kprobes.c

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/*
 * Kernel probes (kprobes) for SuperH
 *
 * Copyright (C) 2007 Chris Smith <[email protected]>
 * Copyright (C) 2006 Lineo Solutions, Inc.
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 */
#include <linux/kprobes.h>
#include <linux/module.h>
#include <linux/ptrace.h>
#include <linux/preempt.h>
#include <linux/kdebug.h>
#include <linux/slab.h>
#include <asm/cacheflush.h>
#include <asm/uaccess.h>

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

static DEFINE_PER_CPU(struct kprobe, saved_current_opcode);
static DEFINE_PER_CPU(struct kprobe, saved_next_opcode);
static DEFINE_PER_CPU(struct kprobe, saved_next_opcode2);

#define OPCODE_JMP(x)   (((x) & 0xF0FF) == 0x402b)
#define OPCODE_JSR(x)   (((x) & 0xF0FF) == 0x400b)
#define OPCODE_BRA(x)   (((x) & 0xF000) == 0xa000)
#define OPCODE_BRAF(x)  (((x) & 0xF0FF) == 0x0023)
#define OPCODE_BSR(x)   (((x) & 0xF000) == 0xb000)
#define OPCODE_BSRF(x)  (((x) & 0xF0FF) == 0x0003)

#define OPCODE_BF_S(x)  (((x) & 0xFF00) == 0x8f00)
#define OPCODE_BT_S(x)  (((x) & 0xFF00) == 0x8d00)

#define OPCODE_BF(x)    (((x) & 0xFF00) == 0x8b00)
#define OPCODE_BT(x)    (((x) & 0xFF00) == 0x8900)

#define OPCODE_RTS(x)   (((x) & 0x000F) == 0x000b)
#define OPCODE_RTE(x)   (((x) & 0xFFFF) == 0x002b)

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

    if (OPCODE_RTE(opcode))
        return -EFAULT; /* Bad breakpoint */

    p->opcode = opcode;

    return 0;
}

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));
}

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

    return 0;
}

int __kprobes kprobe_handle_illslot(unsigned long pc)
{
    struct kprobe *p = get_kprobe((kprobe_opcode_t *) pc + 1);

    if (p != NULL) {
        printk("Warning: removing kprobe from delay slot: 0x%.8x\n",
               (unsigned int)pc + 2);
        unregister_kprobe(p);
        return 0;
    }

    return 1;
}

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
    struct kprobe *saved = &__get_cpu_var(saved_next_opcode);

    if (saved->addr) {
        arch_disarm_kprobe(p);
        arch_disarm_kprobe(saved);

        saved->addr = NULL;
        saved->opcode = 0;

        saved = &__get_cpu_var(saved_next_opcode2);
        if (saved->addr) {
            arch_disarm_kprobe(saved);

            saved->addr = NULL;
            saved->opcode = 0;
        }
    }
}

static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
{
    kcb->prev_kprobe.kp = kprobe_running();
    kcb->prev_kprobe.status = kcb->kprobe_status;
}

static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
{
    __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
    kcb->kprobe_status = kcb->prev_kprobe.status;
}

static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
                     struct kprobe_ctlblk *kcb)
{
    __get_cpu_var(current_kprobe) = p;
}

/*
 * Singlestep is implemented by disabling the current kprobe and setting one
 * on the next instruction, following branches. Two probes are set if the
 * branch is conditional.
 */
static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
    __get_cpu_var(saved_current_opcode).addr = (kprobe_opcode_t *)regs->pc;

    if (p != NULL) {
        struct kprobe *op1, *op2;

        arch_disarm_kprobe(p);

        op1 = &__get_cpu_var(saved_next_opcode);
        op2 = &__get_cpu_var(saved_next_opcode2);

        if (OPCODE_JSR(p->opcode) || OPCODE_JMP(p->opcode)) {
            unsigned int reg_nr = ((p->opcode >> 8) & 0x000F);
            op1->addr = (kprobe_opcode_t *) regs->regs[reg_nr];
        } else if (OPCODE_BRA(p->opcode) || OPCODE_BSR(p->opcode)) {
            unsigned long disp = (p->opcode & 0x0FFF);
            op1->addr =
                (kprobe_opcode_t *) (regs->pc + 4 + disp * 2);

