arch/x86/kernel/kprobes/opt.c - linux - Git at Google

 /*
  *  Kernel Probes Jump Optimization (Optprobes)
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or
  * (at your option) any later version.
  *
  * 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.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *
  * Copyright (C) IBM Corporation, 2002, 2004
  * Copyright (C) Hitachi Ltd., 2012
  */
 #include <linux/kprobes.h>
 #include <linux/ptrace.h>
 #include <linux/string.h>
 #include <linux/slab.h>
 #include <linux/hardirq.h>
 #include <linux/preempt.h>
 #include <linux/extable.h>
 #include <linux/kdebug.h>
 #include <linux/kallsyms.h>
 #include <linux/ftrace.h>

 #include <asm/text-patching.h>
 #include <asm/cacheflush.h>
 #include <asm/desc.h>
 #include <asm/pgtable.h>
 #include <linux/uaccess.h>
 #include <asm/alternative.h>
 #include <asm/insn.h>
 #include <asm/debugreg.h>

 #include "common.h"

 unsigned long __recover_optprobed_insn(kprobe_opcode_t *buf, unsigned long addr)
 {
 	struct optimized_kprobe *op;
 	struct kprobe *kp;
 	long offs;
 	int i;

 	for (i = 0; i < RELATIVEJUMP_SIZE; i++) {
 		kp = get_kprobe((void *)addr - i);
 		/* This function only handles jump-optimized kprobe */
 		if (kp && kprobe_optimized(kp)) {
 			op = container_of(kp, struct optimized_kprobe, kp);
 			/* If op->list is not empty, op is under optimizing */
 			if (list_empty(&op->list))
 				goto found;
 		}
 	}

 	return addr;
 found:
 	/*
 	 * If the kprobe can be optimized, original bytes which can be
 	 * overwritten by jump destination address. In this case, original
 	 * bytes must be recovered from op->optinsn.copied_insn buffer.
 	 */
 	memcpy(buf, (void *)addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
 	if (addr == (unsigned long)kp->addr) {
 		buf[0] = kp->opcode;
 		memcpy(buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);
 	} else {
 		offs = addr - (unsigned long)kp->addr - 1;
 		memcpy(buf, op->optinsn.copied_insn + offs, RELATIVE_ADDR_SIZE - offs);
 	}

 	return (unsigned long)buf;
 }

 /* Insert a move instruction which sets a pointer to eax/rdi (1st arg). */
 static void synthesize_set_arg1(kprobe_opcode_t *addr, unsigned long val)
 {
 #ifdef CONFIG_X86_64
 	*addr++ = 0x48;
 	*addr++ = 0xbf;
 #else
 	*addr++ = 0xb8;
 #endif
 	*(unsigned long *)addr = val;
 }

 asm (
 			".global optprobe_template_entry\n"
 			"optprobe_template_entry:\n"
 #ifdef CONFIG_X86_64
 			/* We don't bother saving the ss register */
 			"	pushq %rsp\n"
 			"	pushfq\n"
 			SAVE_REGS_STRING
 			"	movq %rsp, %rsi\n"
 			".global optprobe_template_val\n"
 			"optprobe_template_val:\n"
 			ASM_NOP5
 			ASM_NOP5
 			".global optprobe_template_call\n"
 			"optprobe_template_call:\n"
 			ASM_NOP5
 			/* Move flags to rsp */
 			"	movq 144(%rsp), %rdx\n"
 			"	movq %rdx, 152(%rsp)\n"
 			RESTORE_REGS_STRING
 			/* Skip flags entry */
 			"	addq $8, %rsp\n"
 			"	popfq\n"
 #else /* CONFIG_X86_32 */
 			"	pushf\n"
 			SAVE_REGS_STRING
 			"	movl %esp, %edx\n"
 			".global optprobe_template_val\n"
 			"optprobe_template_val:\n"
 			ASM_NOP5
 			".global optprobe_template_call\n"
 			"optprobe_template_call:\n"
 			ASM_NOP5
 			RESTORE_REGS_STRING
 			"	addl $4, %esp\n"	/* skip cs */
 			"	popf\n"
 #endif
 			".global optprobe_template_end\n"
 			"optprobe_template_end:\n");

