kprobes/x86: Allow to handle reentered kprobe on single-stepping

[deliverable/linux.git] / arch / x86 / kernel / kprobes / core.c

/*
 *  Kernel Probes (KProbes)
 *
 * 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
 *
 * 2002-Oct	Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
 *		Probes initial implementation ( includes contributions from
 *		Rusty Russell).
 * 2004-July	Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
 *		interface to access function arguments.
 * 2004-Oct	Jim Keniston <jkenisto@us.ibm.com> and Prasanna S Panchamukhi
 *		<prasanna@in.ibm.com> adapted for x86_64 from i386.
 * 2005-Mar	Roland McGrath <roland@redhat.com>
 *		Fixed to handle %rip-relative addressing mode correctly.
 * 2005-May	Hien Nguyen <hien@us.ibm.com>, Jim Keniston
 *		<jkenisto@us.ibm.com> and Prasanna S Panchamukhi
 *		<prasanna@in.ibm.com> added function-return probes.
 * 2005-May	Rusty Lynch <rusty.lynch@intel.com>
 *		Added function return probes functionality
 * 2006-Feb	Masami Hiramatsu <hiramatu@sdl.hitachi.co.jp> added
 *		kprobe-booster and kretprobe-booster for i386.
 * 2007-Dec	Masami Hiramatsu <mhiramat@redhat.com> added kprobe-booster
 *		and kretprobe-booster for x86-64
 * 2007-Dec	Masami Hiramatsu <mhiramat@redhat.com>, Arjan van de Ven
 *		<arjan@infradead.org> and Jim Keniston <jkenisto@us.ibm.com>
 *		unified x86 kprobes code.
 */
#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/module.h>
#include <linux/kdebug.h>
#include <linux/kallsyms.h>
#include <linux/ftrace.h>

#include <asm/cacheflush.h>
#include <asm/desc.h>
#include <asm/pgtable.h>
#include <asm/uaccess.h>
#include <asm/alternative.h>
#include <asm/insn.h>
#include <asm/debugreg.h>

#include "common.h"

void jprobe_return_end(void);

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

#define stack_addr(regs) ((unsigned long *)kernel_stack_pointer(regs))

#define W(row, b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, ba, bb, bc, bd, be, bf)\
	(((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) |   \
	  (b4##UL << 0x4)|(b5##UL << 0x5)|(b6##UL << 0x6)|(b7##UL << 0x7) |   \
	  (b8##UL << 0x8)|(b9##UL << 0x9)|(ba##UL << 0xa)|(bb##UL << 0xb) |   \
	  (bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf))    \
	 << (row % 32))
	/*
	 * Undefined/reserved opcodes, conditional jump, Opcode Extension
	 * Groups, and some special opcodes can not boost.
	 * This is non-const and volatile to keep gcc from statically
	 * optimizing it out, as variable_test_bit makes gcc think only
	 * *(unsigned long*) is used.
	 */
static volatile u32 twobyte_is_boostable[256 / 32] = {
	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f          */
	/*      ----------------------------------------------          */
	W(0x00, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0) | /* 00 */
	W(0x10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) , /* 10 */
	W(0x20, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) | /* 20 */
	W(0x30, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) , /* 30 */
	W(0x40, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 40 */
	W(0x50, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) , /* 50 */
	W(0x60, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1) | /* 60 */
	W(0x70, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1) , /* 70 */
	W(0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) | /* 80 */
	W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 90 */
	W(0xa0, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1) | /* a0 */
	W(0xb0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1) , /* b0 */
	W(0xc0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1) | /* c0 */
	W(0xd0, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1) , /* d0 */
	W(0xe0, 0, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1) | /* e0 */
	W(0xf0, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 0, 1, 1, 1, 0)   /* f0 */
	/*      -----------------------------------------------         */
	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f          */
};
#undef W

struct kretprobe_blackpoint kretprobe_blacklist[] = {
	{"__switch_to", }, /* This function switches only current task, but
			      doesn't switch kernel stack.*/
	{NULL, NULL}	/* Terminator */
};

const int kretprobe_blacklist_size = ARRAY_SIZE(kretprobe_blacklist);

static void __kprobes __synthesize_relative_insn(void *from, void *to, u8 op)
{
	struct __arch_relative_insn {
		u8 op;
		s32 raddr;
	} __packed *insn;

	insn = (struct __arch_relative_insn *)from;
	insn->raddr = (s32)((long)(to) - ((long)(from) + 5));
	insn->op = op;
}

