kprobes.c

Go to the documentation of this file.

/*
 *  Kernel Probes (KProbes)
 *
 * Copyright (C) 2005-2006 Atmel Corporation
 *
 * Based on arch/ppc64/kernel/kprobes.c
 *  Copyright (C) IBM Corporation, 2002, 2004
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/kprobes.h>
#include <linux/ptrace.h>

#include <asm/cacheflush.h>
#include <linux/kdebug.h>
#include <asm/ocd.h>

DEFINE_PER_CPU(struct kprobe *, current_kprobe);
static unsigned long kprobe_status;
static struct pt_regs jprobe_saved_regs;

struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
    int ret = 0;

    if ((unsigned long)p->addr & 0x01) {
        printk("Attempt to register kprobe at an unaligned address\n");
        ret = -EINVAL;
    }

    /* XXX: Might be a good idea to check if p->addr is a valid
     * kernel address as well... */

    if (!ret) {
        pr_debug("copy kprobe at %p\n", p->addr);
        memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
        p->opcode = *p->addr;
    }

    return ret;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
    pr_debug("arming kprobe at %p\n", p->addr);
    ocd_enable(NULL);
    *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)
{
    pr_debug("disarming kprobe at %p\n", p->addr);
    ocd_disable(NULL);
    *p->addr = p->opcode;
    flush_icache_range((unsigned long)p->addr,
               (unsigned long)p->addr + sizeof(kprobe_opcode_t));
}

static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
    unsigned long dc;

    pr_debug("preparing to singlestep over %p (PC=%08lx)\n",
         p->addr, regs->pc);

    BUG_ON(!(sysreg_read(SR) & SYSREG_BIT(SR_D)));

    dc = ocd_read(DC);
    dc |= 1 << OCD_DC_SS_BIT;
    ocd_write(DC, dc);

    /*
     * We must run the instruction from its original location
     * since it may actually reference PC.
     *
     * TODO: Do the instruction replacement directly in icache.
     */
    *p->addr = p->opcode;
    flush_icache_range((unsigned long)p->addr,
               (unsigned long)p->addr + sizeof(kprobe_opcode_t));
}

static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
{
    unsigned long dc;

    pr_debug("resuming execution at PC=%08lx\n", regs->pc);

    dc = ocd_read(DC);
    dc &= ~(1 << OCD_DC_SS_BIT);
    ocd_write(DC, dc);

    *p->addr = BREAKPOINT_INSTRUCTION;
    flush_icache_range((unsigned long)p->addr,
               (unsigned long)p->addr + sizeof(kprobe_opcode_t));
}

static void __kprobes set_current_kprobe(struct kprobe *p)
{
    __get_cpu_var(current_kprobe) = p;
}

static int __kprobes kprobe_handler(struct pt_regs *regs)
{
    struct kprobe *p;
    void *addr = (void *)regs->pc;
    int ret = 0;

    pr_debug("kprobe_handler: kprobe_running=%p\n",
         kprobe_running());

    /*
     * We don't want to be preempted for the entire
     * duration of kprobe processing
     */
    preempt_disable();

    /* Check that we're not recursing */
    if (kprobe_running()) {
        p = get_kprobe(addr);
        if (p) {
            if (kprobe_status == KPROBE_HIT_SS) {
                printk("FIXME: kprobe hit while single-stepping!\n");
                goto no_kprobe;
            }

            printk("FIXME: kprobe hit while handling another kprobe\n");
            goto no_kprobe;
        } else {
            p = kprobe_running();
            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;
    }

    p = get_kprobe(addr);
    if (!p)
        goto no_kprobe;

    kprobe_status = KPROBE_HIT_ACTIVE;
    set_current_kprobe(p);
    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:
    preempt_enable_no_resched();
    return ret;
}

static int __kprobes post_kprobe_handler(struct pt_regs *regs)
{
    struct kprobe *cur = kprobe_running();

    pr_debug("post_kprobe_handler, cur=%p\n", cur);

    if (!cur)
        return 0;

    if (cur->post_handler) {
        kprobe_status = KPROBE_HIT_SSDONE;
        cur->post_handler(cur, regs, 0);
    }

    resume_execution(cur, regs);
    reset_current_kprobe();
    preempt_enable_no_resched();

    return 1;
}

int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
    struct kprobe *cur = kprobe_running();

    pr_debug("kprobe_fault_handler: trapnr=%d\n", trapnr);

    if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
        return 1;

    if (kprobe_status & KPROBE_HIT_SS) {
        resume_execution(cur, regs);
        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;

    pr_debug("kprobe_exceptions_notify: val=%lu, data=%p\n",
         val, data);

    switch (val) {
    case DIE_BREAKPOINT:
        if (kprobe_handler(args->regs))
            ret = NOTIFY_STOP;
        break;
    case DIE_SSTEP:
        if (post_kprobe_handler(args->regs))
            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);

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

    /*
     * TODO: We should probably save some of the stack here as
     * well, since gcc may pass arguments on the stack for certain
     * functions (lots of arguments, large aggregates, varargs)
     */

    /* setup return addr to the jprobe handler routine */
    regs->pc = (unsigned long)jp->entry;
    return 1;
}

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

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;
}

int __init arch_init_kprobes(void)
{
    /* TODO: Register kretprobe trampoline */
    return 0;
}