kprobes: add (un)register_kretprobes for batch registration

[deliverable/linux.git] / kernel / kprobes.c

/*
 *  Kernel Probes (KProbes)
 *  kernel/kprobes.c
 *
 * 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 suggestions from
 *              Rusty Russell).
 * 2004-Aug     Updated by Prasanna S Panchamukhi <prasanna@in.ibm.com> with
 *              hlists and exceptions notifier as suggested by Andi Kleen.
 * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
 *              interface to access function arguments.
 * 2004-Sep     Prasanna S Panchamukhi <prasanna@in.ibm.com> Changed Kprobes
 *              exceptions notifier to be first on the priority list.
 * 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.
 */
#include <linux/kprobes.h>
#include <linux/hash.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/stddef.h>
#include <linux/module.h>
#include <linux/moduleloader.h>
#include <linux/kallsyms.h>
#include <linux/freezer.h>
#include <linux/seq_file.h>
#include <linux/debugfs.h>
#include <linux/kdebug.h>

#include <asm-generic/sections.h>
#include <asm/cacheflush.h>
#include <asm/errno.h>
#include <asm/uaccess.h>

#define KPROBE_HASH_BITS 6
#define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)


/*
 * Some oddball architectures like 64bit powerpc have function descriptors
 * so this must be overridable.
 */
#ifndef kprobe_lookup_name
#define kprobe_lookup_name(name, addr) \
        addr = ((kprobe_opcode_t *)(kallsyms_lookup_name(name)))
#endif

static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];

/* NOTE: change this value only with kprobe_mutex held */
static bool kprobe_enabled;

DEFINE_MUTEX(kprobe_mutex);             /* Protects kprobe_table */
DEFINE_SPINLOCK(kretprobe_lock);        /* Protects kretprobe_inst_table */
static DEFINE_PER_CPU(struct kprobe *, kprobe_instance) = NULL;

/*
 * Normally, functions that we'd want to prohibit kprobes in, are marked
 * __kprobes. But, there are cases where such functions already belong to
 * a different section (__sched for preempt_schedule)
 *
 * For such cases, we now have a blacklist
 */
struct kprobe_blackpoint kprobe_blacklist[] = {
        {"preempt_schedule",},
        {NULL}    /* Terminator */
};

#ifdef __ARCH_WANT_KPROBES_INSN_SLOT
/*
 * kprobe->ainsn.insn points to the copy of the instruction to be
 * single-stepped. x86_64, POWER4 and above have no-exec support and
 * stepping on the instruction on a vmalloced/kmalloced/data page
 * is a recipe for disaster
 */
#define INSNS_PER_PAGE  (PAGE_SIZE/(MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))

struct kprobe_insn_page {
        struct hlist_node hlist;
        kprobe_opcode_t *insns;         /* Page of instruction slots */
        char slot_used[INSNS_PER_PAGE];
        int nused;
        int ngarbage;
};

enum kprobe_slot_state {
        SLOT_CLEAN = 0,
        SLOT_DIRTY = 1,
        SLOT_USED = 2,
};

static struct hlist_head kprobe_insn_pages;
static int kprobe_garbage_slots;
static int collect_garbage_slots(void);

static int __kprobes check_safety(void)
{
        int ret = 0;
#if defined(CONFIG_PREEMPT) && defined(CONFIG_PM)
        ret = freeze_processes();
        if (ret == 0) {
                struct task_struct *p, *q;
                do_each_thread(p, q) {
                        if (p != current && p->state == TASK_RUNNING &&
                            p->pid != 0) {
                                printk("Check failed: %s is running\n",p->comm);
                                ret = -1;
                                goto loop_end;
                        }
                } while_each_thread(p, q);
        }
loop_end:
        thaw_processes();
#else
        synchronize_sched();
#endif
        return ret;
}

/**
 * get_insn_slot() - Find a slot on an executable page for an instruction.
 * We allocate an executable page if there's no room on existing ones.
 */
kprobe_opcode_t __kprobes *get_insn_slot(void)
{
        struct kprobe_insn_page *kip;
        struct hlist_node *pos;

 retry:
        hlist_for_each_entry(kip, pos, &kprobe_insn_pages, hlist) {
                if (kip->nused < INSNS_PER_PAGE) {
                        int i;
                        for (i = 0; i < INSNS_PER_PAGE; i++) {
                                if (kip->slot_used[i] == SLOT_CLEAN) {
                                        kip->slot_used[i] = SLOT_USED;
                                        kip->nused++;
                                        return kip->insns + (i * MAX_INSN_SIZE);
                                }
                        }
                        /* Surprise!  No unused slots.  Fix kip->nused. */
                        kip->nused = INSNS_PER_PAGE;
                }
        }

