// 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>
 */

#define pr_fmt(fmt) "kprobes: " fmt

#include <linux/execmem.h>
#include <linux/extable.h>
#include <linux/kasan.h>
#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/sched/debug.h>
#include <linux/set_memory.h>
#include <linux/slab.h>
#include <linux/stop_machine.h>
#include <linux/stringify.h>
#include <linux/uaccess.h>
#include <linux/vmalloc.h>

#include <asm/cacheflush.h>
#include <asm/daifflags.h>
#include <asm/debug-monitors.h>
#include <asm/insn.h>
#include <asm/irq.h>
#include <asm/text-patching.h>
#include <asm/ptrace.h>
#include <asm/sections.h>
#include <asm/system_misc.h>
#include <asm/traps.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 *, struct kprobe_ctlblk *, struct pt_regs *);

void *alloc_insn_page(void)
{
        void *addr;

        addr = execmem_alloc(EXECMEM_KPROBES, PAGE_SIZE);
        if (!addr)
                return NULL;
        if (set_memory_rox((unsigned long)addr, 1)) {
                execmem_free(addr);
                return NULL;
        }
        return addr;
}

static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
{
        kprobe_opcode_t *addr = p->ainsn.xol_insn;

        /*
         * Prepare insn slot, Mark Rutland points out it depends on a coupe of
         * subtleties:
         *
         * - That the I-cache maintenance for these instructions is complete
         *   *before* the kprobe BRK is written (and aarch64_insn_patch_text_nosync()
         *   ensures this, but just omits causing a Context-Synchronization-Event
         *   on all CPUS).
         *
         * - That the kprobe BRK results in an exception (and consequently a
         *   Context-Synchronoization-Event), which ensures that the CPU will
         *   fetch thesingle-step slot instructions *after* this, ensuring that
         *   the new instructions are used
         *
         * It supposes to place ISB after patching to guarantee I-cache maintenance
         * is observed on all CPUS, however, single-step slot is installed in
         * the BRK exception handler, so it is unnecessary to generate
         * Contex-Synchronization-Event via ISB again.
         */
        aarch64_insn_patch_text_nosync(addr, le32_to_cpu(p->opcode));
        aarch64_insn_patch_text_nosync(addr + 1, BRK64_OPCODE_KPROBES_SS);

        /*
         * Needs restoring of return address after stepping xol.
         */
        p->ainsn.xol_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.xol_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(le32_to_cpu(p->opcode), (long)p->addr, regs);

        /* single step simulated, now go for post processing */
        post_kprobe_handler(p, 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 = *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.xol_insn = NULL;
                break;

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

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

        return 0;
}

/* arm kprobe: install breakpoint in text */
void __kprobes arch_arm_kprobe(struct kprobe *p)
{
        void *addr = p->addr;
        u32 insn = BRK64_OPCODE_KPROBES;

        aarch64_insn_patch_text(&addr, &insn, 1);
}

/* disarm kprobe: remove breakpoint from text */
void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
        void *addr = p->addr;
        u32 insn = le32_to_cpu(p->opcode);

        aarch64_insn_patch_text(&addr, &insn, 1);
}

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

/*
 * Mask all of DAIF while executing the instruction out-of-line, to keep things
 * simple and avoid nesting exceptions. Interrupts do have to be disabled since
 * the kprobe state is per-CPU and doesn't get migrated.
 */
static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
                                                struct pt_regs *regs)
{
        kcb->saved_irqflag = regs->pstate & DAIF_MASK;
        regs->pstate |= DAIF_MASK;
}

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

                kprobes_save_local_irqflag(kcb, 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("Failed to recover from reentered kprobes.\n");
                dump_kprobe(p);
                BUG();
                break;
        default:
                WARN_ON(1);
                return 0;
        }

        return 1;
}

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

                if (kcb->kprobe_status == KPROBE_REENTER) {
                        restore_previous_kprobe(kcb);
                } else {
                        kprobes_restore_local_irqflag(kcb, regs);
                        reset_current_kprobe();
                }

                break;
        }
        return 0;
}

int __kprobes
kprobe_brk_handler(struct pt_regs *regs, unsigned long esr)
{
        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 (WARN_ON_ONCE(!p)) {
                /*
                 * Something went wrong. This BRK used an immediate reserved
                 * for kprobes, but we couldn't find any corresponding probe.
                 */
                return DBG_HOOK_ERROR;
        }

        if (cur_kprobe) {
                /* Hit a kprobe inside another kprobe */
                if (!reenter_kprobe(p, regs, kcb))
                        return DBG_HOOK_ERROR;
        } 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 not need to single-step
                 * Let's just reset current kprobe and exit.
                 */
                if (!p->pre_handler || !p->pre_handler(p, regs))
                        setup_singlestep(p, regs, kcb, 0);
                else
                        reset_current_kprobe();
        }

        return DBG_HOOK_HANDLED;
}

int __kprobes
kprobe_ss_brk_handler(struct pt_regs *regs, unsigned long esr)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        unsigned long addr = instruction_pointer(regs);
        struct kprobe *cur = kprobe_running();

        if (cur && (kcb->kprobe_status & (KPROBE_HIT_SS | KPROBE_REENTER)) &&
            ((unsigned long)&cur->ainsn.xol_insn[1] == addr)) {
                kprobes_restore_local_irqflag(kcb, regs);
                post_kprobe_handler(cur, kcb, regs);

                return DBG_HOOK_HANDLED;
        }

        /* not ours, kprobes should ignore it */
        return DBG_HOOK_ERROR;
}

int __kprobes
kretprobe_brk_handler(struct pt_regs *regs, unsigned long esr)
{
        if (regs->pc != (unsigned long)__kretprobe_trampoline)
                return DBG_HOOK_ERROR;

        regs->pc = kretprobe_trampoline_handler(regs, (void *)regs->regs[29]);
        return DBG_HOOK_HANDLED;
}

/*
 * 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)__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 arch_prepare_kretprobe(struct kretprobe_instance *ri,
                                      struct pt_regs *regs)
{
        ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
        ri->fp = (void *)regs->regs[29];

        /* 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)
{
        return 0;
}