/* Insert a jump instruction at address 'from', which jumps to address 'to'.*/
void __kprobes synthesize_reljump(void *from, void *to)
{
	__synthesize_relative_insn(from, to, RELATIVEJUMP_OPCODE);
}

/* Insert a call instruction at address 'from', which calls address 'to'.*/
void __kprobes synthesize_relcall(void *from, void *to)
{
	__synthesize_relative_insn(from, to, RELATIVECALL_OPCODE);
}

/*
 * Skip the prefixes of the instruction.
 */
static kprobe_opcode_t *__kprobes skip_prefixes(kprobe_opcode_t *insn)
{
	insn_attr_t attr;

	attr = inat_get_opcode_attribute((insn_byte_t)*insn);
	while (inat_is_legacy_prefix(attr)) {
		insn++;
		attr = inat_get_opcode_attribute((insn_byte_t)*insn);
	}
#ifdef CONFIG_X86_64
	if (inat_is_rex_prefix(attr))
		insn++;
#endif
	return insn;
}

/*
 * Returns non-zero if opcode is boostable.
 * RIP relative instructions are adjusted at copying time in 64 bits mode
 */
int __kprobes can_boost(kprobe_opcode_t *opcodes)
{
	kprobe_opcode_t opcode;
	kprobe_opcode_t *orig_opcodes = opcodes;

	if (search_exception_tables((unsigned long)opcodes))
		return 0;	/* Page fault may occur on this address. */

retry:
	if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
		return 0;
	opcode = *(opcodes++);

	/* 2nd-byte opcode */
	if (opcode == 0x0f) {
		if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
			return 0;
		return test_bit(*opcodes,
				(unsigned long *)twobyte_is_boostable);
	}

	switch (opcode & 0xf0) {
#ifdef CONFIG_X86_64
	case 0x40:
		goto retry; /* REX prefix is boostable */
#endif
	case 0x60:
		if (0x63 < opcode && opcode < 0x67)
			goto retry; /* prefixes */
		/* can't boost Address-size override and bound */
		return (opcode != 0x62 && opcode != 0x67);
	case 0x70:
		return 0; /* can't boost conditional jump */
	case 0xc0:
		/* can't boost software-interruptions */
		return (0xc1 < opcode && opcode < 0xcc) || opcode == 0xcf;
	case 0xd0:
		/* can boost AA* and XLAT */
		return (opcode == 0xd4 || opcode == 0xd5 || opcode == 0xd7);
	case 0xe0:
		/* can boost in/out and absolute jmps */
		return ((opcode & 0x04) || opcode == 0xea);
	case 0xf0:
		if ((opcode & 0x0c) == 0 && opcode != 0xf1)
			goto retry; /* lock/rep(ne) prefix */
		/* clear and set flags are boostable */
		return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe));
	default:
		/* segment override prefixes are boostable */
		if (opcode == 0x26 || opcode == 0x36 || opcode == 0x3e)
			goto retry; /* prefixes */
		/* CS override prefix and call are not boostable */
		return (opcode != 0x2e && opcode != 0x9a);
	}
}

static unsigned long
__recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
{
	struct kprobe *kp;

	kp = get_kprobe((void *)addr);
	/* There is no probe, return original address */
	if (!kp)
		return addr;

	/*
	 *  Basically, kp->ainsn.insn has an original instruction.
	 *  However, RIP-relative instruction can not do single-stepping
	 *  at different place, __copy_instruction() tweaks the displacement of
	 *  that instruction. In that case, we can't recover the instruction
	 *  from the kp->ainsn.insn.
	 *
	 *  On the other hand, kp->opcode has a copy of the first byte of
	 *  the probed instruction, which is overwritten by int3. And
	 *  the instruction at kp->addr is not modified by kprobes except
	 *  for the first byte, we can recover the original instruction
	 *  from it and kp->opcode.
	 */
	memcpy(buf, kp->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
	buf[0] = kp->opcode;
	return (unsigned long)buf;
}

/*
 * Recover the probed instruction at addr for further analysis.
 * Caller must lock kprobes by kprobe_mutex, or disable preemption
 * for preventing to release referencing kprobes.
 */
unsigned long recover_probed_instruction(kprobe_opcode_t *buf, unsigned long addr)
{
	unsigned long __addr;

