Linux v2.6.13-rc3

[pohmelfs.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/spinlock.h>
#include <linux/hash.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/moduleloader.h>
#include <asm/cacheflush.h>
#include <asm/errno.h>
#include <asm/kdebug.h>

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

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

unsigned int kprobe_cpu = NR_CPUS;
static DEFINE_SPINLOCK(kprobe_lock);
static struct kprobe *curr_kprobe;

/*
 * 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;
};

static struct hlist_head kprobe_insn_pages;

/**
 * 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 *get_insn_slot(void)
{
        struct kprobe_insn_page *kip;
        struct hlist_node *pos;

        hlist_for_each(pos, &kprobe_insn_pages) {
                kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
                if (kip->nused < INSNS_PER_PAGE) {
                        int i;
                        for (i = 0; i < INSNS_PER_PAGE; i++) {
                                if (!kip->slot_used[i]) {
                                        kip->slot_used[i] = 1;
                                        kip->nused++;
                                        return kip->insns + (i * MAX_INSN_SIZE);
                                }
                        }
                        /* Surprise!  No unused slots.  Fix kip->nused. */
                        kip->nused = INSNS_PER_PAGE;
                }
        }

        /* 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, 0, INSNS_PER_PAGE);
        kip->slot_used[0] = 1;
        kip->nused = 1;
        return kip->insns;
}

void free_insn_slot(kprobe_opcode_t *slot)
{
        struct kprobe_insn_page *kip;
        struct hlist_node *pos;

        hlist_for_each(pos, &kprobe_insn_pages) {
                kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
                if (kip->insns <= slot &&
                    slot < kip->insns + (INSNS_PER_PAGE * MAX_INSN_SIZE)) {
                        int i = (slot - kip->insns) / MAX_INSN_SIZE;
                        kip->slot_used[i] = 0;
                        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;
                }
        }
}

/* Locks kprobe: irqs must be disabled */
void lock_kprobes(void)
{
        spin_lock(&kprobe_lock);
        kprobe_cpu = smp_processor_id();
}

void unlock_kprobes(void)
{
        kprobe_cpu = NR_CPUS;
        spin_unlock(&kprobe_lock);
}

/* You have to be holding the kprobe_lock */
struct kprobe *get_kprobe(void *addr)
{
        struct hlist_head *head;
        struct hlist_node *node;

        head = &kprobe_table[hash_ptr(addr, KPROBE_HASH_BITS)];
        hlist_for_each(node, head) {
                struct kprobe *p = hlist_entry(node, struct kprobe, 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 aggr_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct kprobe *kp;

        list_for_each_entry(kp, &p->list, list) {
                if (kp->pre_handler) {
                        curr_kprobe = kp;
                        if (kp->pre_handler(kp, regs))
                                return 1;
                }
                curr_kprobe = NULL;
        }
        return 0;
}

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

        list_for_each_entry(kp, &p->list, list) {
                if (kp->post_handler) {
                        curr_kprobe = kp;
                        kp->post_handler(kp, regs, flags);
                        curr_kprobe = NULL;
                }
        }
        return;
}

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

static int aggr_break_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct kprobe *kp = curr_kprobe;
        if (curr_kprobe && kp->break_handler) {
                if (kp->break_handler(kp, regs)) {
                        curr_kprobe = NULL;
                        return 1;
                }
        }
        curr_kprobe = NULL;
        return 0;
}

struct kretprobe_instance *get_free_rp_inst(struct kretprobe *rp)
{
        struct hlist_node *node;
        struct kretprobe_instance *ri;
        hlist_for_each_entry(ri, node, &rp->free_instances, uflist)
                return ri;
        return NULL;
}

static struct kretprobe_instance *get_used_rp_inst(struct kretprobe *rp)
{
        struct hlist_node *node;
        struct kretprobe_instance *ri;
        hlist_for_each_entry(ri, node, &rp->used_instances, uflist)
                return ri;
        return NULL;
}

void add_rp_inst(struct kretprobe_instance *ri)
{
        /*
         * Remove rp inst off the free list -
         * Add it back when probed function returns
         */
        hlist_del(&ri->uflist);

        /* Add rp inst onto table */
        INIT_HLIST_NODE(&ri->hlist);
        hlist_add_head(&ri->hlist,
                        &kretprobe_inst_table[hash_ptr(ri->task, KPROBE_HASH_BITS)]);

        /* Also add this rp inst to the used list. */
        INIT_HLIST_NODE(&ri->uflist);
        hlist_add_head(&ri->uflist, &ri->rp->used_instances);
}

void recycle_rp_inst(struct kretprobe_instance *ri)
{
        /* 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 */
                kfree(ri);
}

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

/*
 * This function is called from exit_thread or flush_thread when task tk's
 * stack is being recycled 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 kprobe_flush_task(struct task_struct *tk)
{
        struct kretprobe_instance *ri;
        struct hlist_head *head;
        struct hlist_node *node, *tmp;
        unsigned long flags = 0;

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

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

        /*TODO: consider to only swap the RA after the last pre_handler fired */
        arch_prepare_kretprobe(rp, regs);
        return 0;
}

static inline void free_rp_inst(struct kretprobe *rp)
{
        struct kretprobe_instance *ri;
        while ((ri = get_free_rp_inst(rp)) != NULL) {
                hlist_del(&ri->uflist);
                kfree(ri);
        }
}

