summaryrefslogtreecommitdiffstats
path: root/arch/mips/kernel/kprobes.c
blob: 54cd675c5d1d474153f1d3c6b265bdc1c194b378 (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
/*
 *  Kernel Probes (KProbes)
 *  arch/mips/kernel/kprobes.c
 *
 *  Copyright 2006 Sony Corp.
 *  Copyright 2010 Cavium Networks
 *
 *  Some portions copied from the powerpc version.
 *
 *   Copyright (C) IBM Corporation, 2002, 2004
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; version 2 of the License.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/kprobes.h>
#include <linux/preempt.h>
#include <linux/uaccess.h>
#include <linux/kdebug.h>
#include <linux/slab.h>

#include <asm/ptrace.h>
#include <asm/branch.h>
#include <asm/break.h>

#include "probes-common.h"

static const union mips_instruction breakpoint_insn = {
	.b_format = {
		.opcode = spec_op,
		.code = BRK_KPROBE_BP,
		.func = break_op
	}
};

static const union mips_instruction breakpoint2_insn = {
	.b_format = {
		.opcode = spec_op,
		.code = BRK_KPROBE_SSTEPBP,
		.func = break_op
	}
};

DEFINE_PER_CPU(struct kprobe *, current_kprobe);
DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);

static int __kprobes insn_has_delayslot(union mips_instruction insn)
{
	return __insn_has_delay_slot(insn);
}

/*
 * insn_has_ll_or_sc function checks whether instruction is ll or sc
 * one; putting breakpoint on top of atomic ll/sc pair is bad idea;
 * so we need to prevent it and refuse kprobes insertion for such
 * instructions; cannot do much about breakpoint in the middle of
 * ll/sc pair; it is upto user to avoid those places
 */
static int __kprobes insn_has_ll_or_sc(union mips_instruction insn)
{
	int ret = 0;

	switch (insn.i_format.opcode) {
	case ll_op:
	case lld_op:
	case sc_op:
	case scd_op:
		ret = 1;
		break;
	default:
		break;
	}
	return ret;
}

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
	union mips_instruction insn;
	union mips_instruction prev_insn;
	int ret = 0;

	insn = p->addr[0];

	if (insn_has_ll_or_sc(insn)) {
		pr_notice("Kprobes for ll and sc instructions are not"
			  "supported\n");
		ret = -EINVAL;
		goto out;
	}

	if ((probe_kernel_read(&prev_insn, p->addr - 1,
				sizeof(mips_instruction)) == 0) &&
				insn_has_delayslot(prev_insn)) {
		pr_notice("Kprobes for branch delayslot are not supported\n");
		ret = -EINVAL;
		goto out;
	}

	if (__insn_is_compact_branch(insn)) {
		pr_notice("Kprobes for compact branches are not supported\n");
		ret = -EINVAL;
		goto out;
	}

	/* insn: must be on special executable page on mips. */
	p->ainsn.insn = get_insn_slot();
	if (!p->ainsn.insn) {
		ret = -ENOMEM;
		goto out;
	}

	/*
	 * In the kprobe->ainsn.insn[] array we store the original
	 * instruction at index zero and a break trap instruction at
	 * index one.
	 *
	 * On MIPS arch if the instruction at probed address is a
	 * branch instruction, we need to execute the instruction at
	 * Branch Delayslot (BD) at the time of probe hit. As MIPS also
	 * doesn't have single stepping support, the BD instruction can
	 * not be executed in-line and it would be executed on SSOL slot
	 * using a normal breakpoint instruction in the next slot.
	 * So, read the instruction and save it for later execution.
	 */
	if (insn_has_delayslot(insn))
		memcpy(&p->ainsn.insn[0], p->addr + 1, sizeof(kprobe_opcode_t));
	else
		memcpy(&p->ainsn.insn[0], p->addr, sizeof(kprobe_opcode_t));

	p->ainsn.insn[1] = breakpoint2_insn;
	p->opcode = *p->addr;

out:
	return ret;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
	*p->addr = breakpoint_insn;
	flush_insn_slot(p);
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
	*p->addr = p->opcode;
	flush_insn_slot(p);
}

