kprobes.c

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/*
 *  Kernel Probes (KProbes)
 *  arch/mips/kernel/kprobes.c
 *
 *  Copyright 2006 Sony Corp.
 *  Copyright 2010 Cavium Networks
 *
 *  Some portions copied from the powerpc version.
 *
 *   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 as published by
 *  the Free Software Foundation; version 2 of the License.
 *
 *  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
 */

#include <linux/kprobes.h>
#include <linux/preempt.h>
#include <linux/uaccess.h>
#include <linux/kdebug.h>
#include <linux/slab.h>

#include <asm/ptrace.h>
#include <asm/branch.h>
#include <asm/break.h>
#include <asm/inst.h>

static const union mips_instruction breakpoint_insn = {
    .b_format = {
        .opcode = spec_op,
        .code = BRK_KPROBE_BP,
        .func = break_op
    }
};

static const union mips_instruction breakpoint2_insn = {
    .b_format = {
        .opcode = spec_op,
        .code = BRK_KPROBE_SSTEPBP,
        .func = break_op
    }
};

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

static int __kprobes insn_has_delayslot(union mips_instruction insn)
{
    switch (insn.i_format.opcode) {

        /*
         * This group contains:
         * jr and jalr are in r_format format.
         */
    case spec_op:
        switch (insn.r_format.func) {
        case jr_op:
        case jalr_op:
            break;
        default:
            goto insn_ok;
        }

        /*
         * This group contains:
         * bltz_op, bgez_op, bltzl_op, bgezl_op,
         * bltzal_op, bgezal_op, bltzall_op, bgezall_op.
         */
    case bcond_op:

        /*
         * These are unconditional and in j_format.
         */
    case jal_op:
    case j_op:

        /*
         * These are conditional and in i_format.
         */
    case beq_op:
    case beql_op:
    case bne_op:
    case bnel_op:
    case blez_op:
    case blezl_op:
    case bgtz_op:
    case bgtzl_op:

        /*
         * These are the FPA/cp1 branch instructions.
         */
    case cop1_op:

#ifdef CONFIG_CPU_CAVIUM_OCTEON
    case lwc2_op: /* This is bbit0 on Octeon */
    case ldc2_op: /* This is bbit032 on Octeon */
    case swc2_op: /* This is bbit1 on Octeon */
    case sdc2_op: /* This is bbit132 on Octeon */
#endif
        return 1;
    default:
        break;
    }
insn_ok:
    return 0;
}

/*
 * insn_has_ll_or_sc function checks whether instruction is ll or sc
 * one; putting breakpoint on top of atomic ll/sc pair is bad idea;
 * so we need to prevent it and refuse kprobes insertion for such
 * instructions; cannot do much about breakpoint in the middle of
 * ll/sc pair; it is upto user to avoid those places
 */
static int __kprobes insn_has_ll_or_sc(union mips_instruction insn)
{
    int ret = 0;

    switch (insn.i_format.opcode) {
    case ll_op:
    case lld_op:
    case sc_op:
    case scd_op:
        ret = 1;
        break;
    default:
        break;
    }
    return ret;
}

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
    union mips_instruction insn;
    union mips_instruction prev_insn;
    int ret = 0;

    insn = p->addr[0];

    if (insn_has_ll_or_sc(insn)) {
        pr_notice("Kprobes for ll and sc instructions are not"
              "supported\n");
        ret = -EINVAL;
        goto out;
    }

    if ((probe_kernel_read(&prev_insn, p->addr - 1,
                sizeof(mips_instruction)) == 0) &&
                insn_has_delayslot(prev_insn)) {
        pr_notice("Kprobes for branch delayslot are not supported\n");
        ret = -EINVAL;
        goto out;
    }

    /* insn: must be on special executable page on mips. */
    p->ainsn.insn = get_insn_slot();
    if (!p->ainsn.insn) {
        ret = -ENOMEM;
        goto out;
    }

    /*
     * In the kprobe->ainsn.insn[] array we store the original
     * instruction at index zero and a break trap instruction at
     * index one.
     *
     * On MIPS arch if the instruction at probed address is a
     * branch instruction, we need to execute the instruction at
     * Branch Delayslot (BD) at the time of probe hit. As MIPS also
     * doesn't have single stepping support, the BD instruction can
     * not be executed in-line and it would be executed on SSOL slot
     * using a normal breakpoint instruction in the next slot.
     * So, read the instruction and save it for later execution.
     */
    if (insn_has_delayslot(insn))
        memcpy(&p->ainsn.insn[0], p->addr + 1, sizeof(kprobe_opcode_t));
    else
        memcpy(&p->ainsn.insn[0], p->addr, sizeof(kprobe_opcode_t));

    p->ainsn.insn[1] = breakpoint2_insn;
    p->opcode = *p->addr;

out:
    return ret;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
    *p->addr = breakpoint_insn;
    flush_insn_slot(p);
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
    *p->addr = p->opcode;
    flush_insn_slot(p);
}

