summaryrefslogtreecommitdiff
path: root/arch/x86/kernel/hw_breakpoint.c
blob: bbb0f737aab1904e82a54f08e4ad41b90d435ef5 (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
// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *
 * Copyright (C) 2007 Alan Stern
 * Copyright (C) 2009 IBM Corporation
 * Copyright (C) 2009 Frederic Weisbecker <fweisbec@gmail.com>
 *
 * Authors: Alan Stern <stern@rowland.harvard.edu>
 *          K.Prasad <prasad@linux.vnet.ibm.com>
 *          Frederic Weisbecker <fweisbec@gmail.com>
 */

/*
 * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
 * using the CPU's debug registers.
 */

#include <linux/perf_event.h>
#include <linux/hw_breakpoint.h>
#include <linux/irqflags.h>
#include <linux/notifier.h>
#include <linux/kallsyms.h>
#include <linux/kprobes.h>
#include <linux/percpu.h>
#include <linux/kdebug.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/smp.h>

#include <asm/hw_breakpoint.h>
#include <asm/processor.h>
#include <asm/debugreg.h>
#include <asm/user.h>
#include <asm/desc.h>
#include <asm/tlbflush.h>

/* Per cpu debug control register value */
DEFINE_PER_CPU(unsigned long, cpu_dr7);
EXPORT_PER_CPU_SYMBOL(cpu_dr7);

/* Per cpu debug address registers values */
static DEFINE_PER_CPU(unsigned long, cpu_debugreg[HBP_NUM]);

/*
 * Stores the breakpoints currently in use on each breakpoint address
 * register for each cpus
 */
static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM]);


static inline unsigned long
__encode_dr7(int drnum, unsigned int len, unsigned int type)
{
	unsigned long bp_info;

	bp_info = (len | type) & 0xf;
	bp_info <<= (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE);
	bp_info |= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE));

	return bp_info;
}

/*
 * Encode the length, type, Exact, and Enable bits for a particular breakpoint
 * as stored in debug register 7.
 */
unsigned long encode_dr7(int drnum, unsigned int len, unsigned int type)
{
	return __encode_dr7(drnum, len, type) | DR_GLOBAL_SLOWDOWN;
}

/*
 * Decode the length and type bits for a particular breakpoint as
 * stored in debug register 7.  Return the "enabled" status.
 */
int decode_dr7(unsigned long dr7, int bpnum, unsigned *len, unsigned *type)
{
	int bp_info = dr7 >> (DR_CONTROL_SHIFT + bpnum * DR_CONTROL_SIZE);

	*len = (bp_info & 0xc) | 0x40;
	*type = (bp_info & 0x3) | 0x80;

	return (dr7 >> (bpnum * DR_ENABLE_SIZE)) & 0x3;
}

/*
 * Install a perf counter breakpoint.
 *
 * We seek a free debug address register and use it for this
 * breakpoint. Eventually we enable it in the debug control register.
 *
 * Atomic: we hold the counter->ctx->lock and we only handle variables
 * and registers local to this cpu.
 */
int arch_install_hw_breakpoint(struct perf_event *bp)
{
	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
	unsigned long *dr7;
	int i;

	lockdep_assert_irqs_disabled();

	for (i = 0; i < HBP_NUM; i++) {
		struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);

		if (!*slot) {
			*slot = bp;
			break;
		}
	}

	if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
		return -EBUSY;

	set_debugreg(info->address, i);
	__this_cpu_write(cpu_debugreg[i], info->address);

	dr7 = this_cpu_ptr(&cpu_dr7);
	*dr7 |= encode_dr7(i, info->len, info->type);

	/*
	 * Ensure we first write cpu_dr7 before we set the DR7 register.
	 * This ensures an NMI never see cpu_dr7 0 when DR7 is not.
	 */
	barrier();

	set_debugreg(*dr7, 7);
	if (info->mask)
		set_dr_addr_mask(info->mask, i);

	return 0;
}

/*
 * Uninstall the breakpoint contained in the given counter.
 *
 * First we search the debug address register it uses and then we disable
 * it.
 *
 * Atomic: we hold the counter->ctx->lock and we only handle variables
 * and registers local to this cpu.
 */
void arch_uninstall_hw_breakpoint(struct perf_event *bp)
{
	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
	unsigned long dr7;
	int i;

	lockdep_assert_irqs_disabled();

	for (i = 0; i < HBP_NUM; i++) {
		struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);

		if (*slot == bp) {
			*slot = NULL;
			break;
		}
	}

	if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
		return;

	dr7 = this_cpu_read(cpu_dr7);
	dr7 &= ~__encode_dr7(i, info->len, info->type);

	set_debugreg(dr7, 7);
	if (info->mask)
		set_dr_addr_mask(0, i);