	__addr = __recover_optprobed_insn(buf, addr);
	if (__addr != addr)
		return __addr;

	return __recover_probed_insn(buf, addr);
}

/* Check if paddr is at an instruction boundary */
static int __kprobes can_probe(unsigned long paddr)
{
	unsigned long addr, __addr, offset = 0;
	struct insn insn;
	kprobe_opcode_t buf[MAX_INSN_SIZE];

	if (!kallsyms_lookup_size_offset(paddr, NULL, &offset))
		return 0;

	/* Decode instructions */
	addr = paddr - offset;
	while (addr < paddr) {
		/*
		 * Check if the instruction has been modified by another
		 * kprobe, in which case we replace the breakpoint by the
		 * original instruction in our buffer.
		 * Also, jump optimization will change the breakpoint to
		 * relative-jump. Since the relative-jump itself is
		 * normally used, we just go through if there is no kprobe.
		 */
		__addr = recover_probed_instruction(buf, addr);
		kernel_insn_init(&insn, (void *)__addr);
		insn_get_length(&insn);

		/*
		 * Another debugging subsystem might insert this breakpoint.
		 * In that case, we can't recover it.
		 */
		if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
			return 0;
		addr += insn.length;
	}

	return (addr == paddr);
}

/*
 * Returns non-zero if opcode modifies the interrupt flag.
 */
static int __kprobes is_IF_modifier(kprobe_opcode_t *insn)
{
	/* Skip prefixes */
	insn = skip_prefixes(insn);

	switch (*insn) {
	case 0xfa:		/* cli */
	case 0xfb:		/* sti */
	case 0xcf:		/* iret/iretd */
	case 0x9d:		/* popf/popfd */
		return 1;
	}

	return 0;
}

/*
 * Copy an instruction and adjust the displacement if the instruction
 * uses the %rip-relative addressing mode.
 * If it does, Return the address of the 32-bit displacement word.
 * If not, return null.
 * Only applicable to 64-bit x86.
 */
int __kprobes __copy_instruction(u8 *dest, u8 *src)
{
	struct insn insn;
	kprobe_opcode_t buf[MAX_INSN_SIZE];

	kernel_insn_init(&insn, (void *)recover_probed_instruction(buf, (unsigned long)src));
	insn_get_length(&insn);
	/* Another subsystem puts a breakpoint, failed to recover */
	if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
		return 0;
	memcpy(dest, insn.kaddr, insn.length);

#ifdef CONFIG_X86_64
	if (insn_rip_relative(&insn)) {
		s64 newdisp;
		u8 *disp;
		kernel_insn_init(&insn, dest);
		insn_get_displacement(&insn);
		/*
		 * The copied instruction uses the %rip-relative addressing
		 * mode.  Adjust the displacement for the difference between
		 * the original location of this instruction and the location
		 * of the copy that will actually be run.  The tricky bit here
		 * is making sure that the sign extension happens correctly in
		 * this calculation, since we need a signed 32-bit result to
		 * be sign-extended to 64 bits when it's added to the %rip
		 * value and yield the same 64-bit result that the sign-
		 * extension of the original signed 32-bit displacement would
		 * have given.
		 */
		newdisp = (u8 *) src + (s64) insn.displacement.value - (u8 *) dest;
		if ((s64) (s32) newdisp != newdisp) {
			pr_err("Kprobes error: new displacement does not fit into s32 (%llx)\n", newdisp);
			pr_err("\tSrc: %p, Dest: %p, old disp: %x\n", src, dest, insn.displacement.value);
			return 0;
		}
		disp = (u8 *) dest + insn_offset_displacement(&insn);
		*(s32 *) disp = (s32) newdisp;
	}
#endif
	return insn.length;
}

static int __kprobes arch_copy_kprobe(struct kprobe *p)
{
	int ret;

	/* Copy an instruction with recovering if other optprobe modifies it.*/
	ret = __copy_instruction(p->ainsn.insn, p->addr);
	if (!ret)
		return -EINVAL;

	/*
	 * __copy_instruction can modify the displacement of the instruction,
	 * but it doesn't affect boostable check.
	 */
	if (can_boost(p->ainsn.insn))
		p->ainsn.boostable = 0;
	else
		p->ainsn.boostable = -1;

	/* Check whether the instruction modifies Interrupt Flag or not */
	p->ainsn.if_modifier = is_IF_modifier(p->ainsn.insn);

