// SPDX-License-Identifier: GPL-2.0-only
/*
 * arch/arm64/kernel/probes/kprobes.c
 *
 * Kprobes support for ARM64
 *
 * Copyright (C) 2013 Linaro Limited.
 * Author: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
 */
#include <linux/kasan.h>
#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/extable.h>
#include <linux/slab.h>
#include <linux/stop_machine.h>
#include <linux/sched/debug.h>
#include <linux/set_memory.h>
#include <linux/stringify.h>
#include <linux/vmalloc.h>
#include <asm/traps.h>
#include <asm/ptrace.h>
#include <asm/cacheflush.h>
#include <asm/debug-monitors.h>
#include <asm/daifflags.h>
#include <asm/system_misc.h>
#include <asm/insn.h>
#include <linux/uaccess.h>
#include <asm/irq.h>
#include <asm/sections.h>

#include "decode-insn.h"

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

static void __kprobes
post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);

static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
{
        void *addrs[1];
        u32 insns[1];

        addrs[0] = addr;
        insns[0] = opcode;

        return aarch64_insn_patch_text(addrs, insns, 1);
}

static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
{
        /* prepare insn slot */
        patch_text(p->ainsn.api.insn, p->opcode);

        flush_icache_range((uintptr_t) (p->ainsn.api.insn),
                           (uintptr_t) (p->ainsn.api.insn) +
                           MAX_INSN_SIZE * sizeof(kprobe_opcode_t));

        /*
         * Needs restoring of return address after stepping xol.
         */
        p->ainsn.api.restore = (unsigned long) p->addr +
          sizeof(kprobe_opcode_t);
}

static void __kprobes arch_prepare_simulate(struct kprobe *p)
{
        /* This instructions is not executed xol. No need to adjust the PC */
        p->ainsn.api.restore = 0;
}

static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

        if (p->ainsn.api.handler)
                p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);

        /* single step simulated, now go for post processing */
        post_kprobe_handler(kcb, regs);
}

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

        if (probe_addr & 0x3)
                return -EINVAL;

        /* copy instruction */
        p->opcode = le32_to_cpu(*p->addr);

        if (search_exception_tables(probe_addr))
                return -EINVAL;

        /* decode instruction */
        switch (arm_kprobe_decode_insn(p->addr, &p->ainsn)) {
        case INSN_REJECTED:     /* insn not supported */
                return -EINVAL;

        case INSN_GOOD_NO_SLOT: /* insn need simulation */
                p->ainsn.api.insn = NULL;
                break;

        case INSN_GOOD: /* instruction uses slot */
                p->ainsn.api.insn = get_insn_slot();
                if (!p->ainsn.api.insn)
                        return -ENOMEM;
                break;
        }

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

        return 0;
}

void *alloc_insn_page(void)
{
        void *page;

        page = vmalloc_exec(PAGE_SIZE);
        if (page) {
                set_memory_ro((unsigned long)page, 1);
                set_vm_flush_reset_perms(page);
        }

        return page;
}

/* arm kprobe: install breakpoint in text */
void __kprobes arch_arm_kprobe(struct kprobe *p)
{
        patch_text(p->addr, BRK64_OPCODE_KPROBES);
}

/* disarm kprobe: remove breakpoint from text */
void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
        patch_text(p->addr, p->opcode);
}

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

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

/*
 * 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 __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
                                                struct pt_regs *regs)
{
        kcb->saved_irqflag = regs->pstate & DAIF_MASK;
        regs->pstate |= PSR_I_BIT;
        /* Unmask PSTATE.D for enabling software step exceptions. */
        regs->pstate &= ~PSR_D_BIT;
}

static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
                                                struct pt_regs *regs)
{
        regs->pstate &= ~DAIF_MASK;
        regs->pstate |= kcb->saved_irqflag;
}

static void __kprobes
set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
{
        kcb->ss_ctx.ss_pending = true;
        kcb->ss_ctx.match_addr = addr + sizeof(kprobe_opcode_t);
}

static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
{
        kcb->ss_ctx.ss_pending = false;
        kcb->ss_ctx.match_addr = 0;
}

static void __kprobes setup_singlestep(struct kprobe *p,
                                       struct pt_regs *regs,
                                       struct kprobe_ctlblk *kcb, int reenter)
{
        unsigned long slot;

        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.api.insn) {
                /* prepare for single stepping */
                slot = (unsigned long)p->ainsn.api.insn;

                set_ss_context(kcb, slot);      /* mark pending ss */

                /* IRQs and single stepping do not mix well. */
                kprobes_save_local_irqflag(kcb, regs);
                kernel_enable_single_step(regs);
                instruction_pointer_set(regs, slot);
        } else {
                /* insn simulation */
                arch_simulate_insn(p, regs);
        }
}

static int __kprobes reenter_kprobe(struct kprobe *p,
                                    struct pt_regs *regs,
                                    struct kprobe_ctlblk *kcb)
{
        switch (kcb->kprobe_status) {
        case KPROBE_HIT_SSDONE:
        case KPROBE_HIT_ACTIVE:
                kprobes_inc_nmissed_count(p);
                setup_singlestep(p, regs, kcb, 1);
                break;
        case KPROBE_HIT_SS:
        case KPROBE_REENTER:
                pr_warn("Unrecoverable kprobe detected.\n");
                dump_kprobe(p);
                BUG();
                break;
        default:
                WARN_ON(1);
                return 0;
        }

        return 1;
}

static void __kprobes
post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
{
        struct kprobe *cur = kprobe_running();

        if (!cur)
                return;

        /* return addr restore if non-branching insn */
        if (cur->ainsn.api.restore != 0)
                instruction_pointer_set(regs, cur->ainsn.api.restore);