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
	if (p->ainsn.insn) {
		free_insn_slot(p->ainsn.insn, 0);
		p->ainsn.insn = NULL;
	}
}

static void save_previous_kprobe(struct kprobe_ctlblk *kcb)
{
	kcb->prev_kprobe.kp = kprobe_running();
	kcb->prev_kprobe.status = kcb->kprobe_status;
	kcb->prev_kprobe.old_SR = kcb->kprobe_old_SR;
	kcb->prev_kprobe.saved_SR = kcb->kprobe_saved_SR;
	kcb->prev_kprobe.saved_epc = kcb->kprobe_saved_epc;
}

static void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
{
	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
	kcb->kprobe_status = kcb->prev_kprobe.status;
	kcb->kprobe_old_SR = kcb->prev_kprobe.old_SR;
	kcb->kprobe_saved_SR = kcb->prev_kprobe.saved_SR;
	kcb->kprobe_saved_epc = kcb->prev_kprobe.saved_epc;
}

static void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
			       struct kprobe_ctlblk *kcb)
{
	__this_cpu_write(current_kprobe, p);
	kcb->kprobe_saved_SR = kcb->kprobe_old_SR = (regs->cp0_status & ST0_IE);
	kcb->kprobe_saved_epc = regs->cp0_epc;
}

/**
 * evaluate_branch_instrucion -
 *
 * Evaluate the branch instruction at probed address during probe hit. The
 * result of evaluation would be the updated epc. The insturction in delayslot
 * would actually be single stepped using a normal breakpoint) on SSOL slot.
 *
 * The result is also saved in the kprobe control block for later use,
 * in case we need to execute the delayslot instruction. The latter will be
 * false for NOP instruction in dealyslot and the branch-likely instructions
 * when the branch is taken. And for those cases we set a flag as
 * SKIP_DELAYSLOT in the kprobe control block
 */
static int evaluate_branch_instruction(struct kprobe *p, struct pt_regs *regs,
					struct kprobe_ctlblk *kcb)
{
	union mips_instruction insn = p->opcode;
	long epc;
	int ret = 0;

	epc = regs->cp0_epc;
	if (epc & 3)
		goto unaligned;

	if (p->ainsn.insn->word == 0)
		kcb->flags |= SKIP_DELAYSLOT;
	else
		kcb->flags &= ~SKIP_DELAYSLOT;

	ret = __compute_return_epc_for_insn(regs, insn);
	if (ret < 0)
		return ret;

	if (ret == BRANCH_LIKELY_TAKEN)
		kcb->flags |= SKIP_DELAYSLOT;

	kcb->target_epc = regs->cp0_epc;

	return 0;

unaligned:
	pr_notice("%s: unaligned epc - sending SIGBUS.\n", current->comm);
	force_sig(SIGBUS, current);
	return -EFAULT;

}

static void prepare_singlestep(struct kprobe *p, struct pt_regs *regs,
						struct kprobe_ctlblk *kcb)
{
	int ret = 0;

	regs->cp0_status &= ~ST0_IE;

	/* single step inline if the instruction is a break */
	if (p->opcode.word == breakpoint_insn.word ||
	    p->opcode.word == breakpoint2_insn.word)
		regs->cp0_epc = (unsigned long)p->addr;
	else if (insn_has_delayslot(p->opcode)) {
		ret = evaluate_branch_instruction(p, regs, kcb);
		if (ret < 0) {
			pr_notice("Kprobes: Error in evaluating branch\n");
			return;
		}
	}
	regs->cp0_epc = (unsigned long)&p->ainsn.insn[0];
}

/*
 * Called after single-stepping.  p->addr is the address of the
 * instruction whose first byte has been replaced by the "break 0"
 * instruction.	 To avoid the SMP problems that can occur when we
 * temporarily put back the original opcode to single-step, we
 * single-stepped a copy of the instruction.  The address of this
 * copy is p->ainsn.insn.
 *
 * This function prepares to return from the post-single-step
 * breakpoint trap. In case of branch instructions, the target
 * epc to be restored.
 */
static void __kprobes resume_execution(struct kprobe *p,
				       struct pt_regs *regs,
				       struct kprobe_ctlblk *kcb)
{
	if (insn_has_delayslot(p->opcode))
		regs->cp0_epc = kcb->target_epc;
	else {
		unsigned long orig_epc = kcb->kprobe_saved_epc;
		regs->cp0_epc = orig_epc + 4;
	}
}

static int __kprobes kprobe_handler(struct pt_regs *regs)
{
	struct kprobe *p;
	int ret = 0;
	kprobe_opcode_t *addr;
	struct kprobe_ctlblk *kcb;

	addr = (kprobe_opcode_t *) regs->cp0_epc;

