// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Code for Kernel probes Jump optimization.
 *
 * Copyright 2017, Anju T, IBM Corp.
 */

#include <linux/kprobes.h>
#include <linux/jump_label.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <asm/kprobes.h>
#include <asm/ptrace.h>
#include <asm/cacheflush.h>
#include <asm/code-patching.h>
#include <asm/sstep.h>
#include <asm/ppc-opcode.h>
#include <asm/inst.h>

#define TMPL_CALL_HDLR_IDX      (optprobe_template_call_handler - optprobe_template_entry)
#define TMPL_EMULATE_IDX        (optprobe_template_call_emulate - optprobe_template_entry)
#define TMPL_RET_IDX            (optprobe_template_ret - optprobe_template_entry)
#define TMPL_OP_IDX             (optprobe_template_op_address - optprobe_template_entry)
#define TMPL_INSN_IDX           (optprobe_template_insn - optprobe_template_entry)
#define TMPL_END_IDX            (optprobe_template_end - optprobe_template_entry)

static bool insn_page_in_use;

void *alloc_optinsn_page(void)
{
        if (insn_page_in_use)
                return NULL;
        insn_page_in_use = true;
        return &optinsn_slot;
}

void free_optinsn_page(void *page)
{
        insn_page_in_use = false;
}

/*
 * Check if we can optimize this probe. Returns NIP post-emulation if this can
 * be optimized and 0 otherwise.
 */
static unsigned long can_optimize(struct kprobe *p)
{
        struct pt_regs regs;
        struct instruction_op op;
        unsigned long nip = 0;
        unsigned long addr = (unsigned long)p->addr;

        /*
         * kprobe placed for kretprobe during boot time
         * has a 'nop' instruction, which can be emulated.
         * So further checks can be skipped.
         */
        if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
                return addr + sizeof(kprobe_opcode_t);

        /*
         * We only support optimizing kernel addresses, but not
         * module addresses.
         *
         * FIXME: Optimize kprobes placed in module addresses.
         */
        if (!is_kernel_addr(addr))
                return 0;

        memset(&regs, 0, sizeof(struct pt_regs));
        regs.nip = addr;
        regs.trap = 0x0;
        regs.msr = MSR_KERNEL;

        /*
         * Kprobe placed in conditional branch instructions are
         * not optimized, as we can't predict the nip prior with
         * dummy pt_regs and can not ensure that the return branch
         * from detour buffer falls in the range of address (i.e 32MB).
         * A branch back from trampoline is set up in the detour buffer
         * to the nip returned by the analyse_instr() here.
         *
         * Ensure that the instruction is not a conditional branch,
         * and that can be emulated.
         */
        if (!is_conditional_branch(ppc_inst_read(p->ainsn.insn)) &&
            analyse_instr(&op, &regs, ppc_inst_read(p->ainsn.insn)) == 1) {
                emulate_update_regs(&regs, &op);
                nip = regs.nip;
        }

        return nip;
}

static void optimized_callback(struct optimized_kprobe *op,
                               struct pt_regs *regs)
{
        /* This is possible if op is under delayed unoptimizing */
        if (kprobe_disabled(&op->kp))
                return;

        preempt_disable();

        if (kprobe_running()) {
                kprobes_inc_nmissed_count(&op->kp);
        } else {
                __this_cpu_write(current_kprobe, &op->kp);
                regs_set_return_ip(regs, (unsigned long)op->kp.addr);
                get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
                opt_pre_handler(&op->kp, regs);
                __this_cpu_write(current_kprobe, NULL);
        }

        preempt_enable_no_resched();
}
NOKPROBE_SYMBOL(optimized_callback);

void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
{
        if (op->optinsn.insn) {
                free_optinsn_slot(op->optinsn.insn, 1);
                op->optinsn.insn = NULL;
        }
}

static void patch_imm32_load_insns(unsigned long val, int reg, kprobe_opcode_t *addr)
{
        patch_instruction(addr++, ppc_inst(PPC_RAW_LIS(reg, PPC_HI(val))));
        patch_instruction(addr, ppc_inst(PPC_RAW_ORI(reg, reg, PPC_LO(val))));
}

/*
 * Generate instructions to load provided immediate 64-bit value
 * to register 'reg' and patch these instructions at 'addr'.
 */
static void patch_imm64_load_insns(unsigned long long val, int reg, kprobe_opcode_t *addr)
{
        patch_instruction(addr++, ppc_inst(PPC_RAW_LIS(reg, PPC_HIGHEST(val))));
        patch_instruction(addr++, ppc_inst(PPC_RAW_ORI(reg, reg, PPC_HIGHER(val))));
        patch_instruction(addr++, ppc_inst(PPC_RAW_SLDI(reg, reg, 32)));
        patch_instruction(addr++, ppc_inst(PPC_RAW_ORIS(reg, reg, PPC_HI(val))));
        patch_instruction(addr, ppc_inst(PPC_RAW_ORI(reg, reg, PPC_LO(val))));
}

static void patch_imm_load_insns(unsigned long val, int reg, kprobe_opcode_t *addr)
{
        if (IS_ENABLED(CONFIG_PPC64))
                patch_imm64_load_insns(val, reg, addr);
        else
                patch_imm32_load_insns(val, reg, addr);
}

int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
{
        struct ppc_inst branch_op_callback, branch_emulate_step, temp;
        unsigned long op_callback_addr, emulate_step_addr;
        kprobe_opcode_t *buff;
        long b_offset;
        unsigned long nip, size;
        int rc, i;

        nip = can_optimize(p);
        if (!nip)
                return -EILSEQ;

