// SPDX-License-Identifier: GPL-2.0-only
/*
 *  Kernel Probes (KProbes)
 *  arch/mips/kernel/kprobes.c
 *
 *  Copyright 2006 Sony Corp.
 *  Copyright 2010 Cavium Networks
 *
 *  Some portions copied from the powerpc version.
 *
 *   Copyright (C) IBM Corporation, 2002, 2004
 */

#define pr_fmt(fmt) "kprobes: " fmt

#include <linux/kprobes.h>
#include <linux/preempt.h>
#include <linux/uaccess.h>
#include <linux/kdebug.h>
#include <linux/slab.h>

#include <asm/ptrace.h>
#include <asm/branch.h>
#include <asm/break.h>

#include "probes-common.h"

static const union mips_instruction breakpoint_insn = {
        .b_format = {
                .opcode = spec_op,
                .code = BRK_KPROBE_BP,
                .func = break_op
        }
};

static const union mips_instruction breakpoint2_insn = {
        .b_format = {
                .opcode = spec_op,
                .code = BRK_KPROBE_SSTEPBP,
                .func = break_op
        }
};

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

static int insn_has_delayslot(union mips_instruction insn)
{
        return __insn_has_delay_slot(insn);
}
NOKPROBE_SYMBOL(insn_has_delayslot);

/*
 * insn_has_ll_or_sc function checks whether instruction is ll or sc
 * one; putting breakpoint on top of atomic ll/sc pair is bad idea;
 * so we need to prevent it and refuse kprobes insertion for such
 * instructions; cannot do much about breakpoint in the middle of
 * ll/sc pair; it is up to user to avoid those places
 */
static int insn_has_ll_or_sc(union mips_instruction insn)
{
        int ret = 0;

        switch (insn.i_format.opcode) {
        case ll_op:
        case lld_op:
        case sc_op:
        case scd_op:
                ret = 1;
                break;
        default:
                break;
        }
        return ret;
}
NOKPROBE_SYMBOL(insn_has_ll_or_sc);

int arch_prepare_kprobe(struct kprobe *p)
{
        union mips_instruction insn;
        union mips_instruction prev_insn;
        int ret = 0;

        insn = p->addr[0];

        if (insn_has_ll_or_sc(insn)) {
                pr_notice("Kprobes for ll and sc instructions are not supported\n");
                ret = -EINVAL;
                goto out;
        }

        if (copy_from_kernel_nofault(&prev_insn, p->addr - 1,
                        sizeof(mips_instruction)) == 0 &&
            insn_has_delayslot(prev_insn)) {
                pr_notice("Kprobes for branch delayslot are not supported\n");
                ret = -EINVAL;
                goto out;
        }

        if (__insn_is_compact_branch(insn)) {
                pr_notice("Kprobes for compact branches are not supported\n");
                ret = -EINVAL;
                goto out;
        }

        /* insn: must be on special executable page on mips. */
        p->ainsn.insn = get_insn_slot();
        if (!p->ainsn.insn) {
                ret = -ENOMEM;
                goto out;
        }

        /*
         * In the kprobe->ainsn.insn[] array we store the original
         * instruction at index zero and a break trap instruction at
         * index one.
         *
         * On MIPS arch if the instruction at probed address is a
         * branch instruction, we need to execute the instruction at
         * Branch Delayslot (BD) at the time of probe hit. As MIPS also
         * doesn't have single stepping support, the BD instruction can
         * not be executed in-line and it would be executed on SSOL slot
         * using a normal breakpoint instruction in the next slot.
         * So, read the instruction and save it for later execution.
         */
        if (insn_has_delayslot(insn))
                memcpy(&p->ainsn.insn[0], p->addr + 1, sizeof(kprobe_opcode_t));
        else
                memcpy(&p->ainsn.insn[0], p->addr, sizeof(kprobe_opcode_t));

        p->ainsn.insn[1] = breakpoint2_insn;
        p->opcode = *p->addr;

out:
        return ret;
}
NOKPROBE_SYMBOL(arch_prepare_kprobe);

void arch_arm_kprobe(struct kprobe *p)
{
        *p->addr = breakpoint_insn;
        flush_insn_slot(p);
}
NOKPROBE_SYMBOL(arch_arm_kprobe);

void arch_disarm_kprobe(struct kprobe *p)
{
        *p->addr = p->opcode;
        flush_insn_slot(p);
}
NOKPROBE_SYMBOL(arch_disarm_kprobe);

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

static void save_previous_kprobe(struct kprobe_ctlblk *kcb)
{
        kcb->prev_kprobe.kp = kprobe_running();
        kcb->prev_kprobe.status = kcb->kprobe_status;
        kcb->prev_kprobe.old_SR = kcb->kprobe_old_SR;
        kcb->prev_kprobe.saved_SR = kcb->kprobe_saved_SR;
        kcb->prev_kprobe.saved_epc = kcb->kprobe_saved_epc;
}

static void 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_old_SR = kcb->prev_kprobe.old_SR;
        kcb->kprobe_saved_SR = kcb->prev_kprobe.saved_SR;
        kcb->kprobe_saved_epc = kcb->prev_kprobe.saved_epc;
}

static void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
                               struct kprobe_ctlblk *kcb)
{
        __this_cpu_write(current_kprobe, p);
        kcb->kprobe_saved_SR = kcb->kprobe_old_SR = (regs->cp0_status & ST0_IE);
        kcb->kprobe_saved_epc = regs->cp0_epc;
}