 #define TMPL_MOVE_IDX \
 	((long)&optprobe_template_val - (long)&optprobe_template_entry)
 #define TMPL_CALL_IDX \
 	((long)&optprobe_template_call - (long)&optprobe_template_entry)
 #define TMPL_END_IDX \
 	((long)&optprobe_template_end - (long)&optprobe_template_entry)

 #define INT3_SIZE sizeof(kprobe_opcode_t)

 /* Optimized kprobe call back function: called from optinsn */
 static void
 optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
 {
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 	unsigned long flags;

 	/* This is possible if op is under delayed unoptimizing */
 	if (kprobe_disabled(&op->kp))
 		return;

 	local_irq_save(flags);
 	if (kprobe_running()) {
 		kprobes_inc_nmissed_count(&op->kp);
 	} else {
 		/* Save skipped registers */
 #ifdef CONFIG_X86_64
 		regs->cs = __KERNEL_CS;
 #else
 		regs->cs = __KERNEL_CS | get_kernel_rpl();
 		regs->gs = 0;
 #endif
 		regs->ip = (unsigned long)op->kp.addr + INT3_SIZE;
 		regs->orig_ax = ~0UL;

 		__this_cpu_write(current_kprobe, &op->kp);
 		kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 		opt_pre_handler(&op->kp, regs);
 		__this_cpu_write(current_kprobe, NULL);
 	}
 	local_irq_restore(flags);
 }
 NOKPROBE_SYMBOL(optimized_callback);

 static int copy_optimized_instructions(u8 *dest, u8 *src)
 {
 	int len = 0, ret;

 	while (len < RELATIVEJUMP_SIZE) {
 		ret = __copy_instruction(dest + len, src + len);
 		if (!ret || !can_boost(dest + len))
 			return -EINVAL;
 		len += ret;
 	}
 	/* Check whether the address range is reserved */
 	if (ftrace_text_reserved(src, src + len - 1) ||
 	    alternatives_text_reserved(src, src + len - 1) ||
 	    jump_label_text_reserved(src, src + len - 1))
 		return -EBUSY;

 	return len;
 }

 /* Check whether insn is indirect jump */
 static int insn_is_indirect_jump(struct insn *insn)
 {
 	return ((insn->opcode.bytes[0] == 0xff &&
 		(X86_MODRM_REG(insn->modrm.value) & 6) == 4) || /* Jump */
 		insn->opcode.bytes[0] == 0xea);	/* Segment based jump */
 }

 /* Check whether insn jumps into specified address range */
 static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
 {
 	unsigned long target = 0;

 	switch (insn->opcode.bytes[0]) {
 	case 0xe0:	/* loopne */
 	case 0xe1:	/* loope */
 	case 0xe2:	/* loop */
 	case 0xe3:	/* jcxz */
 	case 0xe9:	/* near relative jump */
 	case 0xeb:	/* short relative jump */
 		break;
 	case 0x0f:
 		if ((insn->opcode.bytes[1] & 0xf0) == 0x80) /* jcc near */
 			break;
 		return 0;
 	default:
 		if ((insn->opcode.bytes[0] & 0xf0) == 0x70) /* jcc short */
 			break;
 		return 0;
 	}
 	target = (unsigned long)insn->next_byte + insn->immediate.value;

 	return (start <= target && target <= start + len);
 }

 /* Decode whole function to ensure any instructions don't jump into target */
 static int can_optimize(unsigned long paddr)
 {
 	unsigned long addr, size = 0, offset = 0;
 	struct insn insn;
 	kprobe_opcode_t buf[MAX_INSN_SIZE];

 	/* Lookup symbol including addr */
 	if (!kallsyms_lookup_size_offset(paddr, &size, &offset))
 		return 0;

 	/*
 	 * Do not optimize in the entry code due to the unstable
 	 * stack handling.
 	 */
 	if ((paddr >= (unsigned long)__entry_text_start) &&
 	    (paddr <  (unsigned long)__entry_text_end))
 		return 0;

 	/* Check there is enough space for a relative jump. */
 	if (size - offset < RELATIVEJUMP_SIZE)
 		return 0;

