// SPDX-License-Identifier: GPL-2.0-only
#include <linux/kdebug.h>
#include <linux/kprobes.h>
#include <linux/preempt.h>
#include <asm/break.h>

#define KPROBE_BP_INSN          __emit_break(BRK_KPROBE_BP)
#define KPROBE_SSTEPBP_INSN     __emit_break(BRK_KPROBE_SSTEPBP)

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

static void arch_prepare_ss_slot(struct kprobe *p)
{
        p->ainsn.insn[0] = *p->addr;
        p->ainsn.insn[1] = KPROBE_SSTEPBP_INSN;
        p->ainsn.restore = (unsigned long)p->addr + LOONGARCH_INSN_SIZE;
}
NOKPROBE_SYMBOL(arch_prepare_ss_slot);

static void arch_prepare_simulate(struct kprobe *p)
{
        p->ainsn.restore = 0;
}
NOKPROBE_SYMBOL(arch_prepare_simulate);

int arch_prepare_kprobe(struct kprobe *p)
{
        union loongarch_instruction insn;

        if ((unsigned long)p->addr & 0x3)
                return -EILSEQ;

        /* copy instruction */
        p->opcode = *p->addr;
        insn.word = p->opcode;

        /* decode instruction */
        if (insns_not_supported(insn))
                return -EINVAL;

        if (insns_need_simulation(insn)) {
                p->ainsn.insn = NULL;
        } else {
                p->ainsn.insn = get_insn_slot();
                if (!p->ainsn.insn)
                        return -ENOMEM;
        }

        /* prepare the instruction */
        if (p->ainsn.insn)
                arch_prepare_ss_slot(p);
        else
                arch_prepare_simulate(p);

        return 0;
}
NOKPROBE_SYMBOL(arch_prepare_kprobe);

/* Install breakpoint in text */
void arch_arm_kprobe(struct kprobe *p)
{
        *p->addr = KPROBE_BP_INSN;
        flush_insn_slot(p);
}
NOKPROBE_SYMBOL(arch_arm_kprobe);

/* Remove breakpoint from text */
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;
}
NOKPROBE_SYMBOL(save_previous_kprobe);

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;
}
NOKPROBE_SYMBOL(restore_previous_kprobe);

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

/*
 * Interrupts need to be disabled before single-step mode is set,
 * and not reenabled until after single-step mode ends.
 * Without disabling interrupt on local CPU, there is a chance of
 * interrupt occurrence in the period of exception return and start
 * of out-of-line single-step, that result in wrongly single stepping
 * into the interrupt handler.
 */
static void save_local_irqflag(struct kprobe_ctlblk *kcb,
                               struct pt_regs *regs)
{
        kcb->saved_status = regs->csr_prmd;
        regs->csr_prmd &= ~CSR_PRMD_PIE;
}
NOKPROBE_SYMBOL(save_local_irqflag);

static void restore_local_irqflag(struct kprobe_ctlblk *kcb,
                                  struct pt_regs *regs)
{
        regs->csr_prmd = kcb->saved_status;
}
NOKPROBE_SYMBOL(restore_local_irqflag);

static void post_kprobe_handler(struct kprobe *cur, struct kprobe_ctlblk *kcb,
                                struct pt_regs *regs)
{
        /* return addr restore if non-branching insn */
        if (cur->ainsn.restore != 0)
                instruction_pointer_set(regs, cur->ainsn.restore);

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

        /*
         * update the kcb status even if the cur->post_handler is
         * not set because reset_curent_kprobe() doesn't update kcb.
         */
        kcb->kprobe_status = KPROBE_HIT_SSDONE;
        if (cur->post_handler)
                cur->post_handler(cur, regs, 0);

        reset_current_kprobe();
        preempt_enable_no_resched();
}
NOKPROBE_SYMBOL(post_kprobe_handler);

static void setup_singlestep(struct kprobe *p, struct pt_regs *regs,
                             struct kprobe_ctlblk *kcb, int reenter)
{
        union loongarch_instruction insn;

        if (reenter) {
                save_previous_kprobe(kcb);
                set_current_kprobe(p);
                kcb->kprobe_status = KPROBE_REENTER;
        } else {
                kcb->kprobe_status = KPROBE_HIT_SS;
        }