        /* restore back original saved kprobe variables and continue */
        if (kcb->kprobe_status == KPROBE_REENTER) {
                restore_previous_kprobe(kcb);
                return;
        }
        /* call post handler */
        kcb->kprobe_status = KPROBE_HIT_SSDONE;
        if (cur->post_handler)  {
                /* post_handler can hit breakpoint and single step
                 * again, so we enable D-flag for recursive exception.
                 */
                cur->post_handler(cur, regs, 0);
        }

        reset_current_kprobe();
}

int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
{
        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.
                 */
                instruction_pointer_set(regs, (unsigned long) cur->addr);
                if (!instruction_pointer(regs))
                        BUG();

                kernel_disable_single_step();

                if (kcb->kprobe_status == KPROBE_REENTER)
                        restore_previous_kprobe(kcb);
                else
                        reset_current_kprobe();

                break;
        case KPROBE_HIT_ACTIVE:
        case KPROBE_HIT_SSDONE:
                /*
                 * 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, fsr))
                        return 1;

                /*
                 * In case the user-specified fault handler returned
                 * zero, try to fix up.
                 */
                if (fixup_exception(regs))
                        return 1;
        }
        return 0;
}

static void __kprobes kprobe_handler(struct pt_regs *regs)
{
        struct kprobe *p, *cur_kprobe;
        struct kprobe_ctlblk *kcb;
        unsigned long addr = instruction_pointer(regs);

        kcb = get_kprobe_ctlblk();
        cur_kprobe = kprobe_running();

        p = get_kprobe((kprobe_opcode_t *) addr);

        if (p) {
                if (cur_kprobe) {
                        if (reenter_kprobe(p, regs, kcb))
                                return;
                } 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, keep PSTATE D-flag enabled until
                         * pre_handler return back.
                         */
                        if (!p->pre_handler || !p->pre_handler(p, regs)) {
                                setup_singlestep(p, regs, kcb, 0);
                        } else
                                reset_current_kprobe();
                }
        }
        /*
         * 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.
         */
}

static int __kprobes
kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
{
        if ((kcb->ss_ctx.ss_pending)
            && (kcb->ss_ctx.match_addr == addr)) {
                clear_ss_context(kcb);  /* clear pending ss */
                return DBG_HOOK_HANDLED;
        }
        /* not ours, kprobes should ignore it */
        return DBG_HOOK_ERROR;
}

static int __kprobes
kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        int retval;

        /* return error if this is not our step */
        retval = kprobe_ss_hit(kcb, instruction_pointer(regs));

        if (retval == DBG_HOOK_HANDLED) {
                kprobes_restore_local_irqflag(kcb, regs);
                kernel_disable_single_step();

                post_kprobe_handler(kcb, regs);
        }

        return retval;
}

static struct step_hook kprobes_step_hook = {
        .fn = kprobe_single_step_handler,
};

static int __kprobes
kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
{
        kprobe_handler(regs);
        return DBG_HOOK_HANDLED;
}

static struct break_hook kprobes_break_hook = {
        .imm = KPROBES_BRK_IMM,
        .fn = kprobe_breakpoint_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)
{
        int ret;

        ret = kprobe_add_area_blacklist((unsigned long)__entry_text_start,
                                        (unsigned long)__entry_text_end);
        if (ret)
                return ret;
        ret = kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
                                        (unsigned long)__irqentry_text_end);
        if (ret)
                return ret;
        ret = kprobe_add_area_blacklist((unsigned long)__exception_text_start,
                                        (unsigned long)__exception_text_end);
        if (ret)
                return ret;
        ret = kprobe_add_area_blacklist((unsigned long)__idmap_text_start,
                                        (unsigned long)__idmap_text_end);
        if (ret)
                return ret;
        ret = kprobe_add_area_blacklist((unsigned long)__hyp_text_start,
                                        (unsigned long)__hyp_text_end);
        if (ret || is_kernel_in_hyp_mode())
                return ret;
        ret = kprobe_add_area_blacklist((unsigned long)__hyp_idmap_text_start,
                                        (unsigned long)__hyp_idmap_text_end);
        return ret;
}

void __kprobes __used *trampoline_probe_handler(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;
        kprobe_opcode_t *correct_ret_addr = NULL;

        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
         * return probes installed on them, and/or more than one
         * return probe was registered for a target function.
         *
         * We can handle this because:
         *     - instances are always pushed into the head of the list
         *     - when multiple return probes are registered for the same
         *       function, the (chronologically) first instance's ret_addr
         *       will be 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;

                orig_ret_address = (unsigned long)ri->ret_addr;

                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);

        correct_ret_addr = ri->ret_addr;
        hlist_for_each_entry_safe(ri, tmp, head, hlist) {
                if (ri->task != current)
                        /* another task is sharing our hash bucket */
                        continue;

                orig_ret_address = (unsigned long)ri->ret_addr;
                if (ri->rp && ri->rp->handler) {
                        __this_cpu_write(current_kprobe, &ri->rp->kp);
                        get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
                        ri->ret_addr = correct_ret_addr;
                        ri->rp->handler(ri, regs);
                        __this_cpu_write(current_kprobe, NULL);
                }

                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_hash_unlock(current, &flags);

        hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
                hlist_del(&ri->hlist);
                kfree(ri);
        }
        return (void *)orig_ret_address;
}

void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
                                      struct pt_regs *regs)
{
        ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];

        /* replace return addr (x30) with trampoline */
        regs->regs[30] = (long)&kretprobe_trampoline;
}

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

int __init arch_init_kprobes(void)
{
        register_kernel_break_hook(&kprobes_break_hook);
        register_kernel_step_hook(&kprobes_step_hook);

        return 0;
}