 	/* Decode instructions */
 	addr = paddr - offset;
 	while (addr < paddr - offset + size) { /* Decode until function end */
 		unsigned long recovered_insn;
 		if (search_exception_tables(addr))
 			/*
 			 * Since some fixup code will jumps into this function,
 			 * we can't optimize kprobe in this function.
 			 */
 			return 0;
 		recovered_insn = recover_probed_instruction(buf, addr);
 		if (!recovered_insn)
 			return 0;
 		kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
 		insn_get_length(&insn);
 		/* Another subsystem puts a breakpoint */
 		if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
 			return 0;
 		/* Recover address */
 		insn.kaddr = (void *)addr;
 		insn.next_byte = (void *)(addr + insn.length);
 		/* Check any instructions don't jump into target */
 		if (insn_is_indirect_jump(&insn) ||
 		    insn_jump_into_range(&insn, paddr + INT3_SIZE,
 					 RELATIVE_ADDR_SIZE))
 			return 0;
 		addr += insn.length;
 	}

 	return 1;
 }

 /* Check optimized_kprobe can actually be optimized. */
 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
 {
 	int i;
 	struct kprobe *p;

 	for (i = 1; i < op->optinsn.size; i++) {
 		p = get_kprobe(op->kp.addr + i);
 		if (p && !kprobe_disabled(p))
 			return -EEXIST;
 	}

 	return 0;
 }

 /* Check the addr is within the optimized instructions. */
 int arch_within_optimized_kprobe(struct optimized_kprobe *op,
 				 unsigned long addr)
 {
 	return ((unsigned long)op->kp.addr <= addr &&
 		(unsigned long)op->kp.addr + op->optinsn.size > addr);
 }

 /* Free optimized instruction slot */
 static
 void __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
 {
 	if (op->optinsn.insn) {
 		free_optinsn_slot(op->optinsn.insn, dirty);
 		op->optinsn.insn = NULL;
 		op->optinsn.size = 0;
 	}
 }

 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
 {
 	__arch_remove_optimized_kprobe(op, 1);
 }

 /*
  * Copy replacing target instructions
  * Target instructions MUST be relocatable (checked inside)
  * This is called when new aggr(opt)probe is allocated or reused.
  */
 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
 				  struct kprobe *__unused)
 {
 	u8 *buf;
 	int ret;
 	long rel;

 	if (!can_optimize((unsigned long)op->kp.addr))
 		return -EILSEQ;

 	op->optinsn.insn = get_optinsn_slot();
 	if (!op->optinsn.insn)
 		return -ENOMEM;

 	/*
 	 * Verify if the address gap is in 2GB range, because this uses
 	 * a relative jump.
 	 */
 	rel = (long)op->optinsn.insn - (long)op->kp.addr + RELATIVEJUMP_SIZE;
 	if (abs(rel) > 0x7fffffff) {
 		__arch_remove_optimized_kprobe(op, 0);
 		return -ERANGE;
 	}

 	buf = (u8 *)op->optinsn.insn;

 	/* Copy instructions into the out-of-line buffer */
 	ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr);
 	if (ret < 0) {
 		__arch_remove_optimized_kprobe(op, 0);
 		return ret;
 	}
 	op->optinsn.size = ret;

 	/* Copy arch-dep-instance from template */
 	memcpy(buf, &optprobe_template_entry, TMPL_END_IDX);

 	/* Set probe information */
 	synthesize_set_arg1(buf + TMPL_MOVE_IDX, (unsigned long)op);

 	/* Set probe function call */
 	synthesize_relcall(buf + TMPL_CALL_IDX, optimized_callback);

 	/* Set returning jmp instruction at the tail of out-of-line buffer */
 	synthesize_reljump(buf + TMPL_END_IDX + op->optinsn.size,
 			   (u8 *)op->kp.addr + op->optinsn.size);

 	flush_icache_range((unsigned long) buf,
 			   (unsigned long) buf + TMPL_END_IDX +
 			   op->optinsn.size + RELATIVEJUMP_SIZE);
 	return 0;
 }

