/*
 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/types.h>
#include <linux/kprobes.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/kdebug.h>
#include <linux/sched.h>
#include <linux/uaccess.h>
#include <asm/cacheflush.h>
#include <asm/current.h>
#include <asm/disasm.h>

#define MIN_STACK_SIZE(addr)    min((unsigned long)MAX_STACK_SIZE, \
                (unsigned long)current_thread_info() + THREAD_SIZE - (addr))

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

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
        /* Attempt to probe at unaligned address */
        if ((unsigned long)p->addr & 0x01)
                return -EINVAL;

        /* Address should not be in exception handling code */

        p->ainsn.is_short = is_short_instr((unsigned long)p->addr);
        p->opcode = *p->addr;

        return 0;
}

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

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
        arch_disarm_kprobe(p);

        /* Can we remove the kprobe in the middle of kprobe handling? */
        if (p->ainsn.t1_addr) {
                *(p->ainsn.t1_addr) = p->ainsn.t1_opcode;

                flush_icache_range((unsigned long)p->ainsn.t1_addr,
                                   (unsigned long)p->ainsn.t1_addr +
                                   sizeof(kprobe_opcode_t));

                p->ainsn.t1_addr = NULL;
        }

        if (p->ainsn.t2_addr) {
                *(p->ainsn.t2_addr) = p->ainsn.t2_opcode;

                flush_icache_range((unsigned long)p->ainsn.t2_addr,
                                   (unsigned long)p->ainsn.t2_addr +
                                   sizeof(kprobe_opcode_t));

                p->ainsn.t2_addr = NULL;
        }
}

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)
{
        __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
        kcb->kprobe_status = kcb->prev_kprobe.status;
}

static inline void __kprobes set_current_kprobe(struct kprobe *p)
{
        __this_cpu_write(current_kprobe, p);
}

static void __kprobes resume_execution(struct kprobe *p, unsigned long addr,
                                       struct pt_regs *regs)
{
        /* Remove the trap instructions inserted for single step and
         * restore the original instructions
         */
        if (p->ainsn.t1_addr) {
                *(p->ainsn.t1_addr) = p->ainsn.t1_opcode;

                flush_icache_range((unsigned long)p->ainsn.t1_addr,
                                   (unsigned long)p->ainsn.t1_addr +
                                   sizeof(kprobe_opcode_t));

                p->ainsn.t1_addr = NULL;
        }

        if (p->ainsn.t2_addr) {
                *(p->ainsn.t2_addr) = p->ainsn.t2_opcode;

                flush_icache_range((unsigned long)p->ainsn.t2_addr,
                                   (unsigned long)p->ainsn.t2_addr +
                                   sizeof(kprobe_opcode_t));

                p->ainsn.t2_addr = NULL;
        }

        return;
}

static void __kprobes setup_singlestep(struct kprobe *p, struct pt_regs *regs)
{
        unsigned long next_pc;
        unsigned long tgt_if_br = 0;
        int is_branch;
        unsigned long bta;

        /* Copy the opcode back to the kprobe location and execute the
         * instruction. Because of this we will not be able to get into the
         * same kprobe until this kprobe is done
         */
        *(p->addr) = p->opcode;

        flush_icache_range((unsigned long)p->addr,
                           (unsigned long)p->addr + sizeof(kprobe_opcode_t));

        /* Now we insert the trap at the next location after this instruction to
         * single step. If it is a branch we insert the trap at possible branch
         * targets
         */

        bta = regs->bta;

        if (regs->status32 & 0x40) {
                /* We are in a delay slot with the branch taken */

                next_pc = bta & ~0x01;

                if (!p->ainsn.is_short) {
                        if (bta & 0x01)
                                regs->blink += 2;
                        else {
                                /* Branch not taken */
                                next_pc += 2;

                                /* next pc is taken from bta after executing the
                                 * delay slot instruction
                                 */
                                regs->bta += 2;
                        }
                }

                is_branch = 0;
        } else
                is_branch =
                    disasm_next_pc((unsigned long)p->addr, regs,
                        (struct callee_regs *) current->thread.callee_reg,
                        &next_pc, &tgt_if_br);

        p->ainsn.t1_addr = (kprobe_opcode_t *) next_pc;
        p->ainsn.t1_opcode = *(p->ainsn.t1_addr);
        *(p->ainsn.t1_addr) = TRAP_S_2_INSTRUCTION;

        flush_icache_range((unsigned long)p->ainsn.t1_addr,
                           (unsigned long)p->ainsn.t1_addr +
                           sizeof(kprobe_opcode_t));

        if (is_branch) {
                p->ainsn.t2_addr = (kprobe_opcode_t *) tgt_if_br;
                p->ainsn.t2_opcode = *(p->ainsn.t2_addr);
                *(p->ainsn.t2_addr) = TRAP_S_2_INSTRUCTION;

                flush_icache_range((unsigned long)p->ainsn.t2_addr,
                                   (unsigned long)p->ainsn.t2_addr +
                                   sizeof(kprobe_opcode_t));
        }
}

int __kprobes arc_kprobe_handler(unsigned long addr, struct pt_regs *regs)
{
        struct kprobe *p;
        struct kprobe_ctlblk *kcb;

        preempt_disable();

        kcb = get_kprobe_ctlblk();
        p = get_kprobe((unsigned long *)addr);

        if (p) {
                /*
                 * We have reentered the kprobe_handler, since another kprobe
                 * was hit while within the handler, we save the original
                 * kprobes and single step on the instruction of the new probe
                 * without calling any user handlers to avoid recursive
                 * kprobes.
                 */
                if (kprobe_running()) {
                        save_previous_kprobe(kcb);
                        set_current_kprobe(p);
                        kprobes_inc_nmissed_count(p);
                        setup_singlestep(p, regs);
                        kcb->kprobe_status = KPROBE_REENTER;
                        return 1;
                }