/*
 * 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 add_new_kprobe(struct kprobe *old_p, struct kprobe *p)
{
        struct kprobe *kp;

        if (p->break_handler) {
                list_for_each_entry(kp, &old_p->list, list) {
                        if (kp->break_handler)
                                return -EEXIST;
                }
                list_add_tail(&p->list, &old_p->list);
        } else
                list_add(&p->list, &old_p->list);
        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);
        ap->addr = p->addr;
        ap->pre_handler = aggr_pre_handler;
        ap->post_handler = aggr_post_handler;
        ap->fault_handler = aggr_fault_handler;
        ap->break_handler = aggr_break_handler;

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

        INIT_HLIST_NODE(&ap->hlist);
        hlist_del(&p->hlist);
        hlist_add_head(&ap->hlist,
                &kprobe_table[hash_ptr(ap->addr, KPROBE_HASH_BITS)]);
}

/*
 * This is the second or subsequent kprobe at the address - handle
 * the intricacies
 * TODO: Move kcalloc outside the spinlock
 */
static int 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 = kcalloc(1, sizeof(struct kprobe), GFP_ATOMIC);
                if (!ap)
                        return -ENOMEM;
                add_aggr_kprobe(ap, old_p);
                copy_kprobe(ap, p);
                ret = add_new_kprobe(ap, p);
        }
        return ret;
}

/* kprobe removal house-keeping routines */
static inline void cleanup_kprobe(struct kprobe *p, unsigned long flags)
{
        arch_disarm_kprobe(p);
        hlist_del(&p->hlist);
        spin_unlock_irqrestore(&kprobe_lock, flags);
        arch_remove_kprobe(p);
}

static inline void cleanup_aggr_kprobe(struct kprobe *old_p,
                struct kprobe *p, unsigned long flags)
{
        list_del(&p->list);
        if (list_empty(&old_p->list)) {
                cleanup_kprobe(old_p, flags);
                kfree(old_p);
        } else
                spin_unlock_irqrestore(&kprobe_lock, flags);
}

int register_kprobe(struct kprobe *p)
{
        int ret = 0;
        unsigned long flags = 0;
        struct kprobe *old_p;

        if ((ret = arch_prepare_kprobe(p)) != 0) {
                goto rm_kprobe;
        }
        spin_lock_irqsave(&kprobe_lock, flags);
        old_p = get_kprobe(p->addr);
        p->nmissed = 0;
        if (old_p) {
                ret = register_aggr_kprobe(old_p, p);
                goto out;
        }

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

        arch_arm_kprobe(p);

out:
        spin_unlock_irqrestore(&kprobe_lock, flags);
rm_kprobe:
        if (ret == -EEXIST)
                arch_remove_kprobe(p);
        return ret;
}

void unregister_kprobe(struct kprobe *p)
{
        unsigned long flags;
        struct kprobe *old_p;

        spin_lock_irqsave(&kprobe_lock, flags);
        old_p = get_kprobe(p->addr);
        if (old_p) {
                if (old_p->pre_handler == aggr_pre_handler)
                        cleanup_aggr_kprobe(old_p, p, flags);
                else
                        cleanup_kprobe(p, flags);
        } else
                spin_unlock_irqrestore(&kprobe_lock, flags);
}

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

int register_jprobe(struct jprobe *jp)
{
        /* 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);
}

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

#ifdef ARCH_SUPPORTS_KRETPROBES

int register_kretprobe(struct kretprobe *rp)
{
        int ret = 0;
        struct kretprobe_instance *inst;
        int i;

        rp->kp.pre_handler = pre_handler_kretprobe;

        /* 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), 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 */
        if ((ret = register_kprobe(&rp->kp)) != 0)
                free_rp_inst(rp);
        return ret;
}

#else /* ARCH_SUPPORTS_KRETPROBES */

int register_kretprobe(struct kretprobe *rp)
{
        return -ENOSYS;
}

#endif /* ARCH_SUPPORTS_KRETPROBES */

void unregister_kretprobe(struct kretprobe *rp)
{
        unsigned long flags;
        struct kretprobe_instance *ri;

        unregister_kprobe(&rp->kp);
        /* No race here */
        spin_lock_irqsave(&kprobe_lock, flags);
        free_rp_inst(rp);
        while ((ri = get_used_rp_inst(rp)) != NULL) {
                ri->rp = NULL;
                hlist_del(&ri->uflist);
        }
        spin_unlock_irqrestore(&kprobe_lock, flags);
}

static int __init init_kprobes(void)
{
        int i, err = 0;

        /* 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]);
        }

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

        return err;
}

__initcall(init_kprobes);

EXPORT_SYMBOL_GPL(register_kprobe);
EXPORT_SYMBOL_GPL(unregister_kprobe);
EXPORT_SYMBOL_GPL(register_jprobe);
EXPORT_SYMBOL_GPL(unregister_jprobe);
EXPORT_SYMBOL_GPL(jprobe_return);
EXPORT_SYMBOL_GPL(register_kretprobe);
EXPORT_SYMBOL_GPL(unregister_kretprobe);