        /* If there are any garbage slots, collect it and try again. */
        if (kprobe_garbage_slots && collect_garbage_slots() == 0) {
                goto retry;
        }
        /* All out of space.  Need to allocate a new page. Use slot 0. */
        kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
        if (!kip)
                return NULL;

        /*
         * Use module_alloc so this page is within +/- 2GB of where the
         * kernel image and loaded module images reside. This is required
         * so x86_64 can correctly handle the %rip-relative fixups.
         */
        kip->insns = module_alloc(PAGE_SIZE);
        if (!kip->insns) {
                kfree(kip);
                return NULL;
        }
        INIT_HLIST_NODE(&kip->hlist);
        hlist_add_head(&kip->hlist, &kprobe_insn_pages);
        memset(kip->slot_used, SLOT_CLEAN, INSNS_PER_PAGE);
        kip->slot_used[0] = SLOT_USED;
        kip->nused = 1;
        kip->ngarbage = 0;
        return kip->insns;
}

/* Return 1 if all garbages are collected, otherwise 0. */
static int __kprobes collect_one_slot(struct kprobe_insn_page *kip, int idx)
{
        kip->slot_used[idx] = SLOT_CLEAN;
        kip->nused--;
        if (kip->nused == 0) {
                /*
                 * Page is no longer in use.  Free it unless
                 * it's the last one.  We keep the last one
                 * so as not to have to set it up again the
                 * next time somebody inserts a probe.
                 */
                hlist_del(&kip->hlist);
                if (hlist_empty(&kprobe_insn_pages)) {
                        INIT_HLIST_NODE(&kip->hlist);
                        hlist_add_head(&kip->hlist,
                                       &kprobe_insn_pages);
                } else {
                        module_free(NULL, kip->insns);
                        kfree(kip);
                }
                return 1;
        }
        return 0;
}

static int __kprobes collect_garbage_slots(void)
{
        struct kprobe_insn_page *kip;
        struct hlist_node *pos, *next;

        /* Ensure no-one is preepmted on the garbages */
        if (check_safety() != 0)
                return -EAGAIN;

        hlist_for_each_entry_safe(kip, pos, next, &kprobe_insn_pages, hlist) {
                int i;
                if (kip->ngarbage == 0)
                        continue;
                kip->ngarbage = 0;      /* we will collect all garbages */
                for (i = 0; i < INSNS_PER_PAGE; i++) {
                        if (kip->slot_used[i] == SLOT_DIRTY &&
                            collect_one_slot(kip, i))
                                break;
                }
        }
        kprobe_garbage_slots = 0;
        return 0;
}

void __kprobes free_insn_slot(kprobe_opcode_t * slot, int dirty)
{
        struct kprobe_insn_page *kip;
        struct hlist_node *pos;

        hlist_for_each_entry(kip, pos, &kprobe_insn_pages, hlist) {
                if (kip->insns <= slot &&
                    slot < kip->insns + (INSNS_PER_PAGE * MAX_INSN_SIZE)) {
                        int i = (slot - kip->insns) / MAX_INSN_SIZE;
                        if (dirty) {
                                kip->slot_used[i] = SLOT_DIRTY;
                                kip->ngarbage++;
                        } else {
                                collect_one_slot(kip, i);
                        }
                        break;
                }
        }

        if (dirty && ++kprobe_garbage_slots > INSNS_PER_PAGE)
                collect_garbage_slots();
}
#endif

/* We have preemption disabled.. so it is safe to use __ versions */
static inline void set_kprobe_instance(struct kprobe *kp)
{
        __get_cpu_var(kprobe_instance) = kp;
}

static inline void reset_kprobe_instance(void)
{
        __get_cpu_var(kprobe_instance) = NULL;
}

/*
 * This routine is called either:
 *      - under the kprobe_mutex - during kprobe_[un]register()
 *                              OR
 *      - with preemption disabled - from arch/xxx/kernel/kprobes.c
 */
struct kprobe __kprobes *get_kprobe(void *addr)
{
        struct hlist_head *head;
        struct hlist_node *node;
        struct kprobe *p;

        head = &kprobe_table[hash_ptr(addr, KPROBE_HASH_BITS)];
        hlist_for_each_entry_rcu(p, node, head, hlist) {
                if (p->addr == addr)
                        return p;
        }
        return NULL;
}