 /*
  * Replace breakpoints (int3) with relative jumps.
  * Caller must call with locking kprobe_mutex and text_mutex.
  */
 void arch_optimize_kprobes(struct list_head *oplist)
 {
 	struct optimized_kprobe *op, *tmp;
 	u8 insn_buf[RELATIVEJUMP_SIZE];

 	list_for_each_entry_safe(op, tmp, oplist, list) {
 		s32 rel = (s32)((long)op->optinsn.insn -
 			((long)op->kp.addr + RELATIVEJUMP_SIZE));

 		WARN_ON(kprobe_disabled(&op->kp));

 		/* Backup instructions which will be replaced by jump address */
 		memcpy(op->optinsn.copied_insn, op->kp.addr + INT3_SIZE,
 		       RELATIVE_ADDR_SIZE);

 		insn_buf[0] = RELATIVEJUMP_OPCODE;
 		*(s32 *)(&insn_buf[1]) = rel;

 		text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE,
 			     op->optinsn.insn);

 		list_del_init(&op->list);
 	}
 }

 /* Replace a relative jump with a breakpoint (int3).  */
 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
 {
 	u8 insn_buf[RELATIVEJUMP_SIZE];

 	/* Set int3 to first byte for kprobes */
 	insn_buf[0] = BREAKPOINT_INSTRUCTION;
 	memcpy(insn_buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);
 	text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE,
 		     op->optinsn.insn);
 }

 /*
  * Recover original instructions and breakpoints from relative jumps.
  * Caller must call with locking kprobe_mutex.
  */
 extern void arch_unoptimize_kprobes(struct list_head *oplist,
 				    struct list_head *done_list)
 {
 	struct optimized_kprobe *op, *tmp;

 	list_for_each_entry_safe(op, tmp, oplist, list) {
 		arch_unoptimize_kprobe(op);
 		list_move(&op->list, done_list);
 	}
 }

 int setup_detour_execution(struct kprobe *p, struct pt_regs *regs, int reenter)
 {
 	struct optimized_kprobe *op;

 	if (p->flags & KPROBE_FLAG_OPTIMIZED) {
 		/* This kprobe is really able to run optimized path. */
 		op = container_of(p, struct optimized_kprobe, kp);
 		/* Detour through copied instructions */
 		regs->ip = (unsigned long)op->optinsn.insn + TMPL_END_IDX;
 		if (!reenter)
 			reset_current_kprobe();
 		preempt_enable_no_resched();
 		return 1;
 	}
 	return 0;
 }
 NOKPROBE_SYMBOL(setup_detour_execution);
	/*
	* Kernel Probes Jump Optimization (Optprobes)
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* 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.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
	*
	* Copyright (C) IBM Corporation, 2002, 2004
	* Copyright (C) Hitachi Ltd., 2012
	*/
	#include <linux/kprobes.h>
	#include <linux/ptrace.h>
	#include <linux/string.h>
	#include <linux/slab.h>
	#include <linux/hardirq.h>
	#include <linux/preempt.h>
	#include <linux/extable.h>
	#include <linux/kdebug.h>
	#include <linux/kallsyms.h>
	#include <linux/ftrace.h>

	#include <asm/text-patching.h>
	#include <asm/cacheflush.h>
	#include <asm/desc.h>
	#include <asm/pgtable.h>
	#include <linux/uaccess.h>
	#include <asm/alternative.h>
	#include <asm/insn.h>
	#include <asm/debugreg.h>

	#include "common.h"

	unsigned long __recover_optprobed_insn(kprobe_opcode_t *buf, unsigned long addr)
	{
	struct optimized_kprobe *op;
	struct kprobe *kp;
	long offs;
	int i;

	for (i = 0; i < RELATIVEJUMP_SIZE; i++) {
	kp = get_kprobe((void *)addr - i);
	/* This function only handles jump-optimized kprobe */
	if (kp && kprobe_optimized(kp)) {
	op = container_of(kp, struct optimized_kprobe, kp);
	/* If op->list is not empty, op is under optimizing */
	if (list_empty(&op->list))
	goto found;
	}
	}

