/*
 * arch/tile/kernel/kprobes.c
 * Kprobes on TILE-Gx
 *
 * Some portions copied from the MIPS version.
 *
 * Copyright (C) IBM Corporation, 2002, 2004
 * Copyright 2006 Sony Corp.
 * Copyright 2010 Cavium Networks
 *
 * Copyright 2012 Tilera Corporation. All Rights Reserved.
 *
 *   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, version 2.
 *
 *   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, GOOD TITLE or
 *   NON INFRINGEMENT.  See the GNU General Public License for
 *   more details.
 */

#include <linux/kprobes.h>
#include <linux/kdebug.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <asm/cacheflush.h>

#include <arch/opcode.h>

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

tile_bundle_bits breakpoint_insn = TILEGX_BPT_BUNDLE;
tile_bundle_bits breakpoint2_insn = TILEGX_BPT_BUNDLE | DIE_SSTEPBP;

/*
 * Check whether instruction is branch or jump, or if executing it
 * has different results depending on where it is executed (e.g. lnk).
 */
static int __kprobes insn_has_control(kprobe_opcode_t insn)
{
        if (get_Mode(insn) != 0) {   /* Y-format bundle */
                if (get_Opcode_Y1(insn) != RRR_1_OPCODE_Y1 ||
                    get_RRROpcodeExtension_Y1(insn) != UNARY_RRR_1_OPCODE_Y1)
                        return 0;

                switch (get_UnaryOpcodeExtension_Y1(insn)) {
                case JALRP_UNARY_OPCODE_Y1:
                case JALR_UNARY_OPCODE_Y1:
                case JRP_UNARY_OPCODE_Y1:
                case JR_UNARY_OPCODE_Y1:
                case LNK_UNARY_OPCODE_Y1:
                        return 1;
                default:
                        return 0;
                }
        }

        switch (get_Opcode_X1(insn)) {
        case BRANCH_OPCODE_X1:  /* branch instructions */
        case JUMP_OPCODE_X1:    /* jump instructions: j and jal */
                return 1;

        case RRR_0_OPCODE_X1:   /* other jump instructions */
                if (get_RRROpcodeExtension_X1(insn) != UNARY_RRR_0_OPCODE_X1)
                        return 0;
                switch (get_UnaryOpcodeExtension_X1(insn)) {
                case JALRP_UNARY_OPCODE_X1:
                case JALR_UNARY_OPCODE_X1:
                case JRP_UNARY_OPCODE_X1:
                case JR_UNARY_OPCODE_X1:
                case LNK_UNARY_OPCODE_X1:
                        return 1;
                default:
                        return 0;
                }
        default:
                return 0;
        }
}

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
        unsigned long addr = (unsigned long)p->addr;

        if (addr & (sizeof(kprobe_opcode_t) - 1))
                return -EINVAL;

        if (insn_has_control(*p->addr)) {
                pr_notice("Kprobes for control instructions are not supported\n");
                return -EINVAL;
        }

        /* insn: must be on special executable page on tile. */
        p->ainsn.insn = get_insn_slot();
        if (!p->ainsn.insn)
                return -ENOMEM;

        /*
         * In the kprobe->ainsn.insn[] array we store the original
         * instruction at index zero and a break trap instruction at
         * index one.
         */
        memcpy(&p->ainsn.insn[0], p->addr, sizeof(kprobe_opcode_t));
        p->ainsn.insn[1] = breakpoint2_insn;
        p->opcode = *p->addr;

        return 0;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
        unsigned long addr_wr;

        /* Operate on writable kernel text mapping. */
        addr_wr = (unsigned long)p->addr - MEM_SV_START + PAGE_OFFSET;

        if (probe_kernel_write((void *)addr_wr, &breakpoint_insn,
                sizeof(breakpoint_insn)))
                pr_err("%s: failed to enable kprobe\n", __func__);

        smp_wmb();
        flush_insn_slot(p);
}

void __kprobes arch_disarm_kprobe(struct kprobe *kp)
{
        unsigned long addr_wr;

        /* Operate on writable kernel text mapping. */
        addr_wr = (unsigned long)kp->addr - MEM_SV_START + PAGE_OFFSET;

        if (probe_kernel_write((void *)addr_wr, &kp->opcode,
                sizeof(kp->opcode)))
                pr_err("%s: failed to enable kprobe\n", __func__);

        smp_wmb();
        flush_insn_slot(kp);
}

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
        if (p->ainsn.insn) {
                free_insn_slot(p->ainsn.insn, 0);
                p->ainsn.insn = NULL;
        }
}