	/*
	 * We don't want to be preempted for the entire
	 * duration of kprobe processing
	 */
	preempt_disable();
	kcb = get_kprobe_ctlblk();

	/* Check we're not actually recursing */
	if (kprobe_running()) {
		p = get_kprobe(addr);
		if (p) {
			if (kcb->kprobe_status == KPROBE_HIT_SS &&
			    p->ainsn.insn->word == breakpoint_insn.word) {
				regs->cp0_status &= ~ST0_IE;
				regs->cp0_status |= kcb->kprobe_saved_SR;
				goto no_kprobe;
			}
			/*
			 * We have reentered the kprobe_handler(), since
			 * another probe was hit while within the handler.
			 * We here save the original kprobes variables and
			 * just single step on the instruction of the new probe
			 * without calling any user handlers.
			 */
			save_previous_kprobe(kcb);
			set_current_kprobe(p, regs, kcb);
			kprobes_inc_nmissed_count(p);
			prepare_singlestep(p, regs, kcb);
			kcb->kprobe_status = KPROBE_REENTER;
			if (kcb->flags & SKIP_DELAYSLOT) {
				resume_execution(p, regs, kcb);
				restore_previous_kprobe(kcb);
				preempt_enable_no_resched();
			}
			return 1;
		} else if (addr->word != breakpoint_insn.word) {
			/*
			 * The breakpoint instruction was removed by
			 * another cpu right after we hit, no further
			 * handling of this interrupt is appropriate
			 */
			ret = 1;
		}
		goto no_kprobe;
	}

	p = get_kprobe(addr);
	if (!p) {
		if (addr->word != breakpoint_insn.word) {
			/*
			 * The breakpoint instruction was removed right
			 * after we hit it.  Another cpu has removed
			 * either a probepoint or a debugger breakpoint
			 * at this address.  In either case, no further
			 * handling of this interrupt is appropriate.
			 */
			ret = 1;
		}
		/* Not one of ours: let kernel handle it */
		goto no_kprobe;
	}

	set_current_kprobe(p, regs, kcb);
	kcb->kprobe_status = KPROBE_HIT_ACTIVE;

	if (p->pre_handler && p->pre_handler(p, regs)) {
		/* handler has already set things up, so skip ss setup */
		reset_current_kprobe();
		preempt_enable_no_resched();
		return 1;
	}

	prepare_singlestep(p, regs, kcb);
	if (kcb->flags & SKIP_DELAYSLOT) {
		kcb->kprobe_status = KPROBE_HIT_SSDONE;
		if (p->post_handler)
			p->post_handler(p, regs, 0);
		resume_execution(p, regs, kcb);
		preempt_enable_no_resched();
	} else
		kcb->kprobe_status = KPROBE_HIT_SS;

	return 1;

no_kprobe:
	preempt_enable_no_resched();
	return ret;

}

static inline int post_kprobe_handler(struct pt_regs *regs)
{
	struct kprobe *cur = kprobe_running();
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	if (!cur)
		return 0;

	if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
		kcb->kprobe_status = KPROBE_HIT_SSDONE;
		cur->post_handler(cur, regs, 0);
	}

	resume_execution(cur, regs, kcb);

	regs->cp0_status |= kcb->kprobe_saved_SR;

