1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * arch/arm/kernel/kprobes.c
4 *
5 * Kprobes on ARM
6 *
7 * Abhishek Sagar <sagar.abhishek@gmail.com>
8 * Copyright (C) 2006, 2007 Motorola Inc.
9 *
10 * Nicolas Pitre <nico@marvell.com>
11 * Copyright (C) 2007 Marvell Ltd.
12 */
13
14#define pr_fmt(fmt) "kprobes: " fmt
15
16#include <linux/kernel.h>
17#include <linux/kprobes.h>
18#include <linux/module.h>
19#include <linux/slab.h>
20#include <linux/stop_machine.h>
21#include <linux/sched/debug.h>
22#include <linux/stringify.h>
23#include <asm/traps.h>
24#include <asm/opcodes.h>
25#include <asm/cacheflush.h>
26#include <linux/percpu.h>
27#include <linux/bug.h>
28#include <asm/patch.h>
29#include <asm/sections.h>
30
31#include "../decode-arm.h"
32#include "../decode-thumb.h"
33#include "core.h"
34
35#define MIN_STACK_SIZE(addr) 				\
36	min((unsigned long)MAX_STACK_SIZE,		\
37	    (unsigned long)current_thread_info() + THREAD_START_SP - (addr))
38
39#define flush_insns(addr, size)				\
40	flush_icache_range((unsigned long)(addr),	\
41			   (unsigned long)(addr) +	\
42			   (size))
43
44DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
45DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
46
47
48int __kprobes arch_prepare_kprobe(struct kprobe *p)
49{
50	kprobe_opcode_t insn;
51	kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
52	unsigned long addr = (unsigned long)p->addr;
53	bool thumb;
54	kprobe_decode_insn_t *decode_insn;
55	const union decode_action *actions;
56	int is;
57	const struct decode_checker **checkers;
58
59#ifdef CONFIG_THUMB2_KERNEL
60	thumb = true;
61	addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
62	insn = __mem_to_opcode_thumb16(((u16 *)addr)[0]);
63	if (is_wide_instruction(insn)) {
64		u16 inst2 = __mem_to_opcode_thumb16(((u16 *)addr)[1]);
65		insn = __opcode_thumb32_compose(insn, inst2);
66		decode_insn = thumb32_probes_decode_insn;
67		actions = kprobes_t32_actions;
68		checkers = kprobes_t32_checkers;
69	} else {
70		decode_insn = thumb16_probes_decode_insn;
71		actions = kprobes_t16_actions;
72		checkers = kprobes_t16_checkers;
73	}
74#else /* !CONFIG_THUMB2_KERNEL */
75	thumb = false;
76	if (addr & 0x3)
77		return -EINVAL;
78	insn = __mem_to_opcode_arm(*p->addr);
79	decode_insn = arm_probes_decode_insn;
80	actions = kprobes_arm_actions;
81	checkers = kprobes_arm_checkers;
82#endif
83
84	p->opcode = insn;
85	p->ainsn.insn = tmp_insn;
86
87	switch ((*decode_insn)(insn, &p->ainsn, true, actions, checkers)) {
88	case INSN_REJECTED:	/* not supported */
89		return -EINVAL;
90
91	case INSN_GOOD:		/* instruction uses slot */
92		p->ainsn.insn = get_insn_slot();
93		if (!p->ainsn.insn)
94			return -ENOMEM;
95		for (is = 0; is < MAX_INSN_SIZE; ++is)
96			p->ainsn.insn[is] = tmp_insn[is];
97		flush_insns(p->ainsn.insn,
98				sizeof(p->ainsn.insn[0]) * MAX_INSN_SIZE);
99		p->ainsn.insn_fn = (probes_insn_fn_t *)
100					((uintptr_t)p->ainsn.insn | thumb);
101		break;
102
103	case INSN_GOOD_NO_SLOT:	/* instruction doesn't need insn slot */
104		p->ainsn.insn = NULL;
105		break;
106	}
107
108	/*
109	 * Never instrument insn like 'str r0, [sp, +/-r1]'. Also, insn likes
110	 * 'str r0, [sp, #-68]' should also be prohibited.
111	 * See __und_svc.