	/*
	 * Ensure the write to cpu_dr7 is after we've set the DR7 register.
	 * This ensures an NMI never see cpu_dr7 0 when DR7 is not.
	 */
	barrier();

	this_cpu_write(cpu_dr7, dr7);
}

static int arch_bp_generic_len(int x86_len)
{
	switch (x86_len) {
	case X86_BREAKPOINT_LEN_1:
		return HW_BREAKPOINT_LEN_1;
	case X86_BREAKPOINT_LEN_2:
		return HW_BREAKPOINT_LEN_2;
	case X86_BREAKPOINT_LEN_4:
		return HW_BREAKPOINT_LEN_4;
#ifdef CONFIG_X86_64
	case X86_BREAKPOINT_LEN_8:
		return HW_BREAKPOINT_LEN_8;
#endif
	default:
		return -EINVAL;
	}
}

int arch_bp_generic_fields(int x86_len, int x86_type,
			   int *gen_len, int *gen_type)
{
	int len;

	/* Type */
	switch (x86_type) {
	case X86_BREAKPOINT_EXECUTE:
		if (x86_len != X86_BREAKPOINT_LEN_X)
			return -EINVAL;

		*gen_type = HW_BREAKPOINT_X;
		*gen_len = sizeof(long);
		return 0;
	case X86_BREAKPOINT_WRITE:
		*gen_type = HW_BREAKPOINT_W;
		break;
	case X86_BREAKPOINT_RW:
		*gen_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
		break;
	default:
		return -EINVAL;
	}

	/* Len */
	len = arch_bp_generic_len(x86_len);
	if (len < 0)
		return -EINVAL;
	*gen_len = len;

	return 0;
}

/*
 * Check for virtual address in kernel space.
 */
int arch_check_bp_in_kernelspace(struct arch_hw_breakpoint *hw)
{
	unsigned long va;
	int len;

	va = hw->address;
	len = arch_bp_generic_len(hw->len);
	WARN_ON_ONCE(len < 0);

	/*
	 * We don't need to worry about va + len - 1 overflowing:
	 * we already require that va is aligned to a multiple of len.
	 */
	return (va >= TASK_SIZE_MAX) || ((va + len - 1) >= TASK_SIZE_MAX);
}

/*
 * Checks whether the range [addr, end], overlaps the area [base, base + size).
 */
static inline bool within_area(unsigned long addr, unsigned long end,
			       unsigned long base, unsigned long size)
{
	return end >= base && addr < (base + size);
}

/*
 * Checks whether the range from addr to end, inclusive, overlaps the fixed
 * mapped CPU entry area range or other ranges used for CPU entry.
 */
static inline bool within_cpu_entry(unsigned long addr, unsigned long end)
{
	int cpu;

	/* CPU entry erea is always used for CPU entry */
	if (within_area(addr, end, CPU_ENTRY_AREA_BASE,
			CPU_ENTRY_AREA_MAP_SIZE))
		return true;

	/*
	 * When FSGSBASE is enabled, paranoid_entry() fetches the per-CPU
	 * GSBASE value via __per_cpu_offset or pcpu_unit_offsets.
	 */
#ifdef CONFIG_SMP
	if (within_area(addr, end, (unsigned long)__per_cpu_offset,
			sizeof(unsigned long) * nr_cpu_ids))
		return true;
#else
	if (within_area(addr, end, (unsigned long)&pcpu_unit_offsets,
			sizeof(pcpu_unit_offsets)))
		return true;
#endif

	for_each_possible_cpu(cpu) {
		/* The original rw GDT is being used after load_direct_gdt() */
		if (within_area(addr, end, (unsigned long)get_cpu_gdt_rw(cpu),
				GDT_SIZE))
			return true;

		/*
		 * cpu_tss_rw is not directly referenced by hardware, but
		 * cpu_tss_rw is also used in CPU entry code,
		 */
		if (within_area(addr, end,
				(unsigned long)&per_cpu(cpu_tss_rw, cpu),
				sizeof(struct tss_struct)))
			return true;