/*
 * Aggregate handlers for multiple kprobes support - these handlers
 * take care of invoking the individual kprobe handlers on p->list
 */
static int __kprobes aggr_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct kprobe *kp;

        list_for_each_entry_rcu(kp, &p->list, list) {
                if (kp->pre_handler) {
                        set_kprobe_instance(kp);
                        if (kp->pre_handler(kp, regs))
                                return 1;
                }
                reset_kprobe_instance();
        }
        return 0;
}

static void __kprobes aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
                                        unsigned long flags)
{
        struct kprobe *kp;

        list_for_each_entry_rcu(kp, &p->list, list) {
                if (kp->post_handler) {
                        set_kprobe_instance(kp);
                        kp->post_handler(kp, regs, flags);
                        reset_kprobe_instance();
                }
        }
}

static int __kprobes aggr_fault_handler(struct kprobe *p, struct pt_regs *regs,
                                        int trapnr)
{
        struct kprobe *cur = __get_cpu_var(kprobe_instance);

        /*
         * if we faulted "during" the execution of a user specified
         * probe handler, invoke just that probe's fault handler
         */
        if (cur && cur->fault_handler) {
                if (cur->fault_handler(cur, regs, trapnr))
                        return 1;
        }
        return 0;
}

static int __kprobes aggr_break_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct kprobe *cur = __get_cpu_var(kprobe_instance);
        int ret = 0;

        if (cur && cur->break_handler) {
                if (cur->break_handler(cur, regs))
                        ret = 1;
        }
        reset_kprobe_instance();
        return ret;
}

/* Walks the list and increments nmissed count for multiprobe case */
void __kprobes kprobes_inc_nmissed_count(struct kprobe *p)
{
        struct kprobe *kp;
        if (p->pre_handler != aggr_pre_handler) {
                p->nmissed++;
        } else {
                list_for_each_entry_rcu(kp, &p->list, list)
                        kp->nmissed++;
        }
        return;
}

/* Called with kretprobe_lock held */
void __kprobes recycle_rp_inst(struct kretprobe_instance *ri,
                                struct hlist_head *head)
{
        /* remove rp inst off the rprobe_inst_table */
        hlist_del(&ri->hlist);
        if (ri->rp) {
                /* remove rp inst off the used list */
                hlist_del(&ri->uflist);
                /* put rp inst back onto the free list */
                INIT_HLIST_NODE(&ri->uflist);
                hlist_add_head(&ri->uflist, &ri->rp->free_instances);
        } else
                /* Unregistering */
                hlist_add_head(&ri->hlist, head);
}

struct hlist_head __kprobes *kretprobe_inst_table_head(struct task_struct *tsk)
{
        return &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)];
}

/*
 * This function is called from finish_task_switch when task tk becomes dead,
 * so that we can recycle any function-return probe instances associated
 * with this task. These left over instances represent probed functions
 * that have been called but will never return.
 */
void __kprobes kprobe_flush_task(struct task_struct *tk)
{
        struct kretprobe_instance *ri;
        struct hlist_head *head, empty_rp;
        struct hlist_node *node, *tmp;
        unsigned long flags = 0;

        INIT_HLIST_HEAD(&empty_rp);
        spin_lock_irqsave(&kretprobe_lock, flags);
        head = kretprobe_inst_table_head(tk);
        hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
                if (ri->task == tk)
                        recycle_rp_inst(ri, &empty_rp);
        }
        spin_unlock_irqrestore(&kretprobe_lock, flags);

        hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
                hlist_del(&ri->hlist);
                kfree(ri);
        }
}

static inline void free_rp_inst(struct kretprobe *rp)
{
        struct kretprobe_instance *ri;
        struct hlist_node *pos, *next;

        hlist_for_each_entry_safe(ri, pos, next, &rp->free_instances, uflist) {
                hlist_del(&ri->uflist);
                kfree(ri);
        }
}

static void __kprobes cleanup_rp_inst(struct kretprobe *rp)
{
        unsigned long flags;
        struct kretprobe_instance *ri;
        struct hlist_node *pos, *next;
        /* No race here */
        spin_lock_irqsave(&kretprobe_lock, flags);
        hlist_for_each_entry_safe(ri, pos, next, &rp->used_instances, uflist) {
                ri->rp = NULL;
                hlist_del(&ri->uflist);
        }
        spin_unlock_irqrestore(&kretprobe_lock, flags);
        free_rp_inst(rp);
}

/*
 * Keep all fields in the kprobe consistent
 */
static inline void copy_kprobe(struct kprobe *old_p, struct kprobe *p)
{
        memcpy(&p->opcode, &old_p->opcode, sizeof(kprobe_opcode_t));
        memcpy(&p->ainsn, &old_p->ainsn, sizeof(struct arch_specific_insn));
}