112	 */
113	if ((p->ainsn.stack_space < 0) ||
114			(p->ainsn.stack_space > MAX_STACK_SIZE))
115		return -EINVAL;
116
117	return 0;
118}
119
120void __kprobes arch_arm_kprobe(struct kprobe *p)
121{
122	unsigned int brkp;
123	void *addr;
124
125	if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
126		/* Remove any Thumb flag */
127		addr = (void *)((uintptr_t)p->addr & ~1);
128
129		if (is_wide_instruction(p->opcode))
130			brkp = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION;
131		else
132			brkp = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION;
133	} else {
134		kprobe_opcode_t insn = p->opcode;
135
136		addr = p->addr;
137		brkp = KPROBE_ARM_BREAKPOINT_INSTRUCTION;
138
139		if (insn >= 0xe0000000)
140			brkp |= 0xe0000000;  /* Unconditional instruction */
141		else
142			brkp |= insn & 0xf0000000;  /* Copy condition from insn */
143	}
144
145	patch_text(addr, brkp);
146}
147
148/*
149 * The actual disarming is done here on each CPU and synchronized using
150 * stop_machine. This synchronization is necessary on SMP to avoid removing
151 * a probe between the moment the 'Undefined Instruction' exception is raised
152 * and the moment the exception handler reads the faulting instruction from
153 * memory. It is also needed to atomically set the two half-words of a 32-bit
154 * Thumb breakpoint.
155 */
156struct patch {
157	void *addr;
158	unsigned int insn;
159};
160
161static int __kprobes_remove_breakpoint(void *data)
162{
163	struct patch *p = data;
164	__patch_text(p->addr, p->insn);
165	return 0;
166}
167
168void __kprobes kprobes_remove_breakpoint(void *addr, unsigned int insn)
169{
170	struct patch p = {
171		.addr = addr,
172		.insn = insn,
173	};
174	stop_machine_cpuslocked(__kprobes_remove_breakpoint, &p,
175				cpu_online_mask);
176}
177
178void __kprobes arch_disarm_kprobe(struct kprobe *p)
179{
180	kprobes_remove_breakpoint((void *)((uintptr_t)p->addr & ~1),
181			p->opcode);
182}
183
184void __kprobes arch_remove_kprobe(struct kprobe *p)
185{
186	if (p->ainsn.insn) {
187		free_insn_slot(p->ainsn.insn, 0);
188		p->ainsn.insn = NULL;
189	}
190}
191
192static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
193{
194	kcb->prev_kprobe.kp = kprobe_running();
195	kcb->prev_kprobe.status = kcb->kprobe_status;
196}
197
198static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
199{
200	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
201	kcb->kprobe_status = kcb->prev_kprobe.status;
202}
203
204static void __kprobes set_current_kprobe(struct kprobe *p)
205{
206	__this_cpu_write(current_kprobe, p);
207}
208
209static void __kprobes
210singlestep_skip(struct kprobe *p, struct pt_regs *regs)
211{
212#ifdef CONFIG_THUMB2_KERNEL
213	regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
214	if (is_wide_instruction(p->opcode))
215		regs->ARM_pc += 4;
216	else
217		regs->ARM_pc += 2;
218#else
219	regs->ARM_pc += 4;
220#endif
221}
222
223static inline void __kprobes
224singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb)
225{
226	p->ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
227}
228
229/*
230 * Called with IRQs disabled. IRQs must remain disabled from that point
231 * all the way until processing this kprobe is complete.  The current
232 * kprobes implementation cannot process more than one nested level of
233 * kprobe, and that level is reserved for user kprobe handlers, so we can't
234 * risk encountering a new kprobe in an interrupt handler.
235 */
236static void __kprobes kprobe_handler(struct pt_regs *regs)
237{
238	struct kprobe *p, *cur;
239	struct kprobe_ctlblk *kcb;
240
241	kcb = get_kprobe_ctlblk();
242	cur = kprobe_running();
243
244#ifdef CONFIG_THUMB2_KERNEL
245	/*
246	 * First look for a probe which was registered using an address with
247	 * bit 0 set, this is the usual situation for pointers to Thumb code.
248	 * If not found, fallback to looking for one with bit 0 clear.
