arch/csky/kernel/probes/kprobes.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0+

 #include <linux/kprobes.h>
 #include <linux/extable.h>
 #include <linux/slab.h>
 #include <linux/stop_machine.h>
 #include <asm/ptrace.h>
 #include <linux/uaccess.h>
 #include <asm/sections.h>
 #include <asm/cacheflush.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 *);

 struct csky_insn_patch {
 	kprobe_opcode_t	*addr;
 	u32		opcode;
 	atomic_t	cpu_count;
 };

 static int __kprobes patch_text_cb(void *priv)
 {
 	struct csky_insn_patch *param = priv;
 	unsigned int addr = (unsigned int)param->addr;

 	if (atomic_inc_return(&param->cpu_count) == 1) {
 		*(u16 *) addr = cpu_to_le16(param->opcode);
 		dcache_wb_range(addr, addr + 2);
 		atomic_inc(&param->cpu_count);
 	} else {
 		while (atomic_read(&param->cpu_count) <= num_online_cpus())
 			cpu_relax();
 	}

 	icache_inv_range(addr, addr + 2);

 	return 0;
 }

 static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
 {
 	struct csky_insn_patch param = { addr, opcode, ATOMIC_INIT(0) };

 	return stop_machine_cpuslocked(patch_text_cb, &param, cpu_online_mask);
 }

 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
 {
 	unsigned long offset = is_insn32(p->opcode) ? 4 : 2;

 	p->ainsn.api.restore = (unsigned long)p->addr + offset;

 	patch_text(p->ainsn.api.insn, p->opcode);
 }

 static void __kprobes arch_prepare_simulate(struct kprobe *p)
 {
 	p->ainsn.api.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.api.handler)
 		p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);

 	post_kprobe_handler(kcb, regs);
 }

 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 {
 	unsigned long probe_addr = (unsigned long)p->addr;

 	if (probe_addr & 0x1) {
 		pr_warn("Address not aligned.\n");
 		return -EINVAL;
 	}

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

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

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

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

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

 	return 0;
 }

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

 /* 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)
 {
 }

 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);
 }

 /*
  * 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_sr = regs->sr;
 	regs->sr &= ~BIT(6);
 }

 static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
 						struct pt_regs *regs)
 {
 	regs->sr = kcb->saved_sr;
 }

 static void __kprobes
 set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr, struct kprobe *p)
 {
 	unsigned long offset = is_insn32(p->opcode) ? 4 : 2;

 	kcb->ss_ctx.ss_pending = true;
 	kcb->ss_ctx.match_addr = addr + offset;
 }

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

 #define TRACE_MODE_SI		BIT(14)
 #define TRACE_MODE_MASK		~(0x3 << 14)
 #define TRACE_MODE_RUN		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.api.insn) {
 		/* prepare for single stepping */
 		slot = (unsigned long)p->ainsn.api.insn;

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

 		/* IRQs and single stepping do not mix well. */
 		kprobes_save_local_irqflag(kcb, regs);
 		regs->sr = (regs->sr & TRACE_MODE_MASK) | TRACE_MODE_SI;
 		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.\n");
 		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.api.restore != 0)
 		regs->pc = cur->ainsn.api.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 trapnr)
 {
 	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.
 		 */
 		regs->pc = (unsigned long) cur->addr;
 		if (!instruction_pointer(regs))
 			BUG();

 		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, trapnr))
 			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_breakpoint_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 1;
 		} 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 will
 			 * modify the execution path and no need to single
 			 * stepping. Let's just reset current kprobe and exit.
 			 *
 			 * pre_handler can hit a breakpoint and can step thru
 			 * before return.
 			 */
 			if (!p->pre_handler || !p->pre_handler(p, regs))
 				setup_singlestep(p, regs, kcb, 0);
 			else
 				reset_current_kprobe();
 		}
 		return 1;
 	}

 	/*
 	 * 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.
 	 */
 	return 0;
 }

 int __kprobes
 kprobe_single_step_handler(struct pt_regs *regs)
 {
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

 	if ((kcb->ss_ctx.ss_pending)
 	    && (kcb->ss_ctx.match_addr == instruction_pointer(regs))) {
 		clear_ss_context(kcb);	/* clear pending ss */

 		kprobes_restore_local_irqflag(kcb, regs);
 		regs->sr = (regs->sr & TRACE_MODE_MASK) | TRACE_MODE_RUN;

 		post_kprobe_handler(kcb, regs);
 		return 1;
 	}
 	return 0;
 }

 /*
  * Provide a blacklist of symbols identifying ranges which cannot be kprobed.
  * This blacklist is exposed to userspace via debugfs (kprobes/blacklist).
  */
 int __init arch_populate_kprobe_blacklist(void)
 {
 	int ret;

 	ret = kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
 					(unsigned long)__irqentry_text_end);
 	return ret;
 }

 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->lr;
 	regs->lr = (unsigned long) &kretprobe_trampoline;
 }