	return addr;
	found:
	/*
	* If the kprobe can be optimized, original bytes which can be
	* overwritten by jump destination address. In this case, original
	* bytes must be recovered from op->optinsn.copied_insn buffer.
	*/
	memcpy(buf, (void )addr, MAX_INSN_SIZE sizeof(kprobe_opcode_t));
	if (addr == (unsigned long)kp->addr) {
	buf[0] = kp->opcode;
	memcpy(buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);
	} else {
	offs = addr - (unsigned long)kp->addr - 1;
	memcpy(buf, op->optinsn.copied_insn + offs, RELATIVE_ADDR_SIZE - offs);
	}

	return (unsigned long)buf;
	}

	/* Insert a move instruction which sets a pointer to eax/rdi (1st arg). */
	static void synthesize_set_arg1(kprobe_opcode_t *addr, unsigned long val)
	{
	#ifdef CONFIG_X86_64
	*addr++ = 0x48;
	*addr++ = 0xbf;
	#else
	*addr++ = 0xb8;
	#endif
	(unsigned long )addr = val;
	}

	asm (
	".global optprobe_template_entry\n"
	"optprobe_template_entry:\n"
	#ifdef CONFIG_X86_64
	/* We don't bother saving the ss register */
	" pushq %rsp\n"
	" pushfq\n"
	SAVE_REGS_STRING
	" movq %rsp, %rsi\n"
	".global optprobe_template_val\n"
	"optprobe_template_val:\n"
	ASM_NOP5
	ASM_NOP5
	".global optprobe_template_call\n"
	"optprobe_template_call:\n"
	ASM_NOP5
	/* Move flags to rsp */
	" movq 144(%rsp), %rdx\n"
	" movq %rdx, 152(%rsp)\n"
	RESTORE_REGS_STRING
	/* Skip flags entry */
	" addq $8, %rsp\n"
	" popfq\n"
	#else /* CONFIG_X86_32 */
	" pushf\n"
	SAVE_REGS_STRING
	" movl %esp, %edx\n"
	".global optprobe_template_val\n"
	"optprobe_template_val:\n"
	ASM_NOP5
	".global optprobe_template_call\n"
	"optprobe_template_call:\n"
	ASM_NOP5
	RESTORE_REGS_STRING
	" addl $4, %esp\n" /* skip cs */
	" popf\n"
	#endif
	".global optprobe_template_end\n"
	"optprobe_template_end:\n");

	#define TMPL_MOVE_IDX \
	((long)&optprobe_template_val - (long)&optprobe_template_entry)
	#define TMPL_CALL_IDX \
	((long)&optprobe_template_call - (long)&optprobe_template_entry)
	#define TMPL_END_IDX \
	((long)&optprobe_template_end - (long)&optprobe_template_entry)

	#define INT3_SIZE sizeof(kprobe_opcode_t)

	/* Optimized kprobe call back function: called from optinsn */
	static void
	optimized_callback(struct optimized_kprobe op, struct pt_regs regs)
	{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
	unsigned long flags;

	/* This is possible if op is under delayed unoptimizing */
	if (kprobe_disabled(&op->kp))
	return;

	local_irq_save(flags);
	if (kprobe_running()) {
	kprobes_inc_nmissed_count(&op->kp);
	} else {
	/* Save skipped registers */
	#ifdef CONFIG_X86_64
	regs->cs = __KERNEL_CS;
	#else
	regs->cs = __KERNEL_CS \| get_kernel_rpl();
	regs->gs = 0;
	#endif
	regs->ip = (unsigned long)op->kp.addr + INT3_SIZE;
	regs->orig_ax = ~0UL;

	__this_cpu_write(current_kprobe, &op->kp);
	kcb->kprobe_status = KPROBE_HIT_ACTIVE;
	opt_pre_handler(&op->kp, regs);
	__this_cpu_write(current_kprobe, NULL);
	}
	local_irq_restore(flags);
	}
	NOKPROBE_SYMBOL(optimized_callback);

	static int copy_optimized_instructions(u8 dest, u8 src)
	{
	int len = 0, ret;

	while (len < RELATIVEJUMP_SIZE) {
	ret = __copy_instruction(dest + len, src + len);
	if (!ret \|\| !can_boost(dest + len))
	return -EINVAL;
	len += ret;
	}
	/* Check whether the address range is reserved */
	if (ftrace_text_reserved(src, src + len - 1) \|\|
	alternatives_text_reserved(src, src + len - 1) \|\|
	jump_label_text_reserved(src, src + len - 1))
	return -EBUSY;

	return len;
	}

	/* Check whether insn is indirect jump */
	static int insn_is_indirect_jump(struct insn *insn)
	{
	return ((insn->opcode.bytes[0] == 0xff &&
	(X86_MODRM_REG(insn->modrm.value) & 6) == 4) \|\| /* Jump */
	insn->opcode.bytes[0] == 0xea); /* Segment based jump */
	}

