summaryrefslogtreecommitdiffstats
path: root/arch/arm64/kernel/probes/kprobes.c
blob: bf97685882883e8970e472edeb0b457cbc2b76e6 (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
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
/*
 * arch/arm64/kernel/probes/kprobes.c
 *
 * Kprobes support for ARM64
 *
 * Copyright (C) 2013 Linaro Limited.
 * Author: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
 *
 * 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.
 *
 * 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.
 *
 */
#include <linux/kasan.h>
#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/stop_machine.h>
#include <linux/stringify.h>
#include <asm/traps.h>
#include <asm/ptrace.h>
#include <asm/cacheflush.h>
#include <asm/debug-monitors.h>
#include <asm/system_misc.h>
#include <asm/insn.h>
#include <asm/uaccess.h>
#include <asm/irq.h>
#include <asm-generic/sections.h>

#include "decode-insn.h"

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

static void __kprobes
post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);

static inline unsigned long min_stack_size(unsigned long addr)
{
	unsigned long size;

	if (on_irq_stack(addr, raw_smp_processor_id()))
		size = IRQ_STACK_PTR(raw_smp_processor_id()) - addr;
	else
		size = (unsigned long)current_thread_info() + THREAD_START_SP - addr;

	return min(size, FIELD_SIZEOF(struct kprobe_ctlblk, jprobes_stack));
}

static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
{
	/* prepare insn slot */
	p->ainsn.insn[0] = cpu_to_le32(p->opcode);

	flush_icache_range((uintptr_t) (p->ainsn.insn),
			   (uintptr_t) (p->ainsn.insn) +
			   MAX_INSN_SIZE * sizeof(kprobe_opcode_t));

	/*
	 * Needs restoring of return address after stepping xol.
	 */
	p->ainsn.restore = (unsigned long) p->addr +
	  sizeof(kprobe_opcode_t);
}

static void __kprobes arch_prepare_simulate(struct kprobe *p)
{
	/* This instructions is not executed xol. No need to adjust the PC */
	p->ainsn.restore = 0;
}

static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	if (p->ainsn.handler)
		p->ainsn.handler((u32)p->opcode, (long)p->addr, regs);

	/* single step simulated, now go for post processing */
	post_kprobe_handler(kcb, regs);
}

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
	unsigned long probe_addr = (unsigned long)p->addr;
	extern char __start_rodata[];
	extern char __end_rodata[];

	if (probe_addr & 0x3)
		return -EINVAL;

	/* copy instruction */
	p->opcode = le32_to_cpu(*p->addr);

	if (in_exception_text(probe_addr))
		return -EINVAL;
	if (probe_addr >= (unsigned long) __start_rodata &&
	    probe_addr <= (unsigned long) __end_rodata)
		return -EINVAL;

	/* decode instruction */
	switch (arm_kprobe_decode_insn(p->addr, &p->ainsn)) {
	case INSN_REJECTED:	/* insn not supported */
		return -EINVAL;

	case INSN_GOOD_NO_SLOT:	/* insn need simulation */
		p->ainsn.insn = NULL;
		break;

	case INSN_GOOD:	/* instruction uses slot */
		p->ainsn.insn = get_insn_slot();
		if (!p->ainsn.insn)
			return -ENOMEM;
		break;
	};

	/* prepare the instruction */
	if (p->ainsn.insn)
		arch_prepare_ss_slot(p);
	else
		arch_prepare_simulate(p);

	return 0;
}

static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
{
	void *addrs[1];
	u32 insns[1];

	addrs[0] = (void *)addr;
	insns[0] = (u32)opcode;

	return aarch64_insn_patch_text(addrs, insns, 1);
}

/* arm kprobe: install breakpoint in text */
void __kprobes arch_arm_kprobe(struct kprobe *p)
{
	patch_text(p->addr, BRK64_OPCODE_KPROBES);
}

/* disarm kprobe: remove breakpoint from text */
void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
	patch_text(p->addr, p->opcode);
}

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 save_previous_kprobe(struct kprobe_ctlblk *kcb)
{
	kcb->prev_kprobe.kp = kprobe_running();
	kcb->prev_kprobe.status = kcb->kprobe_status;
}

static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
{
	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
	kcb->kprobe_status = kcb->prev_kprobe.status;
}

static void __kprobes set_current_kprobe(struct kprobe *p)
{
	__this_cpu_write(current_kprobe, p);
}

