kprobes.c

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/*
 *  Kernel Probes (KProbes)
 *
 * 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 IBM Corp. 2002, 2006
 *
 * s390 port, used ppc64 as template. Mike Grundy <[email protected]>
 */

#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/preempt.h>
#include <linux/stop_machine.h>
#include <linux/kdebug.h>
#include <linux/uaccess.h>
#include <asm/cacheflush.h>
#include <asm/sections.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/hardirq.h>

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

struct kretprobe_blackpoint kretprobe_blacklist[] = { };

static int __kprobes is_prohibited_opcode(kprobe_opcode_t *insn)
{
    switch (insn[0] >> 8) {
    case 0x0c:  /* bassm */
    case 0x0b:  /* bsm   */
    case 0x83:  /* diag  */
    case 0x44:  /* ex    */
    case 0xac:  /* stnsm */
    case 0xad:  /* stosm */
        return -EINVAL;
    }
    switch (insn[0]) {
    case 0x0101:    /* pr    */
    case 0xb25a:    /* bsa   */
    case 0xb240:    /* bakr  */
    case 0xb258:    /* bsg   */
    case 0xb218:    /* pc    */
    case 0xb228:    /* pt    */
    case 0xb98d:    /* epsw  */
        return -EINVAL;
    }
    return 0;
}

static int __kprobes get_fixup_type(kprobe_opcode_t *insn)
{
    /* default fixup method */
    int fixup = FIXUP_PSW_NORMAL;

    switch (insn[0] >> 8) {
    case 0x05:  /* balr */
    case 0x0d:  /* basr */
        fixup = FIXUP_RETURN_REGISTER;
        /* if r2 = 0, no branch will be taken */
        if ((insn[0] & 0x0f) == 0)
            fixup |= FIXUP_BRANCH_NOT_TAKEN;
        break;
    case 0x06:  /* bctr */
    case 0x07:  /* bcr  */
        fixup = FIXUP_BRANCH_NOT_TAKEN;
        break;
    case 0x45:  /* bal  */
    case 0x4d:  /* bas  */
        fixup = FIXUP_RETURN_REGISTER;
        break;
    case 0x47:  /* bc   */
    case 0x46:  /* bct  */
    case 0x86:  /* bxh  */
    case 0x87:  /* bxle */
        fixup = FIXUP_BRANCH_NOT_TAKEN;
        break;
    case 0x82:  /* lpsw */
        fixup = FIXUP_NOT_REQUIRED;
        break;
    case 0xb2:  /* lpswe */
        if ((insn[0] & 0xff) == 0xb2)
            fixup = FIXUP_NOT_REQUIRED;
        break;
    case 0xa7:  /* bras */
        if ((insn[0] & 0x0f) == 0x05)
            fixup |= FIXUP_RETURN_REGISTER;
        break;
    case 0xc0:
        if ((insn[0] & 0x0f) == 0x00 || /* larl  */
            (insn[0] & 0x0f) == 0x05)   /* brasl */
        fixup |= FIXUP_RETURN_REGISTER;
        break;
    case 0xeb:
        if ((insn[2] & 0xff) == 0x44 || /* bxhg  */
            (insn[2] & 0xff) == 0x45)   /* bxleg */
            fixup = FIXUP_BRANCH_NOT_TAKEN;
        break;
    case 0xe3:  /* bctg */
        if ((insn[2] & 0xff) == 0x46)
            fixup = FIXUP_BRANCH_NOT_TAKEN;
        break;
    }
    return fixup;
}

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
    if ((unsigned long) p->addr & 0x01)
        return -EINVAL;