		/*
		 * cpu_tlbstate.user_pcid_flush_mask is used for CPU entry.
		 * If a data breakpoint on it, it will cause an unwanted #DB.
		 * Protect the full cpu_tlbstate structure to be sure.
		 */
		if (within_area(addr, end,
				(unsigned long)&per_cpu(cpu_tlbstate, cpu),
				sizeof(struct tlb_state)))
			return true;

		/*
		 * When in guest (X86_FEATURE_HYPERVISOR), local_db_save()
		 * will read per-cpu cpu_dr7 before clear dr7 register.
		 */
		if (within_area(addr, end, (unsigned long)&per_cpu(cpu_dr7, cpu),
				sizeof(cpu_dr7)))
			return true;
	}

	return false;
}

static int arch_build_bp_info(struct perf_event *bp,
			      const struct perf_event_attr *attr,
			      struct arch_hw_breakpoint *hw)
{
	unsigned long bp_end;

	bp_end = attr->bp_addr + attr->bp_len - 1;
	if (bp_end < attr->bp_addr)
		return -EINVAL;

	/*
	 * Prevent any breakpoint of any type that overlaps the CPU
	 * entry area and data.  This protects the IST stacks and also
	 * reduces the chance that we ever find out what happens if
	 * there's a data breakpoint on the GDT, IDT, or TSS.
	 */
	if (within_cpu_entry(attr->bp_addr, bp_end))
		return -EINVAL;

	hw->address = attr->bp_addr;
	hw->mask = 0;

	/* Type */
	switch (attr->bp_type) {
	case HW_BREAKPOINT_W:
		hw->type = X86_BREAKPOINT_WRITE;
		break;
	case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
		hw->type = X86_BREAKPOINT_RW;
		break;
	case HW_BREAKPOINT_X:
		/*
		 * We don't allow kernel breakpoints in places that are not
		 * acceptable for kprobes.  On non-kprobes kernels, we don't
		 * allow kernel breakpoints at all.
		 */
		if (attr->bp_addr >= TASK_SIZE_MAX) {
			if (within_kprobe_blacklist(attr->bp_addr))
				return -EINVAL;
		}

		hw->type = X86_BREAKPOINT_EXECUTE;
		/*
		 * x86 inst breakpoints need to have a specific undefined len.
		 * But we still need to check userspace is not trying to setup
		 * an unsupported length, to get a range breakpoint for example.
		 */
		if (attr->bp_len == sizeof(long)) {
			hw->len = X86_BREAKPOINT_LEN_X;
			return 0;
		}
		fallthrough;
	default:
		return -EINVAL;
	}

	/* Len */
	switch (attr->bp_len) {
	case HW_BREAKPOINT_LEN_1:
		hw->len = X86_BREAKPOINT_LEN_1;
		break;
	case HW_BREAKPOINT_LEN_2:
		hw->len = X86_BREAKPOINT_LEN_2;
		break;
	case HW_BREAKPOINT_LEN_4:
		hw->len = X86_BREAKPOINT_LEN_4;
		break;
#ifdef CONFIG_X86_64
	case HW_BREAKPOINT_LEN_8:
		hw->len = X86_BREAKPOINT_LEN_8;
		break;
#endif
	default:
		/* AMD range breakpoint */
		if (!is_power_of_2(attr->bp_len))
			return -EINVAL;
		if (attr->bp_addr & (attr->bp_len - 1))
			return -EINVAL;

		if (!boot_cpu_has(X86_FEATURE_BPEXT))
			return -EOPNOTSUPP;

		/*
		 * It's impossible to use a range breakpoint to fake out
		 * user vs kernel detection because bp_len - 1 can't
		 * have the high bit set.  If we ever allow range instruction
		 * breakpoints, then we'll have to check for kprobe-blacklisted
		 * addresses anywhere in the range.
		 */
		hw->mask = attr->bp_len - 1;
		hw->len = X86_BREAKPOINT_LEN_1;
	}

	return 0;
}

/*
 * Validate the arch-specific HW Breakpoint register settings
 */
int hw_breakpoint_arch_parse(struct perf_event *bp,
			     const struct perf_event_attr *attr,
			     struct arch_hw_breakpoint *hw)
{
	unsigned int align;
	int ret;


	ret = arch_build_bp_info(bp, attr, hw);
	if (ret)
		return ret;

	switch (hw->len) {
	case X86_BREAKPOINT_LEN_1:
		align = 0;
		if (hw->mask)
			align = hw->mask;
		break;
	case X86_BREAKPOINT_LEN_2:
		align = 1;
		break;
	case X86_BREAKPOINT_LEN_4:
		align = 3;
		break;
#ifdef CONFIG_X86_64
	case X86_BREAKPOINT_LEN_8:
		align = 7;
		break;
#endif
	default:
		WARN_ON_ONCE(1);
		return -EINVAL;
	}