        if (p->ainsn.insn) {
                /* IRQs and single stepping do not mix well */
                save_local_irqflag(kcb, regs);
                /* set ip register to prepare for single stepping */
                regs->csr_era = (unsigned long)p->ainsn.insn;
        } else {
                /* simulate single steping */
                insn.word = p->opcode;
                arch_simulate_insn(insn, regs);
                /* now go for post processing */
                post_kprobe_handler(p, kcb, regs);
        }
}
NOKPROBE_SYMBOL(setup_singlestep);

static bool reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
                           struct kprobe_ctlblk *kcb)
{
        switch (kcb->kprobe_status) {
        case KPROBE_HIT_SS:
        case KPROBE_HIT_SSDONE:
        case KPROBE_HIT_ACTIVE:
                kprobes_inc_nmissed_count(p);
                setup_singlestep(p, regs, kcb, 1);
                break;
        case KPROBE_REENTER:
                pr_warn("Failed to recover from reentered kprobes.\n");
                dump_kprobe(p);
                WARN_ON_ONCE(1);
                break;
        default:
                WARN_ON(1);
                return false;
        }

        return true;
}
NOKPROBE_SYMBOL(reenter_kprobe);

bool kprobe_breakpoint_handler(struct pt_regs *regs)
{
        struct kprobe_ctlblk *kcb;
        struct kprobe *p, *cur_kprobe;
        kprobe_opcode_t *addr = (kprobe_opcode_t *)regs->csr_era;

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

        p = get_kprobe(addr);
        if (p) {
                if (cur_kprobe) {
                        if (reenter_kprobe(p, regs, kcb))
                                return true;
                } else {
                        /* Probe hit */
                        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, it will
                         * modify the execution path and no need to single
                         * stepping. Let's just reset current kprobe and exit.
                         *
                         * pre_handler can hit a breakpoint and can step thru
                         * before return.
                         */
                        if (!p->pre_handler || !p->pre_handler(p, regs)) {
                                setup_singlestep(p, regs, kcb, 0);
                        } else {
                                reset_current_kprobe();
                                preempt_enable_no_resched();
                        }
                        return true;
                }
        }

        if (*addr != KPROBE_BP_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.
                 * Return back to original instruction, and continue.
                 */
                regs->csr_era = (unsigned long)addr;
                preempt_enable_no_resched();
                return true;
        }

        preempt_enable_no_resched();
        return false;
}
NOKPROBE_SYMBOL(kprobe_breakpoint_handler);

bool kprobe_singlestep_handler(struct pt_regs *regs)
{
        struct kprobe *cur = kprobe_running();
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        unsigned long addr = instruction_pointer(regs);

        if (cur && (kcb->kprobe_status & (KPROBE_HIT_SS | KPROBE_REENTER)) &&
            ((unsigned long)&cur->ainsn.insn[1] == addr)) {
                restore_local_irqflag(kcb, regs);
                post_kprobe_handler(cur, kcb, regs);
                return true;
        }

        preempt_enable_no_resched();
        return false;
}
NOKPROBE_SYMBOL(kprobe_singlestep_handler);

bool kprobe_fault_handler(struct pt_regs *regs, int 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 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.
                 */
                regs->csr_era = (unsigned long)cur->addr;
                WARN_ON_ONCE(!instruction_pointer(regs));

                if (kcb->kprobe_status == KPROBE_REENTER) {
                        restore_previous_kprobe(kcb);
                } else {
                        restore_local_irqflag(kcb, regs);
                        reset_current_kprobe();
                }
                preempt_enable_no_resched();
                break;
        }
        return false;
}
NOKPROBE_SYMBOL(kprobe_fault_handler);

/*
 * Provide a blacklist of symbols identifying ranges which cannot be kprobed.
 * This blacklist is exposed to userspace via debugfs (kprobes/blacklist).
 */
int __init arch_populate_kprobe_blacklist(void)
{
        return kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
                                         (unsigned long)__irqentry_text_end);
}

int __init arch_init_kprobes(void)
{
        return 0;
}

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