Merge branch 'tracing/hw-breakpoints' into perf/core

[linux-2.6/linux-2.6-openrd.git] / arch / x86 / kernel / kprobes.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 <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>

void jprobe_return_end(void);

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

#ifdef CONFIG_X86_64
#define stack_addr(regs) ((unsigned long *)regs->sp)
#else
/*
 * "&regs->sp" looks wrong, but it's correct for x86_32.  x86_32 CPUs
 * don't save the ss and esp registers if the CPU is already in kernel
 * mode when it traps.  So for kprobes, regs->sp and regs->ss are not
 * the [nonexistent] saved stack pointer and ss register, but rather
 * the top 8 bytes of the pre-int3 stack.  So &regs->sp happens to
 * point to the top of the pre-int3 stack.
 */
#define stack_addr(regs) ((unsigned long *)&regs->sp)
#endif

#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.
         */
static const 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);

/* Insert a jump instruction at address 'from', which jumps to address 'to'.*/
static void __kprobes set_jmp_op(void *from, void *to)
{
        struct __arch_jmp_op {
                char op;
                s32 raddr;
        } __attribute__((packed)) * jop;
        jop = (struct __arch_jmp_op *)from;
        jop->raddr = (s32)((long)(to) - ((long)(from) + 5));
        jop->op = RELATIVEJUMP_INSTRUCTION;
}

/*
 * Check for the REX prefix which can only exist on X86_64
 * X86_32 always returns 0
 */
static int __kprobes is_REX_prefix(kprobe_opcode_t *insn)
{
#ifdef CONFIG_X86_64
        if ((*insn & 0xf0) == 0x40)
                return 1;
#endif
        return 0;
}

/*
 * Returns non-zero if opcode is boostable.
 * RIP relative instructions are adjusted at copying time in 64 bits mode
 */
static 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);
        }
}

/* Recover the probed instruction at addr for further analysis. */
static int recover_probed_instruction(kprobe_opcode_t *buf, unsigned long addr)
{
        struct kprobe *kp;
        kp = get_kprobe((void *)addr);
        if (!kp)
                return -EINVAL;

        /*
         *  Basically, kp->ainsn.insn has an original instruction.
         *  However, RIP-relative instruction can not do single-stepping
         *  at different place, fix_riprel() 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 0;
}

/* Dummy buffers for kallsyms_lookup */
static char __dummy_buf[KSYM_NAME_LEN];

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

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

        /* Decode instructions */
        addr = paddr - offset;
        while (addr < paddr) {
                kernel_insn_init(&insn, (void *)addr);
                insn_get_opcode(&insn);

                /*
                 * Check if the instruction has been modified by another
                 * kprobe, in which case we replace the breakpoint by the
                 * original instruction in our buffer.
                 */
                if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION) {
                        ret = recover_probed_instruction(buf, addr);
                        if (ret)
                                /*
                                 * Another debugging subsystem might insert
                                 * this breakpoint. In that case, we can't
                                 * recover it.
                                 */
                                return 0;
                        kernel_insn_init(&insn, buf);
                }
                insn_get_length(&insn);
                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)
{
        switch (*insn) {
        case 0xfa:              /* cli */
        case 0xfb:              /* sti */
        case 0xcf:              /* iret/iretd */
        case 0x9d:              /* popf/popfd */
                return 1;
        }

        /*
         * on X86_64, 0x40-0x4f are REX prefixes so we need to look
         * at the next byte instead.. but of course not recurse infinitely
         */
        if (is_REX_prefix(insn))
                return is_IF_modifier(++insn);

        return 0;
}

/*
 * 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.
 */
static void __kprobes fix_riprel(struct kprobe *p)
{
#ifdef CONFIG_X86_64
        struct insn insn;
        kernel_insn_init(&insn, p->ainsn.insn);

        if (insn_rip_relative(&insn)) {
                s64 newdisp;
                u8 *disp;
                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 *) p->addr + (s64) insn.displacement.value -
                          (u8 *) p->ainsn.insn;
                BUG_ON((s64) (s32) newdisp != newdisp); /* Sanity check.  */
                disp = (u8 *) p->ainsn.insn + insn_offset_displacement(&insn);
                *(s32 *) disp = (s32) newdisp;
        }
#endif
}

static void __kprobes arch_copy_kprobe(struct kprobe *p)
{
        memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));

        fix_riprel(p);

        if (can_boost(p->addr))
                p->ainsn.boostable = 0;
        else
                p->ainsn.boostable = -1;

        p->opcode = *p->addr;
}

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
        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)
{
        __get_cpu_var(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)
{
        __get_cpu_var(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_DEBUGCTLMSR))
                update_debugctlmsr(0);
}

static void __kprobes restore_btf(void)
{
        if (test_thread_flag(TIF_DEBUGCTLMSR))
                update_debugctlmsr(current->thread.debugctlmsr);
}

static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
        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;
}

