summaryrefslogtreecommitdiffstats
path: root/arch/arm/probes/kprobes/core.c
blob: 90b5bc723c83f0163831d003920d1a7bb80f7c47 (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
// SPDX-License-Identifier: GPL-2.0-only
/*
 * arch/arm/kernel/kprobes.c
 *
 * Kprobes on ARM
 *
 * Abhishek Sagar <sagar.abhishek@gmail.com>
 * Copyright (C) 2006, 2007 Motorola Inc.
 *
 * Nicolas Pitre <nico@marvell.com>
 * Copyright (C) 2007 Marvell Ltd.
 */

#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/stop_machine.h>
#include <linux/sched/debug.h>
#include <linux/stringify.h>
#include <asm/traps.h>
#include <asm/opcodes.h>
#include <asm/cacheflush.h>
#include <linux/percpu.h>
#include <linux/bug.h>
#include <asm/patch.h>
#include <asm/sections.h>

#include "../decode-arm.h"
#include "../decode-thumb.h"
#include "core.h"

#define MIN_STACK_SIZE(addr) 				\
	min((unsigned long)MAX_STACK_SIZE,		\
	    (unsigned long)current_thread_info() + THREAD_START_SP - (addr))

#define flush_insns(addr, size)				\
	flush_icache_range((unsigned long)(addr),	\
			   (unsigned long)(addr) +	\
			   (size))

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


int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
	kprobe_opcode_t insn;
	kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
	unsigned long addr = (unsigned long)p->addr;
	bool thumb;
	kprobe_decode_insn_t *decode_insn;
	const union decode_action *actions;
	int is;
	const struct decode_checker **checkers;

#ifdef CONFIG_THUMB2_KERNEL
	thumb = true;
	addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
	insn = __mem_to_opcode_thumb16(((u16 *)addr)[0]);
	if (is_wide_instruction(insn)) {
		u16 inst2 = __mem_to_opcode_thumb16(((u16 *)addr)[1]);
		insn = __opcode_thumb32_compose(insn, inst2);
		decode_insn = thumb32_probes_decode_insn;
		actions = kprobes_t32_actions;
		checkers = kprobes_t32_checkers;
	} else {
		decode_insn = thumb16_probes_decode_insn;
		actions = kprobes_t16_actions;
		checkers = kprobes_t16_checkers;
	}
#else /* !CONFIG_THUMB2_KERNEL */
	thumb = false;
	if (addr & 0x3)
		return -EINVAL;
	insn = __mem_to_opcode_arm(*p->addr);
	decode_insn = arm_probes_decode_insn;
	actions = kprobes_arm_actions;
	checkers = kprobes_arm_checkers;
#endif

	p->opcode = insn;
	p->ainsn.insn = tmp_insn;

	switch ((*decode_insn)(insn, &p->ainsn, true, actions, checkers)) {
	case INSN_REJECTED:	/* not supported */
		return -EINVAL;

	case INSN_GOOD:		/* instruction uses slot */
		p->ainsn.insn = get_insn_slot();
		if (!p->ainsn.insn)
			return -ENOMEM;
		for (is = 0; is < MAX_INSN_SIZE; ++is)
			p->ainsn.insn[is] = tmp_insn[is];
		flush_insns(p->ainsn.insn,
				sizeof(p->ainsn.insn[0]) * MAX_INSN_SIZE);
		p->ainsn.insn_fn = (probes_insn_fn_t *)
					((uintptr_t)p->ainsn.insn | thumb);
		break;

	case INSN_GOOD_NO_SLOT:	/* instruction doesn't need insn slot */
		p->ainsn.insn = NULL;
		break;
	}

