// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  Kernel Probes Jump Optimization (Optprobes)
 *
 * Copyright (C) IBM Corporation, 2002, 2004
 * Copyright (C) Hitachi Ltd., 2012
 * Copyright (C) Huawei Inc., 2014
 */

#include <linux/kprobes.h>
#include <linux/jump_label.h>
#include <asm/kprobes.h>
#include <asm/cacheflush.h>
/* for arm_gen_branch */
#include <asm/insn.h>
/* for patch_text */
#include <asm/patch.h>

#include "core.h"

/*
 * See register_usage_flags. If the probed instruction doesn't use PC,
 * we can copy it into template and have it executed directly without
 * simulation or emulation.
 */
#define ARM_REG_PC      15
#define can_kprobe_direct_exec(m)       (!test_bit(ARM_REG_PC, &(m)))

/*
 * NOTE: the first sub and add instruction will be modified according
 * to the stack cost of the instruction.
 */
asm (
                        ".global optprobe_template_entry\n"
                        "optprobe_template_entry:\n"
                        ".global optprobe_template_sub_sp\n"
                        "optprobe_template_sub_sp:"
                        "       sub     sp, sp, #0xff\n"
                        "       stmia   sp, {r0 - r14} \n"
                        ".global optprobe_template_add_sp\n"
                        "optprobe_template_add_sp:"
                        "       add     r3, sp, #0xff\n"
                        "       str     r3, [sp, #52]\n"
                        "       mrs     r4, cpsr\n"
                        "       str     r4, [sp, #64]\n"
                        "       mov     r1, sp\n"
                        "       ldr     r0, 1f\n"
                        "       ldr     r2, 2f\n"
                        /*
                         * AEABI requires an 8-bytes alignment stack. If
                         * SP % 8 != 0 (SP % 4 == 0 should be ensured),
                         * alloc more bytes here.
                         */
                        "       and     r4, sp, #4\n"
                        "       sub     sp, sp, r4\n"
#if __LINUX_ARM_ARCH__ >= 5
                        "       blx     r2\n"
#else
                        "       mov     lr, pc\n"
                        "       mov     pc, r2\n"
#endif
                        "       add     sp, sp, r4\n"
                        "       ldr     r1, [sp, #64]\n"
                        "       tst     r1, #"__stringify(PSR_T_BIT)"\n"
                        "       ldrne   r2, [sp, #60]\n"
                        "       orrne   r2, #1\n"
                        "       strne   r2, [sp, #60] @ set bit0 of PC for thumb\n"
                        "       msr     cpsr_cxsf, r1\n"
                        ".global optprobe_template_restore_begin\n"
                        "optprobe_template_restore_begin:\n"
                        "       ldmia   sp, {r0 - r15}\n"
                        ".global optprobe_template_restore_orig_insn\n"
                        "optprobe_template_restore_orig_insn:\n"
                        "       nop\n"
                        ".global optprobe_template_restore_end\n"
                        "optprobe_template_restore_end:\n"
                        "       nop\n"
                        ".global optprobe_template_val\n"
                        "optprobe_template_val:\n"
                        "1:     .long 0\n"
                        ".global optprobe_template_call\n"
                        "optprobe_template_call:\n"
                        "2:     .long 0\n"
                        ".global optprobe_template_end\n"
                        "optprobe_template_end:\n");

#define TMPL_VAL_IDX \
        ((unsigned long *)optprobe_template_val - (unsigned long *)optprobe_template_entry)
#define TMPL_CALL_IDX \
        ((unsigned long *)optprobe_template_call - (unsigned long *)optprobe_template_entry)
#define TMPL_END_IDX \
        ((unsigned long *)optprobe_template_end - (unsigned long *)optprobe_template_entry)
#define TMPL_ADD_SP \
        ((unsigned long *)optprobe_template_add_sp - (unsigned long *)optprobe_template_entry)
#define TMPL_SUB_SP \
        ((unsigned long *)optprobe_template_sub_sp - (unsigned long *)optprobe_template_entry)
#define TMPL_RESTORE_BEGIN \
        ((unsigned long *)optprobe_template_restore_begin - (unsigned long *)optprobe_template_entry)
#define TMPL_RESTORE_ORIGN_INSN \
        ((unsigned long *)optprobe_template_restore_orig_insn - (unsigned long *)optprobe_template_entry)
#define TMPL_RESTORE_END \
        ((unsigned long *)optprobe_template_restore_end - (unsigned long *)optprobe_template_entry)

