Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial

[GitHub/moto-9609/android_kernel_motorola_exynos9610.git] / arch / s390 / kernel / kprobes.c

/*
 *  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 <grundym@us.ibm.com>
 */

#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 <linux/module.h>
#include <linux/slab.h>
#include <linux/hardirq.h>
#include <asm/cacheflush.h>
#include <asm/sections.h>
#include <asm/dis.h>

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

struct kretprobe_blackpoint kretprobe_blacklist[] = { };

DEFINE_INSN_CACHE_OPS(dmainsn);

static void *alloc_dmainsn_page(void)
{
        return (void *)__get_free_page(GFP_KERNEL | GFP_DMA);
}

static void free_dmainsn_page(void *page)
{
        free_page((unsigned long)page);
}

struct kprobe_insn_cache kprobe_dmainsn_slots = {
        .mutex = __MUTEX_INITIALIZER(kprobe_dmainsn_slots.mutex),
        .alloc = alloc_dmainsn_page,
        .free = free_dmainsn_page,
        .pages = LIST_HEAD_INIT(kprobe_dmainsn_slots.pages),
        .insn_size = MAX_INSN_SIZE,
};

static int __kprobes is_prohibited_opcode(kprobe_opcode_t *insn)
{
        if (!is_known_insn((unsigned char *)insn))
                return -EINVAL;
        switch (insn[0] >> 8) {
        case 0x0c:      /* bassm */
        case 0x0b:      /* bsm   */
        case 0x83:      /* diag  */
        case 0x44:      /* ex    */
        case 0xac:      /* stnsm */
        case 0xad:      /* stosm */
                return -EINVAL;
        case 0xc6:
                switch (insn[0] & 0x0f) {
                case 0x00: /* exrl   */
                        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) == 0x05)   /* brasl */
                        fixup |= FIXUP_RETURN_REGISTER;
                break;
        case 0xeb:
                switch (insn[2] & 0xff) {
                case 0x44: /* bxhg  */
                case 0x45: /* bxleg */
                        fixup = FIXUP_BRANCH_NOT_TAKEN;
                        break;
                }
                break;
        case 0xe3:      /* bctg */
                if ((insn[2] & 0xff) == 0x46)
                        fixup = FIXUP_BRANCH_NOT_TAKEN;
                break;
        case 0xec:
                switch (insn[2] & 0xff) {
                case 0xe5: /* clgrb */
                case 0xe6: /* cgrb  */
                case 0xf6: /* crb   */
                case 0xf7: /* clrb  */
                case 0xfc: /* cgib  */
                case 0xfd: /* cglib */
                case 0xfe: /* cib   */
                case 0xff: /* clib  */
                        fixup = FIXUP_BRANCH_NOT_TAKEN;
                        break;
                }
                break;
        }
        return fixup;
}

static int __kprobes is_insn_relative_long(kprobe_opcode_t *insn)
{
        /* Check if we have a RIL-b or RIL-c format instruction which
         * we need to modify in order to avoid instruction emulation. */
        switch (insn[0] >> 8) {
        case 0xc0:
                if ((insn[0] & 0x0f) == 0x00) /* larl */
                        return true;
                break;
        case 0xc4:
                switch (insn[0] & 0x0f) {
                case 0x02: /* llhrl  */
                case 0x04: /* lghrl  */
                case 0x05: /* lhrl   */
                case 0x06: /* llghrl */
                case 0x07: /* sthrl  */
                case 0x08: /* lgrl   */
                case 0x0b: /* stgrl  */
                case 0x0c: /* lgfrl  */
                case 0x0d: /* lrl    */
                case 0x0e: /* llgfrl */
                case 0x0f: /* strl   */
                        return true;
                }
                break;
        case 0xc6:
                switch (insn[0] & 0x0f) {
                case 0x02: /* pfdrl  */
                case 0x04: /* cghrl  */
                case 0x05: /* chrl   */
                case 0x06: /* clghrl */
                case 0x07: /* clhrl  */
                case 0x08: /* cgrl   */
                case 0x0a: /* clgrl  */
                case 0x0c: /* cgfrl  */
                case 0x0d: /* crl    */
                case 0x0e: /* clgfrl */
                case 0x0f: /* clrl   */
                        return true;
                }
                break;
        }
        return false;
}

static void __kprobes copy_instruction(struct kprobe *p)
{
        s64 disp, new_disp;
        u64 addr, new_addr;

        memcpy(p->ainsn.insn, p->addr, insn_length(p->opcode >> 8));
        if (!is_insn_relative_long(p->ainsn.insn))
                return;
        /*
         * For pc-relative instructions in RIL-b or RIL-c format patch the
         * RI2 displacement field. We have already made sure that the insn
         * slot for the patched instruction is within the same 2GB area
         * as the original instruction (either kernel image or module area).
         * Therefore the new displacement will always fit.
         */
        disp = *(s32 *)&p->ainsn.insn[1];
        addr = (u64)(unsigned long)p->addr;
        new_addr = (u64)(unsigned long)p->ainsn.insn;
        new_disp = ((addr + (disp * 2)) - new_addr) / 2;
        *(s32 *)&p->ainsn.insn[1] = new_disp;
}

static inline int is_kernel_addr(void *addr)
{
        return addr < (void *)_end;
}

static inline int is_module_addr(void *addr)
{
#ifdef CONFIG_64BIT
        BUILD_BUG_ON(MODULES_LEN > (1UL << 31));
        if (addr < (void *)MODULES_VADDR)
                return 0;
        if (addr > (void *)MODULES_END)
                return 0;
#endif
        return 1;
}

static int __kprobes s390_get_insn_slot(struct kprobe *p)
{
        /*
         * Get an insn slot that is within the same 2GB area like the original
         * instruction. That way instructions with a 32bit signed displacement
         * field can be patched and executed within the insn slot.
         */
        p->ainsn.insn = NULL;
        if (is_kernel_addr(p->addr))
                p->ainsn.insn = get_dmainsn_slot();
        else if (is_module_addr(p->addr))
                p->ainsn.insn = get_insn_slot();
        return p->ainsn.insn ? 0 : -ENOMEM;
}

static void __kprobes s390_free_insn_slot(struct kprobe *p)
{
        if (!p->ainsn.insn)
                return;
        if (is_kernel_addr(p->addr))
                free_dmainsn_slot(p->ainsn.insn, 0);
        else
                free_insn_slot(p->ainsn.insn, 0);
        p->ainsn.insn = NULL;
}

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;
        if (s390_get_insn_slot(p))
                return -ENOMEM;
        p->opcode = *p->addr;
        copy_instruction(p);
        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)
{
        s390_free_insn_slot(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 *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, 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, 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, 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 = insn_length(p->ainsn.insn[0] >> 8);
                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 accounting
                 * 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;
}