/*
 * The D-flag (Debug mask) is set (masked) upon debug exception entry.
 * Kprobes needs to clear (unmask) D-flag -ONLY- in case of recursive
 * probe i.e. when probe hit from kprobe handler context upon
 * executing the pre/post handlers. In this case we return with
 * D-flag clear so that single-stepping can be carried-out.
 *
 * Leave D-flag set in all other cases.
 */
static void __kprobes
spsr_set_debug_flag(struct pt_regs *regs, int mask)
{
	unsigned long spsr = regs->pstate;

	if (mask)
		spsr |= PSR_D_BIT;
	else
		spsr &= ~PSR_D_BIT;

	regs->pstate = spsr;
}

/*
 * Interrupts need to be disabled before single-step mode is set, and not
 * reenabled until after single-step mode ends.
 * Without disabling interrupt on local CPU, there is a chance of
 * interrupt occurrence in the period of exception return and  start of
 * out-of-line single-step, that result in wrongly single stepping
 * into the interrupt handler.
 */
static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
						struct pt_regs *regs)
{
	kcb->saved_irqflag = regs->pstate;
	regs->pstate |= PSR_I_BIT;
}

static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
						struct pt_regs *regs)
{
	if (kcb->saved_irqflag & PSR_I_BIT)
		regs->pstate |= PSR_I_BIT;
	else
		regs->pstate &= ~PSR_I_BIT;
}

static void __kprobes
set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
{
	kcb->ss_ctx.ss_pending = true;
	kcb->ss_ctx.match_addr = addr + sizeof(kprobe_opcode_t);
}

static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
{
	kcb->ss_ctx.ss_pending = false;
	kcb->ss_ctx.match_addr = 0;
}

static void __kprobes setup_singlestep(struct kprobe *p,
				       struct pt_regs *regs,
				       struct kprobe_ctlblk *kcb, int reenter)
{
	unsigned long slot;

	if (reenter) {
		save_previous_kprobe(kcb);
		set_current_kprobe(p);
		kcb->kprobe_status = KPROBE_REENTER;
	} else {
		kcb->kprobe_status = KPROBE_HIT_SS;
	}


	if (p->ainsn.insn) {
		/* prepare for single stepping */
		slot = (unsigned long)p->ainsn.insn;

		set_ss_context(kcb, slot);	/* mark pending ss */

		if (kcb->kprobe_status == KPROBE_REENTER)
			spsr_set_debug_flag(regs, 0);
		else
			WARN_ON(regs->pstate & PSR_D_BIT);

		/* IRQs and single stepping do not mix well. */
		kprobes_save_local_irqflag(kcb, regs);
		kernel_enable_single_step(regs);
		instruction_pointer_set(regs, slot);
	} else {
		/* insn simulation */
		arch_simulate_insn(p, regs);
	}
}

static int __kprobes reenter_kprobe(struct kprobe *p,
				    struct pt_regs *regs,
				    struct kprobe_ctlblk *kcb)
{
	switch (kcb->kprobe_status) {
	case KPROBE_HIT_SSDONE:
	case KPROBE_HIT_ACTIVE:
		kprobes_inc_nmissed_count(p);
		setup_singlestep(p, regs, kcb, 1);
		break;
	case KPROBE_HIT_SS:
	case KPROBE_REENTER:
		pr_warn("Unrecoverable kprobe detected at %p.\n", p->addr);
		dump_kprobe(p);
		BUG();
		break;
	default:
		WARN_ON(1);
		return 0;
	}

	return 1;
}

static void __kprobes
post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
{
	struct kprobe *cur = kprobe_running();

	if (!cur)
		return;

	/* return addr restore if non-branching insn */
	if (cur->ainsn.restore != 0)
		instruction_pointer_set(regs, cur->ainsn.restore);

