// SPDX-License-Identifier: GPL-2.0
/* arch/sparc64/kernel/kprobes.c
 *
 * Copyright (C) 2004 David S. Miller <davem@davemloft.net>
 */

#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/extable.h>
#include <linux/kdebug.h>
#include <linux/slab.h>
#include <linux/context_tracking.h>
#include <asm/signal.h>
#include <asm/cacheflush.h>
#include <linux/uaccess.h>

/* We do not have hardware single-stepping on sparc64.
 * So we implement software single-stepping with breakpoint
 * traps.  The top-level scheme is similar to that used
 * in the x86 kprobes implementation.
 *
 * In the kprobe->ainsn.insn[] array we store the original
 * instruction at index zero and a break instruction at
 * index one.
 *
 * When we hit a kprobe we:
 * - Run the pre-handler
 * - Remember "regs->tnpc" and interrupt level stored in
 *   "regs->tstate" so we can restore them later
 * - Disable PIL interrupts
 * - Set regs->tpc to point to kprobe->ainsn.insn[0]
 * - Set regs->tnpc to point to kprobe->ainsn.insn[1]
 * - Mark that we are actively in a kprobe
 *
 * At this point we wait for the second breakpoint at
 * kprobe->ainsn.insn[1] to hit.  When it does we:
 * - Run the post-handler
 * - Set regs->tpc to "remembered" regs->tnpc stored above,
 *   restore the PIL interrupt level in "regs->tstate" as well
 * - Make any adjustments necessary to regs->tnpc in order
 *   to handle relative branches correctly.  See below.
 * - Mark that we are no longer actively in a kprobe.
 */

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

struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
        if ((unsigned long) p->addr & 0x3UL)
                return -EILSEQ;

        p->ainsn.insn[0] = *p->addr;
        flushi(&p->ainsn.insn[0]);

        p->ainsn.insn[1] = BREAKPOINT_INSTRUCTION_2;
        flushi(&p->ainsn.insn[1]);

        p->opcode = *p->addr;
        return 0;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
        *p->addr = BREAKPOINT_INSTRUCTION;
        flushi(p->addr);
}

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

static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
{
        kcb->prev_kprobe.kp = kprobe_running();
        kcb->prev_kprobe.status = kcb->kprobe_status;
        kcb->prev_kprobe.orig_tnpc = kcb->kprobe_orig_tnpc;
        kcb->prev_kprobe.orig_tstate_pil = kcb->kprobe_orig_tstate_pil;
}

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;
        kcb->kprobe_orig_tnpc = kcb->prev_kprobe.orig_tnpc;
        kcb->kprobe_orig_tstate_pil = kcb->prev_kprobe.orig_tstate_pil;
}

static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
                                struct kprobe_ctlblk *kcb)
{
        __this_cpu_write(current_kprobe, p);
        kcb->kprobe_orig_tnpc = regs->tnpc;
        kcb->kprobe_orig_tstate_pil = (regs->tstate & TSTATE_PIL);
}

static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs,
                        struct kprobe_ctlblk *kcb)
{
        regs->tstate |= TSTATE_PIL;

        /*single step inline, if it a breakpoint instruction*/
        if (p->opcode == BREAKPOINT_INSTRUCTION) {
                regs->tpc = (unsigned long) p->addr;
                regs->tnpc = kcb->kprobe_orig_tnpc;
        } else {
                regs->tpc = (unsigned long) &p->ainsn.insn[0];
                regs->tnpc = (unsigned long) &p->ainsn.insn[1];
        }
}

static int __kprobes kprobe_handler(struct pt_regs *regs)
{
        struct kprobe *p;
        void *addr = (void *) regs->tpc;
        int ret = 0;
        struct kprobe_ctlblk *kcb;

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

        if (kprobe_running()) {
                p = get_kprobe(addr);
                if (p) {
                        if (kcb->kprobe_status == KPROBE_HIT_SS) {
                                regs->tstate = ((regs->tstate & ~TSTATE_PIL) |
                                        kcb->kprobe_orig_tstate_pil);
                                goto no_kprobe;
                        }
                        /* We have reentered the kprobe_handler(), since
                         * another probe was hit while within the handler.
                         * We here save the original kprobes variables and
                         * just single step on the instruction of the new probe
                         * without calling any user handlers.
                         */
                        save_previous_kprobe(kcb);
                        set_current_kprobe(p, regs, kcb);
                        kprobes_inc_nmissed_count(p);
                        kcb->kprobe_status = KPROBE_REENTER;
                        prepare_singlestep(p, regs, kcb);
                        return 1;
                } else if (*(u32 *)addr != BREAKPOINT_INSTRUCTION) {
                        /* The breakpoint instruction was removed by
                         * another cpu right after we hit, no further
                         * handling of this interrupt is appropriate
                         */
                        ret = 1;
                }
                goto no_kprobe;
        }

