kprobes.c

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/*
 *  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 <[email protected]> Kernel
 *      Probes initial implementation ( includes contributions from
 *      Rusty Russell).
 * 2004-July    Suparna Bhattacharya <[email protected]> added jumper probes
 *      interface to access function arguments.
 * 2004-Oct Jim Keniston <[email protected]> and Prasanna S Panchamukhi
 *      <[email protected]> adapted for x86_64 from i386.
 * 2005-Mar Roland McGrath <[email protected]>
 *      Fixed to handle %rip-relative addressing mode correctly.
 * 2005-May Hien Nguyen <[email protected]>, Jim Keniston
 *      <[email protected]> and Prasanna S Panchamukhi
 *      <[email protected]> added function-return probes.
 * 2005-May Rusty Lynch <[email protected]>
 *      Added function return probes functionality
 * 2006-Feb Masami Hiramatsu <[email protected]> added
 *      kprobe-booster and kretprobe-booster for i386.
 * 2007-Dec Masami Hiramatsu <[email protected]> added kprobe-booster
 *      and kretprobe-booster for x86-64
 * 2007-Dec Masami Hiramatsu <[email protected]>, Arjan van de Ven
 *      <[email protected]> and Jim Keniston <[email protected]>
 *      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 "kprobes-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;
    } __attribute__((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;
        BUG_ON((s64) (s32) newdisp != newdisp); /* Sanity check.  */
        disp = (u8 *) dest + insn_offset_displacement(&insn);
        *(s32 *) disp = (s32) newdisp;
    }
#endif
    return insn.length;
}

static void __kprobes arch_copy_kprobe(struct kprobe *p)
{
    /* Copy an instruction with recovering if other optprobe modifies it.*/
    __copy_instruction(p->ainsn.insn, p->addr);

    /*
     * __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;

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

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 (is_IF_modifier(p->ainsn.insn))
        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:
        kprobes_inc_nmissed_count(p);
        setup_singlestep(p, regs, kcb, 1);
        break;
    case KPROBE_HIT_SS:
        /* 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;
}

#ifdef KPROBES_CAN_USE_FTRACE
static void __kprobes skip_singlestep(struct kprobe *p, struct pt_regs *regs,
                      struct kprobe_ctlblk *kcb)
{
    /*
     * Emulate singlestep (and also recover regs->ip)
     * as if there is a 5byte nop
     */
    regs->ip = (unsigned long)p->addr + MCOUNT_INSN_SIZE;
    if (unlikely(p->post_handler)) {
        kcb->kprobe_status = KPROBE_HIT_SSDONE;
        p->post_handler(p, regs, 0);
    }
    __this_cpu_write(current_kprobe, NULL);
}
#endif

/*
 * 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)) {
#ifdef KPROBES_CAN_USE_FTRACE
            if (kprobe_ftrace(p)) {
                skip_singlestep(p, regs, kcb);
                return 1;
            }
#endif
            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
 */
static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
{
    struct kretprobe_instance *ri = NULL;
    struct hlist_head *head, empty_rp;
    struct hlist_node *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, node, 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, node, 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, node, 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();

    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->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();
        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;

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

#ifdef KPROBES_CAN_USE_FTRACE
/* Ftrace callback handler for kprobes */
void __kprobes kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
                     struct ftrace_ops *ops, struct pt_regs *regs)
{
    struct kprobe *p;
    struct kprobe_ctlblk *kcb;
    unsigned long flags;

    /* Disable irq for emulating a breakpoint and avoiding preempt */
    local_irq_save(flags);

    p = get_kprobe((kprobe_opcode_t *)ip);
    if (unlikely(!p) || kprobe_disabled(p))
        goto end;

    kcb = get_kprobe_ctlblk();
    if (kprobe_running()) {
        kprobes_inc_nmissed_count(p);
    } else {
        /* Kprobe handler expects regs->ip = ip + 1 as breakpoint hit */
        regs->ip = ip + sizeof(kprobe_opcode_t);

        __this_cpu_write(current_kprobe, p);
        kcb->kprobe_status = KPROBE_HIT_ACTIVE;
        if (!p->pre_handler || !p->pre_handler(p, regs))
            skip_singlestep(p, regs, kcb);
        /*
         * If pre_handler returns !0, it sets regs->ip and
         * resets current kprobe.
         */
    }
end:
    local_irq_restore(flags);
}

int __kprobes arch_prepare_kprobe_ftrace(struct kprobe *p)
{
    p->ainsn.insn = NULL;
    p->ainsn.boostable = -1;
    return 0;
}
#endif

int __init arch_init_kprobes(void)
{
    return arch_init_optprobes();
}

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