	/*
	 * Check that the low-order bits of the address are appropriate
	 * for the alignment implied by len.
	 */
	if (hw->address & align)
		return -EINVAL;

	return 0;
}

/*
 * Release the user breakpoints used by ptrace
 */
void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
{
	int i;
	struct thread_struct *t = &tsk->thread;

	for (i = 0; i < HBP_NUM; i++) {
		unregister_hw_breakpoint(t->ptrace_bps[i]);
		t->ptrace_bps[i] = NULL;
	}

	t->virtual_dr6 = 0;
	t->ptrace_dr7 = 0;
}

void hw_breakpoint_restore(void)
{
	set_debugreg(__this_cpu_read(cpu_debugreg[0]), 0);
	set_debugreg(__this_cpu_read(cpu_debugreg[1]), 1);
	set_debugreg(__this_cpu_read(cpu_debugreg[2]), 2);
	set_debugreg(__this_cpu_read(cpu_debugreg[3]), 3);
	set_debugreg(DR6_RESERVED, 6);
	set_debugreg(__this_cpu_read(cpu_dr7), 7);
}
EXPORT_SYMBOL_GPL(hw_breakpoint_restore);

/*
 * Handle debug exception notifications.
 *
 * Return value is either NOTIFY_STOP or NOTIFY_DONE as explained below.
 *
 * NOTIFY_DONE returned if one of the following conditions is true.
 * i) When the causative address is from user-space and the exception
 * is a valid one, i.e. not triggered as a result of lazy debug register
 * switching
 * ii) When there are more bits than trap<n> set in DR6 register (such
 * as BD, BS or BT) indicating that more than one debug condition is
 * met and requires some more action in do_debug().
 *
 * NOTIFY_STOP returned for all other cases
 *
 */
static int hw_breakpoint_handler(struct die_args *args)
{
	int i, rc = NOTIFY_STOP;
	struct perf_event *bp;
	unsigned long *dr6_p;
	unsigned long dr6;
	bool bpx;

	/* The DR6 value is pointed by args->err */
	dr6_p = (unsigned long *)ERR_PTR(args->err);
	dr6 = *dr6_p;

	/* Do an early return if no trap bits are set in DR6 */
	if ((dr6 & DR_TRAP_BITS) == 0)
		return NOTIFY_DONE;

	/* Handle all the breakpoints that were triggered */
	for (i = 0; i < HBP_NUM; ++i) {
		if (likely(!(dr6 & (DR_TRAP0 << i))))
			continue;

		bp = this_cpu_read(bp_per_reg[i]);
		if (!bp)
			continue;

		bpx = bp->hw.info.type == X86_BREAKPOINT_EXECUTE;

		/*
		 * TF and data breakpoints are traps and can be merged, however
		 * instruction breakpoints are faults and will be raised
		 * separately.
		 *
		 * However DR6 can indicate both TF and instruction
		 * breakpoints. In that case take TF as that has precedence and
		 * delay the instruction breakpoint for the next exception.
		 */
		if (bpx && (dr6 & DR_STEP))
			continue;

		/*
		 * Reset the 'i'th TRAP bit in dr6 to denote completion of
		 * exception handling
		 */
		(*dr6_p) &= ~(DR_TRAP0 << i);

		perf_bp_event(bp, args->regs);

		/*
		 * Set up resume flag to avoid breakpoint recursion when
		 * returning back to origin.
		 */
		if (bpx)
			args->regs->flags |= X86_EFLAGS_RF;
	}

	/*
	 * Further processing in do_debug() is needed for a) user-space
	 * breakpoints (to generate signals) and b) when the system has
	 * taken exception due to multiple causes
	 */
	if ((current->thread.virtual_dr6 & DR_TRAP_BITS) ||
	    (dr6 & (~DR_TRAP_BITS)))
		rc = NOTIFY_DONE;

	return rc;
}

/*
 * Handle debug exception notifications.
 */
int hw_breakpoint_exceptions_notify(
		struct notifier_block *unused, unsigned long val, void *data)
{
	if (val != DIE_DEBUG)
		return NOTIFY_DONE;

	return hw_breakpoint_handler(data);
}

void hw_breakpoint_pmu_read(struct perf_event *bp)
{
	/* TODO */
}