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

                /* If we have no pre-handler or it returned 0, we continue with
                 * normal processing. If we have a pre-handler and it returned
                 * non-zero - which means user handler setup registers to exit
                 * to another instruction, we must skip the single stepping.
                 */
                if (!p->pre_handler || !p->pre_handler(p, regs)) {
                        setup_singlestep(p, regs);
                        kcb->kprobe_status = KPROBE_HIT_SS;
                } else {
                        reset_current_kprobe();
                        preempt_enable_no_resched();
                }

                return 1;
        }

        /* no_kprobe: */
        preempt_enable_no_resched();
        return 0;
}

static int __kprobes arc_post_kprobe_handler(unsigned long addr,
                                         struct pt_regs *regs)
{
        struct kprobe *cur = kprobe_running();
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

        if (!cur)
                return 0;

        resume_execution(cur, addr, regs);

        /* Rearm the kprobe */
        arch_arm_kprobe(cur);

        /*
         * When we return from trap instruction we go to the next instruction
         * We restored the actual instruction in resume_exectuiont and we to
         * return to the same address and execute it
         */
        regs->ret = addr;

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

        if (kcb->kprobe_status == KPROBE_REENTER) {
                restore_previous_kprobe(kcb);
                goto out;
        }

        reset_current_kprobe();

out:
        preempt_enable_no_resched();
        return 1;
}

/*
 * Fault can be for the instruction being single stepped or for the
 * pre/post handlers in the module.
 * This is applicable for applications like user probes, where we have the
 * probe in user space and the handlers in the kernel
 */

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

        switch (kcb->kprobe_status) {
        case KPROBE_HIT_SS:
        case KPROBE_REENTER:
                /*
                 * We are here because the instruction being single stepped
                 * caused the fault. We reset the current kprobe and allow the
                 * exception handler as if it is regular exception. In our
                 * case it doesn't matter because the system will be halted
                 */
                resume_execution(cur, (unsigned long)cur->addr, regs);

                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 are here because the instructions in the pre/post handler
                 * caused the fault.
                 */

                /* 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 (fixup_exception(regs))
                        return 1;

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

        default:
                break;
        }
        return 0;
}

int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
                                       unsigned long val, void *data)
{
        struct die_args *args = data;
        unsigned long addr = args->err;
        int ret = NOTIFY_DONE;

        switch (val) {
        case DIE_IERR:
                if (arc_kprobe_handler(addr, args->regs))
                        return NOTIFY_STOP;
                break;

        case DIE_TRAP:
                if (arc_post_kprobe_handler(addr, args->regs))
                        return NOTIFY_STOP;
                break;

        default:
                break;
        }

        return ret;
}

static void __used kretprobe_trampoline_holder(void)
{
        __asm__ __volatile__(".global kretprobe_trampoline\n"
                             "kretprobe_trampoline:\n" "nop\n");
}

void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
                                      struct pt_regs *regs)
{

        ri->ret_addr = (kprobe_opcode_t *) regs->blink;

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

static int __kprobes trampoline_probe_handler(struct kprobe *p,
                                              struct pt_regs *regs)
{
        struct kretprobe_instance *ri = NULL;
        struct hlist_head *head, empty_rp;
        struct hlist_node *tmp;
        unsigned long flags, orig_ret_address = 0;
        unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;

        INIT_HLIST_HEAD(&empty_rp);
        kretprobe_hash_lock(current, &head, &flags);

        /*
         * It is possible to have multiple instances associated with a given
         * task either because an multiple functions in the call path
         * have a return probe installed on them, and/or more than one return
         * return probe was registered for a target function.
         *
         * We can handle this because:
         *     - instances are always inserted at the head of the list
         *     - when multiple return probes are registered for the same
         *       function, the first instance's ret_addr will point to the
         *       real return address, and all the rest will point to
         *       kretprobe_trampoline
         */
        hlist_for_each_entry_safe(ri, tmp, head, hlist) {
                if (ri->task != current)
                        /* another task is sharing our hash bucket */
                        continue;

                if (ri->rp && ri->rp->handler)
                        ri->rp->handler(ri, regs);

                orig_ret_address = (unsigned long)ri->ret_addr;
                recycle_rp_inst(ri, &empty_rp);

                if (orig_ret_address != trampoline_address) {
                        /*
                         * This is the real return address. Any other
                         * instances associated with this task are for
                         * other calls deeper on the call stack
                         */
                        break;
                }
        }

        kretprobe_assert(ri, orig_ret_address, trampoline_address);
        regs->ret = orig_ret_address;

        kretprobe_hash_unlock(current, &flags);

        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 the kprobe handler
         * that we don't want the post_handler to run
         */
        return 1;
}

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

int __init arch_init_kprobes(void)
{
        /* Registering the trampoline code for the kret probe */
        return register_kprobe(&trampoline_p);
}

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

        return 0;
}

void trap_is_kprobe(unsigned long address, struct pt_regs *regs)
{
        notify_die(DIE_TRAP, "kprobe_trap", regs, address, 0, SIGTRAP);
}