	/* restore back original saved kprobe variables and continue */
	if (kcb->kprobe_status == KPROBE_REENTER) {
		restore_previous_kprobe(kcb);
		return;
	}
	/* call post handler */
	kcb->kprobe_status = KPROBE_HIT_SSDONE;
	if (cur->post_handler)	{
		/* post_handler can hit breakpoint and single step
		 * again, so we enable D-flag for recursive exception.
		 */
		cur->post_handler(cur, regs, 0);
	}

	reset_current_kprobe();
}

int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
{
	struct kprobe *cur = kprobe_running();
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	switch (kcb->kprobe_status) {
	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 ip points back to the probe address
		 * and allow the page fault handler to continue as a
		 * normal page fault.
		 */
		instruction_pointer_set(regs, (unsigned long) cur->addr);
		if (!instruction_pointer(regs))
			BUG();

		kernel_disable_single_step();
		if (kcb->kprobe_status == KPROBE_REENTER)
			spsr_set_debug_flag(regs, 1);

		if (kcb->kprobe_status == KPROBE_REENTER)
			restore_previous_kprobe(kcb);
		else
			reset_current_kprobe();

		break;
	case KPROBE_HIT_ACTIVE:
	case KPROBE_HIT_SSDONE:
		/*
		 * We increment the nmissed count for accounting,
		 * we can also use npre/npostfault count for accounting
		 * 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, fsr))
			return 1;

		/*
		 * In case the user-specified fault handler returned
		 * zero, try to fix up.
		 */
		if (fixup_exception(regs))
			return 1;
	}
	return 0;
}

int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
				       unsigned long val, void *data)
{
	return NOTIFY_DONE;
}

static void __kprobes kprobe_handler(struct pt_regs *regs)
{
	struct kprobe *p, *cur_kprobe;
	struct kprobe_ctlblk *kcb;
	unsigned long addr = instruction_pointer(regs);

	kcb = get_kprobe_ctlblk();
	cur_kprobe = kprobe_running();

	p = get_kprobe((kprobe_opcode_t *) addr);

	if (p) {
		if (cur_kprobe) {
			if (reenter_kprobe(p, regs, kcb))
				return;
		} else {
			/* Probe hit */
			set_current_kprobe(p);
			kcb->kprobe_status = KPROBE_HIT_ACTIVE;

			/*
			 * If we have no pre-handler or it returned 0, we
			 * continue with normal processing.  If we have a
			 * pre-handler and it returned non-zero, it prepped
			 * for calling the break_handler below on re-entry,
			 * so get out doing nothing more here.
			 *
			 * pre_handler can hit a breakpoint and can step thru
			 * before return, keep PSTATE D-flag enabled until
			 * pre_handler return back.
			 */
			if (!p->pre_handler || !p->pre_handler(p, regs)) {
				setup_singlestep(p, regs, kcb, 0);
				return;
			}
		}
	} else if ((le32_to_cpu(*(kprobe_opcode_t *) addr) ==
	    BRK64_OPCODE_KPROBES) && cur_kprobe) {
		/* We probably hit a jprobe.  Call its break handler. */
		if (cur_kprobe->break_handler  &&
		     cur_kprobe->break_handler(cur_kprobe, regs)) {
			setup_singlestep(cur_kprobe, regs, kcb, 0);
			return;
		}
	}
	/*
	 * 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.
	 * Return back to original instruction, and continue.
	 */
}

static int __kprobes
kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
{
	if ((kcb->ss_ctx.ss_pending)
	    && (kcb->ss_ctx.match_addr == addr)) {
		clear_ss_context(kcb);	/* clear pending ss */
		return DBG_HOOK_HANDLED;
	}
	/* not ours, kprobes should ignore it */
	return DBG_HOOK_ERROR;
}

int __kprobes
kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
	int retval;

	/* return error if this is not our step */
	retval = kprobe_ss_hit(kcb, instruction_pointer(regs));

	if (retval == DBG_HOOK_HANDLED) {
		kprobes_restore_local_irqflag(kcb, regs);
		kernel_disable_single_step();

		if (kcb->kprobe_status == KPROBE_REENTER)
			spsr_set_debug_flag(regs, 1);

		post_kprobe_handler(kcb, regs);
	}

	return retval;
}

int __kprobes
kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
{
	kprobe_handler(regs);
	return DBG_HOOK_HANDLED;
}