        } else if (OPCODE_BRAF(p->opcode) || OPCODE_BSRF(p->opcode)) {
            unsigned int reg_nr = ((p->opcode >> 8) & 0x000F);
            op1->addr =
                (kprobe_opcode_t *) (regs->pc + 4 +
                         regs->regs[reg_nr]);

        } else if (OPCODE_RTS(p->opcode)) {
            op1->addr = (kprobe_opcode_t *) regs->pr;

        } else if (OPCODE_BF(p->opcode) || OPCODE_BT(p->opcode)) {
            unsigned long disp = (p->opcode & 0x00FF);
            /* case 1 */
            op1->addr = p->addr + 1;
            /* case 2 */
            op2->addr =
                (kprobe_opcode_t *) (regs->pc + 4 + disp * 2);
            op2->opcode = *(op2->addr);
            arch_arm_kprobe(op2);

        } else if (OPCODE_BF_S(p->opcode) || OPCODE_BT_S(p->opcode)) {
            unsigned long disp = (p->opcode & 0x00FF);
            /* case 1 */
            op1->addr = p->addr + 2;
            /* case 2 */
            op2->addr =
                (kprobe_opcode_t *) (regs->pc + 4 + disp * 2);
            op2->opcode = *(op2->addr);
            arch_arm_kprobe(op2);

        } else {
            op1->addr = p->addr + 1;
        }

        op1->opcode = *(op1->addr);
        arch_arm_kprobe(op1);
    }
}

/* Called with kretprobe_lock held */
void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
                      struct pt_regs *regs)
{
    ri->ret_addr = (kprobe_opcode_t *) regs->pr;

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

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

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

    addr = (kprobe_opcode_t *) (regs->pc);

    /* 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 == BREAKPOINT_INSTRUCTION) {
                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->kprobe_status = KPROBE_REENTER;
            return 1;
        } else {
            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) {
        /* Not one of ours: let kernel handle it */
        if (*(kprobe_opcode_t *)addr != BREAKPOINT_INSTRUCTION) {
            /*
             * 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;
        }

        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->kprobe_status = KPROBE_HIT_SS;
    return 1;

no_kprobe:
    preempt_enable_no_resched();
    return ret;
}

/*
 * For function-return probes, init_kprobes() establishes a probepoint
 * here. When a retprobed function returns, this probe is hit and
 * trampoline_probe_handler() runs, calling the kretprobe's handler.
 */
static void __used kretprobe_trampoline_holder(void)
{
    asm volatile (".globl kretprobe_trampoline\n"
              "kretprobe_trampoline:\n\t"
              "nop\n");
}

/*
 * Called when we hit the probe point at kretprobe_trampoline
 */
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 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) {
            __get_cpu_var(current_kprobe) = &ri->rp->kp;
            ri->rp->handler(ri, regs);
            __get_cpu_var(current_kprobe) = NULL;
        }

        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);

    regs->pc = orig_ret_address;
    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);
    }

    return orig_ret_address;
}

static int __kprobes post_kprobe_handler(struct pt_regs *regs)
{
    struct kprobe *cur = kprobe_running();
    struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
    kprobe_opcode_t *addr = NULL;
    struct kprobe *p = NULL;

    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);
    }

    p = &__get_cpu_var(saved_next_opcode);
    if (p->addr) {
        arch_disarm_kprobe(p);
        p->addr = NULL;
        p->opcode = 0;

        addr = __get_cpu_var(saved_current_opcode).addr;
        __get_cpu_var(saved_current_opcode).addr = NULL;

        p = get_kprobe(addr);
        arch_arm_kprobe(p);

        p = &__get_cpu_var(saved_next_opcode2);
        if (p->addr) {
            arch_disarm_kprobe(p);
            p->addr = NULL;
            p->opcode = 0;
        }
    }