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
    free_insn_slot(p->ainsn.insn, 0);
}

static void save_previous_kprobe(struct kprobe_ctlblk *kcb)
{
    kcb->prev_kprobe.kp = kprobe_running();
    kcb->prev_kprobe.status = kcb->kprobe_status;
    kcb->prev_kprobe.old_SR = kcb->kprobe_old_SR;
    kcb->prev_kprobe.saved_SR = kcb->kprobe_saved_SR;
    kcb->prev_kprobe.saved_epc = kcb->kprobe_saved_epc;
}

static void 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_SR = kcb->prev_kprobe.old_SR;
    kcb->kprobe_saved_SR = kcb->prev_kprobe.saved_SR;
    kcb->kprobe_saved_epc = kcb->prev_kprobe.saved_epc;
}

static void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
                   struct kprobe_ctlblk *kcb)
{
    __get_cpu_var(current_kprobe) = p;
    kcb->kprobe_saved_SR = kcb->kprobe_old_SR = (regs->cp0_status & ST0_IE);
    kcb->kprobe_saved_epc = regs->cp0_epc;
}

static int evaluate_branch_instruction(struct kprobe *p, struct pt_regs *regs,
                    struct kprobe_ctlblk *kcb)
{
    union mips_instruction insn = p->opcode;
    long epc;
    int ret = 0;

    epc = regs->cp0_epc;
    if (epc & 3)
        goto unaligned;

    if (p->ainsn.insn->word == 0)
        kcb->flags |= SKIP_DELAYSLOT;
    else
        kcb->flags &= ~SKIP_DELAYSLOT;

    ret = __compute_return_epc_for_insn(regs, insn);
    if (ret < 0)
        return ret;

    if (ret == BRANCH_LIKELY_TAKEN)
        kcb->flags |= SKIP_DELAYSLOT;

    kcb->target_epc = regs->cp0_epc;

    return 0;

unaligned:
    pr_notice("%s: unaligned epc - sending SIGBUS.\n", current->comm);
    force_sig(SIGBUS, current);
    return -EFAULT;

}

static void prepare_singlestep(struct kprobe *p, struct pt_regs *regs,
                        struct kprobe_ctlblk *kcb)
{
    int ret = 0;

    regs->cp0_status &= ~ST0_IE;

    /* single step inline if the instruction is a break */
    if (p->opcode.word == breakpoint_insn.word ||
        p->opcode.word == breakpoint2_insn.word)
        regs->cp0_epc = (unsigned long)p->addr;
    else if (insn_has_delayslot(p->opcode)) {
        ret = evaluate_branch_instruction(p, regs, kcb);
        if (ret < 0) {
            pr_notice("Kprobes: Error in evaluating branch\n");
            return;
        }
    }
    regs->cp0_epc = (unsigned long)&p->ainsn.insn[0];
}

/*
 * Called after single-stepping.  p->addr is the address of the
 * instruction whose first byte has been replaced by the "break 0"
 * 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
 * breakpoint trap. In case of branch instructions, the target
 * epc to be restored.
 */
static void __kprobes resume_execution(struct kprobe *p,
                       struct pt_regs *regs,
                       struct kprobe_ctlblk *kcb)
{
    if (insn_has_delayslot(p->opcode))
        regs->cp0_epc = kcb->target_epc;
    else {
        unsigned long orig_epc = kcb->kprobe_saved_epc;
        regs->cp0_epc = orig_epc + 4;
    }
}

static int __kprobes kprobe_handler(struct pt_regs *regs)
{
    struct kprobe *p;
    int ret = 0;
    kprobe_opcode_t *addr;
    struct kprobe_ctlblk *kcb;

    addr = (kprobe_opcode_t *) regs->cp0_epc;

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

    /* Check we're not actually recursing */
    if (kprobe_running()) {
        p = get_kprobe(addr);
        if (p) {
            if (kcb->kprobe_status == KPROBE_HIT_SS &&
                p->ainsn.insn->word == breakpoint_insn.word) {
                regs->cp0_status &= ~ST0_IE;
                regs->cp0_status |= kcb->kprobe_saved_SR;
                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(kcb);
            set_current_kprobe(p, regs, kcb);
            kprobes_inc_nmissed_count(p);
            prepare_singlestep(p, regs, kcb);
            kcb->kprobe_status = KPROBE_REENTER;
            if (kcb->flags & SKIP_DELAYSLOT) {
                resume_execution(p, regs, kcb);
                restore_previous_kprobe(kcb);
                preempt_enable_no_resched();
            }
            return 1;
        } else {
            if (addr->word != breakpoint_insn.word) {
                /*
                 * The breakpoint instruction was removed by
                 * another cpu right after we hit, no further
                 * handling of this interrupt is appropriate
                 */
                ret = 1;
                goto no_kprobe;
            }
            p = __get_cpu_var(current_kprobe);
            if (p->break_handler && p->break_handler(p, regs))
                goto ss_probe;
        }
        goto no_kprobe;
    }

    p = get_kprobe(addr);
    if (!p) {
        if (addr->word != breakpoint_insn.word) {
            /*
             * 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;
    }

    set_current_kprobe(p, regs, kcb);
    kcb->kprobe_status = KPROBE_HIT_ACTIVE;