/*
* Add the new probe to old_p->list. Fail if this is the
* second jprobe at the address - two jprobes can't coexist
*/
static int __kprobes add_new_kprobe(struct kprobe *old_p, struct kprobe *p)
{
        if (p->break_handler) {
                if (old_p->break_handler)
                        return -EEXIST;
                list_add_tail_rcu(&p->list, &old_p->list);
                old_p->break_handler = aggr_break_handler;
        } else
                list_add_rcu(&p->list, &old_p->list);
        if (p->post_handler && !old_p->post_handler)
                old_p->post_handler = aggr_post_handler;
        return 0;
}

/*
 * Fill in the required fields of the "manager kprobe". Replace the
 * earlier kprobe in the hlist with the manager kprobe
 */
static inline void add_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
{
        copy_kprobe(p, ap);
        flush_insn_slot(ap);
        ap->addr = p->addr;
        ap->pre_handler = aggr_pre_handler;
        ap->fault_handler = aggr_fault_handler;
        if (p->post_handler)
                ap->post_handler = aggr_post_handler;
        if (p->break_handler)
                ap->break_handler = aggr_break_handler;

        INIT_LIST_HEAD(&ap->list);
        list_add_rcu(&p->list, &ap->list);

        hlist_replace_rcu(&p->hlist, &ap->hlist);
}

/*
 * This is the second or subsequent kprobe at the address - handle
 * the intricacies
 */
static int __kprobes register_aggr_kprobe(struct kprobe *old_p,
                                          struct kprobe *p)
{
        int ret = 0;
        struct kprobe *ap;

        if (old_p->pre_handler == aggr_pre_handler) {
                copy_kprobe(old_p, p);
                ret = add_new_kprobe(old_p, p);
        } else {
                ap = kzalloc(sizeof(struct kprobe), GFP_KERNEL);
                if (!ap)
                        return -ENOMEM;
                add_aggr_kprobe(ap, old_p);
                copy_kprobe(ap, p);
                ret = add_new_kprobe(ap, p);
        }
        return ret;
}

static int __kprobes in_kprobes_functions(unsigned long addr)
{
        struct kprobe_blackpoint *kb;

        if (addr >= (unsigned long)__kprobes_text_start &&
            addr < (unsigned long)__kprobes_text_end)
                return -EINVAL;
        /*
         * If there exists a kprobe_blacklist, verify and
         * fail any probe registration in the prohibited area
         */
        for (kb = kprobe_blacklist; kb->name != NULL; kb++) {
                if (kb->start_addr) {
                        if (addr >= kb->start_addr &&
                            addr < (kb->start_addr + kb->range))
                                return -EINVAL;
                }
        }
        return 0;
}

/*
 * If we have a symbol_name argument, look it up and add the offset field
 * to it. This way, we can specify a relative address to a symbol.
 */
static kprobe_opcode_t __kprobes *kprobe_addr(struct kprobe *p)
{
        kprobe_opcode_t *addr = p->addr;
        if (p->symbol_name) {
                if (addr)
                        return NULL;
                kprobe_lookup_name(p->symbol_name, addr);
        }

        if (!addr)
                return NULL;
        return (kprobe_opcode_t *)(((char *)addr) + p->offset);
}

static int __kprobes __register_kprobe(struct kprobe *p,
        unsigned long called_from)
{
        int ret = 0;
        struct kprobe *old_p;
        struct module *probed_mod;
        kprobe_opcode_t *addr;

        addr = kprobe_addr(p);
        if (!addr)
                return -EINVAL;
        p->addr = addr;

        if (!kernel_text_address((unsigned long) p->addr) ||
            in_kprobes_functions((unsigned long) p->addr))
                return -EINVAL;

        p->mod_refcounted = 0;

        /*
         * Check if are we probing a module.
         */
        probed_mod = module_text_address((unsigned long) p->addr);
        if (probed_mod) {
                struct module *calling_mod = module_text_address(called_from);
                /*
                 * We must allow modules to probe themself and in this case
                 * avoid incrementing the module refcount, so as to allow
                 * unloading of self probing modules.
                 */
                if (calling_mod && calling_mod != probed_mod) {
                        if (unlikely(!try_module_get(probed_mod)))
                                return -EINVAL;
                        p->mod_refcounted = 1;
                } else
                        probed_mod = NULL;
        }

        p->nmissed = 0;
        INIT_LIST_HEAD(&p->list);
        mutex_lock(&kprobe_mutex);
        old_p = get_kprobe(p->addr);
        if (old_p) {
                ret = register_aggr_kprobe(old_p, p);
                goto out;
        }

        ret = arch_prepare_kprobe(p);
        if (ret)
                goto out;

