[PATCH] Kprobes: rearrange preempt_disable/enable() calls

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / arch / ppc64 / kernel / kprobes.c

/*
 *  Kernel Probes (KProbes)
 *  arch/ppc64/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 contributions from
 *              Rusty Russell).
 * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
 *              interface to access function arguments.
 * 2004-Nov     Ananth N Mavinakayanahalli <ananth@in.ibm.com> kprobes port
 *              for PPC64
 */

#include <linux/config.h>
#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/spinlock.h>
#include <linux/preempt.h>
#include <asm/cacheflush.h>
#include <asm/kdebug.h>
#include <asm/sstep.h>

static DECLARE_MUTEX(kprobe_mutex);

static struct kprobe *current_kprobe;
static unsigned long kprobe_status, kprobe_saved_msr;
static struct kprobe *kprobe_prev;
static unsigned long kprobe_status_prev, kprobe_saved_msr_prev;
static struct pt_regs jprobe_saved_regs;

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
        int ret = 0;
        kprobe_opcode_t insn = *p->addr;

        if ((unsigned long)p->addr & 0x03) {
                printk("Attempt to register kprobe at an unaligned address\n");
                ret = -EINVAL;
        } else if (IS_MTMSRD(insn) || IS_RFID(insn)) {
                printk("Cannot register a kprobe on rfid or mtmsrd\n");
                ret = -EINVAL;
        }

        /* insn must be on a special executable page on ppc64 */
        if (!ret) {
                down(&kprobe_mutex);
                p->ainsn.insn = get_insn_slot();
                up(&kprobe_mutex);
                if (!p->ainsn.insn)
                        ret = -ENOMEM;
        }
        return ret;
}

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

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
        *p->addr = BREAKPOINT_INSTRUCTION;
        flush_icache_range((unsigned long) p->addr,
                           (unsigned long) p->addr + sizeof(kprobe_opcode_t));
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
        *p->addr = p->opcode;
        flush_icache_range((unsigned long) p->addr,
                           (unsigned long) p->addr + sizeof(kprobe_opcode_t));
}

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
        down(&kprobe_mutex);
        free_insn_slot(p->ainsn.insn);
        up(&kprobe_mutex);
}

static inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
        kprobe_opcode_t insn = *p->ainsn.insn;

        regs->msr |= MSR_SE;

        /* single step inline if it is a trap variant */
        if (is_trap(insn))
                regs->nip = (unsigned long)p->addr;
        else
                regs->nip = (unsigned long)p->ainsn.insn;
}

static inline void save_previous_kprobe(void)
{
        kprobe_prev = current_kprobe;
        kprobe_status_prev = kprobe_status;
        kprobe_saved_msr_prev = kprobe_saved_msr;
}

static inline void restore_previous_kprobe(void)
{
        current_kprobe = kprobe_prev;
        kprobe_status = kprobe_status_prev;
        kprobe_saved_msr = kprobe_saved_msr_prev;
}

void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
                                      struct pt_regs *regs)
{
        struct kretprobe_instance *ri;

        if ((ri = get_free_rp_inst(rp)) != NULL) {
                ri->rp = rp;
                ri->task = current;
                ri->ret_addr = (kprobe_opcode_t *)regs->link;

                /* Replace the return addr with trampoline addr */
                regs->link = (unsigned long)kretprobe_trampoline;
                add_rp_inst(ri);
        } else {
                rp->nmissed++;
        }
}

static inline int kprobe_handler(struct pt_regs *regs)
{
        struct kprobe *p;
        int ret = 0;
        unsigned int *addr = (unsigned int *)regs->nip;

        /* Check we're not actually recursing */
        if (kprobe_running()) {
                /* We *are* holding lock here, so this is safe.
                   Disarm the probe we just hit, and ignore it. */
                p = get_kprobe(addr);
                if (p) {
                        kprobe_opcode_t insn = *p->ainsn.insn;
                        if (kprobe_status == KPROBE_HIT_SS &&
                                        is_trap(insn)) {
                                regs->msr &= ~MSR_SE;
                                regs->msr |= kprobe_saved_msr;
                                unlock_kprobes();
                                goto no_kprobe;
                        }
                        /* We have reentered the kprobe_handler(), since
                         * another probe was hit while within the handler.
                         * We here save the original kprobes variables and
                         * just single step on the instruction of the new probe
                         * without calling any user handlers.
                         */
                        save_previous_kprobe();
                        current_kprobe = p;
                        kprobe_saved_msr = regs->msr;
                        p->nmissed++;
                        prepare_singlestep(p, regs);
                        kprobe_status = KPROBE_REENTER;
                        return 1;
                } else {
                        p = current_kprobe;
                        if (p->break_handler && p->break_handler(p, regs)) {
                                goto ss_probe;
                        }
                }
                /* If it's not ours, can't be delete race, (we hold lock). */
                goto no_kprobe;
        }

        lock_kprobes();
        p = get_kprobe(addr);
        if (!p) {
                unlock_kprobes();
                if (*addr != BREAKPOINT_INSTRUCTION) {
                        /*
                         * PowerPC has multiple variants of the "trap"
                         * instruction. If the current instruction is a
                         * trap variant, it could belong to someone else
                         */
                        kprobe_opcode_t cur_insn = *addr;
                        if (is_trap(cur_insn))
                                goto no_kprobe;
                        /*
                         * 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.
                         */
                        ret = 1;
                }
                /* Not one of ours: let kernel handle it */
                goto no_kprobe;
        }