    /* Make sure the probe isn't going on a difficult instruction */
    if (is_prohibited_opcode(p->addr))
        return -EINVAL;

    p->opcode = *p->addr;
    memcpy(p->ainsn.insn, p->addr, ((p->opcode >> 14) + 3) & -2);

    return 0;
}

struct ins_replace_args {
    kprobe_opcode_t *ptr;
    kprobe_opcode_t opcode;
};

static int __kprobes swap_instruction(void *aref)
{
    struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
    unsigned long status = kcb->kprobe_status;
    struct ins_replace_args *args = aref;

    kcb->kprobe_status = KPROBE_SWAP_INST;
    probe_kernel_write(args->ptr, &args->opcode, sizeof(args->opcode));
    kcb->kprobe_status = status;
    return 0;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
    struct ins_replace_args args;

    args.ptr = p->addr;
    args.opcode = BREAKPOINT_INSTRUCTION;
    stop_machine(swap_instruction, &args, NULL);
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
    struct ins_replace_args args;

    args.ptr = p->addr;
    args.opcode = p->opcode;
    stop_machine(swap_instruction, &args, NULL);
}

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
}

static void __kprobes enable_singlestep(struct kprobe_ctlblk *kcb,
                    struct pt_regs *regs,
                    unsigned long ip)
{
    struct per_regs per_kprobe;

    /* Set up the PER control registers %cr9-%cr11 */
    per_kprobe.control = PER_EVENT_IFETCH;
    per_kprobe.start = ip;
    per_kprobe.end = ip;

    /* Save control regs and psw mask */
    __ctl_store(kcb->kprobe_saved_ctl, 9, 11);
    kcb->kprobe_saved_imask = regs->psw.mask &
        (PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT);

    /* Set PER control regs, turns on single step for the given address */
    __ctl_load(per_kprobe, 9, 11);
    regs->psw.mask |= PSW_MASK_PER;
    regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT);
    regs->psw.addr = ip | PSW_ADDR_AMODE;
}

static void __kprobes disable_singlestep(struct kprobe_ctlblk *kcb,
                     struct pt_regs *regs,
                     unsigned long ip)
{
    /* Restore control regs and psw mask, set new psw address */
    __ctl_load(kcb->kprobe_saved_ctl, 9, 11);
    regs->psw.mask &= ~PSW_MASK_PER;
    regs->psw.mask |= kcb->kprobe_saved_imask;
    regs->psw.addr = ip | PSW_ADDR_AMODE;
}

/*
 * Activate a kprobe by storing its pointer to current_kprobe. The
 * previous kprobe is stored in kcb->prev_kprobe. A stack of up to
 * two kprobes can be active, see KPROBE_REENTER.
 */
static void __kprobes push_kprobe(struct kprobe_ctlblk *kcb, struct kprobe *p)
{
    kcb->prev_kprobe.kp = __get_cpu_var(current_kprobe);
    kcb->prev_kprobe.status = kcb->kprobe_status;
    __get_cpu_var(current_kprobe) = p;
}

/*
 * Deactivate a kprobe by backing up to the previous state. If the
 * current state is KPROBE_REENTER prev_kprobe.kp will be non-NULL,
 * for any other state prev_kprobe.kp will be NULL.
 */
static void __kprobes pop_kprobe(struct kprobe_ctlblk *kcb)
{
    __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
    kcb->kprobe_status = kcb->prev_kprobe.status;
}

void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
                    struct pt_regs *regs)
{
    ri->ret_addr = (kprobe_opcode_t *) regs->gprs[14];

    /* Replace the return addr with trampoline addr */
    regs->gprs[14] = (unsigned long) &kretprobe_trampoline;
}

static void __kprobes kprobe_reenter_check(struct kprobe_ctlblk *kcb,
                       struct kprobe *p)
{
    switch (kcb->kprobe_status) {
    case KPROBE_HIT_SSDONE:
    case KPROBE_HIT_ACTIVE:
        kprobes_inc_nmissed_count(p);
        break;
    case KPROBE_HIT_SS:
    case KPROBE_REENTER:
    default:
        /*
         * A kprobe on the code path to single step an instruction
         * is a BUG. The code path resides in the .kprobes.text
         * section and is executed with interrupts disabled.
         */
        printk(KERN_EMERG "Invalid kprobe detected at %p.\n", p->addr);
        dump_kprobe(p);
        BUG();
    }
}

static int __kprobes kprobe_handler(struct pt_regs *regs)
{
    struct kprobe_ctlblk *kcb;
    struct kprobe *p;