        p = get_kprobe(addr);
        if (!p) {
                if (*(u32 *)addr != BREAKPOINT_INSTRUCTION) {
                        /*
                         * 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.
                         */
                        ret = 1;
                }
                /* Not one of ours: let kernel handle it */
                goto no_kprobe;
        }

        set_current_kprobe(p, regs, kcb);
        kcb->kprobe_status = KPROBE_HIT_ACTIVE;
        if (p->pre_handler && p->pre_handler(p, regs)) {
                reset_current_kprobe();
                preempt_enable_no_resched();
                return 1;
        }

        prepare_singlestep(p, regs, kcb);
        kcb->kprobe_status = KPROBE_HIT_SS;
        return 1;

no_kprobe:
        preempt_enable_no_resched();
        return ret;
}

/* If INSN is a relative control transfer instruction,
 * return the corrected branch destination value.
 *
 * regs->tpc and regs->tnpc still hold the values of the
 * program counters at the time of trap due to the execution
 * of the BREAKPOINT_INSTRUCTION_2 at p->ainsn.insn[1]
 * 
 */
static unsigned long __kprobes relbranch_fixup(u32 insn, struct kprobe *p,
                                               struct pt_regs *regs)
{
        unsigned long real_pc = (unsigned long) p->addr;

        /* Branch not taken, no mods necessary.  */
        if (regs->tnpc == regs->tpc + 0x4UL)
                return real_pc + 0x8UL;

        /* The three cases are call, branch w/prediction,
         * and traditional branch.
         */
        if ((insn & 0xc0000000) == 0x40000000 ||
            (insn & 0xc1c00000) == 0x00400000 ||
            (insn & 0xc1c00000) == 0x00800000) {
                unsigned long ainsn_addr;

                ainsn_addr = (unsigned long) &p->ainsn.insn[0];

                /* The instruction did all the work for us
                 * already, just apply the offset to the correct
                 * instruction location.
                 */
                return (real_pc + (regs->tnpc - ainsn_addr));
        }

        /* It is jmpl or some other absolute PC modification instruction,
         * leave NPC as-is.
         */
        return regs->tnpc;
}

/* If INSN is an instruction which writes its PC location
 * into a destination register, fix that up.
 */
static void __kprobes retpc_fixup(struct pt_regs *regs, u32 insn,
                                  unsigned long real_pc)
{
        unsigned long *slot = NULL;

        /* Simplest case is 'call', which always uses %o7 */
        if ((insn & 0xc0000000) == 0x40000000) {
                slot = &regs->u_regs[UREG_I7];
        }

        /* 'jmpl' encodes the register inside of the opcode */
        if ((insn & 0xc1f80000) == 0x81c00000) {
                unsigned long rd = ((insn >> 25) & 0x1f);

                if (rd <= 15) {
                        slot = &regs->u_regs[rd];
                } else {
                        /* Hard case, it goes onto the stack. */
                        flushw_all();

                        rd -= 16;
                        slot = (unsigned long *)
                                (regs->u_regs[UREG_FP] + STACK_BIAS);
                        slot += rd;
                }
        }
        if (slot != NULL)
                *slot = real_pc;
}

/*
 * Called after single-stepping.  p->addr is the address of the
 * instruction which has been replaced by the breakpoint
 * instruction.  To avoid the SMP problems that can occur when we
 * temporarily put back the original opcode to single-step, we
 * single-stepped a copy of the instruction.  The address of this
 * copy is &p->ainsn.insn[0].
 *
 * This function prepares to return from the post-single-step
 * breakpoint trap.
 */
static void __kprobes resume_execution(struct kprobe *p,
                struct pt_regs *regs, struct kprobe_ctlblk *kcb)
{
        u32 insn = p->ainsn.insn[0];

        regs->tnpc = relbranch_fixup(insn, p, regs);

        /* This assignment must occur after relbranch_fixup() */
        regs->tpc = kcb->kprobe_orig_tnpc;

        retpc_fixup(regs, insn, (unsigned long) p->addr);

        regs->tstate = ((regs->tstate & ~TSTATE_PIL) |
                        kcb->kprobe_orig_tstate_pil);
}

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

        if (!cur)
                return 0;

        if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
                kcb->kprobe_status = KPROBE_HIT_SSDONE;
                cur->post_handler(cur, regs, 0);
        }

        resume_execution(cur, regs, kcb);

        /*Restore back the original saved kprobes variables and continue. */
        if (kcb->kprobe_status == KPROBE_REENTER) {
                restore_previous_kprobe(kcb);
                goto out;
        }
        reset_current_kprobe();
out:
        preempt_enable_no_resched();

        return 1;
}

int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
        struct kprobe *cur = kprobe_running();
        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
        const struct exception_table_entry *entry;