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)
{
#if !defined(CONFIG_PREEMPT) || defined(CONFIG_FREEZER)
        if (p->ainsn.boostable == 1 && !p->post_handler) {
                /* Boost up -- we can execute copied instructions directly */
                reset_current_kprobe();
                regs->ip = (unsigned long)p->ainsn.insn;
                preempt_enable_no_resched();
                return;
        }
#endif
        prepare_singlestep(p, regs);
        kcb->kprobe_status = KPROBE_HIT_SS;
}

/*
 * 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:
                save_previous_kprobe(kcb);
                set_current_kprobe(p, regs, kcb);
                kprobes_inc_nmissed_count(p);
                prepare_singlestep(p, regs);
                kcb->kprobe_status = KPROBE_REENTER;
                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;
}

/*
 * Interrupts are disabled on entry as trap3 is an interrupt gate and they
 * remain disabled thorough out 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));
        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;
                return 1;
        }

        /*
         * 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);
                        return 1;
                }
        } else if (kprobe_running()) {
                p = __get_cpu_var(current_kprobe);
                if (p->break_handler && p->break_handler(p, regs)) {
                        setup_singlestep(p, regs, kcb);
                        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"
                        /*
                         * Skip cs, ip, orig_ax.
                         * trampoline_handler() will plug in these values
                         */
                        "       subq $24, %rsp\n"
                        "       pushq %rdi\n"
                        "       pushq %rsi\n"
                        "       pushq %rdx\n"
                        "       pushq %rcx\n"
                        "       pushq %rax\n"
                        "       pushq %r8\n"
                        "       pushq %r9\n"
                        "       pushq %r10\n"
                        "       pushq %r11\n"
                        "       pushq %rbx\n"
                        "       pushq %rbp\n"
                        "       pushq %r12\n"
                        "       pushq %r13\n"
                        "       pushq %r14\n"
                        "       pushq %r15\n"
                        "       movq %rsp, %rdi\n"
                        "       call trampoline_handler\n"
                        /* Replace saved sp with true return address. */
                        "       movq %rax, 152(%rsp)\n"
                        "       popq %r15\n"
                        "       popq %r14\n"
                        "       popq %r13\n"
                        "       popq %r12\n"
                        "       popq %rbp\n"
                        "       popq %rbx\n"
                        "       popq %r11\n"
                        "       popq %r10\n"
                        "       popq %r9\n"
                        "       popq %r8\n"
                        "       popq %rax\n"
                        "       popq %rcx\n"
                        "       popq %rdx\n"
                        "       popq %rsi\n"
                        "       popq %rdi\n"
                        /* Skip orig_ax, ip, cs */
                        "       addq $24, %rsp\n"
                        "       popfq\n"
#else
                        "       pushf\n"
                        /*
                         * Skip cs, ip, orig_ax and gs.
                         * trampoline_handler() will plug in these values
                         */
                        "       subl $16, %esp\n"
                        "       pushl %fs\n"
                        "       pushl %es\n"
                        "       pushl %ds\n"
                        "       pushl %eax\n"
                        "       pushl %ebp\n"
                        "       pushl %edi\n"
                        "       pushl %esi\n"
                        "       pushl %edx\n"
                        "       pushl %ecx\n"
                        "       pushl %ebx\n"
                        "       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"
                        "       popl %ebx\n"
                        "       popl %ecx\n"
                        "       popl %edx\n"
                        "       popl %esi\n"
                        "       popl %edi\n"
                        "       popl %ebp\n"
                        "       popl %eax\n"
                        /* Skip ds, es, fs, gs, orig_ax and ip */
                        "       addl $24, %esp\n"
                        "       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;

        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;

                if (ri->rp && ri->rp->handler) {
                        __get_cpu_var(current_kprobe) = &ri->rp->kp;
                        get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
                        ri->rp->handler(ri, regs);
                        __get_cpu_var(current_kprobe) = NULL;
                }

                orig_ret_address = (unsigned long)ri->ret_addr;
                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_assert(ri, orig_ret_address, trampoline_address);

        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 the REX prefix*/
        if (is_REX_prefix(insn))
                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.
                         */
                        set_jmp_op((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 thoroughout 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_registers(saved_regs);
                        printk(KERN_ERR "Current registers\n");
                        show_registers(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;
}