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

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;
        kcb->kprobe_saved_pc = kcb->prev_kprobe.saved_pc;
}

static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
                        struct kprobe_ctlblk *kcb)
{
        __this_cpu_write(current_kprobe, p);
        kcb->kprobe_saved_pc = regs->pc;
}

static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
        /* Single step inline if the instruction is a break. */
        if (p->opcode == breakpoint_insn ||
            p->opcode == breakpoint2_insn)
                regs->pc = (unsigned long)p->addr;
        else
                regs->pc = (unsigned long)&p->ainsn.insn[0];
}

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

        addr = (kprobe_opcode_t *)regs->pc;

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

        /* 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[0] == breakpoint_insn) {
                                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 {
                        if (*addr != breakpoint_insn) {
                                /*
                                 * The breakpoint instruction was removed by
                                 * another cpu right after we hit, no further
                                 * handling of this interrupt is appropriate.
                                 */
                                ret = 1;
                                goto no_kprobe;
                        }
                        p = __this_cpu_read(current_kprobe);
                        if (p->break_handler && p->break_handler(p, regs))
                                goto ss_probe;
                }
                goto no_kprobe;
        }

        p = get_kprobe(addr);
        if (!p) {
                if (*addr != breakpoint_insn) {
                        /*
                         * 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;
                }
                /* Not one of ours: let kernel handle it. */
                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;
}

/*
 * Called after single-stepping.  p->addr is the address of the
 * instruction that has been replaced by the breakpoint. 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.
 *
 * This function prepares to return from the post-single-step
 * breakpoint trap.
 */
static void __kprobes resume_execution(struct kprobe *p,
                                       struct pt_regs *regs,
                                       struct kprobe_ctlblk *kcb)
{
        unsigned long orig_pc = kcb->kprobe_saved_pc;
        regs->pc = orig_pc + 8;
}

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

        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);
        }

        resume_execution(cur, regs, kcb);

        /* 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;
}

static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
        struct kprobe *cur = kprobe_running();
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

        if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
                return 1;

        if (kcb->kprobe_status & KPROBE_HIT_SS) {
                /*
                 * We are here because the instruction being single
                 * stepped caused a page fault. We reset the current
                 * kprobe and the ip points back to the probe address
                 * and allow the page fault handler to continue as a
                 * normal page fault.
                 */
                resume_execution(cur, regs, kcb);
                reset_current_kprobe();
                preempt_enable_no_resched();
        }
        return 0;
}

/*
 * Wrapper routine 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;
        int ret = NOTIFY_DONE;

        switch (val) {
        case DIE_BREAK:
                if (kprobe_handler(args->regs))
                        ret = NOTIFY_STOP;
                break;
        case DIE_SSTEPBP:
                if (post_kprobe_handler(args->regs))
                        ret = NOTIFY_STOP;
                break;
        case DIE_PAGE_FAULT:
                /* kprobe_running() needs smp_processor_id(). */
                preempt_disable();

                if (kprobe_running()
                    && kprobe_fault_handler(args->regs, args->trapnr))
                        ret = NOTIFY_STOP;
                preempt_enable();
                break;
        default:
                break;
        }
        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();

        kcb->jprobe_saved_regs = *regs;
        kcb->jprobe_saved_sp = regs->sp;

        memcpy(kcb->jprobes_stack, (void *)kcb->jprobe_saved_sp,
               MIN_JPROBES_STACK_SIZE(kcb->jprobe_saved_sp));

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

        return 1;
}

/* Defined in the inline asm below. */
void jprobe_return_end(void);

void __kprobes jprobe_return(void)
{
        asm volatile(
                "bpt\n\t"
                ".globl jprobe_return_end\n"
                "jprobe_return_end:\n");
}

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

        if (regs->pc >= (unsigned long)jprobe_return &&
            regs->pc <= (unsigned long)jprobe_return_end) {
                *regs = kcb->jprobe_saved_regs;
                memcpy((void *)kcb->jprobe_saved_sp, kcb->jprobes_stack,
                       MIN_JPROBES_STACK_SIZE(kcb->jprobe_saved_sp));
                preempt_enable_no_resched();

                return 1;
        }
        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(
                "nop\n\t"
                ".global kretprobe_trampoline\n"
                "kretprobe_trampoline:\n\t"
                "nop\n\t"
                : : : "memory");
}

void kretprobe_trampoline(void);

void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
                                      struct pt_regs *regs)
{
        ri->ret_addr = (kprobe_opcode_t *) regs->lr;

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

/*
 * 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 = 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 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);
        instruction_pointer(regs) = orig_ret_address;

        reset_current_kprobe();
        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;
}

int __kprobes arch_trampoline_kprobe(struct kprobe *p)
{
        if (p->addr == (kprobe_opcode_t *)kretprobe_trampoline)
                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)
{
        register_kprobe(&trampoline_p);
        return 0;
}