249	 */
250	p = get_kprobe((kprobe_opcode_t *)(regs->ARM_pc | 1));
251	if (!p)
252		p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
253
254#else /* ! CONFIG_THUMB2_KERNEL */
255	p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
256#endif
257
258	if (p) {
259		if (!p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
260			/*
261			 * Probe hit but conditional execution check failed,
262			 * so just skip the instruction and continue as if
263			 * nothing had happened.
264			 * In this case, we can skip recursing check too.
265			 */
266			singlestep_skip(p, regs);
267		} else if (cur) {
268			/* Kprobe is pending, so we're recursing. */
269			switch (kcb->kprobe_status) {
270			case KPROBE_HIT_ACTIVE:
271			case KPROBE_HIT_SSDONE:
272			case KPROBE_HIT_SS:
273				/* A pre- or post-handler probe got us here. */
274				kprobes_inc_nmissed_count(p);
275				save_previous_kprobe(kcb);
276				set_current_kprobe(p);
277				kcb->kprobe_status = KPROBE_REENTER;
278				singlestep(p, regs, kcb);
279				restore_previous_kprobe(kcb);
280				break;
281			case KPROBE_REENTER:
282				/* A nested probe was hit in FIQ, it is a BUG */
283				pr_warn("Failed to recover from reentered kprobes.\n");
284				dump_kprobe(p);
285				fallthrough;
286			default:
287				/* impossible cases */
288				BUG();
289			}
290		} else {
291			/* Probe hit and conditional execution check ok. */
292			set_current_kprobe(p);
293			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
294
295			/*
296			 * If we have no pre-handler or it returned 0, we
297			 * continue with normal processing. If we have a
298			 * pre-handler and it returned non-zero, it will
299			 * modify the execution path and no need to single
300			 * stepping. Let's just reset current kprobe and exit.
301			 */
302			if (!p->pre_handler || !p->pre_handler(p, regs)) {
303				kcb->kprobe_status = KPROBE_HIT_SS;
304				singlestep(p, regs, kcb);
305				if (p->post_handler) {
306					kcb->kprobe_status = KPROBE_HIT_SSDONE;
307					p->post_handler(p, regs, 0);
308				}
309			}
310			reset_current_kprobe();
311		}
312	} else {
313		/*
314		 * The probe was removed and a race is in progress.
315		 * There is nothing we can do about it.  Let's restart
316		 * the instruction.  By the time we can restart, the
317		 * real instruction will be there.
318		 */
319	}
320}
321
322static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
323{
324	unsigned long flags;
325	local_irq_save(flags);
326	kprobe_handler(regs);
327	local_irq_restore(flags);
328	return 0;
329}
330
331int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
332{
333	struct kprobe *cur = kprobe_running();
334	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
335
336	switch (kcb->kprobe_status) {
337	case KPROBE_HIT_SS:
338	case KPROBE_REENTER:
339		/*
340		 * We are here because the instruction being single
341		 * stepped caused a page fault. We reset the current
342		 * kprobe and the PC to point back to the probe address
343		 * and allow the page fault handler to continue as a
344		 * normal page fault.
345		 */
346		regs->ARM_pc = (long)cur->addr;
347		if (kcb->kprobe_status == KPROBE_REENTER) {
348			restore_previous_kprobe(kcb);
349		} else {
350			reset_current_kprobe();
351		}
352		break;
353	}
354
355	return 0;
356}
357
358int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
359				       unsigned long val, void *data)
360{
361	/*
362	 * notify_die() is currently never called on ARM,
363	 * so this callback is currently empty.
364	 */
365	return NOTIFY_DONE;
366}
367
368/*
369 * When a retprobed function returns, trampoline_handler() is called,
370 * calling the kretprobe's handler. We construct a struct pt_regs to
371 * give a view of registers r0-r11, sp, lr, and pc to the user
372 * return-handler. This is not a complete pt_regs structure, but that
373 * should be enough for stacktrace from the return handler with or
374 * without pt_regs.