	/* Also, displacement change doesn't affect the first byte */
	p->opcode = p->ainsn.insn[0];

	return 0;
}

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
	if (alternatives_text_reserved(p->addr, p->addr))
		return -EINVAL;

	if (!can_probe((unsigned long)p->addr))
		return -EILSEQ;
	/* insn: must be on special executable page on x86. */
	p->ainsn.insn = get_insn_slot();
	if (!p->ainsn.insn)
		return -ENOMEM;

	return arch_copy_kprobe(p);
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
	text_poke(p->addr, ((unsigned char []){BREAKPOINT_INSTRUCTION}), 1);
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
	text_poke(p->addr, &p->opcode, 1);
}

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
	if (p->ainsn.insn) {
		free_insn_slot(p->ainsn.insn, (p->ainsn.boostable == 1));
		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;
	kcb->prev_kprobe.old_flags = kcb->kprobe_old_flags;
	kcb->prev_kprobe.saved_flags = kcb->kprobe_saved_flags;
}

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;
	kcb->kprobe_old_flags = kcb->prev_kprobe.old_flags;
	kcb->kprobe_saved_flags = kcb->prev_kprobe.saved_flags;
}

static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
				struct kprobe_ctlblk *kcb)
{
	__this_cpu_write(current_kprobe, p);
	kcb->kprobe_saved_flags = kcb->kprobe_old_flags
		= (regs->flags & (X86_EFLAGS_TF | X86_EFLAGS_IF));
	if (p->ainsn.if_modifier)
		kcb->kprobe_saved_flags &= ~X86_EFLAGS_IF;
}

static void __kprobes clear_btf(void)
{
	if (test_thread_flag(TIF_BLOCKSTEP)) {
		unsigned long debugctl = get_debugctlmsr();

		debugctl &= ~DEBUGCTLMSR_BTF;
		update_debugctlmsr(debugctl);
	}
}

static void __kprobes restore_btf(void)
{
	if (test_thread_flag(TIF_BLOCKSTEP)) {
		unsigned long debugctl = get_debugctlmsr();

		debugctl |= DEBUGCTLMSR_BTF;
		update_debugctlmsr(debugctl);
	}
}

void __kprobes
arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs)
{
	unsigned long *sara = stack_addr(regs);

	ri->ret_addr = (kprobe_opcode_t *) *sara;

	/* Replace the return addr with trampoline addr */
	*sara = (unsigned long) &kretprobe_trampoline;
}

static void __kprobes
setup_singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb, int reenter)
{
	if (setup_detour_execution(p, regs, reenter))
		return;

#if !defined(CONFIG_PREEMPT)
	if (p->ainsn.boostable == 1 && !p->post_handler) {
		/* Boost up -- we can execute copied instructions directly */
		if (!reenter)
			reset_current_kprobe();
		/*
		 * Reentering boosted probe doesn't reset current_kprobe,
		 * nor set current_kprobe, because it doesn't use single
		 * stepping.
		 */
		regs->ip = (unsigned long)p->ainsn.insn;
		preempt_enable_no_resched();
		return;
	}
#endif
	if (reenter) {
		save_previous_kprobe(kcb);
		set_current_kprobe(p, regs, kcb);
		kcb->kprobe_status = KPROBE_REENTER;
	} else
		kcb->kprobe_status = KPROBE_HIT_SS;
	/* Prepare real single stepping */
	clear_btf();
	regs->flags |= X86_EFLAGS_TF;
	regs->flags &= ~X86_EFLAGS_IF;
	/* single step inline if the instruction is an int3 */
	if (p->opcode == BREAKPOINT_INSTRUCTION)
		regs->ip = (unsigned long)p->addr;
	else
		regs->ip = (unsigned long)p->ainsn.insn;
}

