/*
 * arch/arm/kernel/kprobes.c
 *
 * Kprobes on ARM
 *
 * Abhishek Sagar <sagar.abhishek@gmail.com>
 * Copyright (C) 2006, 2007 Motorola Inc.
 *
 * Nicolas Pitre <nico@marvell.com>
 * Copyright (C) 2007 Marvell Ltd.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 */

#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/stop_machine.h>
#include <linux/sched/debug.h>
#include <linux/stringify.h>
#include <asm/traps.h>
#include <asm/opcodes.h>
#include <asm/cacheflush.h>
#include <linux/percpu.h>
#include <linux/bug.h>
#include <asm/patch.h>

#include "../decode-arm.h"
#include "../decode-thumb.h"
#include "core.h"

#define MIN_STACK_SIZE(addr)                            \
        min((unsigned long)MAX_STACK_SIZE,              \
            (unsigned long)current_thread_info() + THREAD_START_SP - (addr))

#define flush_insns(addr, size)                         \
        flush_icache_range((unsigned long)(addr),       \
                           (unsigned long)(addr) +      \
                           (size))

/* Used as a marker in ARM_pc to note when we're in a jprobe. */
#define JPROBE_MAGIC_ADDR               0xffffffff

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


int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
        kprobe_opcode_t insn;
        kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
        unsigned long addr = (unsigned long)p->addr;
        bool thumb;
        kprobe_decode_insn_t *decode_insn;
        const union decode_action *actions;
        int is;
        const struct decode_checker **checkers;

        if (in_exception_text(addr))
                return -EINVAL;

#ifdef CONFIG_THUMB2_KERNEL
        thumb = true;
        addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
        insn = __mem_to_opcode_thumb16(((u16 *)addr)[0]);
        if (is_wide_instruction(insn)) {
                u16 inst2 = __mem_to_opcode_thumb16(((u16 *)addr)[1]);
                insn = __opcode_thumb32_compose(insn, inst2);
                decode_insn = thumb32_probes_decode_insn;
                actions = kprobes_t32_actions;
                checkers = kprobes_t32_checkers;
        } else {
                decode_insn = thumb16_probes_decode_insn;
                actions = kprobes_t16_actions;
                checkers = kprobes_t16_checkers;
        }
#else /* !CONFIG_THUMB2_KERNEL */
        thumb = false;
        if (addr & 0x3)
                return -EINVAL;
        insn = __mem_to_opcode_arm(*p->addr);
        decode_insn = arm_probes_decode_insn;
        actions = kprobes_arm_actions;
        checkers = kprobes_arm_checkers;
#endif

        p->opcode = insn;
        p->ainsn.insn = tmp_insn;

        switch ((*decode_insn)(insn, &p->ainsn, true, actions, checkers)) {
        case INSN_REJECTED:     /* not supported */
                return -EINVAL;

        case INSN_GOOD:         /* instruction uses slot */
                p->ainsn.insn = get_insn_slot();
                if (!p->ainsn.insn)
                        return -ENOMEM;
                for (is = 0; is < MAX_INSN_SIZE; ++is)
                        p->ainsn.insn[is] = tmp_insn[is];
                flush_insns(p->ainsn.insn,
                                sizeof(p->ainsn.insn[0]) * MAX_INSN_SIZE);
                p->ainsn.insn_fn = (probes_insn_fn_t *)
                                        ((uintptr_t)p->ainsn.insn | thumb);
                break;

        case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
                p->ainsn.insn = NULL;
                break;
        }

        /*
         * Never instrument insn like 'str r0, [sp, +/-r1]'. Also, insn likes
         * 'str r0, [sp, #-68]' should also be prohibited.
         * See __und_svc.
         */
        if ((p->ainsn.stack_space < 0) ||
                        (p->ainsn.stack_space > MAX_STACK_SIZE))
                return -EINVAL;

        return 0;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
        unsigned int brkp;
        void *addr;

        if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
                /* Remove any Thumb flag */
                addr = (void *)((uintptr_t)p->addr & ~1);

                if (is_wide_instruction(p->opcode))
                        brkp = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION;
                else
                        brkp = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION;
        } else {
                kprobe_opcode_t insn = p->opcode;

                addr = p->addr;
                brkp = KPROBE_ARM_BREAKPOINT_INSTRUCTION;