/*
 * ARM can always optimize an instruction when using ARM ISA, except
 * instructions like 'str r0, [sp, r1]' which store to stack and unable
 * to determine stack space consumption statically.
 */
int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
{
        return optinsn->insn != NULL;
}

/*
 * In ARM ISA, kprobe opt always replace one instruction (4 bytes
 * aligned and 4 bytes long). It is impossible to encounter another
 * kprobe in the address range. So always return 0.
 */
int arch_check_optimized_kprobe(struct optimized_kprobe *op)
{
        return 0;
}

/* Caller must ensure addr & 3 == 0 */
static int can_optimize(struct kprobe *kp)
{
        if (kp->ainsn.stack_space < 0)
                return 0;
        /*
         * 255 is the biggest imm can be used in 'sub r0, r0, #<imm>'.
         * Number larger than 255 needs special encoding.
         */
        if (kp->ainsn.stack_space > 255 - sizeof(struct pt_regs))
                return 0;
        return 1;
}

/* Free optimized instruction slot */
static void
__arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
{
        if (op->optinsn.insn) {
                free_optinsn_slot(op->optinsn.insn, dirty);
                op->optinsn.insn = NULL;
        }
}

extern void kprobe_handler(struct pt_regs *regs);

static void
optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
{
        unsigned long flags;
        struct kprobe *p = &op->kp;
        struct kprobe_ctlblk *kcb;

        /* Save skipped registers */
        regs->ARM_pc = (unsigned long)op->kp.addr;
        regs->ARM_ORIG_r0 = ~0UL;

        local_irq_save(flags);
        kcb = get_kprobe_ctlblk();

        if (kprobe_running()) {
                kprobes_inc_nmissed_count(&op->kp);
        } else {
                __this_cpu_write(current_kprobe, &op->kp);
                kcb->kprobe_status = KPROBE_HIT_ACTIVE;
                opt_pre_handler(&op->kp, regs);
                __this_cpu_write(current_kprobe, NULL);
        }

        /*
         * We singlestep the replaced instruction only when it can't be
         * executed directly during restore.
         */
        if (!p->ainsn.kprobe_direct_exec)
                op->kp.ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);

        local_irq_restore(flags);
}
NOKPROBE_SYMBOL(optimized_callback)

int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *orig)
{
        kprobe_opcode_t *code;
        unsigned long rel_chk;
        unsigned long val;
        unsigned long stack_protect = sizeof(struct pt_regs);

        if (!can_optimize(orig))
                return -EILSEQ;

        code = get_optinsn_slot();
        if (!code)
                return -ENOMEM;

        /*
         * Verify if the address gap is in 32MiB range, because this uses
         * a relative jump.
         *
         * kprobe opt use a 'b' instruction to branch to optinsn.insn.
         * According to ARM manual, branch instruction is:
         *
         *   31  28 27           24 23             0
         *  +------+---+---+---+---+----------------+
         *  | cond | 1 | 0 | 1 | 0 |      imm24     |
         *  +------+---+---+---+---+----------------+
         *
         * imm24 is a signed 24 bits integer. The real branch offset is computed
         * by: imm32 = SignExtend(imm24:'00', 32);
         *
         * So the maximum forward branch should be:
         *   (0x007fffff << 2) = 0x01fffffc =  0x1fffffc
         * The maximum backword branch should be:
         *   (0xff800000 << 2) = 0xfe000000 = -0x2000000
         *
         * We can simply check (rel & 0xfe000003):
         *  if rel is positive, (rel & 0xfe000000) shoule be 0
         *  if rel is negitive, (rel & 0xfe000000) should be 0xfe000000
         *  the last '3' is used for alignment checking.
         */
        rel_chk = (unsigned long)((long)code -
                        (long)orig->addr + 8) & 0xfe000003;

        if ((rel_chk != 0) && (rel_chk != 0xfe000000)) {
                /*
                 * Different from x86, we free code buf directly instead of
                 * calling __arch_remove_optimized_kprobe() because
                 * we have not fill any field in op.
                 */
                free_optinsn_slot(code, 0);
                return -ERANGE;
        }