	/* Check whether insn jumps into specified address range */
	static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
	{
	unsigned long target = 0;

	switch (insn->opcode.bytes[0]) {
	case 0xe0: /* loopne */
	case 0xe1: /* loope */
	case 0xe2: /* loop */
	case 0xe3: /* jcxz */
	case 0xe9: /* near relative jump */
	case 0xeb: /* short relative jump */
	break;
	case 0x0f:
	if ((insn->opcode.bytes[1] & 0xf0) == 0x80) /* jcc near */
	break;
	return 0;
	default:
	if ((insn->opcode.bytes[0] & 0xf0) == 0x70) /* jcc short */
	break;
	return 0;
	}
	target = (unsigned long)insn->next_byte + insn->immediate.value;

	return (start <= target && target <= start + len);
	}

	/* Decode whole function to ensure any instructions don't jump into target */
	static int can_optimize(unsigned long paddr)
	{
	unsigned long addr, size = 0, offset = 0;
	struct insn insn;
	kprobe_opcode_t buf[MAX_INSN_SIZE];

	/* Lookup symbol including addr */
	if (!kallsyms_lookup_size_offset(paddr, &size, &offset))
	return 0;

	/*
	* Do not optimize in the entry code due to the unstable
	* stack handling.
	*/
	if ((paddr >= (unsigned long)__entry_text_start) &&
	(paddr < (unsigned long)__entry_text_end))
	return 0;

	/* Check there is enough space for a relative jump. */
	if (size - offset < RELATIVEJUMP_SIZE)
	return 0;

	/* Decode instructions */
	addr = paddr - offset;
	while (addr < paddr - offset + size) { /* Decode until function end */
	unsigned long recovered_insn;
	if (search_exception_tables(addr))
	/*
	* Since some fixup code will jumps into this function,
	* we can't optimize kprobe in this function.
	*/
	return 0;
	recovered_insn = recover_probed_instruction(buf, addr);
	if (!recovered_insn)
	return 0;
	kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
	insn_get_length(&insn);
	/* Another subsystem puts a breakpoint */
	if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
	return 0;
	/* Recover address */
	insn.kaddr = (void *)addr;
	insn.next_byte = (void *)(addr + insn.length);
	/* Check any instructions don't jump into target */
	if (insn_is_indirect_jump(&insn) \|\|
	insn_jump_into_range(&insn, paddr + INT3_SIZE,
	RELATIVE_ADDR_SIZE))
	return 0;
	addr += insn.length;
	}

	return 1;
	}

	/* Check optimized_kprobe can actually be optimized. */
	int arch_check_optimized_kprobe(struct optimized_kprobe *op)
	{
	int i;
	struct kprobe *p;

	for (i = 1; i < op->optinsn.size; i++) {
	p = get_kprobe(op->kp.addr + i);
	if (p && !kprobe_disabled(p))
	return -EEXIST;
	}

	return 0;
	}

	/* Check the addr is within the optimized instructions. */
	int arch_within_optimized_kprobe(struct optimized_kprobe *op,
	unsigned long addr)
	{
	return ((unsigned long)op->kp.addr <= addr &&
	(unsigned long)op->kp.addr + op->optinsn.size > addr);
	}

	/* Free optimized instruction slot */
	static
	void __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
	{
	if (op->optinsn.insn) {
	free_optinsn_slot(op->optinsn.insn, dirty);
	op->optinsn.insn = NULL;
	op->optinsn.size = 0;
	}
	}

	void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
	{
	__arch_remove_optimized_kprobe(op, 1);
	}