	/* Restore back the original saved kprobes variables and continue. */
	if (kcb->kprobe_status == KPROBE_REENTER) {
		restore_previous_kprobe(kcb);
		goto out;
	}
	reset_current_kprobe();
out:
	preempt_enable_no_resched();

	return 1;
}

static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
	struct kprobe *cur = kprobe_running();
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
		return 1;

	if (kcb->kprobe_status & KPROBE_HIT_SS) {
		resume_execution(cur, regs, kcb);
		regs->cp0_status |= kcb->kprobe_old_SR;

		reset_current_kprobe();
		preempt_enable_no_resched();
	}
	return 0;
}

/*
 * Wrapper routine for handling exceptions.
 */
int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
				       unsigned long val, void *data)
{

	struct die_args *args = (struct die_args *)data;
	int ret = NOTIFY_DONE;

	switch (val) {
	case DIE_BREAK:
		if (kprobe_handler(args->regs))
			ret = NOTIFY_STOP;
		break;
	case DIE_SSTEPBP:
		if (post_kprobe_handler(args->regs))
			ret = NOTIFY_STOP;
		break;

	case DIE_PAGE_FAULT:
		/* kprobe_running() needs smp_processor_id() */
		preempt_disable();

		if (kprobe_running()
		    && kprobe_fault_handler(args->regs, args->trapnr))
			ret = NOTIFY_STOP;
		preempt_enable();
		break;
	default:
		break;
	}
	return ret;
}

/*
 * Function return probe trampoline:
 *	- init_kprobes() establishes a probepoint here
 *	- When the probed function returns, this probe causes the
 *	  handlers to fire
 */
static void __used kretprobe_trampoline_holder(void)
{
	asm volatile(
		".set push\n\t"
		/* Keep the assembler from reordering and placing JR here. */
		".set noreorder\n\t"
		"nop\n\t"
		".global kretprobe_trampoline\n"
		"kretprobe_trampoline:\n\t"
		"nop\n\t"
		".set pop"
		: : : "memory");
}

void kretprobe_trampoline(void);

void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
				      struct pt_regs *regs)
{
	ri->ret_addr = (kprobe_opcode_t *) regs->regs[31];

	/* Replace the return addr with trampoline addr */
	regs->regs[31] = (unsigned long)kretprobe_trampoline;
}

/*
 * Called when the probe at kretprobe trampoline is hit
 */
static int __kprobes trampoline_probe_handler(struct kprobe *p,
						struct pt_regs *regs)
{
	struct kretprobe_instance *ri = NULL;
	struct hlist_head *head, empty_rp;
	struct hlist_node *tmp;
	unsigned long flags, orig_ret_address = 0;
	unsigned long trampoline_address = (unsigned long)kretprobe_trampoline;

	INIT_HLIST_HEAD(&empty_rp);
	kretprobe_hash_lock(current, &head, &flags);

	/*
	 * It is possible to have multiple instances associated with a given
	 * task either because an multiple functions in the call path
	 * have a return probe installed on them, and/or more than one return
	 * return probe was registered for a target function.
	 *
	 * We can handle this because:
	 *     - instances are always inserted at the head of the list
	 *     - when multiple return probes are registered for the same
	 *	 function, the first instance's ret_addr will point to the
	 *	 real return address, and all the rest will point to
	 *	 kretprobe_trampoline
	 */
	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
		if (ri->task != current)
			/* another task is sharing our hash bucket */
			continue;

		if (ri->rp && ri->rp->handler)
			ri->rp->handler(ri, regs);

		orig_ret_address = (unsigned long)ri->ret_addr;
		recycle_rp_inst(ri, &empty_rp);

		if (orig_ret_address != trampoline_address)
			/*
			 * This is the real return address. Any other
			 * instances associated with this task are for
			 * other calls deeper on the call stack
			 */
			break;
	}

	kretprobe_assert(ri, orig_ret_address, trampoline_address);
	instruction_pointer(regs) = orig_ret_address;

	kretprobe_hash_unlock(current, &flags);

	hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
		hlist_del(&ri->hlist);
		kfree(ri);
	}
	/*
	 * By returning a non-zero value, we are telling
	 * kprobe_handler() that we don't want the post_handler
	 * to run (and have re-enabled preemption)
	 */
	return 1;
}

int __kprobes arch_trampoline_kprobe(struct kprobe *p)
{
	if (p->addr == (kprobe_opcode_t *)kretprobe_trampoline)
		return 1;

	return 0;
}

static struct kprobe trampoline_p = {
	.addr = (kprobe_opcode_t *)kretprobe_trampoline,
	.pre_handler = trampoline_probe_handler
};

int __init arch_init_kprobes(void)
{
	return register_kprobe(&trampoline_p);
}