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

	kcb->jprobe_saved_regs = *regs;
	/*
	 * As Linus pointed out, gcc assumes that the callee
	 * owns the argument space and could overwrite it, e.g.
	 * tailcall optimization. So, to be absolutely safe
	 * we also save and restore enough stack bytes to cover
	 * the argument area.
	 */
	kasan_disable_current();
	memcpy(kcb->jprobes_stack, (void *)stack_ptr,
	       min_stack_size(stack_ptr));
	kasan_enable_current();

	instruction_pointer_set(regs, (unsigned long) jp->entry);
	preempt_disable();
	pause_graph_tracing();
	return 1;
}

void __kprobes jprobe_return(void)
{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	/*
	 * Jprobe handler return by entering break exception,
	 * encoded same as kprobe, but with following conditions
	 * -a special PC to identify it from the other kprobes.
	 * -restore stack addr to original saved pt_regs
	 */
	asm volatile("				mov sp, %0	\n"
		     "jprobe_return_break:	brk %1		\n"
		     :
		     : "r" (kcb->jprobe_saved_regs.sp),
		       "I" (BRK64_ESR_KPROBES)
		     : "memory");

	unreachable();
}

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
	long stack_addr = kcb->jprobe_saved_regs.sp;
	long orig_sp = kernel_stack_pointer(regs);
	struct jprobe *jp = container_of(p, struct jprobe, kp);
	extern const char jprobe_return_break[];

	if (instruction_pointer(regs) != (u64) jprobe_return_break)
		return 0;

	if (orig_sp != stack_addr) {
		struct pt_regs *saved_regs =
		    (struct pt_regs *)kcb->jprobe_saved_regs.sp;
		pr_err("current sp %lx does not match saved sp %lx\n",
		       orig_sp, stack_addr);
		pr_err("Saved registers for jprobe %p\n", jp);
		show_regs(saved_regs);
		pr_err("Current registers\n");
		show_regs(regs);
		BUG();
	}
	unpause_graph_tracing();
	*regs = kcb->jprobe_saved_regs;
	kasan_disable_current();
	memcpy((void *)stack_addr, kcb->jprobes_stack,
	       min_stack_size(stack_addr));
	kasan_enable_current();
	preempt_enable_no_resched();
	return 1;
}

bool arch_within_kprobe_blacklist(unsigned long addr)
{
	extern char __idmap_text_start[], __idmap_text_end[];
	extern char __hyp_idmap_text_start[], __hyp_idmap_text_end[];

	if ((addr >= (unsigned long)__kprobes_text_start &&
	    addr < (unsigned long)__kprobes_text_end) ||
	    (addr >= (unsigned long)__entry_text_start &&
	    addr < (unsigned long)__entry_text_end) ||
	    (addr >= (unsigned long)__idmap_text_start &&
	    addr < (unsigned long)__idmap_text_end) ||
	    !!search_exception_tables(addr))
		return true;

	if (!is_kernel_in_hyp_mode()) {
		if ((addr >= (unsigned long)__hyp_text_start &&
		    addr < (unsigned long)__hyp_text_end) ||
		    (addr >= (unsigned long)__hyp_idmap_text_start &&
		    addr < (unsigned long)__hyp_idmap_text_end))
			return true;
	}

	return false;
}

void __kprobes __used *trampoline_probe_handler(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;
	kprobe_opcode_t *correct_ret_addr = NULL;

	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 multiple functions in the call path have
	 * return probes installed on them, and/or more than one
	 * return probe was registered for a target function.
	 *
	 * We can handle this because:
	 *     - instances are always pushed into the head of the list
	 *     - when multiple return probes are registered for the same
	 *	 function, the (chronologically) first instance's ret_addr
	 *	 will be 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;

		orig_ret_address = (unsigned long)ri->ret_addr;

		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);

	correct_ret_addr = ri->ret_addr;
	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
		if (ri->task != current)
			/* another task is sharing our hash bucket */
			continue;

		orig_ret_address = (unsigned long)ri->ret_addr;
		if (ri->rp && ri->rp->handler) {
			__this_cpu_write(current_kprobe, &ri->rp->kp);
			get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
			ri->ret_addr = correct_ret_addr;
			ri->rp->handler(ri, regs);
			__this_cpu_write(current_kprobe, NULL);
		}

		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_hash_unlock(current, &flags);

	hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
		hlist_del(&ri->hlist);
		kfree(ri);
	}
	return (void *)orig_ret_address;
}

void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
				      struct pt_regs *regs)
{
	ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];

	/* replace return addr (x30) with trampoline */
	regs->regs[30] = (long)&kretprobe_trampoline;
}

int __kprobes arch_trampoline_kprobe(struct kprobe *p)
{
	return 0;
}

int __init arch_init_kprobes(void)
{
	return 0;
}