!(data->flags & X86_EFLAGS_TF))
			regs->flags &= ~X86_EFLAGS_TF;
		if (data->flags & X86_EFLAGS_IF)
			regs->flags |= X86_EFLAGS_IF;
		return;
	}

	if (kmemcheck_enabled)
		n = kmemcheck_hide_all();
	else
		n = kmemcheck_show_all();

	if (n == 0)
		return;

	--data->balance;

	data->n_addrs = 0;

	if (!(data->flags & X86_EFLAGS_TF))
		regs->flags &= ~X86_EFLAGS_TF;
	if (data->flags & X86_EFLAGS_IF)
		regs->flags |= X86_EFLAGS_IF;
}

void kmemcheck_show_pages(struct page *p, unsigned int n)
{
	unsigned int i;

	for (i = 0; i < n; ++i) {
		unsigned long address;
		pte_t *pte;
		unsigned int level;

		address = (unsigned long) page_address(&p[i]);
		pte = lookup_address(address, &level);
		BUG_ON(!pte);
		BUG_ON(level != PG_LEVEL_4K);

		set_pte(pte, __pte(pte_val(*pte) | _PAGE_PRESENT));
		set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_HIDDEN));
		__flush_tlb_one(address);
	}
}

bool kmemcheck_page_is_tracked(struct page *p)
{
	/* This will also check the "hidden" flag of the PTE. */
	return kmemcheck_pte_lookup((unsigned long) page_address(p));
}

void kmemcheck_hide_pages(struct page *p, unsigned int n)
{
	unsigned int i;

	for (i = 0; i < n; ++i) {
		unsigned long address;
		pte_t *pte;
		unsigned int level;

		address = (unsigned long) page_address(&p[i]);
		pte = lookup_address(address, &level);
		BUG_ON(!pte);
		BUG_ON(level != PG_LEVEL_4K);

		set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_PRESENT));
		set_pte(pte, __pte(pte_val(*pte) | _PAGE_HIDDEN));
		__flush_tlb_one(address);
	}
}

/* Access may NOT cross page boundary */
static void kmemcheck_read_strict(struct pt_regs *regs,
	unsigned long addr, unsigned int size)
{
	void *shadow;
	enum kmemcheck_shadow status;

	shadow = kmemcheck_shadow_lookup(addr);
	if (!shadow)
		return;

	kmemcheck_save_addr(addr);
	status = kmemcheck_shadow_test(shadow, size);
	if (status == KMEMCHECK_SHADOW_INITIALIZED)
		return;

	if (kmemcheck_enabled)
		kmemcheck_error_save(status, addr, size, regs);

	if (kmemcheck_enabled == 2)
		kmemcheck_enabled = 0;

	/* Don't warn about it again. */
	kmemcheck_shadow_set(shadow, size);
}

/* Access may cross page boundary */
static void kmemcheck_read(struct pt_regs *regs,
	unsigned long addr, unsigned int size)
{
	unsigned long page = addr & PAGE_MASK;
	unsigned long next_addr = addr + size - 1;
	unsigned long next_page = next_addr & PAGE_MASK;

	if (likely(page == next_page)) {
		kmemcheck_read_strict(regs, addr, size);
		return;
	}

	/*
	 * What we do is basically to split the access across the
	 * two pages and handle each part separately. Yes, this means
	 * that we may now see reads that are 3 + 5 bytes, for
	 * example (and if both are uninitialized, there will be two
	 * reports), but it makes the code a lot simpler.
	 */
	kmemcheck_read_strict(regs, addr, next_page - addr);
	kmemcheck_read_strict(regs, next_page, next_addr - next_page);
}

static void kmemcheck_write_strict(struct pt_regs *regs,
	unsigned long addr, unsigned int size)
{
	void *shadow;

	shadow = kmemcheck_shadow_lookup(addr);
	if (!shadow)
		return;

	kmemcheck_save_addr(addr);
	kmemcheck_shadow_set(shadow, size);
}

static void kmemcheck_write(struct pt_regs *regs,
	unsigned long addr, unsigned int size)
{
	unsigned long page = addr & PAGE_MASK;
	unsigned long next_addr = addr + size - 1;
	unsigned long next_page = next_addr & PAGE_MASK;

	if (likely(page == next_page)) {
		kmemcheck_write_strict(regs, addr, size);
		return;
	}

	/* See comment in kmemcheck_read(). */
	kmemcheck_write_strict(regs, addr, next_page - addr);
	kmemcheck_write_strict(regs, next_page, next_addr - next_page);
}

/*
 * Copying is hard. We have two addresses, each of which may be split across
 * a page (and each page will have different shadow addresses).
 */
static void kmemcheck_copy(struct pt_regs *regs,
	unsigned long src_addr, unsigned long dst_addr, unsigned int size)
{
	uint8_t shadow[8];
	enum kmemcheck_shadow status;

	unsigned long page;
	unsigned long next_addr;
	unsigned long next_page;

	uint8_t *x;
	unsigned int i;
	unsigned int n;

	BUG_ON(size > sizeof(shadow));

	page = src_addr & PAGE_MASK;
	next_addr = src_addr + size - 1;
	next_page = next_addr & PAGE_MASK;

	if (likely(page == next_page)) {
		/* Same page */
		x = kmemcheck_shadow_lookup(src_addr);
		if (x) {
			kmemcheck_save_addr(src_addr);
			for (i = 0; i < size; ++i)
				shadow[i] = x[i];
		} else {
			for (i = 0; i < size; ++i)
				shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
		}
	} else {
		n = next_page - src_addr;
		BUG_ON(n > sizeof(shadow));