    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, kcb);
    if (kcb->flags & SKIP_DELAYSLOT) {
        kcb->kprobe_status = KPROBE_HIT_SSDONE;
        if (p->post_handler)
            p->post_handler(p, regs, 0);
        resume_execution(p, regs, kcb);
        preempt_enable_no_resched();
    } else
        kcb->kprobe_status = KPROBE_HIT_SS;

    return 1;

no_kprobe:
    preempt_enable_no_resched();
    return ret;

}

static inline int post_kprobe_handler(struct pt_regs *regs)
{
    struct kprobe *cur = kprobe_running();
    struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

    if (!cur)
        return 0;

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

    resume_execution(cur, regs, kcb);

    regs->cp0_status |= kcb->kprobe_saved_SR;

    /* 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();

    return 1;
}

static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
    struct kprobe *cur = kprobe_running();
    struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

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

    if (kcb->kprobe_status & KPROBE_HIT_SS) {
        resume_execution(cur, regs, kcb);
        regs->cp0_status |= kcb->kprobe_old_SR;

        reset_current_kprobe();
        preempt_enable_no_resched();
    }
    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 = (struct die_args *)data;
    int ret = NOTIFY_DONE;

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

    case DIE_PAGE_FAULT:
        /* kprobe_running() needs smp_processor_id() */
        preempt_disable();

        if (kprobe_running()
            && kprobe_fault_handler(args->regs, args->trapnr))
            ret = NOTIFY_STOP;
        preempt_enable();
        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);
    struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

    kcb->jprobe_saved_regs = *regs;
    kcb->jprobe_saved_sp = regs->regs[29];

    memcpy(kcb->jprobes_stack, (void *)kcb->jprobe_saved_sp,
           MIN_JPROBES_STACK_SIZE(kcb->jprobe_saved_sp));

    regs->cp0_epc = (unsigned long)(jp->entry);

    return 1;
}

/* Defined in the inline asm below. */
void jprobe_return_end(void);

void __kprobes jprobe_return(void)
{
    /* Assembler quirk necessitates this '0,code' business.  */
    asm volatile(
        "break 0,%0\n\t"
        ".globl jprobe_return_end\n"
        "jprobe_return_end:\n"
        : : "n" (BRK_KPROBE_BP) : "memory");
}

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
    struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

    if (regs->cp0_epc >= (unsigned long)jprobe_return &&
        regs->cp0_epc <= (unsigned long)jprobe_return_end) {
        *regs = kcb->jprobe_saved_regs;
        memcpy((void *)kcb->jprobe_saved_sp, kcb->jprobes_stack,
               MIN_JPROBES_STACK_SIZE(kcb->jprobe_saved_sp));
        preempt_enable_no_resched();

        return 1;
    }
    return 0;
}

/*
 * Function return probe trampoline:
 *  - init_kprobes() establishes a probepoint here
 *  - When the probed function returns, this probe causes the
 *    handlers to fire
 */
static void __used kretprobe_trampoline_holder(void)
{
    asm volatile(
        ".set push\n\t"
        /* Keep the assembler from reordering and placing JR here. */
        ".set noreorder\n\t"
        "nop\n\t"
        ".global kretprobe_trampoline\n"
        "kretprobe_trampoline:\n\t"
        "nop\n\t"
        ".set pop"
        : : : "memory");
}

void kretprobe_trampoline(void);

void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
                      struct pt_regs *regs)
{
    ri->ret_addr = (kprobe_opcode_t *) regs->regs[31];

    /* Replace the return addr with trampoline addr */
    regs->regs[31] = (unsigned long)kretprobe_trampoline;
}

/*
 * Called when the probe at kretprobe trampoline is hit
 */
static int __kprobes trampoline_probe_handler(struct kprobe *p,
                        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);

    /*
     * 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 than 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, &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);
    instruction_pointer(regs) = orig_ret_address;

    reset_current_kprobe();
    kretprobe_hash_unlock(current, &flags);
    preempt_enable_no_resched();

    hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
        hlist_del(&ri->hlist);
        kfree(ri);
    }
    /*
     * By returning a non-zero value, we are telling
     * kprobe_handler() that we don't want the post_handler
     * to run (and have re-enabled preemption)
     */
    return 1;
}

int __kprobes arch_trampoline_kprobe(struct kprobe *p)
{
    if (p->addr == (kprobe_opcode_t *)kretprobe_trampoline)
        return 1;

    return 0;
}

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);
}