        INIT_HLIST_NODE(&p->hlist);
        hlist_add_head_rcu(&p->hlist,
                       &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);

        if (kprobe_enabled)
                arch_arm_kprobe(p);

out:
        mutex_unlock(&kprobe_mutex);

        if (ret && probed_mod)
                module_put(probed_mod);
        return ret;
}

/*
 * Unregister a kprobe without a scheduler synchronization.
 */
static int __kprobes __unregister_kprobe_top(struct kprobe *p)
{
        struct kprobe *old_p, *list_p;

        old_p = get_kprobe(p->addr);
        if (unlikely(!old_p))
                return -EINVAL;

        if (p != old_p) {
                list_for_each_entry_rcu(list_p, &old_p->list, list)
                        if (list_p == p)
                        /* kprobe p is a valid probe */
                                goto valid_p;
                return -EINVAL;
        }
valid_p:
        if (old_p == p ||
            (old_p->pre_handler == aggr_pre_handler &&
             list_is_singular(&old_p->list))) {
                /*
                 * Only probe on the hash list. Disarm only if kprobes are
                 * enabled - otherwise, the breakpoint would already have
                 * been removed. We save on flushing icache.
                 */
                if (kprobe_enabled)
                        arch_disarm_kprobe(p);
                hlist_del_rcu(&old_p->hlist);
        } else {
                if (p->break_handler)
                        old_p->break_handler = NULL;
                if (p->post_handler) {
                        list_for_each_entry_rcu(list_p, &old_p->list, list) {
                                if ((list_p != p) && (list_p->post_handler))
                                        goto noclean;
                        }
                        old_p->post_handler = NULL;
                }
noclean:
                list_del_rcu(&p->list);
        }
        return 0;
}

static void __kprobes __unregister_kprobe_bottom(struct kprobe *p)
{
        struct module *mod;
        struct kprobe *old_p;

        if (p->mod_refcounted) {
                mod = module_text_address((unsigned long)p->addr);
                if (mod)
                        module_put(mod);
        }

        if (list_empty(&p->list) || list_is_singular(&p->list)) {
                if (!list_empty(&p->list)) {
                        /* "p" is the last child of an aggr_kprobe */
                        old_p = list_entry(p->list.next, struct kprobe, list);
                        list_del(&p->list);
                        kfree(old_p);
                }
                arch_remove_kprobe(p);
        }
}

static int __register_kprobes(struct kprobe **kps, int num,
        unsigned long called_from)
{
        int i, ret = 0;

        if (num <= 0)
                return -EINVAL;
        for (i = 0; i < num; i++) {
                ret = __register_kprobe(kps[i], called_from);
                if (ret < 0 && i > 0) {
                        unregister_kprobes(kps, i);
                        break;
                }
        }
        return ret;
}

/*
 * Registration and unregistration functions for kprobe.
 */
int __kprobes register_kprobe(struct kprobe *p)
{
        return __register_kprobes(&p, 1,
                                  (unsigned long)__builtin_return_address(0));
}

void __kprobes unregister_kprobe(struct kprobe *p)
{
        unregister_kprobes(&p, 1);
}

int __kprobes register_kprobes(struct kprobe **kps, int num)
{
        return __register_kprobes(kps, num,
                                  (unsigned long)__builtin_return_address(0));
}

void __kprobes unregister_kprobes(struct kprobe **kps, int num)
{
        int i;

        if (num <= 0)
                return;
        mutex_lock(&kprobe_mutex);
        for (i = 0; i < num; i++)
                if (__unregister_kprobe_top(kps[i]) < 0)
                        kps[i]->addr = NULL;
        mutex_unlock(&kprobe_mutex);

        synchronize_sched();
        for (i = 0; i < num; i++)
                if (kps[i]->addr)
                        __unregister_kprobe_bottom(kps[i]);
}

static struct notifier_block kprobe_exceptions_nb = {
        .notifier_call = kprobe_exceptions_notify,
        .priority = 0x7fffffff /* we need to be notified first */
};

unsigned long __weak arch_deref_entry_point(void *entry)
{
        return (unsigned long)entry;
}

int __kprobes register_jprobe(struct jprobe *jp)
{
        unsigned long addr = arch_deref_entry_point(jp->entry);

        if (!kernel_text_address(addr))
                return -EINVAL;

        /* Todo: Verify probepoint is a function entry point */
        jp->kp.pre_handler = setjmp_pre_handler;
        jp->kp.break_handler = longjmp_break_handler;

        return __register_kprobe(&jp->kp,
                (unsigned long)__builtin_return_address(0));
}

void __kprobes unregister_jprobe(struct jprobe *jp)
{
        unregister_kprobe(&jp->kp);
}