	/*
	* Copy replacing target instructions
	* Target instructions MUST be relocatable (checked inside)
	* This is called when new aggr(opt)probe is allocated or reused.
	*/
	int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
	struct kprobe *__unused)
	{
	u8 *buf;
	int ret;
	long rel;

	if (!can_optimize((unsigned long)op->kp.addr))
	return -EILSEQ;

	op->optinsn.insn = get_optinsn_slot();
	if (!op->optinsn.insn)
	return -ENOMEM;

	/*
	* Verify if the address gap is in 2GB range, because this uses
	* a relative jump.
	*/
	rel = (long)op->optinsn.insn - (long)op->kp.addr + RELATIVEJUMP_SIZE;
	if (abs(rel) > 0x7fffffff) {
	__arch_remove_optimized_kprobe(op, 0);
	return -ERANGE;
	}

	buf = (u8 *)op->optinsn.insn;

	/* Copy instructions into the out-of-line buffer */
	ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr);
	if (ret < 0) {
	__arch_remove_optimized_kprobe(op, 0);
	return ret;
	}
	op->optinsn.size = ret;

	/* Copy arch-dep-instance from template */
	memcpy(buf, &optprobe_template_entry, TMPL_END_IDX);

	/* Set probe information */
	synthesize_set_arg1(buf + TMPL_MOVE_IDX, (unsigned long)op);

	/* Set probe function call */
	synthesize_relcall(buf + TMPL_CALL_IDX, optimized_callback);

	/* Set returning jmp instruction at the tail of out-of-line buffer */
	synthesize_reljump(buf + TMPL_END_IDX + op->optinsn.size,
	(u8 *)op->kp.addr + op->optinsn.size);

	flush_icache_range((unsigned long) buf,
	(unsigned long) buf + TMPL_END_IDX +
	op->optinsn.size + RELATIVEJUMP_SIZE);
	return 0;
	}

	/*
	* Replace breakpoints (int3) with relative jumps.
	* Caller must call with locking kprobe_mutex and text_mutex.
	*/
	void arch_optimize_kprobes(struct list_head *oplist)
	{
	struct optimized_kprobe op, tmp;
	u8 insn_buf[RELATIVEJUMP_SIZE];

	list_for_each_entry_safe(op, tmp, oplist, list) {
	s32 rel = (s32)((long)op->optinsn.insn -
	((long)op->kp.addr + RELATIVEJUMP_SIZE));

	WARN_ON(kprobe_disabled(&op->kp));

	/* Backup instructions which will be replaced by jump address */
	memcpy(op->optinsn.copied_insn, op->kp.addr + INT3_SIZE,
	RELATIVE_ADDR_SIZE);

	insn_buf[0] = RELATIVEJUMP_OPCODE;
	(s32 )(&insn_buf[1]) = rel;

	text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE,
	op->optinsn.insn);

	list_del_init(&op->list);
	}
	}

	/* Replace a relative jump with a breakpoint (int3). */
	void arch_unoptimize_kprobe(struct optimized_kprobe *op)
	{
	u8 insn_buf[RELATIVEJUMP_SIZE];

	/* Set int3 to first byte for kprobes */
	insn_buf[0] = BREAKPOINT_INSTRUCTION;
	memcpy(insn_buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);
	text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE,
	op->optinsn.insn);
	}

	/*
	* Recover original instructions and breakpoints from relative jumps.
	* Caller must call with locking kprobe_mutex.
	*/
	extern void arch_unoptimize_kprobes(struct list_head *oplist,
	struct list_head *done_list)
	{
	struct optimized_kprobe op, tmp;

	list_for_each_entry_safe(op, tmp, oplist, list) {
	arch_unoptimize_kprobe(op);
	list_move(&op->list, done_list);
	}
	}

	int setup_detour_execution(struct kprobe p, struct pt_regs regs, int reenter)
	{
	struct optimized_kprobe *op;

	if (p->flags & KPROBE_FLAG_OPTIMIZED) {
	/* This kprobe is really able to run optimized path. */
	op = container_of(p, struct optimized_kprobe, kp);
	/* Detour through copied instructions */
	regs->ip = (unsigned long)op->optinsn.insn + TMPL_END_IDX;
	if (!reenter)
	reset_current_kprobe();
	preempt_enable_no_resched();
	return 1;
	}
	return 0;
	}
	NOKPROBE_SYMBOL(setup_detour_execution);