    /* 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;
}

int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
    struct kprobe *cur = kprobe_running();
    struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
    const struct exception_table_entry *entry;

    switch (kcb->kprobe_status) {
    case KPROBE_HIT_SS:
    case KPROBE_REENTER:
        /*
         * We are here because the instruction being single
         * stepped caused a page fault. We reset the current
         * kprobe, point the pc back to the probe address
         * and allow the page fault handler to continue as a
         * normal page fault.
         */
        regs->pc = (unsigned long)cur->addr;
        if (kcb->kprobe_status == KPROBE_REENTER)
            restore_previous_kprobe(kcb);
        else
            reset_current_kprobe();
        preempt_enable_no_resched();
        break;
    case KPROBE_HIT_ACTIVE:
    case KPROBE_HIT_SSDONE:
        /*
         * We increment the nmissed count for accounting,
         * we can also use npre/npostfault count for accounting
         * these specific fault cases.
         */
        kprobes_inc_nmissed_count(cur);

        /*
         * We come here because instructions in the pre/post
         * handler caused the page_fault, this could happen
         * if handler tries to access user space by
         * copy_from_user(), get_user() etc. Let the
         * user-specified handler try to fix it first.
         */
        if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
            return 1;

        /*
         * In case the user-specified fault handler returned
         * zero, try to fix up.
         */
        if ((entry = search_exception_tables(regs->pc)) != NULL) {
            regs->pc = entry->fixup;
            return 1;
        }

        /*
         * fixup_exception() could not handle it,
         * Let do_page_fault() fix it.
         */
        break;
    default:
        break;
    }

    return 0;
}

/*
 * Wrapper routine to for handling exceptions.
 */
int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
                       unsigned long val, void *data)
{
    struct kprobe *p = NULL;
    struct die_args *args = (struct die_args *)data;
    int ret = NOTIFY_DONE;
    kprobe_opcode_t *addr = NULL;
    struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

    addr = (kprobe_opcode_t *) (args->regs->pc);
    if (val == DIE_TRAP) {
        if (!kprobe_running()) {
            if (kprobe_handler(args->regs)) {
                ret = NOTIFY_STOP;
            } else {
                /* Not a kprobe trap */
                ret = NOTIFY_DONE;
            }
        } else {
            p = get_kprobe(addr);
            if ((kcb->kprobe_status == KPROBE_HIT_SS) ||
                (kcb->kprobe_status == KPROBE_REENTER)) {
                if (post_kprobe_handler(args->regs))
                    ret = NOTIFY_STOP;
            } else {
                if (kprobe_handler(args->regs)) {
                    ret = NOTIFY_STOP;
                } else {
                    p = __get_cpu_var(current_kprobe);
                    if (p->break_handler &&
                        p->break_handler(p, args->regs))
                        ret = NOTIFY_STOP;
                }
            }
        }
    }

    return ret;
}

int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
    struct jprobe *jp = container_of(p, struct jprobe, kp);
    unsigned long addr;
    struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

    kcb->jprobe_saved_regs = *regs;
    kcb->jprobe_saved_r15 = regs->regs[15];
    addr = kcb->jprobe_saved_r15;

    /*
     * TBD: As Linus pointed out, gcc assumes that the callee
     * owns the argument space and could overwrite it, e.g.
     * tailcall optimization. So, to be absolutely safe
     * we also save and restore enough stack bytes to cover
     * the argument area.
     */
    memcpy(kcb->jprobes_stack, (kprobe_opcode_t *) addr,
           MIN_STACK_SIZE(addr));

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

    return 1;
}

void __kprobes jprobe_return(void)
{
    asm volatile ("trapa #0x3a\n\t" "jprobe_return_end:\n\t" "nop\n\t");
}

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
    struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
    unsigned long stack_addr = kcb->jprobe_saved_r15;
    u8 *addr = (u8 *)regs->pc;

    if ((addr >= (u8 *)jprobe_return) &&
        (addr <= (u8 *)jprobe_return_end)) {
        *regs = kcb->jprobe_saved_regs;

        memcpy((kprobe_opcode_t *)stack_addr, kcb->jprobes_stack,
               MIN_STACK_SIZE(stack_addr));

        kcb->kprobe_status = KPROBE_HIT_SS;
        preempt_enable_no_resched();
        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);
}