		/* First page */
		x = kmemcheck_shadow_lookup(src_addr);
		if (x) {
			kmemcheck_save_addr(src_addr);
			for (i = 0; i < n; ++i)
				shadow[i] = x[i];
		} else {
			/* Not tracked */
			for (i = 0; i < n; ++i)
				shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
		}

		/* Second page */
		x = kmemcheck_shadow_lookup(next_page);
		if (x) {
			kmemcheck_save_addr(next_page);
			for (i = n; i < size; ++i)
				shadow[i] = x[i - n];
		} else {
			/* Not tracked */
			for (i = n; i < size; ++i)
				shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
		}
	}

	page = dst_addr & PAGE_MASK;
	next_addr = dst_addr + size - 1;
	next_page = next_addr & PAGE_MASK;

	if (likely(page == next_page)) {
		/* Same page */
		x = kmemcheck_shadow_lookup(dst_addr);
		if (x) {
			kmemcheck_save_addr(dst_addr);
			for (i = 0; i < size; ++i) {
				x[i] = shadow[i];
				shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
			}
		}
	} else {
		n = next_page - dst_addr;
		BUG_ON(n > sizeof(shadow));

		/* First page */
		x = kmemcheck_shadow_lookup(dst_addr);
		if (x) {
			kmemcheck_save_addr(dst_addr);
			for (i = 0; i < n; ++i) {
				x[i] = shadow[i];
				shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
			}
		}

		/* Second page */
		x = kmemcheck_shadow_lookup(next_page);
		if (x) {
			kmemcheck_save_addr(next_page);
			for (i = n; i < size; ++i) {
				x[i - n] = shadow[i];
				shadow[i] = KMEMCHECK_SHADOW_INITIALIZED;
			}
		}
	}

	status = kmemcheck_shadow_test(shadow, size);
	if (status == KMEMCHECK_SHADOW_INITIALIZED)
		return;

	if (kmemcheck_enabled)
		kmemcheck_error_save(status, src_addr, size, regs);

	if (kmemcheck_enabled == 2)
		kmemcheck_enabled = 0;
}

enum kmemcheck_method {
	KMEMCHECK_READ,
	KMEMCHECK_WRITE,
};

static void kmemcheck_access(struct pt_regs *regs,
	unsigned long fallback_address, enum kmemcheck_method fallback_method)
{
	const uint8_t *insn;
	const uint8_t *insn_primary;
	unsigned int size;

	struct kmemcheck_context *data = &__get_cpu_var(kmemcheck_context);

	/* Recursive fault -- ouch. */
	if (data->busy) {
		kmemcheck_show_addr(fallback_address);
		kmemcheck_error_save_bug(regs);
		return;
	}

	data->busy = true;

	insn = (const uint8_t *) regs->ip;
	insn_primary = kmemcheck_opcode_get_primary(insn);

	kmemcheck_opcode_decode(insn, &size);

	switch (insn_primary[0]) {
#ifdef CONFIG_KMEMCHECK_BITOPS_OK
		/* AND, OR, XOR */
		/*
		 * Unfortunately, these instructions have to be excluded from
		 * our regular checking since they access only some (and not
		 * all) bits. This clears out "bogus" bitfield-access warnings.
		 */
	case 0x80:
	case 0x81:
	case 0x82:
	case 0x83:
		switch ((insn_primary[1] >> 3) & 7) {
			/* OR */
		case 1:
			/* AND */
		case 4:
			/* XOR */
		case 6:
			kmemcheck_write(regs, fallback_address, size);
			goto out;

			/* ADD */
		case 0:
			/* ADC */
		case 2:
			/* SBB */
		case 3:
			/* SUB */
		case 5:
			/* CMP */
		case 7:
			break;
		}
		break;
#endif

		/* MOVS, MOVSB, MOVSW, MOVSD */
	case 0xa4:
	case 0xa5:
		/*
		 * These instructions are special because they take two
		 * addresses, but we only get one page fault.
		 */
		kmemcheck_copy(regs, regs->si, regs->di, size);
		goto out;

		/* CMPS, CMPSB, CMPSW, CMPSD */
	case 0xa6:
	case 0xa7:
		kmemcheck_read(regs, regs->si, size);
		kmemcheck_read(regs, regs->di, size);
		goto out;
	}

	/*
	 * If the opcode isn't special in any way, we use the data from the
	 * page fault handler to determine the address and type of memory
	 * access.
	 */
	switch (fallback_method) {
	case KMEMCHECK_READ:
		kmemcheck_read(regs, fallback_address, size);
		goto out;
	case KMEMCHECK_WRITE:
		kmemcheck_write(regs, fallback_address, size);
		goto out;
	}

out:
	data->busy = false;
}

bool kmemcheck_fault(struct pt_regs *regs, unsigned long address,
	unsigned long error_code)
{
	pte_t *pte;

	/*
	 * XXX: Is it safe to assume that memory accesses from virtual 86
	 * mode or non-kernel code segments will _never_ access kernel
	 * memory (e.g. tracked pages)? For now, we need this to avoid
	 * invoking kmemcheck for PnP BIOS calls.
	 */
	if (regs->flags & X86_VM_MASK)
		return false;
	if (regs->cs != __KERNEL_CS)
		return false;

	pte = kmemcheck_pte_lookup(address);
	if (!pte)
		return false;

	if (error_code & 2)
		kmemcheck_access(regs, address, KMEMCHECK_WRITE);
	else
		kmemcheck_access(regs, address, KMEMCHECK_READ);

	kmemcheck_show(regs);
	return true;
}

bool kmemcheck_trap(struct pt_regs *regs)
{
	if (!kmemcheck_active(regs))
		return false;

	/* We're done. */
	kmemcheck_hide(regs);
	return true;
}