#ifdef CONFIG_KRETPROBES
/*
 * This kprobe pre_handler is registered with every kretprobe. When probe
 * hits it will set up the return probe.
 */
static int __kprobes pre_handler_kretprobe(struct kprobe *p,
                                           struct pt_regs *regs)
{
        struct kretprobe *rp = container_of(p, struct kretprobe, kp);
        unsigned long flags = 0;

        /*TODO: consider to only swap the RA after the last pre_handler fired */
        spin_lock_irqsave(&kretprobe_lock, flags);
        if (!hlist_empty(&rp->free_instances)) {
                struct kretprobe_instance *ri;

                ri = hlist_entry(rp->free_instances.first,
                                 struct kretprobe_instance, uflist);
                ri->rp = rp;
                ri->task = current;

                if (rp->entry_handler && rp->entry_handler(ri, regs)) {
                        spin_unlock_irqrestore(&kretprobe_lock, flags);
                        return 0;
                }

                arch_prepare_kretprobe(ri, regs);

                /* XXX(hch): why is there no hlist_move_head? */
                hlist_del(&ri->uflist);
                hlist_add_head(&ri->uflist, &ri->rp->used_instances);
                hlist_add_head(&ri->hlist, kretprobe_inst_table_head(ri->task));
        } else
                rp->nmissed++;
        spin_unlock_irqrestore(&kretprobe_lock, flags);
        return 0;
}

static int __kprobes __register_kretprobe(struct kretprobe *rp,
                                          unsigned long called_from)
{
        int ret = 0;
        struct kretprobe_instance *inst;
        int i;
        void *addr;

        if (kretprobe_blacklist_size) {
                addr = kprobe_addr(&rp->kp);
                if (!addr)
                        return -EINVAL;

                for (i = 0; kretprobe_blacklist[i].name != NULL; i++) {
                        if (kretprobe_blacklist[i].addr == addr)
                                return -EINVAL;
                }
        }

        rp->kp.pre_handler = pre_handler_kretprobe;
        rp->kp.post_handler = NULL;
        rp->kp.fault_handler = NULL;
        rp->kp.break_handler = NULL;

        /* Pre-allocate memory for max kretprobe instances */
        if (rp->maxactive <= 0) {
#ifdef CONFIG_PREEMPT
                rp->maxactive = max(10, 2 * NR_CPUS);
#else
                rp->maxactive = NR_CPUS;
#endif
        }
        INIT_HLIST_HEAD(&rp->used_instances);
        INIT_HLIST_HEAD(&rp->free_instances);
        for (i = 0; i < rp->maxactive; i++) {
                inst = kmalloc(sizeof(struct kretprobe_instance) +
                               rp->data_size, GFP_KERNEL);
                if (inst == NULL) {
                        free_rp_inst(rp);
                        return -ENOMEM;
                }
                INIT_HLIST_NODE(&inst->uflist);
                hlist_add_head(&inst->uflist, &rp->free_instances);
        }

        rp->nmissed = 0;
        /* Establish function entry probe point */
        ret = __register_kprobe(&rp->kp, called_from);
        if (ret != 0)
                free_rp_inst(rp);
        return ret;
}

static int __register_kretprobes(struct kretprobe **rps, int num,
        unsigned long called_from)
{
        int ret = 0, i;

        if (num <= 0)
                return -EINVAL;
        for (i = 0; i < num; i++) {
                ret = __register_kretprobe(rps[i], called_from);
                if (ret < 0 && i > 0) {
                        unregister_kretprobes(rps, i);
                        break;
                }
        }
        return ret;
}

int __kprobes register_kretprobe(struct kretprobe *rp)
{
        return __register_kretprobes(&rp, 1,
                        (unsigned long)__builtin_return_address(0));
}

void __kprobes unregister_kretprobe(struct kretprobe *rp)
{
        unregister_kretprobes(&rp, 1);
}

int __kprobes register_kretprobes(struct kretprobe **rps, int num)
{
        return __register_kretprobes(rps, num,
                        (unsigned long)__builtin_return_address(0));
}

void __kprobes unregister_kretprobes(struct kretprobe **rps, int num)
{
        int i;

        if (num <= 0)
                return;
        mutex_lock(&kprobe_mutex);
        for (i = 0; i < num; i++)
                if (__unregister_kprobe_top(&rps[i]->kp) < 0)
                        rps[i]->kp.addr = NULL;
        mutex_unlock(&kprobe_mutex);

        synchronize_sched();
        for (i = 0; i < num; i++) {
                if (rps[i]->kp.addr) {
                        __unregister_kprobe_bottom(&rps[i]->kp);
                        cleanup_rp_inst(rps[i]);
                }
        }
}