    /*
     * We want to disable preemption for the entire duration of kprobe
     * processing. That includes the calls to the pre/post handlers
     * and single stepping the kprobe instruction.
     */
    preempt_disable();
    kcb = get_kprobe_ctlblk();
    p = get_kprobe((void *)((regs->psw.addr & PSW_ADDR_INSN) - 2));

    if (p) {
        if (kprobe_running()) {
            /*
             * We have hit a kprobe while another is still
             * active. This can happen in the pre and post
             * handler. Single step the instruction of the
             * new probe but do not call any handler function
             * of this secondary kprobe.
             * push_kprobe and pop_kprobe saves and restores
             * the currently active kprobe.
             */
            kprobe_reenter_check(kcb, p);
            push_kprobe(kcb, p);
            kcb->kprobe_status = KPROBE_REENTER;
        } else {
            /*
             * If we have no pre-handler or it returned 0, we
             * continue with single stepping. If we have a
             * pre-handler and it returned non-zero, it prepped
             * for calling the break_handler below on re-entry
             * for jprobe processing, so get out doing nothing
             * more here.
             */
            push_kprobe(kcb, p);
            kcb->kprobe_status = KPROBE_HIT_ACTIVE;
            if (p->pre_handler && p->pre_handler(p, regs))
                return 1;
            kcb->kprobe_status = KPROBE_HIT_SS;
        }
        enable_singlestep(kcb, regs, (unsigned long) p->ainsn.insn);
        return 1;
    } else if (kprobe_running()) {
        p = __get_cpu_var(current_kprobe);
        if (p->break_handler && p->break_handler(p, regs)) {
            /*
             * Continuation after the jprobe completed and
             * caused the jprobe_return trap. The jprobe
             * break_handler "returns" to the original
             * function that still has the kprobe breakpoint
             * installed. We continue with single stepping.
             */
            kcb->kprobe_status = KPROBE_HIT_SS;
            enable_singlestep(kcb, regs,
                      (unsigned long) p->ainsn.insn);
            return 1;
        } /* else:
           * No kprobe at this address and the current kprobe
           * has no break handler (no jprobe!). The kernel just
           * exploded, let the standard trap handler pick up the
           * pieces.
           */
    } /* else:
       * No kprobe at this address and no active kprobe. The trap has
       * not been caused by a kprobe breakpoint. The race of breakpoint
       * vs. kprobe remove does not exist because on s390 as we use
       * stop_machine to arm/disarm the breakpoints.
       */
    preempt_enable_no_resched();
    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(".global kretprobe_trampoline\n"
             "kretprobe_trampoline: bcr 0,0\n");
}

/*
 * 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;
    struct hlist_head *head, empty_rp;
    struct hlist_node *node, *tmp;
    unsigned long flags, orig_ret_address;
    unsigned long trampoline_address;
    kprobe_opcode_t *correct_ret_addr;

    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
     */
    ri = NULL;
    orig_ret_address = 0;
    correct_ret_addr = NULL;
    trampoline_address = (unsigned long) &kretprobe_trampoline;
    hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
        if (ri->task != current)
            /* another task is sharing our hash bucket */
            continue;

        orig_ret_address = (unsigned long) ri->ret_addr;

        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);

    correct_ret_addr = ri->ret_addr;
    hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
        if (ri->task != current)
            /* another task is sharing our hash bucket */
            continue;

        orig_ret_address = (unsigned long) ri->ret_addr;

        if (ri->rp && ri->rp->handler) {
            ri->ret_addr = correct_ret_addr;
            ri->rp->handler(ri, regs);
        }

        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;
    }

    regs->psw.addr = orig_ret_address | PSW_ADDR_AMODE;

    pop_kprobe(get_kprobe_ctlblk());
    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;
}

