arch/arm/probes/kprobes/core.c - linux - Git at Google

 // 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);
 				fallthrough;
 			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;
 	}

 	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)
 {
 	return (void *)kretprobe_trampoline_handler(regs, &kretprobe_trampoline,
 						    (void *)regs->ARM_fp);
 }

 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 				      struct pt_regs *regs)
 {
 	ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
 	ri->fp = (void *)regs->ARM_fp;

 	/* 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);
 }
	// 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);
	fallthrough;
	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;
	}

	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)
	{
	return (void *)kretprobe_trampoline_handler(regs, &kretprobe_trampoline,
	(void *)regs->ARM_fp);
	}

	void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
	struct pt_regs *regs)
	{
	ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
	ri->fp = (void *)regs->ARM_fp;

	/* 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);
	}