#else /* CONFIG_KRETPROBES */
int __kprobes register_kretprobe(struct kretprobe *rp)
{
        return -ENOSYS;
}

int __kprobes register_kretprobes(struct kretprobe **rps, int num)
{
        return -ENOSYS;
}
void __kprobes unregister_kretprobe(struct kretprobe *rp)
{
}

void __kprobes unregister_kretprobes(struct kretprobe **rps, int num)
{
}

static int __kprobes pre_handler_kretprobe(struct kprobe *p,
                                           struct pt_regs *regs)
{
        return 0;
}

#endif /* CONFIG_KRETPROBES */

static int __init init_kprobes(void)
{
        int i, err = 0;
        unsigned long offset = 0, size = 0;
        char *modname, namebuf[128];
        const char *symbol_name;
        void *addr;
        struct kprobe_blackpoint *kb;

        /* FIXME allocate the probe table, currently defined statically */
        /* initialize all list heads */
        for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
                INIT_HLIST_HEAD(&kprobe_table[i]);
                INIT_HLIST_HEAD(&kretprobe_inst_table[i]);
        }

        /*
         * Lookup and populate the kprobe_blacklist.
         *
         * Unlike the kretprobe blacklist, we'll need to determine
         * the range of addresses that belong to the said functions,
         * since a kprobe need not necessarily be at the beginning
         * of a function.
         */
        for (kb = kprobe_blacklist; kb->name != NULL; kb++) {
                kprobe_lookup_name(kb->name, addr);
                if (!addr)
                        continue;

                kb->start_addr = (unsigned long)addr;
                symbol_name = kallsyms_lookup(kb->start_addr,
                                &size, &offset, &modname, namebuf);
                if (!symbol_name)
                        kb->range = 0;
                else
                        kb->range = size;
        }

        if (kretprobe_blacklist_size) {
                /* lookup the function address from its name */
                for (i = 0; kretprobe_blacklist[i].name != NULL; i++) {
                        kprobe_lookup_name(kretprobe_blacklist[i].name,
                                           kretprobe_blacklist[i].addr);
                        if (!kretprobe_blacklist[i].addr)
                                printk("kretprobe: lookup failed: %s\n",
                                       kretprobe_blacklist[i].name);
                }
        }

        /* By default, kprobes are enabled */
        kprobe_enabled = true;

        err = arch_init_kprobes();
        if (!err)
                err = register_die_notifier(&kprobe_exceptions_nb);

        if (!err)
                init_test_probes();
        return err;
}

#ifdef CONFIG_DEBUG_FS
static void __kprobes report_probe(struct seq_file *pi, struct kprobe *p,
                const char *sym, int offset,char *modname)
{
        char *kprobe_type;

        if (p->pre_handler == pre_handler_kretprobe)
                kprobe_type = "r";
        else if (p->pre_handler == setjmp_pre_handler)
                kprobe_type = "j";
        else
                kprobe_type = "k";
        if (sym)
                seq_printf(pi, "%p  %s  %s+0x%x  %s\n", p->addr, kprobe_type,
                        sym, offset, (modname ? modname : " "));
        else
                seq_printf(pi, "%p  %s  %p\n", p->addr, kprobe_type, p->addr);
}

static void __kprobes *kprobe_seq_start(struct seq_file *f, loff_t *pos)
{
        return (*pos < KPROBE_TABLE_SIZE) ? pos : NULL;
}

static void __kprobes *kprobe_seq_next(struct seq_file *f, void *v, loff_t *pos)
{
        (*pos)++;
        if (*pos >= KPROBE_TABLE_SIZE)
                return NULL;
        return pos;
}

static void __kprobes kprobe_seq_stop(struct seq_file *f, void *v)
{
        /* Nothing to do */
}

static int __kprobes show_kprobe_addr(struct seq_file *pi, void *v)
{
        struct hlist_head *head;
        struct hlist_node *node;
        struct kprobe *p, *kp;
        const char *sym = NULL;
        unsigned int i = *(loff_t *) v;
        unsigned long offset = 0;
        char *modname, namebuf[128];

        head = &kprobe_table[i];
        preempt_disable();
        hlist_for_each_entry_rcu(p, node, head, hlist) {
                sym = kallsyms_lookup((unsigned long)p->addr, NULL,
                                        &offset, &modname, namebuf);
                if (p->pre_handler == aggr_pre_handler) {
                        list_for_each_entry_rcu(kp, &p->list, list)
                                report_probe(pi, kp, sym, offset, modname);
                } else
                        report_probe(pi, p, sym, offset, modname);
        }
        preempt_enable();
        return 0;
}

static struct seq_operations kprobes_seq_ops = {
        .start = kprobe_seq_start,
        .next  = kprobe_seq_next,
        .stop  = kprobe_seq_stop,
        .show  = show_kprobe_addr
};

static int __kprobes kprobes_open(struct inode *inode, struct file *filp)
{
        return seq_open(filp, &kprobes_seq_ops);
}

static struct file_operations debugfs_kprobes_operations = {
        .open           = kprobes_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release,
};

static void __kprobes enable_all_kprobes(void)
{
        struct hlist_head *head;
        struct hlist_node *node;
        struct kprobe *p;
        unsigned int i;

        mutex_lock(&kprobe_mutex);

