summaryrefslogtreecommitdiff
path: root/arch/s390/kernel/kprobes.c
blob: 86783efa24eebd95af298fc488d08ac8f30bb009 (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
/*
 *  Kernel Probes (KProbes)
 *
 * 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; either version 2 of the License, or
 * (at your option) any later version.
 *
 * 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.
 *
 * Copyright (C) IBM Corporation, 2002, 2006
 *
 * s390 port, used ppc64 as template. Mike Grundy <grundym@us.ibm.com>
 */

#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/preempt.h>
#include <linux/stop_machine.h>
#include <linux/kdebug.h>
#include <linux/uaccess.h>
#include <asm/cacheflush.h>
#include <asm/sections.h>
#include <linux/module.h>

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

struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
	/* Make sure the probe isn't going on a difficult instruction */
	if (is_prohibited_opcode((kprobe_opcode_t *) p->addr))
		return -EINVAL;

	if ((unsigned long)p->addr & 0x01)
		return -EINVAL;

	/* Use the get_insn_slot() facility for correctness */
	if (!(p->ainsn.insn = get_insn_slot()))
		return -ENOMEM;

	memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));

	get_instruction_type(&p->ainsn);
	p->opcode = *p->addr;
	return 0;
}

int __kprobes is_prohibited_opcode(kprobe_opcode_t *instruction)
{
	switch (*(__u8 *) instruction) {
	case 0x0c:	/* bassm */
	case 0x0b:	/* bsm	 */
	case 0x83:	/* diag  */
	case 0x44:	/* ex	 */
		return -EINVAL;
	}
	switch (*(__u16 *) instruction) {
	case 0x0101:	/* pr	 */
	case 0xb25a:	/* bsa	 */
	case 0xb240:	/* bakr  */
	case 0xb258:	/* bsg	 */
	case 0xb218:	/* pc	 */
	case 0xb228:	/* pt	 */
		return -EINVAL;
	}
	return 0;
}

void __kprobes get_instruction_type(struct arch_specific_insn *ainsn)
{
	/* default fixup method */
	ainsn->fixup = FIXUP_PSW_NORMAL;

	/* save r1 operand */
	ainsn->reg = (*ainsn->insn & 0xf0) >> 4;

	/* save the instruction length (pop 5-5) in bytes */
	switch (*(__u8 *) (ainsn->insn) >> 6) {
	case 0:
		ainsn->ilen = 2;
		break;
	case 1:
	case 2:
		ainsn->ilen = 4;
		break;
	case 3:
		ainsn->ilen = 6;
		break;
	}

	switch (*(__u8 *) ainsn->insn) {
	case 0x05:	/* balr	*/
	case 0x0d:	/* basr */
		ainsn->fixup = FIXUP_RETURN_REGISTER;
		/* if r2 = 0, no branch will be taken */
		if ((*ainsn->insn & 0x0f) == 0)
			ainsn->fixup |= FIXUP_BRANCH_NOT_TAKEN;
		break;
	case 0x06:	/* bctr	*/
	case 0x07:	/* bcr	*/
		ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
		break;
	case 0x45:	/* bal	*/
	case 0x4d:	/* bas	*/
		ainsn->fixup = FIXUP_RETURN_REGISTER;
		break;
	case 0x47:	/* bc	*/
	case 0x46:	/* bct	*/
	case 0x86:	/* bxh	*/
	case 0x87:	/* bxle	*/
		ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
		break;
	case 0x82:	/* lpsw	*/
		ainsn->fixup = FIXUP_NOT_REQUIRED;
		break;
	case 0xb2:	/* lpswe */
		if (*(((__u8 *) ainsn->insn) + 1) == 0xb2) {
			ainsn->fixup = FIXUP_NOT_REQUIRED;
		}
		break;
	case 0xa7:	/* bras	*/
		if ((*ainsn->insn & 0x0f) == 0x05) {
			ainsn->fixup |= FIXUP_RETURN_REGISTER;
		}
		break;
	case 0xc0:
		if ((*ainsn->insn & 0x0f) == 0x00  /* larl  */
			|| (*ainsn->insn & 0x0f) == 0x05) /* brasl */
		ainsn->fixup |= FIXUP_RETURN_REGISTER;
		break;
	case 0xeb:
		if (*(((__u8 *) ainsn->insn) + 5 ) == 0x44 ||	/* bxhg  */
			*(((__u8 *) ainsn->insn) + 5) == 0x45) {/* bxleg */
			ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
		}
		break;
	case 0xe3:	/* bctg	*/
		if (*(((__u8 *) ainsn->insn) + 5) == 0x46) {
			ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
		}
		break;
	}
}

static int __kprobes swap_instruction(void *aref)
{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
	unsigned long status = kcb->kprobe_status;
	struct ins_replace_args *args = aref;
	int rc;

	kcb->kprobe_status = KPROBE_SWAP_INST;
	rc = probe_kernel_write(args->ptr, &args->new, sizeof(args->new));
	kcb->kprobe_status = status;
	return rc;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
	struct ins_replace_args args;

	args.ptr = p->addr;
	args.old = p->opcode;
	args.new = BREAKPOINT_INSTRUCTION;
	stop_machine(swap_instruction, &args, NULL);
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
	struct ins_replace_args args;

	args.ptr = p->addr;
	args.old = BREAKPOINT_INSTRUCTION;
	args.new = p->opcode;
	stop_machine(swap_instruction, &args, NULL);
}

