Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

[cris-mirror.git] / arch / s390 / kernel / kprobes.c

// SPDX-License-Identifier: GPL-2.0+
/*
 *  Kernel Probes (KProbes)
 *
 * 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/extable.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/hardirq.h>
#include <linux/ftrace.h>
#include <asm/set_memory.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)
{
        void *page;

        page = (void *) __get_free_page(GFP_KERNEL | GFP_DMA);
        if (page)
                set_memory_x((unsigned long) page, 1);
        return page;
}

static void free_dmainsn_page(void *page)
{
        set_memory_nx((unsigned long) page, 1);
        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 void copy_instruction(struct kprobe *p)
{
        unsigned long ip = (unsigned long) p->addr;
        s64 disp, new_disp;
        u64 addr, new_addr;

        if (ftrace_location(ip) == ip) {
                /*
                 * If kprobes patches the instruction that is morphed by
                 * ftrace make sure that kprobes always sees the branch
                 * "jg .+24" that skips the mcount block or the "brcl 0,0"
                 * in case of hotpatch.
                 */
                ftrace_generate_nop_insn((struct ftrace_insn *)p->ainsn.insn);
                p->ainsn.is_ftrace_insn = 1;
        } else
                memcpy(p->ainsn.insn, p->addr, insn_length(*p->addr >> 8));
        p->opcode = p->ainsn.insn[0];
        if (!probe_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;
}
NOKPROBE_SYMBOL(copy_instruction);

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

static int 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;
}
NOKPROBE_SYMBOL(s390_get_insn_slot);

static void 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;
}
NOKPROBE_SYMBOL(s390_free_insn_slot);

int 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 (probe_is_prohibited_opcode(p->addr))
                return -EINVAL;
        if (s390_get_insn_slot(p))
                return -ENOMEM;
        copy_instruction(p);
        return 0;
}
NOKPROBE_SYMBOL(arch_prepare_kprobe);

int arch_check_ftrace_location(struct kprobe *p)
{
        return 0;
}

struct swap_insn_args {
        struct kprobe *p;
        unsigned int arm_kprobe : 1;
};

static int swap_instruction(void *data)
{
        struct swap_insn_args *args = data;
        struct ftrace_insn new_insn, *insn;
        struct kprobe *p = args->p;
        size_t len;

        new_insn.opc = args->arm_kprobe ? BREAKPOINT_INSTRUCTION : p->opcode;
        len = sizeof(new_insn.opc);
        if (!p->ainsn.is_ftrace_insn)
                goto skip_ftrace;
        len = sizeof(new_insn);
        insn = (struct ftrace_insn *) p->addr;
        if (args->arm_kprobe) {
                if (is_ftrace_nop(insn))
                        new_insn.disp = KPROBE_ON_FTRACE_NOP;
                else
                        new_insn.disp = KPROBE_ON_FTRACE_CALL;
        } else {
                ftrace_generate_call_insn(&new_insn, (unsigned long)p->addr);
                if (insn->disp == KPROBE_ON_FTRACE_NOP)
                        ftrace_generate_nop_insn(&new_insn);
        }
skip_ftrace:
        s390_kernel_write(p->addr, &new_insn, len);
        return 0;
}
NOKPROBE_SYMBOL(swap_instruction);

void arch_arm_kprobe(struct kprobe *p)
{
        struct swap_insn_args args = {.p = p, .arm_kprobe = 1};

        stop_machine_cpuslocked(swap_instruction, &args, NULL);
}
NOKPROBE_SYMBOL(arch_arm_kprobe);

void arch_disarm_kprobe(struct kprobe *p)
{
        struct swap_insn_args args = {.p = p, .arm_kprobe = 0};

        stop_machine_cpuslocked(swap_instruction, &args, NULL);
}
NOKPROBE_SYMBOL(arch_disarm_kprobe);

void arch_remove_kprobe(struct kprobe *p)
{
        s390_free_insn_slot(p);
}
NOKPROBE_SYMBOL(arch_remove_kprobe);

static void 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;
}
NOKPROBE_SYMBOL(enable_singlestep);

static void 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;
}
NOKPROBE_SYMBOL(disable_singlestep);

/*
 * 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 push_kprobe(struct kprobe_ctlblk *kcb, struct kprobe *p)
{
        kcb->prev_kprobe.kp = __this_cpu_read(current_kprobe);
        kcb->prev_kprobe.status = kcb->kprobe_status;
        __this_cpu_write(current_kprobe, p);
}
NOKPROBE_SYMBOL(push_kprobe);

/*
 * 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 pop_kprobe(struct kprobe_ctlblk *kcb)
{
        __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
        kcb->kprobe_status = kcb->prev_kprobe.status;
}
NOKPROBE_SYMBOL(pop_kprobe);

void 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;
}
NOKPROBE_SYMBOL(arch_prepare_kretprobe);

static void 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.
                 */
                pr_err("Invalid kprobe detected.\n");
                dump_kprobe(p);
                BUG();
        }
}
NOKPROBE_SYMBOL(kprobe_reenter_check);

static int 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 - 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 = __this_cpu_read(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;
}
NOKPROBE_SYMBOL(kprobe_handler);

/*
 * 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 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;

        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;
}
NOKPROBE_SYMBOL(trampoline_probe_handler);

/*
 * 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 resume_execution(struct kprobe *p, struct pt_regs *regs)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        unsigned long ip = regs->psw.addr;
        int fixup = probe_get_fixup_type(p->ainsn.insn);

        /* Check if the kprobes location is an enabled ftrace caller */
        if (p->ainsn.is_ftrace_insn) {
                struct ftrace_insn *insn = (struct ftrace_insn *) p->addr;
                struct ftrace_insn call_insn;

                ftrace_generate_call_insn(&call_insn, (unsigned long) p->addr);
                /*
                 * A kprobe on an enabled ftrace call site actually single
                 * stepped an unconditional branch (ftrace nop equivalent).
                 * Now we need to fixup things and pretend that a brasl r0,...
                 * was executed instead.
                 */
                if (insn->disp == KPROBE_ON_FTRACE_CALL) {
                        ip += call_insn.disp * 2 - MCOUNT_INSN_SIZE;
                        regs->gprs[0] = (unsigned long)p->addr + sizeof(*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);
}
NOKPROBE_SYMBOL(resume_execution);

static int 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;
}
NOKPROBE_SYMBOL(post_kprobe_handler);

static int 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_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);
                if (entry) {
                        regs->psw.addr = extable_fixup(entry);
                        return 1;
                }

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

int 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;
}
NOKPROBE_SYMBOL(kprobe_fault_handler);

/*
 * Wrapper routine to for handling exceptions.
 */
int 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;
}
NOKPROBE_SYMBOL(kprobe_exceptions_notify);

int 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;
        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));

        /*
         * jprobes use jprobe_return() which skips the normal return
         * path of the function, and this messes up the accounting of the
         * function graph tracer to get messed up.
         *
         * Pause function graph tracing while performing the jprobe function.
         */
        pause_graph_tracing();
        return 1;
}
NOKPROBE_SYMBOL(setjmp_pre_handler);

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

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

        /* It's OK to start function graph tracing again */
        unpause_graph_tracing();

        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;
}
NOKPROBE_SYMBOL(longjmp_break_handler);

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