	/*
	 * Never instrument insn like 'str r0, [sp, +/-r1]'. Also, insn likes
	 * 'str r0, [sp, #-68]' should also be prohibited.
	 * See __und_svc.
	 */
	if ((p->ainsn.stack_space < 0) ||
			(p->ainsn.stack_space > MAX_STACK_SIZE))
		return -EINVAL;

	return 0;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
	unsigned int brkp;
	void *addr;

	if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
		/* Remove any Thumb flag */
		addr = (void *)((uintptr_t)p->addr & ~1);

		if (is_wide_instruction(p->opcode))
			brkp = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION;
		else
			brkp = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION;
	} else {
		kprobe_opcode_t insn = p->opcode;

		addr = p->addr;
		brkp = KPROBE_ARM_BREAKPOINT_INSTRUCTION;

		if (insn >= 0xe0000000)
			brkp |= 0xe0000000;  /* Unconditional instruction */
		else
			brkp |= insn & 0xf0000000;  /* Copy condition from insn */
	}

	patch_text(addr, brkp);
}

/*
 * The actual disarming is done here on each CPU and synchronized using
 * stop_machine. This synchronization is necessary on SMP to avoid removing
 * a probe between the moment the 'Undefined Instruction' exception is raised
 * and the moment the exception handler reads the faulting instruction from
 * memory. It is also needed to atomically set the two half-words of a 32-bit
 * Thumb breakpoint.
 */
struct patch {
	void *addr;
	unsigned int insn;
};

static int __kprobes_remove_breakpoint(void *data)
{
	struct patch *p = data;
	__patch_text(p->addr, p->insn);
	return 0;
}

void __kprobes kprobes_remove_breakpoint(void *addr, unsigned int insn)
{
	struct patch p = {
		.addr = addr,
		.insn = insn,
	};
	stop_machine_cpuslocked(__kprobes_remove_breakpoint, &p,
				cpu_online_mask);
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
	kprobes_remove_breakpoint((void *)((uintptr_t)p->addr & ~1),
			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);
}

static void __kprobes
singlestep_skip(struct kprobe *p, struct pt_regs *regs)
{
#ifdef CONFIG_THUMB2_KERNEL
	regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
	if (is_wide_instruction(p->opcode))
		regs->ARM_pc += 4;
	else
		regs->ARM_pc += 2;
#else
	regs->ARM_pc += 4;
#endif
}

static inline void __kprobes
singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb)
{
	p->ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
}

/*
 * Called with IRQs disabled. IRQs must remain disabled from that point
 * all the way until processing this kprobe is complete.  The current
 * kprobes implementation cannot process more than one nested level of
 * kprobe, and that level is reserved for user kprobe handlers, so we can't
 * risk encountering a new kprobe in an interrupt handler.
 */
void __kprobes kprobe_handler(struct pt_regs *regs)
{
	struct kprobe *p, *cur;
	struct kprobe_ctlblk *kcb;

	kcb = get_kprobe_ctlblk();
	cur = kprobe_running();

#ifdef CONFIG_THUMB2_KERNEL
	/*
	 * First look for a probe which was registered using an address with
	 * bit 0 set, this is the usual situation for pointers to Thumb code.
	 * If not found, fallback to looking for one with bit 0 clear.
	 */
	p = get_kprobe((kprobe_opcode_t *)(regs->ARM_pc | 1));
	if (!p)
		p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);

#else /* ! CONFIG_THUMB2_KERNEL */
	p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
#endif

	if (p) {
		if (!p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
			/*
			 * Probe hit but conditional execution check failed,
			 * so just skip the instruction and continue as if
			 * nothing had happened.
			 * In this case, we can skip recursing check too.
			 */
			singlestep_skip(p, regs);
		} else if (cur) {
			/* Kprobe is pending, so we're recursing. */
			switch (kcb->kprobe_status) {
			case KPROBE_HIT_ACTIVE:
			case KPROBE_HIT_SSDONE:
			case KPROBE_HIT_SS:
				/* A pre- or post-handler probe got us here. */
				kprobes_inc_nmissed_count(p);
				save_previous_kprobe(kcb);
				set_current_kprobe(p);
				kcb->kprobe_status = KPROBE_REENTER;
				singlestep(p, regs, kcb);
				restore_previous_kprobe(kcb);
				break;
			case KPROBE_REENTER:
				/* A nested probe was hit in FIQ, it is a BUG */
				pr_warn("Unrecoverable kprobe detected.\n");
				dump_kprobe(p);
				/* fall through */
			default:
				/* impossible cases */
				BUG();
			}
		} else {
			/* Probe hit and conditional execution check ok. */
			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 will
			 * modify the execution path and no need to single
			 * stepping. Let's just reset current kprobe and exit.
			 */
			if (!p->pre_handler || !p->pre_handler(p, regs)) {
				kcb->kprobe_status = KPROBE_HIT_SS;
				singlestep(p, regs, kcb);
				if (p->post_handler) {
					kcb->kprobe_status = KPROBE_HIT_SSDONE;
					p->post_handler(p, regs, 0);
				}
			}
			reset_current_kprobe();
		}
	} else {
		/*
		 * The probe was removed and a race is in progress.
		 * There is nothing we can do about it.  Let's restart
		 * the instruction.  By the time we can restart, the
		 * real instruction will be there.
		 */
	}
}