/*
 * We have reentered the kprobe_handler(), since another probe was hit while
 * within the handler. We save the original kprobes variables and just single
 * step on the instruction of the new probe without calling any user handlers.
 */
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:
	case KPROBE_HIT_SS:
		kprobes_inc_nmissed_count(p);
		setup_singlestep(p, regs, kcb, 1);
		break;
	case KPROBE_REENTER:
		/* A probe has been hit in the codepath leading up to, or just
		 * after, single-stepping of a probed instruction. This entire
		 * codepath should strictly reside in .kprobes.text section.
		 * Raise a BUG or we'll continue in an endless reentering loop
		 * and eventually a stack overflow.
		 */
		printk(KERN_WARNING "Unrecoverable kprobe detected at %p.\n",
		       p->addr);
		dump_kprobe(p);
		BUG();
	default:
		/* impossible cases */
		WARN_ON(1);
		return 0;
	}

	return 1;
}

/*
 * Interrupts are disabled on entry as trap3 is an interrupt gate and they
 * remain disabled throughout this function.
 */
static int __kprobes kprobe_handler(struct pt_regs *regs)
{
	kprobe_opcode_t *addr;
	struct kprobe *p;
	struct kprobe_ctlblk *kcb;

	addr = (kprobe_opcode_t *)(regs->ip - sizeof(kprobe_opcode_t));
	/*
	 * We don't want to be preempted for the entire
	 * duration of kprobe processing. We conditionally
	 * re-enable preemption at the end of this function,
	 * and also in reenter_kprobe() and setup_singlestep().
	 */
	preempt_disable();

	kcb = get_kprobe_ctlblk();
	p = get_kprobe(addr);

	if (p) {
		if (kprobe_running()) {
			if (reenter_kprobe(p, regs, kcb))
				return 1;
		} else {
			set_current_kprobe(p, regs, kcb);
			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 prepped
			 * for calling the break_handler below on re-entry
			 * for jprobe processing, so get out doing nothing
			 * more here.
			 */
			if (!p->pre_handler || !p->pre_handler(p, regs))
				setup_singlestep(p, regs, kcb, 0);
			return 1;
		}
	} else if (*addr != BREAKPOINT_INSTRUCTION) {
		/*
		 * 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.
		 * Back up over the (now missing) int3 and run
		 * the original instruction.
		 */
		regs->ip = (unsigned long)addr;
		preempt_enable_no_resched();
		return 1;
	} else if (kprobe_running()) {
		p = __this_cpu_read(current_kprobe);
		if (p->break_handler && p->break_handler(p, regs)) {
			if (!skip_singlestep(p, regs, kcb))
				setup_singlestep(p, regs, kcb, 0);
			return 1;
		}
	} /* else: not a kprobe fault; let the kernel handle it */

	preempt_enable_no_resched();
	return 0;
}

/*
 * When a retprobed function returns, this code saves registers and
 * calls trampoline_handler() runs, which calls the kretprobe's handler.
 */
static void __used __kprobes kretprobe_trampoline_holder(void)
{
	asm volatile (
			".global kretprobe_trampoline\n"
			"kretprobe_trampoline: \n"
#ifdef CONFIG_X86_64
			/* We don't bother saving the ss register */
			"	pushq %rsp\n"
			"	pushfq\n"
			SAVE_REGS_STRING
			"	movq %rsp, %rdi\n"
			"	call trampoline_handler\n"
			/* Replace saved sp with true return address. */
			"	movq %rax, 152(%rsp)\n"
			RESTORE_REGS_STRING
			"	popfq\n"
#else
			"	pushf\n"
			SAVE_REGS_STRING
			"	movl %esp, %eax\n"
			"	call trampoline_handler\n"
			/* Move flags to cs */
			"	movl 56(%esp), %edx\n"
			"	movl %edx, 52(%esp)\n"
			/* Replace saved flags with true return address. */
			"	movl %eax, 56(%esp)\n"
			RESTORE_REGS_STRING
			"	popf\n"
#endif
			"	ret\n");
}

/*
 * Called from kretprobe_trampoline
 */
__visible __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);
	/* fixup registers */
#ifdef CONFIG_X86_64
	regs->cs = __KERNEL_CS;
#else
	regs->cs = __KERNEL_CS | get_kernel_rpl();
	regs->gs = 0;
#endif
	regs->ip = trampoline_address;
	regs->orig_ax = ~0UL;