/**
 * evaluate_branch_instrucion -
 *
 * Evaluate the branch instruction at probed address during probe hit. The
 * result of evaluation would be the updated epc. The insturction in delayslot
 * would actually be single stepped using a normal breakpoint) on SSOL slot.
 *
 * The result is also saved in the kprobe control block for later use,
 * in case we need to execute the delayslot instruction. The latter will be
 * false for NOP instruction in dealyslot and the branch-likely instructions
 * when the branch is taken. And for those cases we set a flag as
 * SKIP_DELAYSLOT in the kprobe control block
 */
static int evaluate_branch_instruction(struct kprobe *p, struct pt_regs *regs,
                                        struct kprobe_ctlblk *kcb)
{
        union mips_instruction insn = p->opcode;
        long epc;
        int ret = 0;

        epc = regs->cp0_epc;
        if (epc & 3)
                goto unaligned;

        if (p->ainsn.insn->word == 0)
                kcb->flags |= SKIP_DELAYSLOT;
        else
                kcb->flags &= ~SKIP_DELAYSLOT;

        ret = __compute_return_epc_for_insn(regs, insn);
        if (ret < 0)
                return ret;

        if (ret == BRANCH_LIKELY_TAKEN)
                kcb->flags |= SKIP_DELAYSLOT;

        kcb->target_epc = regs->cp0_epc;

        return 0;

unaligned:
        pr_notice("Failed to emulate branch instruction because of unaligned epc - sending SIGBUS to %s.\n", current->comm);
        force_sig(SIGBUS);
        return -EFAULT;

}

static void prepare_singlestep(struct kprobe *p, struct pt_regs *regs,
                                                struct kprobe_ctlblk *kcb)
{
        int ret = 0;

        regs->cp0_status &= ~ST0_IE;

        /* single step inline if the instruction is a break */
        if (p->opcode.word == breakpoint_insn.word ||
            p->opcode.word == breakpoint2_insn.word)
                regs->cp0_epc = (unsigned long)p->addr;
        else if (insn_has_delayslot(p->opcode)) {
                ret = evaluate_branch_instruction(p, regs, kcb);
                if (ret < 0)
                        return;
        }
        regs->cp0_epc = (unsigned long)&p->ainsn.insn[0];
}

/*
 * Called after single-stepping.  p->addr is the address of the
 * instruction whose first byte has been replaced by the "break 0"
 * 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.
 *
 * This function prepares to return from the post-single-step
 * breakpoint trap. In case of branch instructions, the target
 * epc to be restored.
 */
static void resume_execution(struct kprobe *p,
                                       struct pt_regs *regs,
                                       struct kprobe_ctlblk *kcb)
{
        if (insn_has_delayslot(p->opcode))
                regs->cp0_epc = kcb->target_epc;
        else {
                unsigned long orig_epc = kcb->kprobe_saved_epc;
                regs->cp0_epc = orig_epc + 4;
        }
}
NOKPROBE_SYMBOL(resume_execution);

static int 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->cp0_epc;

        /*
         * 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->word == breakpoint_insn.word) {
                                regs->cp0_status &= ~ST0_IE;
                                regs->cp0_status |= kcb->kprobe_saved_SR;
                                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);
                        kcb->kprobe_status = KPROBE_REENTER;
                        if (kcb->flags & SKIP_DELAYSLOT) {
                                resume_execution(p, regs, kcb);
                                restore_previous_kprobe(kcb);
                                preempt_enable_no_resched();
                        }
                        return 1;
                } else if (addr->word != breakpoint_insn.word) {
                        /*
                         * 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 = get_kprobe(addr);
        if (!p) {
                if (addr->word != breakpoint_insn.word) {
                        /*
                         * 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 */
                reset_current_kprobe();
                preempt_enable_no_resched();
                return 1;
        }

        prepare_singlestep(p, regs, kcb);
        if (kcb->flags & SKIP_DELAYSLOT) {
                kcb->kprobe_status = KPROBE_HIT_SSDONE;
                if (p->post_handler)
                        p->post_handler(p, regs, 0);
                resume_execution(p, regs, kcb);
                preempt_enable_no_resched();
        } else
                kcb->kprobe_status = KPROBE_HIT_SS;

        return 1;

no_kprobe:
        preempt_enable_no_resched();
        return ret;

}
NOKPROBE_SYMBOL(kprobe_handler);

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);

        regs->cp0_status |= kcb->kprobe_saved_SR;

        /* 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;
}

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

        if (kcb->kprobe_status & KPROBE_HIT_SS) {
                resume_execution(cur, regs, kcb);
                regs->cp0_status |= kcb->kprobe_old_SR;

                reset_current_kprobe();
                preempt_enable_no_resched();
        }
        return 0;
}

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

/*
 * 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(
                ".set push\n\t"
                /* Keep the assembler from reordering and placing JR here. */
                ".set noreorder\n\t"
                "nop\n\t"
                ".global __kretprobe_trampoline\n"
                "__kretprobe_trampoline:\n\t"
                "nop\n\t"
                ".set pop"
                : : : "memory");
}

void __kretprobe_trampoline(void);

void arch_prepare_kretprobe(struct kretprobe_instance *ri,
                                      struct pt_regs *regs)
{
        ri->ret_addr = (kprobe_opcode_t *) regs->regs[31];
        ri->fp = NULL;

        /* Replace the return addr with trampoline addr */
        regs->regs[31] = (unsigned long)__kretprobe_trampoline;
}
NOKPROBE_SYMBOL(arch_prepare_kretprobe);

/*
 * Called when the probe at kretprobe trampoline is hit
 */
static int trampoline_probe_handler(struct kprobe *p,
                                                struct pt_regs *regs)
{
        instruction_pointer(regs) = __kretprobe_trampoline_handler(regs, NULL);
        /*
         * 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);

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

        return 0;
}
NOKPROBE_SYMBOL(arch_trampoline_kprobe);

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

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