                if (insn >= 0xe0000000)
                        brkp |= 0xe0000000;  /* Unconditional instruction */
                else
                        brkp |= insn & 0xf0000000;  /* Copy condition from insn */
        }

        patch_text(addr, brkp);
}

/*
 * The actual disarming is done here on each CPU and synchronized using
 * stop_machine. This synchronization is necessary on SMP to avoid removing
 * a probe between the moment the 'Undefined Instruction' exception is raised
 * and the moment the exception handler reads the faulting instruction from
 * memory. It is also needed to atomically set the two half-words of a 32-bit
 * Thumb breakpoint.
 */
struct patch {
        void *addr;
        unsigned int insn;
};

static int __kprobes_remove_breakpoint(void *data)
{
        struct patch *p = data;
        __patch_text(p->addr, p->insn);
        return 0;
}

void __kprobes kprobes_remove_breakpoint(void *addr, unsigned int insn)
{
        struct patch p = {
                .addr = addr,
                .insn = insn,
        };
        stop_machine(__kprobes_remove_breakpoint, &p, cpu_online_mask);
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
        kprobes_remove_breakpoint((void *)((uintptr_t)p->addr & ~1),
                        p->opcode);
}

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

static void __kprobes
singlestep_skip(struct kprobe *p, struct pt_regs *regs)
{
#ifdef CONFIG_THUMB2_KERNEL
        regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
        if (is_wide_instruction(p->opcode))
                regs->ARM_pc += 4;
        else
                regs->ARM_pc += 2;
#else
        regs->ARM_pc += 4;
#endif
}

static inline void __kprobes
singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb)
{
        p->ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
}

/*
 * Called with IRQs disabled. IRQs must remain disabled from that point
 * all the way until processing this kprobe is complete.  The current
 * kprobes implementation cannot process more than one nested level of
 * kprobe, and that level is reserved for user kprobe handlers, so we can't
 * risk encountering a new kprobe in an interrupt handler.
 */
void __kprobes kprobe_handler(struct pt_regs *regs)
{
        struct kprobe *p, *cur;
        struct kprobe_ctlblk *kcb;

        kcb = get_kprobe_ctlblk();
        cur = kprobe_running();

#ifdef CONFIG_THUMB2_KERNEL
        /*
         * First look for a probe which was registered using an address with
         * bit 0 set, this is the usual situation for pointers to Thumb code.
         * If not found, fallback to looking for one with bit 0 clear.
         */
        p = get_kprobe((kprobe_opcode_t *)(regs->ARM_pc | 1));
        if (!p)
                p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);

#else /* ! CONFIG_THUMB2_KERNEL */
        p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
#endif

        if (p) {
                if (!p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
                        /*
                         * Probe hit but conditional execution check failed,
                         * so just skip the instruction and continue as if
                         * nothing had happened.
                         * In this case, we can skip recursing check too.
                         */
                        singlestep_skip(p, regs);
                } else if (cur) {
                        /* Kprobe is pending, so we're recursing. */
                        switch (kcb->kprobe_status) {
                        case KPROBE_HIT_ACTIVE:
                        case KPROBE_HIT_SSDONE:
                        case KPROBE_HIT_SS:
                                /* A pre- or post-handler probe got us here. */
                                kprobes_inc_nmissed_count(p);
                                save_previous_kprobe(kcb);
                                set_current_kprobe(p);
                                kcb->kprobe_status = KPROBE_REENTER;
                                singlestep(p, regs, kcb);
                                restore_previous_kprobe(kcb);
                                break;
                        case KPROBE_REENTER:
                                /* A nested probe was hit in FIQ, it is a BUG */
                                pr_warn("Unrecoverable kprobe detected at %p.\n",
                                        p->addr);
                                /* fall through */
                        default:
                                /* impossible cases */
                                BUG();
                        }
                } else {
                        /* Probe hit and conditional execution check ok. */
                        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 prepped
                         * for calling the break_handler below on re-entry,
                         * so get out doing nothing more here.
                         */
                        if (!p->pre_handler || !p->pre_handler(p, regs)) {
                                kcb->kprobe_status = KPROBE_HIT_SS;
                                singlestep(p, regs, kcb);
                                if (p->post_handler) {
                                        kcb->kprobe_status = KPROBE_HIT_SSDONE;
                                        p->post_handler(p, regs, 0);
                                }
                                reset_current_kprobe();
                        }
                }
        } else if (cur) {
                /* We probably hit a jprobe.  Call its break handler. */
                if (cur->break_handler && cur->break_handler(cur, regs)) {
                        kcb->kprobe_status = KPROBE_HIT_SS;
                        singlestep(cur, regs, kcb);
                        if (cur->post_handler) {
                                kcb->kprobe_status = KPROBE_HIT_SSDONE;
                                cur->post_handler(cur, regs, 0);
                        }
                }
                reset_current_kprobe();
        } else {
                /*
                 * The probe was removed and a race is in progress.
                 * There is nothing we can do about it.  Let's restart
                 * the instruction.  By the time we can restart, the
                 * real instruction will be there.
                 */
        }
}