	/*
	 * 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;
}

/*
 * Called after single-stepping.  p->addr is the address of the
 * instruction whose first byte has been replaced by the "int 3"
 * instruction.  To avoid the SMP problems that can occur when we
 * temporarily put back the original opcode to single-step, we
 * single-stepped a copy of the instruction.  The address of this
 * copy is p->ainsn.insn.
 *
 * This function prepares to return from the post-single-step
 * interrupt.  We have to fix up the stack as follows:
 *
 * 0) Except in the case of absolute or indirect jump or call instructions,
 * the new ip is relative to the copied instruction.  We need to make
 * it relative to the original instruction.
 *
 * 1) If the single-stepped instruction was pushfl, then the TF and IF
 * flags are set in the just-pushed flags, and may need to be cleared.
 *
 * 2) If the single-stepped instruction was a call, the return address
 * that is atop the stack is the address following the copied instruction.
 * We need to make it the address following the original instruction.
 *
 * If this is the first time we've single-stepped the instruction at
 * this probepoint, and the instruction is boostable, boost it: add a
 * jump instruction after the copied instruction, that jumps to the next
 * instruction after the probepoint.
 */
static void __kprobes
resume_execution(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb)
{
	unsigned long *tos = stack_addr(regs);
	unsigned long copy_ip = (unsigned long)p->ainsn.insn;
	unsigned long orig_ip = (unsigned long)p->addr;
	kprobe_opcode_t *insn = p->ainsn.insn;

	/* Skip prefixes */
	insn = skip_prefixes(insn);

	regs->flags &= ~X86_EFLAGS_TF;
	switch (*insn) {
	case 0x9c:	/* pushfl */
		*tos &= ~(X86_EFLAGS_TF | X86_EFLAGS_IF);
		*tos |= kcb->kprobe_old_flags;
		break;
	case 0xc2:	/* iret/ret/lret */
	case 0xc3:
	case 0xca:
	case 0xcb:
	case 0xcf:
	case 0xea:	/* jmp absolute -- ip is correct */
		/* ip is already adjusted, no more changes required */
		p->ainsn.boostable = 1;
		goto no_change;
	case 0xe8:	/* call relative - Fix return addr */
		*tos = orig_ip + (*tos - copy_ip);
		break;
#ifdef CONFIG_X86_32
	case 0x9a:	/* call absolute -- same as call absolute, indirect */
		*tos = orig_ip + (*tos - copy_ip);
		goto no_change;
#endif
	case 0xff:
		if ((insn[1] & 0x30) == 0x10) {
			/*
			 * call absolute, indirect
			 * Fix return addr; ip is correct.
			 * But this is not boostable
			 */
			*tos = orig_ip + (*tos - copy_ip);
			goto no_change;
		} else if (((insn[1] & 0x31) == 0x20) ||
			   ((insn[1] & 0x31) == 0x21)) {
			/*
			 * jmp near and far, absolute indirect
			 * ip is correct. And this is boostable
			 */
			p->ainsn.boostable = 1;
			goto no_change;
		}
	default:
		break;
	}

	if (p->ainsn.boostable == 0) {
		if ((regs->ip > copy_ip) &&
		    (regs->ip - copy_ip) + 5 < MAX_INSN_SIZE) {
			/*
			 * These instructions can be executed directly if it
			 * jumps back to correct address.
			 */
			synthesize_reljump((void *)regs->ip,
				(void *)orig_ip + (regs->ip - copy_ip));
			p->ainsn.boostable = 1;
		} else {
			p->ainsn.boostable = -1;
		}
	}

	regs->ip += orig_ip - copy_ip;

no_change:
	restore_btf();
}

/*
 * Interrupts are disabled on entry as trap1 is an interrupt gate and they
 * remain disabled throughout this function.
 */
static int __kprobes post_kprobe_handler(struct pt_regs *regs)
{
	struct kprobe *cur = kprobe_running();
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	if (!cur)
		return 0;

	resume_execution(cur, regs, kcb);
	regs->flags |= kcb->kprobe_saved_flags;

	if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
		kcb->kprobe_status = KPROBE_HIT_SSDONE;
		cur->post_handler(cur, regs, 0);
	}

	/* Restore back the original saved kprobes variables and continue. */
	if (kcb->kprobe_status == KPROBE_REENTER) {
		restore_previous_kprobe(kcb);
		goto out;
	}
	reset_current_kprobe();
out:
	preempt_enable_no_resched();