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 __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
	per_cr_bits kprobe_per_regs[1];

	memset(kprobe_per_regs, 0, sizeof(per_cr_bits));
	regs->psw.addr = (unsigned long)p->ainsn.insn | PSW_ADDR_AMODE;

	/* Set up the per control reg info, will pass to lctl */
	kprobe_per_regs[0].em_instruction_fetch = 1;
	kprobe_per_regs[0].starting_addr = (unsigned long)p->ainsn.insn;
	kprobe_per_regs[0].ending_addr = (unsigned long)p->ainsn.insn + 1;

	/* Set the PER control regs, turns on single step for this address */
	__ctl_load(kprobe_per_regs, 9, 11);
	regs->psw.mask |= PSW_MASK_PER;
	regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
}

static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
{
	kcb->prev_kprobe.kp = kprobe_running();
	kcb->prev_kprobe.status = kcb->kprobe_status;
	kcb->prev_kprobe.kprobe_saved_imask = kcb->kprobe_saved_imask;
	memcpy(kcb->prev_kprobe.kprobe_saved_ctl, kcb->kprobe_saved_ctl,
					sizeof(kcb->kprobe_saved_ctl));
}

static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
{
	__get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
	kcb->kprobe_status = kcb->prev_kprobe.status;
	kcb->kprobe_saved_imask = kcb->prev_kprobe.kprobe_saved_imask;
	memcpy(kcb->kprobe_saved_ctl, kcb->prev_kprobe.kprobe_saved_ctl,
					sizeof(kcb->kprobe_saved_ctl));
}

static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
						struct kprobe_ctlblk *kcb)
{
	__get_cpu_var(current_kprobe) = p;
	/* Save the interrupt and per flags */
	kcb->kprobe_saved_imask = regs->psw.mask &
	    (PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
	/* Save the control regs that govern PER */
	__ctl_store(kcb->kprobe_saved_ctl, 9, 11);
}

void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
					struct pt_regs *regs)
{
	ri->ret_addr = (kprobe_opcode_t *) regs->gprs[14];

	/* Replace the return addr with trampoline addr */
	regs->gprs[14] = (unsigned long)&kretprobe_trampoline;
}

static int __kprobes kprobe_handler(struct pt_regs *regs)
{
	struct kprobe *p;
	int ret = 0;
	unsigned long *addr = (unsigned long *)
		((regs->psw.addr & PSW_ADDR_INSN) - 2);
	struct kprobe_ctlblk *kcb;

	/*
	 * 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 == BREAKPOINT_INSTRUCTION) {
				regs->psw.mask &= ~PSW_MASK_PER;
				regs->psw.mask |= kcb->kprobe_saved_imask;
				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->kprobe_status = KPROBE_REENTER;
			return 1;
		} else {
			p = __get_cpu_var(current_kprobe);
			if (p->break_handler && p->break_handler(p, regs)) {
				goto ss_probe;
			}
		}
		goto no_kprobe;
	}

	p = get_kprobe(addr);
	if (!p)
		/*
		 * No kprobe at this address. The fault has not been
		 * caused by a kprobe breakpoint. The race of breakpoint
		 * vs. kprobe remove does not exist because on s390 we
		 * use stop_machine to arm/disarm the breakpoints.
		 */
		goto no_kprobe;

	kcb->kprobe_status = KPROBE_HIT_ACTIVE;
	set_current_kprobe(p, regs, kcb);
	if (p->pre_handler && p->pre_handler(p, regs))
		/* handler has already set things up, so skip ss setup */
		return 1;

ss_probe:
	prepare_singlestep(p, regs);
	kcb->kprobe_status = KPROBE_HIT_SS;
	return 1;

no_kprobe:
	preempt_enable_no_resched();
	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(".global kretprobe_trampoline\n"
		     "kretprobe_trampoline: bcr 0,0\n");
}

/*
 * 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 *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, node, 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);
	regs->psw.addr = orig_ret_address | PSW_ADDR_AMODE;

	reset_current_kprobe();
	kretprobe_hash_unlock(current, &flags);
	preempt_enable_no_resched();

	hlist_for_each_entry_safe(ri, node, 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;
}