375 */
376void __naked __kprobes __kretprobe_trampoline(void)
377{
378	__asm__ __volatile__ (
379#ifdef CONFIG_FRAME_POINTER
380		"ldr	lr, =__kretprobe_trampoline	\n\t"
381	/* __kretprobe_trampoline makes a framepointer on pt_regs. */
382#ifdef CONFIG_CC_IS_CLANG
383		"stmdb	sp, {sp, lr, pc}	\n\t"
384		"sub	sp, sp, #12		\n\t"
385		/* In clang case, pt_regs->ip = lr. */
386		"stmdb	sp!, {r0 - r11, lr}	\n\t"
387		/* fp points regs->r11 (fp) */
388		"add	fp, sp,	#44		\n\t"
389#else /* !CONFIG_CC_IS_CLANG */
390		/* In gcc case, pt_regs->ip = fp. */
391		"stmdb	sp, {fp, sp, lr, pc}	\n\t"
392		"sub	sp, sp, #16		\n\t"
393		"stmdb	sp!, {r0 - r11}		\n\t"
394		/* fp points regs->r15 (pc) */
395		"add	fp, sp, #60		\n\t"
396#endif /* CONFIG_CC_IS_CLANG */
397#else /* !CONFIG_FRAME_POINTER */
398		"sub	sp, sp, #16		\n\t"
399		"stmdb	sp!, {r0 - r11}		\n\t"
400#endif /* CONFIG_FRAME_POINTER */
401		"mov	r0, sp			\n\t"
402		"bl	trampoline_handler	\n\t"
403		"mov	lr, r0			\n\t"
404		"ldmia	sp!, {r0 - r11}		\n\t"
405		"add	sp, sp, #16		\n\t"
406#ifdef CONFIG_THUMB2_KERNEL
407		"bx	lr			\n\t"
408#else
409		"mov	pc, lr			\n\t"
410#endif
411		: : : "memory");
412}
413
414/* Called from __kretprobe_trampoline */
415static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
416{
417	return (void *)kretprobe_trampoline_handler(regs, (void *)regs->ARM_fp);
418}
419
420void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
421				      struct pt_regs *regs)
422{
423	ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
424	ri->fp = (void *)regs->ARM_fp;
425
426	/* Replace the return addr with trampoline addr. */
427	regs->ARM_lr = (unsigned long)&__kretprobe_trampoline;
428}
429
430int __kprobes arch_trampoline_kprobe(struct kprobe *p)
431{
432	return 0;
433}
434
435#ifdef CONFIG_THUMB2_KERNEL
436
437static struct undef_hook kprobes_thumb16_break_hook = {
438	.instr_mask	= 0xffff,
439	.instr_val	= KPROBE_THUMB16_BREAKPOINT_INSTRUCTION,
440	.cpsr_mask	= MODE_MASK,
441	.cpsr_val	= SVC_MODE,
442	.fn		= kprobe_trap_handler,
443};
444
445static struct undef_hook kprobes_thumb32_break_hook = {
446	.instr_mask	= 0xffffffff,
447	.instr_val	= KPROBE_THUMB32_BREAKPOINT_INSTRUCTION,
448	.cpsr_mask	= MODE_MASK,
449	.cpsr_val	= SVC_MODE,
450	.fn		= kprobe_trap_handler,
451};
452
453#else  /* !CONFIG_THUMB2_KERNEL */
454
455static struct undef_hook kprobes_arm_break_hook = {
456	.instr_mask	= 0x0fffffff,
457	.instr_val	= KPROBE_ARM_BREAKPOINT_INSTRUCTION,
458	.cpsr_mask	= MODE_MASK,
459	.cpsr_val	= SVC_MODE,
460	.fn		= kprobe_trap_handler,
461};
462
463#endif /* !CONFIG_THUMB2_KERNEL */
464
465int __init arch_init_kprobes(void)
466{
467	arm_probes_decode_init();
468#ifdef CONFIG_THUMB2_KERNEL
469	register_undef_hook(&kprobes_thumb16_break_hook);
470	register_undef_hook(&kprobes_thumb32_break_hook);
471#else
472	register_undef_hook(&kprobes_arm_break_hook);
473#endif
474	return 0;
475}
476
477bool arch_within_kprobe_blacklist(unsigned long addr)
478{
479	void *a = (void *)addr;
480
481	return __in_irqentry_text(addr) ||
482	       in_entry_text(addr) ||
483	       in_idmap_text(addr) ||
484	       memory_contains(__kprobes_text_start, __kprobes_text_end, a, 1);
485}
486