        /* Copy arch-dep-instance from template. */
        memcpy(code, (unsigned long *)optprobe_template_entry,
                        TMPL_END_IDX * sizeof(kprobe_opcode_t));

        /* Adjust buffer according to instruction. */
        BUG_ON(orig->ainsn.stack_space < 0);

        stack_protect += orig->ainsn.stack_space;

        /* Should have been filtered by can_optimize(). */
        BUG_ON(stack_protect > 255);

        /* Create a 'sub sp, sp, #<stack_protect>' */
        code[TMPL_SUB_SP] = __opcode_to_mem_arm(0xe24dd000 | stack_protect);
        /* Create a 'add r3, sp, #<stack_protect>' */
        code[TMPL_ADD_SP] = __opcode_to_mem_arm(0xe28d3000 | stack_protect);

        /* Set probe information */
        val = (unsigned long)op;
        code[TMPL_VAL_IDX] = val;

        /* Set probe function call */
        val = (unsigned long)optimized_callback;
        code[TMPL_CALL_IDX] = val;

        /* If possible, copy insn and have it executed during restore */
        orig->ainsn.kprobe_direct_exec = false;
        if (can_kprobe_direct_exec(orig->ainsn.register_usage_flags)) {
                kprobe_opcode_t final_branch = arm_gen_branch(
                                (unsigned long)(&code[TMPL_RESTORE_END]),
                                (unsigned long)(op->kp.addr) + 4);
                if (final_branch != 0) {
                        /*
                         * Replace original 'ldmia sp, {r0 - r15}' with
                         * 'ldmia {r0 - r14}', restore all registers except pc.
                         */
                        code[TMPL_RESTORE_BEGIN] = __opcode_to_mem_arm(0xe89d7fff);

                        /* The original probed instruction */
                        code[TMPL_RESTORE_ORIGN_INSN] = __opcode_to_mem_arm(orig->opcode);

                        /* Jump back to next instruction */
                        code[TMPL_RESTORE_END] = __opcode_to_mem_arm(final_branch);
                        orig->ainsn.kprobe_direct_exec = true;
                }
        }

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

        /* Set op->optinsn.insn means prepared. */
        op->optinsn.insn = code;
        return 0;
}

void __kprobes arch_optimize_kprobes(struct list_head *oplist)
{
        struct optimized_kprobe *op, *tmp;

        list_for_each_entry_safe(op, tmp, oplist, list) {
                unsigned long insn;
                WARN_ON(kprobe_disabled(&op->kp));

                /*
                 * Backup instructions which will be replaced
                 * by jump address
                 */
                memcpy(op->optinsn.copied_insn, op->kp.addr,
                                RELATIVEJUMP_SIZE);

                insn = arm_gen_branch((unsigned long)op->kp.addr,
                                (unsigned long)op->optinsn.insn);
                BUG_ON(insn == 0);

                /*
                 * Make it a conditional branch if replaced insn
                 * is consitional
                 */
                insn = (__mem_to_opcode_arm(
                          op->optinsn.copied_insn[0]) & 0xf0000000) |
                        (insn & 0x0fffffff);

                /*
                 * Similar to __arch_disarm_kprobe, operations which
                 * removing breakpoints must be wrapped by stop_machine
                 * to avoid racing.
                 */
                kprobes_remove_breakpoint(op->kp.addr, insn);

                list_del_init(&op->list);
        }
}

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

/*
 * Recover original instructions and breakpoints from relative jumps.
 * Caller must call with locking kprobe_mutex.
 */
void arch_unoptimize_kprobes(struct list_head *oplist,
                            struct list_head *done_list)
{
        struct optimized_kprobe *op, *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);
}

void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
{
        __arch_remove_optimized_kprobe(op, 1);
}