/*
 * Called after single-stepping.  p->addr is the address of the
 * instruction whose first byte has been replaced by the "breakpoint"
 * 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.
 */
static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	regs->psw.addr &= PSW_ADDR_INSN;

	if (p->ainsn.fixup & FIXUP_PSW_NORMAL)
		regs->psw.addr = (unsigned long)p->addr +
				((unsigned long)regs->psw.addr -
				 (unsigned long)p->ainsn.insn);

	if (p->ainsn.fixup & FIXUP_BRANCH_NOT_TAKEN)
		if ((unsigned long)regs->psw.addr -
		    (unsigned long)p->ainsn.insn == p->ainsn.ilen)
			regs->psw.addr = (unsigned long)p->addr + p->ainsn.ilen;

	if (p->ainsn.fixup & FIXUP_RETURN_REGISTER)
		regs->gprs[p->ainsn.reg] = ((unsigned long)p->addr +
						(regs->gprs[p->ainsn.reg] -
						(unsigned long)p->ainsn.insn))
						| PSW_ADDR_AMODE;

	regs->psw.addr |= PSW_ADDR_AMODE;
	/* turn off PER mode */
	regs->psw.mask &= ~PSW_MASK_PER;
	/* Restore the original per control regs */
	__ctl_load(kcb->kprobe_saved_ctl, 9, 11);
	regs->psw.mask |= kcb->kprobe_saved_imask;
}

static int __kprobes 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);

	/*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();

	/*
	 * if somebody else is singlestepping across a probe point, psw mask
	 * will have PER set, in which case, continue the remaining processing
	 * of do_single_step, as if this is not a probe hit.
	 */
	if (regs->psw.mask & PSW_MASK_PER) {
		return 0;
	}

	return 1;
}

int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
	struct kprobe *cur = kprobe_running();
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
	const struct exception_table_entry *entry;

	switch(kcb->kprobe_status) {
	case KPROBE_SWAP_INST:
		/* We are here because the instruction replacement failed */
		return 0;
	case KPROBE_HIT_SS:
	case KPROBE_REENTER:
		/*
		 * We are here because the instruction being single
		 * stepped caused a page fault. We reset the current
		 * kprobe and the nip points back to the probe address
		 * and allow the page fault handler to continue as a
		 * normal page fault.
		 */
		regs->psw.addr = (unsigned long)cur->addr | PSW_ADDR_AMODE;
		regs->psw.mask &= ~PSW_MASK_PER;
		regs->psw.mask |= kcb->kprobe_saved_imask;
		if (kcb->kprobe_status == KPROBE_REENTER)
			restore_previous_kprobe(kcb);
		else
			reset_current_kprobe();
		preempt_enable_no_resched();
		break;
	case KPROBE_HIT_ACTIVE:
	case KPROBE_HIT_SSDONE:
		/*
		 * We increment the nmissed count for accounting,
		 * we can also use npre/npostfault count for accouting
		 * these specific fault cases.
		 */
		kprobes_inc_nmissed_count(cur);

		/*
		 * We come here because instructions in the pre/post
		 * handler caused the page_fault, this could happen
		 * if handler tries to access user space by
		 * copy_from_user(), get_user() etc. Let the
		 * user-specified handler try to fix it first.
		 */
		if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
			return 1;

		/*
		 * In case the user-specified fault handler returned
		 * zero, try to fix up.
		 */
		entry = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
		if (entry) {
			regs->psw.addr = entry->fixup | PSW_ADDR_AMODE;
			return 1;
		}

		/*
		 * fixup_exception() could not handle it,
		 * Let do_page_fault() fix it.
		 */
		break;
	default:
		break;
	}
	return 0;
}

/*
 * Wrapper routine to 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_BPT:
		if (kprobe_handler(args->regs))
			ret = NOTIFY_STOP;
		break;
	case DIE_SSTEP:
		if (post_kprobe_handler(args->regs))
			ret = NOTIFY_STOP;
		break;
	case DIE_TRAP:
		/* 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;
}

int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
	struct jprobe *jp = container_of(p, struct jprobe, kp);
	unsigned long addr;
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));

	/* setup return addr to the jprobe handler routine */
	regs->psw.addr = (unsigned long)(jp->entry) | PSW_ADDR_AMODE;

	/* r14 is the function return address */
	kcb->jprobe_saved_r14 = (unsigned long)regs->gprs[14];
	/* r15 is the stack pointer */
	kcb->jprobe_saved_r15 = (unsigned long)regs->gprs[15];
	addr = (unsigned long)kcb->jprobe_saved_r15;

	memcpy(kcb->jprobes_stack, (kprobe_opcode_t *) addr,
	       MIN_STACK_SIZE(addr));
	return 1;
}

void __kprobes jprobe_return(void)
{
	asm volatile(".word 0x0002");
}

void __kprobes jprobe_return_end(void)
{
	asm volatile("bcr 0,0");
}

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
	unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_r15);

	/* Put the regs back */
	memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
	/* put the stack back */
	memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
	       MIN_STACK_SIZE(stack_addr));
	preempt_enable_no_resched();
	return 1;
}

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);
}

int __kprobes arch_trampoline_kprobe(struct kprobe *p)
{
	if (p->addr == (kprobe_opcode_t *) & kretprobe_trampoline)
		return 1;
	return 0;
}