        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 tpc points back to the probe address
                 * and allow the page fault handler to continue as a
                 * normal page fault.
                 */
                regs->tpc = (unsigned long)cur->addr;
                regs->tnpc = kcb->kprobe_orig_tnpc;
                regs->tstate = ((regs->tstate & ~TSTATE_PIL) |
                                kcb->kprobe_orig_tstate_pil);
                if (kcb->kprobe_status == KPROBE_REENTER)
                        restore_previous_kprobe(kcb);
                else
                        reset_current_kprobe();
                preempt_enable_no_resched();
                break;
        case KPROBE_HIT_ACTIVE:
        case KPROBE_HIT_SSDONE:
                /*
                 * In case the user-specified fault handler returned
                 * zero, try to fix up.
                 */

                entry = search_exception_tables(regs->tpc);
                if (entry) {
                        regs->tpc = entry->fixup;
                        regs->tnpc = regs->tpc + 4;
                        return 1;
                }

                /*
                 * fixup_exception() could not handle it,
                 * Let do_page_fault() fix it.
                 */
                break;
        default:
                break;
        }

        return 0;
}

/*
 * Wrapper routine to for handling exceptions.
 */
int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
                                       unsigned long val, void *data)
{
        struct die_args *args = (struct die_args *)data;
        int ret = NOTIFY_DONE;

        if (args->regs && user_mode(args->regs))
                return ret;

        switch (val) {
        case DIE_DEBUG:
                if (kprobe_handler(args->regs))
                        ret = NOTIFY_STOP;
                break;
        case DIE_DEBUG_2:
                if (post_kprobe_handler(args->regs))
                        ret = NOTIFY_STOP;
                break;
        default:
                break;
        }
        return ret;
}

asmlinkage void __kprobes kprobe_trap(unsigned long trap_level,
                                      struct pt_regs *regs)
{
        enum ctx_state prev_state = exception_enter();

        BUG_ON(trap_level != 0x170 && trap_level != 0x171);

        if (user_mode(regs)) {
                local_irq_enable();
                bad_trap(regs, trap_level);
                goto out;
        }

        /* trap_level == 0x170 --> ta 0x70
         * trap_level == 0x171 --> ta 0x71
         */
        if (notify_die((trap_level == 0x170) ? DIE_DEBUG : DIE_DEBUG_2,
                       (trap_level == 0x170) ? "debug" : "debug_2",
                       regs, 0, trap_level, SIGTRAP) != NOTIFY_STOP)
                bad_trap(regs, trap_level);
out:
        exception_exit(prev_state);
}

/* The value stored in the return address register is actually 2
 * instructions before where the callee will return to.
 * Sequences usually look something like this
 *
 *              call    some_function   <--- return register points here
 *               nop                    <--- call delay slot
 *              whatever                <--- where callee returns to
 *
 * To keep trampoline_probe_handler logic simpler, we normalize the
 * value kept in ri->ret_addr so we don't need to keep adjusting it
 * back and forth.
 */
void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
                                      struct pt_regs *regs)
{
        ri->ret_addr = (kprobe_opcode_t *)(regs->u_regs[UREG_RETPC] + 8);
        ri->fp = NULL;

        /* Replace the return addr with trampoline addr */
        regs->u_regs[UREG_RETPC] =
                ((unsigned long)__kretprobe_trampoline) - 8;
}

/*
 * Called when the probe at kretprobe trampoline is hit
 */
static int __kprobes trampoline_probe_handler(struct kprobe *p,
                                              struct pt_regs *regs)
{
        unsigned long orig_ret_address = 0;

        orig_ret_address = __kretprobe_trampoline_handler(regs, NULL);
        regs->tpc = orig_ret_address;
        regs->tnpc = orig_ret_address + 4;

        /*
         * By returning a non-zero value, we are telling
         * kprobe_handler() that we don't want the post_handler
         * to run (and have re-enabled preemption)
         */
        return 1;
}

static void __used kretprobe_trampoline_holder(void)
{
        asm volatile(".global __kretprobe_trampoline\n"
                     "__kretprobe_trampoline:\n"
                     "\tnop\n"
                     "\tnop\n");
}
static struct kprobe trampoline_p = {
        .addr = (kprobe_opcode_t *) &__kretprobe_trampoline,
        .pre_handler = trampoline_probe_handler
};

int __init arch_init_kprobes(void)
{
        return register_kprobe(&trampoline_p);
}

int __kprobes arch_trampoline_kprobe(struct kprobe *p)
{
        if (p->addr == (kprobe_opcode_t *)&__kretprobe_trampoline)
                return 1;

        return 0;
}