        /* If kprobes are already enabled, just return */
        if (kprobe_enabled)
                goto already_enabled;

        for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
                head = &kprobe_table[i];
                hlist_for_each_entry_rcu(p, node, head, hlist)
                        arch_arm_kprobe(p);
        }

        kprobe_enabled = true;
        printk(KERN_INFO "Kprobes globally enabled\n");

already_enabled:
        mutex_unlock(&kprobe_mutex);
        return;
}

static void __kprobes disable_all_kprobes(void)
{
        struct hlist_head *head;
        struct hlist_node *node;
        struct kprobe *p;
        unsigned int i;

        mutex_lock(&kprobe_mutex);

        /* If kprobes are already disabled, just return */
        if (!kprobe_enabled)
                goto already_disabled;

        kprobe_enabled = false;
        printk(KERN_INFO "Kprobes globally disabled\n");
        for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
                head = &kprobe_table[i];
                hlist_for_each_entry_rcu(p, node, head, hlist) {
                        if (!arch_trampoline_kprobe(p))
                                arch_disarm_kprobe(p);
                }
        }

        mutex_unlock(&kprobe_mutex);
        /* Allow all currently running kprobes to complete */
        synchronize_sched();
        return;

already_disabled:
        mutex_unlock(&kprobe_mutex);
        return;
}

/*
 * XXX: The debugfs bool file interface doesn't allow for callbacks
 * when the bool state is switched. We can reuse that facility when
 * available
 */
static ssize_t read_enabled_file_bool(struct file *file,
               char __user *user_buf, size_t count, loff_t *ppos)
{
        char buf[3];

        if (kprobe_enabled)
                buf[0] = '1';
        else
                buf[0] = '0';
        buf[1] = '\n';
        buf[2] = 0x00;
        return simple_read_from_buffer(user_buf, count, ppos, buf, 2);
}

static ssize_t write_enabled_file_bool(struct file *file,
               const char __user *user_buf, size_t count, loff_t *ppos)
{
        char buf[32];
        int buf_size;

        buf_size = min(count, (sizeof(buf)-1));
        if (copy_from_user(buf, user_buf, buf_size))
                return -EFAULT;

        switch (buf[0]) {
        case 'y':
        case 'Y':
        case '1':
                enable_all_kprobes();
                break;
        case 'n':
        case 'N':
        case '0':
                disable_all_kprobes();
                break;
        }

        return count;
}

static struct file_operations fops_kp = {
        .read =         read_enabled_file_bool,
        .write =        write_enabled_file_bool,
};

static int __kprobes debugfs_kprobe_init(void)
{
        struct dentry *dir, *file;
        unsigned int value = 1;

        dir = debugfs_create_dir("kprobes", NULL);
        if (!dir)
                return -ENOMEM;

        file = debugfs_create_file("list", 0444, dir, NULL,
                                &debugfs_kprobes_operations);
        if (!file) {
                debugfs_remove(dir);
                return -ENOMEM;
        }

        file = debugfs_create_file("enabled", 0600, dir,
                                        &value, &fops_kp);
        if (!file) {
                debugfs_remove(dir);
                return -ENOMEM;
        }

        return 0;
}

late_initcall(debugfs_kprobe_init);
#endif /* CONFIG_DEBUG_FS */

module_init(init_kprobes);

EXPORT_SYMBOL_GPL(register_kprobe);
EXPORT_SYMBOL_GPL(unregister_kprobe);
EXPORT_SYMBOL_GPL(register_kprobes);
EXPORT_SYMBOL_GPL(unregister_kprobes);
EXPORT_SYMBOL_GPL(register_jprobe);
EXPORT_SYMBOL_GPL(unregister_jprobe);
#ifdef CONFIG_KPROBES
EXPORT_SYMBOL_GPL(jprobe_return);
#endif

#ifdef CONFIG_KPROBES
EXPORT_SYMBOL_GPL(register_kretprobe);
EXPORT_SYMBOL_GPL(unregister_kretprobe);
EXPORT_SYMBOL_GPL(register_kretprobes);
EXPORT_SYMBOL_GPL(unregister_kretprobes);
#endif