static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
{
        unsigned long flags;
        local_irq_save(flags);
        kprobe_handler(regs);
        local_irq_restore(flags);
        return 0;
}

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 PC to point back to the probe address
                 * and allow the page fault handler to continue as a
                 * normal page fault.
                 */
                regs->ARM_pc = (long)cur->addr;
                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.
                 */
                if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
                        return 1;
                break;

        default:
                break;
        }

        return 0;
}

int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
                                       unsigned long val, void *data)
{
        /*
         * notify_die() is currently never called on ARM,
         * so this callback is currently empty.
         */
        return NOTIFY_DONE;
}

/*
 * When a retprobed function returns, trampoline_handler() is called,
 * calling the kretprobe's handler. We construct a struct pt_regs to
 * give a view of registers r0-r11 to the user return-handler.  This is
 * not a complete pt_regs structure, but that should be plenty sufficient
 * for kretprobe handlers which should normally be interested in r0 only
 * anyway.
 */
void __naked __kprobes kretprobe_trampoline(void)
{
        __asm__ __volatile__ (
                "stmdb  sp!, {r0 - r11}         \n\t"
                "mov    r0, sp                  \n\t"
                "bl     trampoline_handler      \n\t"
                "mov    lr, r0                  \n\t"
                "ldmia  sp!, {r0 - r11}         \n\t"
#ifdef CONFIG_THUMB2_KERNEL
                "bx     lr                      \n\t"
#else
                "mov    pc, lr                  \n\t"
#endif
                : : : "memory");
}

/* Called from kretprobe_trampoline */
static __used __kprobes void *trampoline_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
         * a return probe installed on them, and/or more than one return
         * probe was registered for a target function.
         *
         * We can handle this because:
         *     - instances are always inserted at the head of the list
         *     - when multiple return probes are registered for the same
         *       function, the first instance's ret_addr will point to 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->ARM_lr;

        /* Replace the return addr with trampoline addr. */
        regs->ARM_lr = (unsigned long)&kretprobe_trampoline;
}

int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct jprobe *jp = container_of(p, struct jprobe, kp);
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        long sp_addr = regs->ARM_sp;
        long cpsr;

        kcb->jprobe_saved_regs = *regs;
        memcpy(kcb->jprobes_stack, (void *)sp_addr, MIN_STACK_SIZE(sp_addr));
        regs->ARM_pc = (long)jp->entry;

        cpsr = regs->ARM_cpsr | PSR_I_BIT;
#ifdef CONFIG_THUMB2_KERNEL
        /* Set correct Thumb state in cpsr */
        if (regs->ARM_pc & 1)
                cpsr |= PSR_T_BIT;
        else
                cpsr &= ~PSR_T_BIT;
#endif
        regs->ARM_cpsr = cpsr;

        preempt_disable();
        return 1;
}

void __kprobes jprobe_return(void)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

        __asm__ __volatile__ (
                /*
                 * Setup an empty pt_regs. Fill SP and PC fields as
                 * they're needed by longjmp_break_handler.
                 *
                 * We allocate some slack between the original SP and start of
                 * our fabricated regs. To be precise we want to have worst case
                 * covered which is STMFD with all 16 regs so we allocate 2 *
                 * sizeof(struct_pt_regs)).
                 *
                 * This is to prevent any simulated instruction from writing
                 * over the regs when they are accessing the stack.
                 */
#ifdef CONFIG_THUMB2_KERNEL
                "sub    r0, %0, %1              \n\t"
                "mov    sp, r0                  \n\t"
#else
                "sub    sp, %0, %1              \n\t"
#endif
                "ldr    r0, ="__stringify(JPROBE_MAGIC_ADDR)"\n\t"
                "str    %0, [sp, %2]            \n\t"
                "str    r0, [sp, %3]            \n\t"
                "mov    r0, sp                  \n\t"
                "bl     kprobe_handler          \n\t"