        /*
         * This preempt_disable() matches the preempt_enable_no_resched()
         * in post_kprobe_handler().
         */
        preempt_disable();
        kprobe_status = KPROBE_HIT_ACTIVE;
        current_kprobe = p;
        kprobe_saved_msr = regs->msr;
        if (p->pre_handler && p->pre_handler(p, regs))
                /* handler has already set things up, so skip ss setup */
                return 1;

ss_probe:
        prepare_singlestep(p, regs);
        kprobe_status = KPROBE_HIT_SS;
        return 1;

no_kprobe:
        return ret;
}

/*
 * Function return probe trampoline:
 *      - init_kprobes() establishes a probepoint here
 *      - When the probed function returns, this probe
 *              causes the handlers to fire
 */
void kretprobe_trampoline_holder(void)
{
        asm volatile(".global kretprobe_trampoline\n"
                        "kretprobe_trampoline:\n"
                        "nop\n");
}

/*
 * Called when the probe at kretprobe trampoline is hit
 */
int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct kretprobe_instance *ri = NULL;
        struct hlist_head *head;
        struct hlist_node *node, *tmp;
        unsigned long orig_ret_address = 0;
        unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;

        head = kretprobe_inst_table_head(current);

        /*
         * It is possible to have multiple instances associated with a given
         * task either because an multiple functions in the call path
         * have a return probe installed on them, and/or more then one return
         * return probe was registered for a target function.
         *
         * We can handle this because:
         *     - instances are always inserted at the head of the list
         *     - when multiple return probes are registered for the same
         *       function, the first instance's ret_addr will point to 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)
                        ri->rp->handler(ri, regs);

                orig_ret_address = (unsigned long)ri->ret_addr;
                recycle_rp_inst(ri);

                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;
        }

        BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
        regs->nip = orig_ret_address;

        unlock_kprobes();
        preempt_enable_no_resched();

        /*
         * By returning a non-zero value, we are telling
         * kprobe_handler() that we have handled unlocking
         * and re-enabling preemption.
         */
        return 1;
}

/*
 * Called after single-stepping.  p->addr is the address of the
 * instruction whose first byte has been replaced by the "breakpoint"
 * 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.
 */
static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
{
        int ret;
        unsigned int insn = *p->ainsn.insn;

        regs->nip = (unsigned long)p->addr;
        ret = emulate_step(regs, insn);
        if (ret == 0)
                regs->nip = (unsigned long)p->addr + 4;
}

static inline int post_kprobe_handler(struct pt_regs *regs)
{
        if (!kprobe_running())
                return 0;

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

        resume_execution(current_kprobe, regs);
        regs->msr |= kprobe_saved_msr;

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

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

        return 1;
}

/* Interrupts disabled, kprobe_lock held. */
static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
        if (current_kprobe->fault_handler
            && current_kprobe->fault_handler(current_kprobe, regs, trapnr))
                return 1;

        if (kprobe_status & KPROBE_HIT_SS) {
                resume_execution(current_kprobe, regs);
                regs->msr &= ~MSR_SE;
                regs->msr |= kprobe_saved_msr;

                unlock_kprobes();
                preempt_enable_no_resched();
        }
        return 0;
}

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

        /*
         * Interrupts are not disabled here.  We need to disable
         * preemption, because kprobe_running() uses smp_processor_id().
         */
        preempt_disable();
        switch (val) {
        case DIE_BPT:
                if (kprobe_handler(args->regs))
                        ret = NOTIFY_STOP;
                break;
        case DIE_SSTEP:
                if (post_kprobe_handler(args->regs))
                        ret = NOTIFY_STOP;
                break;
        case DIE_PAGE_FAULT:
                if (kprobe_running() &&
                    kprobe_fault_handler(args->regs, args->trapnr))
                        ret = NOTIFY_STOP;
                break;
        default:
                break;
        }
        preempt_enable_no_resched();
        return ret;
}

int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct jprobe *jp = container_of(p, struct jprobe, kp);

        memcpy(&jprobe_saved_regs, regs, sizeof(struct pt_regs));

        /* setup return addr to the jprobe handler routine */
        regs->nip = (unsigned long)(((func_descr_t *)jp->entry)->entry);
        regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);

        return 1;
}

void __kprobes jprobe_return(void)
{
        asm volatile("trap" ::: "memory");
}

void __kprobes jprobe_return_end(void)
{
};

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
        /*
         * FIXME - we should ideally be validating that we got here 'cos
         * of the "trap" in jprobe_return() above, before restoring the
         * saved regs...
         */
        memcpy(regs, &jprobe_saved_regs, sizeof(struct pt_regs));
        return 1;
}

static struct kprobe trampoline_p = {
        .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
        .pre_handler = trampoline_probe_handler
};

int __init arch_init_kprobes(void)
{
        return register_kprobe(&trampoline_p);
}