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

 int __init arch_init_kprobes(void)
 {
 	return 0;
 }
	// SPDX-License-Identifier: GPL-2.0+

	#include <linux/kprobes.h>
	#include <linux/extable.h>
	#include <linux/slab.h>
	#include <linux/stop_machine.h>
	#include <asm/ptrace.h>
	#include <linux/uaccess.h>
	#include <asm/sections.h>
	#include <asm/cacheflush.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 );

	struct csky_insn_patch {
	kprobe_opcode_t *addr;
	u32 opcode;
	atomic_t cpu_count;
	};

	static int __kprobes patch_text_cb(void *priv)
	{
	struct csky_insn_patch *param = priv;
	unsigned int addr = (unsigned int)param->addr;

	if (atomic_inc_return(&param->cpu_count) == 1) {
	(u16 ) addr = cpu_to_le16(param->opcode);
	dcache_wb_range(addr, addr + 2);
	atomic_inc(&param->cpu_count);
	} else {
	while (atomic_read(&param->cpu_count) <= num_online_cpus())
	cpu_relax();
	}

	icache_inv_range(addr, addr + 2);

	return 0;
	}

	static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
	{
	struct csky_insn_patch param = { addr, opcode, ATOMIC_INIT(0) };

	return stop_machine_cpuslocked(patch_text_cb, &param, cpu_online_mask);
	}

	static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
	{
	unsigned long offset = is_insn32(p->opcode) ? 4 : 2;

	p->ainsn.api.restore = (unsigned long)p->addr + offset;

	patch_text(p->ainsn.api.insn, p->opcode);
	}

	static void __kprobes arch_prepare_simulate(struct kprobe *p)
	{
	p->ainsn.api.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.api.handler)
	p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);

	post_kprobe_handler(kcb, regs);
	}

	int __kprobes arch_prepare_kprobe(struct kprobe *p)
	{
	unsigned long probe_addr = (unsigned long)p->addr;

	if (probe_addr & 0x1) {
	pr_warn("Address not aligned.\n");
	return -EINVAL;
	}

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

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

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

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

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

	return 0;
	}

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

	/* 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)
	{
	}

	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);
	}

	/*
	* 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_sr = regs->sr;
	regs->sr &= ~BIT(6);
	}

	static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
	struct pt_regs *regs)
	{
	regs->sr = kcb->saved_sr;
	}

	static void __kprobes
	set_ss_context(struct kprobe_ctlblk kcb, unsigned long addr, struct kprobe p)
	{
	unsigned long offset = is_insn32(p->opcode) ? 4 : 2;

	kcb->ss_ctx.ss_pending = true;
	kcb->ss_ctx.match_addr = addr + offset;
	}

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

	#define TRACE_MODE_SI BIT(14)
	#define TRACE_MODE_MASK ~(0x3 << 14)
	#define TRACE_MODE_RUN 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.api.insn) {
	/* prepare for single stepping */
	slot = (unsigned long)p->ainsn.api.insn;

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

	/* IRQs and single stepping do not mix well. */
	kprobes_save_local_irqflag(kcb, regs);
	regs->sr = (regs->sr & TRACE_MODE_MASK) \| TRACE_MODE_SI;
	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.\n");
	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.api.restore != 0)
	regs->pc = cur->ainsn.api.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 trapnr)
	{
	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.
	*/
	regs->pc = (unsigned long) cur->addr;
	if (!instruction_pointer(regs))
	BUG();

	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, trapnr))
	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_breakpoint_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 1;
	} 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 will
	* modify the execution path and no need to single
	* stepping. Let's just reset current kprobe and exit.
	*
	* pre_handler can hit a breakpoint and can step thru
	* before return.
	*/
	if (!p->pre_handler \|\| !p->pre_handler(p, regs))
	setup_singlestep(p, regs, kcb, 0);
	else
	reset_current_kprobe();
	}
	return 1;
	}

	/*
	* 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.
	*/
	return 0;
	}

	int __kprobes
	kprobe_single_step_handler(struct pt_regs *regs)
	{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	if ((kcb->ss_ctx.ss_pending)
	&& (kcb->ss_ctx.match_addr == instruction_pointer(regs))) {
	clear_ss_context(kcb); /* clear pending ss */

	kprobes_restore_local_irqflag(kcb, regs);
	regs->sr = (regs->sr & TRACE_MODE_MASK) \| TRACE_MODE_RUN;

	post_kprobe_handler(kcb, regs);
	return 1;
	}
	return 0;
	}

	/*
	* Provide a blacklist of symbols identifying ranges which cannot be kprobed.
	* This blacklist is exposed to userspace via debugfs (kprobes/blacklist).
	*/
	int __init arch_populate_kprobe_blacklist(void)
	{
	int ret;

	ret = kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
	(unsigned long)__irqentry_text_end);
	return ret;
	}

	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->lr;
	regs->lr = (unsigned long) &kretprobe_trampoline;
	}

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

	int __init arch_init_kprobes(void)
	{
	return 0;
	}