                /*
                 * Return to the context saved by setjmp_pre_handler
                 * and restored by longjmp_break_handler.
                 */
#ifdef CONFIG_THUMB2_KERNEL
                "ldr    lr, [sp, %2]            \n\t" /* lr = saved sp */
                "ldrd   r0, r1, [sp, %5]        \n\t" /* r0,r1 = saved lr,pc */
                "ldr    r2, [sp, %4]            \n\t" /* r2 = saved psr */
                "stmdb  lr!, {r0, r1, r2}       \n\t" /* push saved lr and */
                                                      /* rfe context */
                "ldmia  sp, {r0 - r12}          \n\t"
                "mov    sp, lr                  \n\t"
                "ldr    lr, [sp], #4            \n\t"
                "rfeia  sp!                     \n\t"
#else
                "ldr    r0, [sp, %4]            \n\t"
                "msr    cpsr_cxsf, r0           \n\t"
                "ldmia  sp, {r0 - pc}           \n\t"
#endif
                :
                : "r" (kcb->jprobe_saved_regs.ARM_sp),
                  "I" (sizeof(struct pt_regs) * 2),
                  "J" (offsetof(struct pt_regs, ARM_sp)),
                  "J" (offsetof(struct pt_regs, ARM_pc)),
                  "J" (offsetof(struct pt_regs, ARM_cpsr)),
                  "J" (offsetof(struct pt_regs, ARM_lr))
                : "memory", "cc");
}

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        long stack_addr = kcb->jprobe_saved_regs.ARM_sp;
        long orig_sp = regs->ARM_sp;
        struct jprobe *jp = container_of(p, struct jprobe, kp);

        if (regs->ARM_pc == JPROBE_MAGIC_ADDR) {
                if (orig_sp != stack_addr) {
                        struct pt_regs *saved_regs =
                                (struct pt_regs *)kcb->jprobe_saved_regs.ARM_sp;
                        printk("current sp %lx does not match saved sp %lx\n",
                               orig_sp, stack_addr);
                        printk("Saved registers for jprobe %p\n", jp);
                        show_regs(saved_regs);
                        printk("Current registers\n");
                        show_regs(regs);
                        BUG();
                }
                *regs = kcb->jprobe_saved_regs;
                memcpy((void *)stack_addr, kcb->jprobes_stack,
                       MIN_STACK_SIZE(stack_addr));
                preempt_enable_no_resched();
                return 1;
        }
        return 0;
}

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

#ifdef CONFIG_THUMB2_KERNEL

static struct undef_hook kprobes_thumb16_break_hook = {
        .instr_mask     = 0xffff,
        .instr_val      = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION,
        .cpsr_mask      = MODE_MASK,
        .cpsr_val       = SVC_MODE,
        .fn             = kprobe_trap_handler,
};

static struct undef_hook kprobes_thumb32_break_hook = {
        .instr_mask     = 0xffffffff,
        .instr_val      = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION,
        .cpsr_mask      = MODE_MASK,
        .cpsr_val       = SVC_MODE,
        .fn             = kprobe_trap_handler,
};

#else  /* !CONFIG_THUMB2_KERNEL */

static struct undef_hook kprobes_arm_break_hook = {
        .instr_mask     = 0x0fffffff,
        .instr_val      = KPROBE_ARM_BREAKPOINT_INSTRUCTION,
        .cpsr_mask      = MODE_MASK,
        .cpsr_val       = SVC_MODE,
        .fn             = kprobe_trap_handler,
};

#endif /* !CONFIG_THUMB2_KERNEL */

int __init arch_init_kprobes()
{
        arm_probes_decode_init();
#ifdef CONFIG_THUMB2_KERNEL
        register_undef_hook(&kprobes_thumb16_break_hook);
        register_undef_hook(&kprobes_thumb32_break_hook);
#else
        register_undef_hook(&kprobes_arm_break_hook);
#endif
        return 0;
}