        /* Allocate instruction slot for detour buffer */
        buff = get_optinsn_slot();
        if (!buff)
                return -ENOMEM;

        /*
         * OPTPROBE uses 'b' instruction to branch to optinsn.insn.
         *
         * The target address has to be relatively nearby, to permit use
         * of branch instruction in powerpc, because the address is specified
         * in an immediate field in the instruction opcode itself, ie 24 bits
         * in the opcode specify the address. Therefore the address should
         * be within 32MB on either side of the current instruction.
         */
        b_offset = (unsigned long)buff - (unsigned long)p->addr;
        if (!is_offset_in_branch_range(b_offset))
                goto error;

        /* Check if the return address is also within 32MB range */
        b_offset = (unsigned long)(buff + TMPL_RET_IDX) - nip;
        if (!is_offset_in_branch_range(b_offset))
                goto error;

        /* Setup template */
        /* We can optimize this via patch_instruction_window later */
        size = (TMPL_END_IDX * sizeof(kprobe_opcode_t)) / sizeof(int);
        pr_devel("Copying template to %p, size %lu\n", buff, size);
        for (i = 0; i < size; i++) {
                rc = patch_instruction(buff + i, ppc_inst(*(optprobe_template_entry + i)));
                if (rc < 0)
                        goto error;
        }

        /*
         * Fixup the template with instructions to:
         * 1. load the address of the actual probepoint
         */
        patch_imm_load_insns((unsigned long)op, 3, buff + TMPL_OP_IDX);

        /*
         * 2. branch to optimized_callback() and emulate_step()
         */
        op_callback_addr = ppc_kallsyms_lookup_name("optimized_callback");
        emulate_step_addr = ppc_kallsyms_lookup_name("emulate_step");
        if (!op_callback_addr || !emulate_step_addr) {
                WARN(1, "Unable to lookup optimized_callback()/emulate_step()\n");
                goto error;
        }

        rc = create_branch(&branch_op_callback, buff + TMPL_CALL_HDLR_IDX,
                           op_callback_addr, BRANCH_SET_LINK);

        rc |= create_branch(&branch_emulate_step, buff + TMPL_EMULATE_IDX,
                            emulate_step_addr, BRANCH_SET_LINK);

        if (rc)
                goto error;

        patch_instruction(buff + TMPL_CALL_HDLR_IDX, branch_op_callback);
        patch_instruction(buff + TMPL_EMULATE_IDX, branch_emulate_step);

        /*
         * 3. load instruction to be emulated into relevant register, and
         */
        if (IS_ENABLED(CONFIG_PPC64)) {
                temp = ppc_inst_read(p->ainsn.insn);
                patch_imm_load_insns(ppc_inst_as_ulong(temp), 4, buff + TMPL_INSN_IDX);
        } else {
                patch_imm_load_insns((unsigned long)p->ainsn.insn, 4, buff + TMPL_INSN_IDX);
        }

        /*
         * 4. branch back from trampoline
         */
        patch_branch(buff + TMPL_RET_IDX, nip, 0);

        flush_icache_range((unsigned long)buff, (unsigned long)(&buff[TMPL_END_IDX]));

        op->optinsn.insn = buff;

        return 0;

error:
        free_optinsn_slot(buff, 0);
        return -ERANGE;

}

int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
{
        return optinsn->insn != NULL;
}

/*
 * On powerpc, Optprobes always replaces one instruction (4 bytes
 * aligned and 4 bytes long). It is impossible to encounter another
 * kprobe in this address range. So always return 0.
 */
int arch_check_optimized_kprobe(struct optimized_kprobe *op)
{
        return 0;
}

void arch_optimize_kprobes(struct list_head *oplist)
{
        struct ppc_inst instr;
        struct optimized_kprobe *op;
        struct optimized_kprobe *tmp;

        list_for_each_entry_safe(op, tmp, oplist, list) {
                /*
                 * Backup instructions which will be replaced
                 * by jump address
                 */
                memcpy(op->optinsn.copied_insn, op->kp.addr, RELATIVEJUMP_SIZE);
                create_branch(&instr, op->kp.addr, (unsigned long)op->optinsn.insn, 0);
                patch_instruction(op->kp.addr, instr);
                list_del_init(&op->list);
        }
}

void arch_unoptimize_kprobe(struct optimized_kprobe *op)
{
        arch_arm_kprobe(&op->kp);
}

void arch_unoptimize_kprobes(struct list_head *oplist, struct list_head *done_list)
{
        struct optimized_kprobe *op;
        struct optimized_kprobe *tmp;

        list_for_each_entry_safe(op, tmp, oplist, list) {
                arch_unoptimize_kprobe(op);
                list_move(&op->list, done_list);
        }
}

int arch_within_optimized_kprobe(struct optimized_kprobe *op, unsigned long addr)
{
        return ((unsigned long)op->kp.addr <= addr &&
                (unsigned long)op->kp.addr + RELATIVEJUMP_SIZE > addr);
}