// SPDX-License-Identifier: GPL-2.0
/*
 * arch/parisc/kernel/kprobes.c
 *
 * PA-RISC kprobes implementation
 *
 * Copyright (c) 2019 Sven Schnelle <svens@stackframe.org>
 * Copyright (c) 2022 Helge Deller <deller@gmx.de>
 */

#include <linux/types.h>
#include <linux/kprobes.h>
#include <linux/slab.h>
#include <asm/cacheflush.h>
#include <asm/text-patching.h>

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

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
        if ((unsigned long)p->addr & 3UL)
                return -EINVAL;

        p->ainsn.insn = get_insn_slot();
        if (!p->ainsn.insn)
                return -ENOMEM;

        /*
         * Set up new instructions. Second break instruction will
         * trigger call of parisc_kprobe_ss_handler().
         */
        p->opcode = *p->addr;
        p->ainsn.insn[0] = p->opcode;
        p->ainsn.insn[1] = PARISC_KPROBES_BREAK_INSN2;

        flush_insn_slot(p);
        return 0;
}

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
        if (!p->ainsn.insn)
                return;

        free_insn_slot(p->ainsn.insn, 0);
        p->ainsn.insn = NULL;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
        patch_text(p->addr, PARISC_KPROBES_BREAK_INSN);
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
        patch_text(p->addr, p->opcode);
}

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 setup_singlestep(struct kprobe *p,
                struct kprobe_ctlblk *kcb, struct pt_regs *regs)
{
        kcb->iaoq[0] = regs->iaoq[0];
        kcb->iaoq[1] = regs->iaoq[1];
        instruction_pointer_set(regs, (unsigned long)p->ainsn.insn);
}

int __kprobes parisc_kprobe_break_handler(struct pt_regs *regs)
{
        struct kprobe *p;
        struct kprobe_ctlblk *kcb;

        preempt_disable();

        kcb = get_kprobe_ctlblk();
        p = get_kprobe((unsigned long *)regs->iaoq[0]);

        if (!p) {
                preempt_enable_no_resched();
                return 0;
        }

        if (kprobe_running()) {
                /*
                 * 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.
                 */
                save_previous_kprobe(kcb);
                set_current_kprobe(p);
                kprobes_inc_nmissed_count(p);
                setup_singlestep(p, kcb, 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, kcb, regs);
                kcb->kprobe_status = KPROBE_HIT_SS;
        } else {
                reset_current_kprobe();
                preempt_enable_no_resched();
        }
        return 1;
}

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

        if (!p)
                return 0;

        if (regs->iaoq[0] != (unsigned long)p->ainsn.insn+4)
                return 0;

        /* restore back original saved kprobe variables and continue */
        if (kcb->kprobe_status == KPROBE_REENTER) {
                restore_previous_kprobe(kcb);
                return 1;
        }

        /* for absolute branch instructions we can copy iaoq_b. for relative
         * branch instructions we need to calculate the new address based on the
         * difference between iaoq_f and iaoq_b. We cannot use iaoq_b without
         * modifications because it's based on our ainsn.insn address.
         */

        if (p->post_handler)
                p->post_handler(p, regs, 0);

        switch (regs->iir >> 26) {
        case 0x38: /* BE */
        case 0x39: /* BE,L */
        case 0x3a: /* BV */
        case 0x3b: /* BVE */
                /* for absolute branches, regs->iaoq[1] has already the right
                 * address
                 */
                regs->iaoq[0] = kcb->iaoq[1];
                break;
        default:
                regs->iaoq[0] = kcb->iaoq[1];
                regs->iaoq[1] = regs->iaoq[0] + 4;
                break;
        }
        kcb->kprobe_status = KPROBE_HIT_SSDONE;
        reset_current_kprobe();
        return 1;
}

void __kretprobe_trampoline(void)
{
        asm volatile("nop");
        asm volatile("nop");
}

static int __kprobes trampoline_probe_handler(struct kprobe *p,
                                              struct pt_regs *regs);

static struct kprobe trampoline_p = {
        .pre_handler = trampoline_probe_handler
};

static int __kprobes trampoline_probe_handler(struct kprobe *p,
                                              struct pt_regs *regs)
{
        __kretprobe_trampoline_handler(regs, NULL);

        return 1;
}

void arch_kretprobe_fixup_return(struct pt_regs *regs,
                                 kprobe_opcode_t *correct_ret_addr)
{
        regs->gr[2] = (unsigned long)correct_ret_addr;
}

void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
                                      struct pt_regs *regs)
{
        ri->ret_addr = (kprobe_opcode_t *)regs->gr[2];
        ri->fp = NULL;

        /* Replace the return addr with trampoline addr. */
        regs->gr[2] = (unsigned long)trampoline_p.addr;
}

int __kprobes arch_trampoline_kprobe(struct kprobe *p)
{
        return p->addr == trampoline_p.addr;
}

int __init arch_init_kprobes(void)
{
        trampoline_p.addr = (kprobe_opcode_t *)
                dereference_function_descriptor(__kretprobe_trampoline);
        return register_kprobe(&trampoline_p);
}