static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
{
	unsigned long flags;
	local_irq_save(flags);
	kprobe_handler(regs);
	local_irq_restore(flags);
	return 0;
}

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 PC to point back to the probe address
		 * and allow the page fault handler to continue as a
		 * normal page fault.
		 */
		regs->ARM_pc = (long)cur->addr;
		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.
		 */
		if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
			return 1;
		break;

	default:
		break;
	}

	return 0;
}

int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
				       unsigned long val, void *data)
{
	/*
	 * notify_die() is currently never called on ARM,
	 * so this callback is currently empty.
	 */
	return NOTIFY_DONE;
}

/*
 * When a retprobed function returns, trampoline_handler() is called,
 * calling the kretprobe's handler. We construct a struct pt_regs to
 * give a view of registers r0-r11 to the user return-handler.  This is
 * not a complete pt_regs structure, but that should be plenty sufficient
 * for kretprobe handlers which should normally be interested in r0 only
 * anyway.
 */
void __naked __kprobes kretprobe_trampoline(void)
{
	__asm__ __volatile__ (
		"stmdb	sp!, {r0 - r11}		\n\t"
		"mov	r0, sp			\n\t"
		"bl	trampoline_handler	\n\t"
		"mov	lr, r0			\n\t"
		"ldmia	sp!, {r0 - r11}		\n\t"
#ifdef CONFIG_THUMB2_KERNEL
		"bx	lr			\n\t"
#else
		"mov	pc, lr			\n\t"
#endif
		: : : "memory");
}

/* Called from kretprobe_trampoline */
static __used __kprobes void *trampoline_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
	 * a return probe installed on them, and/or more than one 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;

		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->ARM_lr;

	/* Replace the return addr with trampoline addr. */
	regs->ARM_lr = (unsigned long)&kretprobe_trampoline;
}

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

#ifdef CONFIG_THUMB2_KERNEL

static struct undef_hook kprobes_thumb16_break_hook = {
	.instr_mask	= 0xffff,
	.instr_val	= KPROBE_THUMB16_BREAKPOINT_INSTRUCTION,
	.cpsr_mask	= MODE_MASK,
	.cpsr_val	= SVC_MODE,
	.fn		= kprobe_trap_handler,
};

static struct undef_hook kprobes_thumb32_break_hook = {
	.instr_mask	= 0xffffffff,
	.instr_val	= KPROBE_THUMB32_BREAKPOINT_INSTRUCTION,
	.cpsr_mask	= MODE_MASK,
	.cpsr_val	= SVC_MODE,
	.fn		= kprobe_trap_handler,
};

#else  /* !CONFIG_THUMB2_KERNEL */

static struct undef_hook kprobes_arm_break_hook = {
	.instr_mask	= 0x0fffffff,
	.instr_val	= KPROBE_ARM_BREAKPOINT_INSTRUCTION,
	.cpsr_mask	= MODE_MASK,
	.cpsr_val	= SVC_MODE,
	.fn		= kprobe_trap_handler,
};

#endif /* !CONFIG_THUMB2_KERNEL */

int __init arch_init_kprobes()
{
	arm_probes_decode_init();
#ifdef CONFIG_THUMB2_KERNEL
	register_undef_hook(&kprobes_thumb16_break_hook);
	register_undef_hook(&kprobes_thumb32_break_hook);
#else
	register_undef_hook(&kprobes_arm_break_hook);
#endif
	return 0;
}

bool arch_within_kprobe_blacklist(unsigned long addr)
{
	void *a = (void *)addr;

	return __in_irqentry_text(addr) ||
	       in_entry_text(addr) ||
	       in_idmap_text(addr) ||
	       memory_contains(__kprobes_text_start, __kprobes_text_end, a, 1);
}