/*
 * 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)
{
    struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
    unsigned long ip = regs->psw.addr & PSW_ADDR_INSN;
    int fixup = get_fixup_type(p->ainsn.insn);

    if (fixup & FIXUP_PSW_NORMAL)
        ip += (unsigned long) p->addr - (unsigned long) p->ainsn.insn;

    if (fixup & FIXUP_BRANCH_NOT_TAKEN) {
        int ilen = ((p->ainsn.insn[0] >> 14) + 3) & -2;
        if (ip - (unsigned long) p->ainsn.insn == ilen)
            ip = (unsigned long) p->addr + ilen;
    }

    if (fixup & FIXUP_RETURN_REGISTER) {
        int reg = (p->ainsn.insn[0] & 0xf0) >> 4;
        regs->gprs[reg] += (unsigned long) p->addr -
                   (unsigned long) p->ainsn.insn;
    }

    disable_singlestep(kcb, regs, ip);
}

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

    if (!p)
        return 0;

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

    resume_execution(p, regs);
    pop_kprobe(kcb);
    preempt_enable_no_resched();

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

    return 1;
}

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

    switch(kcb->kprobe_status) {
    case KPROBE_SWAP_INST:
        /* We are here because the instruction replacement failed */
        return 0;
    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 and the nip points back to the probe address
         * and allow the page fault handler to continue as a
         * normal page fault.
         */
        disable_singlestep(kcb, regs, (unsigned long) p->addr);
        pop_kprobe(kcb);
        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 accouting
         * these specific fault cases.
         */
        kprobes_inc_nmissed_count(p);

        /*
         * 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 (p->fault_handler && p->fault_handler(p, regs, trapnr))
            return 1;

        /*
         * In case the user-specified fault handler returned
         * zero, try to fix up.
         */
        entry = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
        if (entry) {
            regs->psw.addr = extable_fixup(entry) | PSW_ADDR_AMODE;
            return 1;
        }

        /*
         * fixup_exception() could not handle it,
         * Let do_page_fault() fix it.
         */
        break;
    default:
        break;
    }
    return 0;
}

int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
    int ret;

    if (regs->psw.mask & (PSW_MASK_IO | PSW_MASK_EXT))
        local_irq_disable();
    ret = kprobe_trap_handler(regs, trapnr);
    if (regs->psw.mask & (PSW_MASK_IO | PSW_MASK_EXT))
        local_irq_restore(regs->psw.mask & ~PSW_MASK_PER);
    return ret;
}

/*
 * 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;
    struct pt_regs *regs = args->regs;
    int ret = NOTIFY_DONE;

    if (regs->psw.mask & (PSW_MASK_IO | PSW_MASK_EXT))
        local_irq_disable();

    switch (val) {
    case DIE_BPT:
        if (kprobe_handler(regs))
            ret = NOTIFY_STOP;
        break;
    case DIE_SSTEP:
        if (post_kprobe_handler(regs))
            ret = NOTIFY_STOP;
        break;
    case DIE_TRAP:
        if (!preemptible() && kprobe_running() &&
            kprobe_trap_handler(regs, args->trapnr))
            ret = NOTIFY_STOP;
        break;
    default:
        break;
    }

    if (regs->psw.mask & (PSW_MASK_IO | PSW_MASK_EXT))
        local_irq_restore(regs->psw.mask & ~PSW_MASK_PER);

    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();
    unsigned long stack;

    memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));

    /* setup return addr to the jprobe handler routine */
    regs->psw.addr = (unsigned long) jp->entry | PSW_ADDR_AMODE;
    regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT);

    /* r15 is the stack pointer */
    stack = (unsigned long) regs->gprs[15];

    memcpy(kcb->jprobes_stack, (void *) stack, MIN_STACK_SIZE(stack));
    return 1;
}

void __kprobes jprobe_return(void)
{
    asm volatile(".word 0x0002");
}

static void __used __kprobes jprobe_return_end(void)
{
    asm volatile("bcr 0,0");
}

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

    stack = (unsigned long) kcb->jprobe_saved_regs.gprs[15];

    /* Put the regs back */
    memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
    /* put the stack back */
    memcpy((void *) stack, kcb->jprobes_stack, MIN_STACK_SIZE(stack));
    preempt_enable_no_resched();
    return 1;
}

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

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

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