	/*
	 * if somebody else is singlestepping across a probe point, flags
	 * will have TF set, in which case, continue the remaining processing
	 * of do_debug, as if this is not a probe hit.
	 */
	if (regs->flags & X86_EFLAGS_TF)
		return 0;

	return 1;
}

int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
	struct kprobe *cur = kprobe_running();
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	if (unlikely(regs->ip == (unsigned long)cur->ainsn.insn)) {
		/* This must happen on single-stepping */
		WARN_ON(kcb->kprobe_status != KPROBE_HIT_SS &&
			kcb->kprobe_status != 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->ip = (unsigned long)cur->addr;
		regs->flags |= kcb->kprobe_old_flags;
		if (kcb->kprobe_status == KPROBE_REENTER)
			restore_previous_kprobe(kcb);
		else
			reset_current_kprobe();
		preempt_enable_no_resched();
	} else if (kcb->kprobe_status == KPROBE_HIT_ACTIVE ||
		   kcb->kprobe_status == 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;

		/*
		 * fixup routine could not handle it,
		 * Let do_page_fault() fix it.
		 */
	}

	return 0;
}

/*
 * Wrapper routine for handling exceptions.
 */
int __kprobes
kprobe_exceptions_notify(struct notifier_block *self, unsigned long val, void *data)
{
	struct die_args *args = data;
	int ret = NOTIFY_DONE;

	if (args->regs && user_mode_vm(args->regs))
		return ret;

	switch (val) {
	case DIE_INT3:
		if (kprobe_handler(args->regs))
			ret = NOTIFY_STOP;
		break;
	case DIE_DEBUG:
		if (post_kprobe_handler(args->regs)) {
			/*
			 * Reset the BS bit in dr6 (pointed by args->err) to
			 * denote completion of processing
			 */
			(*(unsigned long *)ERR_PTR(args->err)) &= ~DR_STEP;
			ret = NOTIFY_STOP;
		}
		break;
	case DIE_GPF:
		/*
		 * To be potentially processing a kprobe fault and to
		 * trust the result from kprobe_running(), we have
		 * be non-preemptible.
		 */
		if (!preemptible() && kprobe_running() &&
		    kprobe_fault_handler(args->regs, args->trapnr))
			ret = NOTIFY_STOP;
		break;
	default:
		break;
	}
	return ret;
}

int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
	struct jprobe *jp = container_of(p, struct jprobe, kp);
	unsigned long addr;
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	kcb->jprobe_saved_regs = *regs;
	kcb->jprobe_saved_sp = stack_addr(regs);
	addr = (unsigned long)(kcb->jprobe_saved_sp);

	/*
	 * As Linus pointed out, gcc assumes that the callee
	 * owns the argument space and could overwrite it, e.g.
	 * tailcall optimization. So, to be absolutely safe
	 * we also save and restore enough stack bytes to cover
	 * the argument area.
	 */
	memcpy(kcb->jprobes_stack, (kprobe_opcode_t *)addr,
	       MIN_STACK_SIZE(addr));
	regs->flags &= ~X86_EFLAGS_IF;
	trace_hardirqs_off();
	regs->ip = (unsigned long)(jp->entry);
	return 1;
}

void __kprobes jprobe_return(void)
{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	asm volatile (
#ifdef CONFIG_X86_64
			"       xchg   %%rbx,%%rsp	\n"
#else
			"       xchgl   %%ebx,%%esp	\n"
#endif
			"       int3			\n"
			"       .globl jprobe_return_end\n"
			"       jprobe_return_end:	\n"
			"       nop			\n"::"b"
			(kcb->jprobe_saved_sp):"memory");
}

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
	u8 *addr = (u8 *) (regs->ip - 1);
	struct jprobe *jp = container_of(p, struct jprobe, kp);

	if ((addr > (u8 *) jprobe_return) &&
	    (addr < (u8 *) jprobe_return_end)) {
		if (stack_addr(regs) != kcb->jprobe_saved_sp) {
			struct pt_regs *saved_regs = &kcb->jprobe_saved_regs;
			printk(KERN_ERR
			       "current sp %p does not match saved sp %p\n",
			       stack_addr(regs), kcb->jprobe_saved_sp);
			printk(KERN_ERR "Saved registers for jprobe %p\n", jp);
			show_regs(saved_regs);
			printk(KERN_ERR "Current registers\n");
			show_regs(regs);
			BUG();
		}
		*regs = kcb->jprobe_saved_regs;
		memcpy((kprobe_opcode_t *)(kcb->jprobe_saved_sp),
		       kcb->jprobes_stack,
		       MIN_STACK_SIZE(kcb->jprobe_saved_sp));
		preempt_enable_no_resched();
		return 1;
	}
	return 0;
}

int __init arch_init_kprobes(void)
{
	return 0;
}

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