/*
 * arch/arm/probes/decode.c
 *
 * Copyright (C) 2011 Jon Medhurst <tixy@yxit.co.uk>.
 *
 * Some contents moved here from arch/arm/include/asm/kprobes-arm.c which is
 * Copyright (C) 2006, 2007 Motorola Inc.
 *
 * 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.
 */

#include <linux/kernel.h>
#include <linux/types.h>
#include <asm/system_info.h>
#include <asm/ptrace.h>
#include <linux/bug.h>

#include "decode.h"


#ifndef find_str_pc_offset

/*
 * For STR and STM instructions, an ARM core may choose to use either
 * a +8 or a +12 displacement from the current instruction's address.
 * Whichever value is chosen for a given core, it must be the same for
 * both instructions and may not change.  This function measures it.
 */

int str_pc_offset;

void __init find_str_pc_offset(void)
{
        int addr, scratch, ret;

        __asm__ (
                "sub    %[ret], pc, #4          \n\t"
                "str    pc, %[addr]             \n\t"
                "ldr    %[scr], %[addr]         \n\t"
                "sub    %[ret], %[scr], %[ret]  \n\t"
                : [ret] "=r" (ret), [scr] "=r" (scratch), [addr] "+m" (addr));

        str_pc_offset = ret;
}

#endif /* !find_str_pc_offset */


#ifndef test_load_write_pc_interworking

bool load_write_pc_interworks;

void __init test_load_write_pc_interworking(void)
{
        int arch = cpu_architecture();
        BUG_ON(arch == CPU_ARCH_UNKNOWN);
        load_write_pc_interworks = arch >= CPU_ARCH_ARMv5T;
}

#endif /* !test_load_write_pc_interworking */


#ifndef test_alu_write_pc_interworking

bool alu_write_pc_interworks;

void __init test_alu_write_pc_interworking(void)
{
        int arch = cpu_architecture();
        BUG_ON(arch == CPU_ARCH_UNKNOWN);
        alu_write_pc_interworks = arch >= CPU_ARCH_ARMv7;
}

#endif /* !test_alu_write_pc_interworking */


void __init arm_probes_decode_init(void)
{
        find_str_pc_offset();
        test_load_write_pc_interworking();
        test_alu_write_pc_interworking();
}


static unsigned long __kprobes __check_eq(unsigned long cpsr)
{
        return cpsr & PSR_Z_BIT;
}

static unsigned long __kprobes __check_ne(unsigned long cpsr)
{
        return (~cpsr) & PSR_Z_BIT;
}

static unsigned long __kprobes __check_cs(unsigned long cpsr)
{
        return cpsr & PSR_C_BIT;
}

static unsigned long __kprobes __check_cc(unsigned long cpsr)
{
        return (~cpsr) & PSR_C_BIT;
}

static unsigned long __kprobes __check_mi(unsigned long cpsr)
{
        return cpsr & PSR_N_BIT;
}

static unsigned long __kprobes __check_pl(unsigned long cpsr)
{
        return (~cpsr) & PSR_N_BIT;
}

static unsigned long __kprobes __check_vs(unsigned long cpsr)
{
        return cpsr & PSR_V_BIT;
}

static unsigned long __kprobes __check_vc(unsigned long cpsr)
{
        return (~cpsr) & PSR_V_BIT;
}

static unsigned long __kprobes __check_hi(unsigned long cpsr)
{
        cpsr &= ~(cpsr >> 1); /* PSR_C_BIT &= ~PSR_Z_BIT */
        return cpsr & PSR_C_BIT;
}

static unsigned long __kprobes __check_ls(unsigned long cpsr)
{
        cpsr &= ~(cpsr >> 1); /* PSR_C_BIT &= ~PSR_Z_BIT */
        return (~cpsr) & PSR_C_BIT;
}

static unsigned long __kprobes __check_ge(unsigned long cpsr)
{
        cpsr ^= (cpsr << 3); /* PSR_N_BIT ^= PSR_V_BIT */
        return (~cpsr) & PSR_N_BIT;
}

static unsigned long __kprobes __check_lt(unsigned long cpsr)
{
        cpsr ^= (cpsr << 3); /* PSR_N_BIT ^= PSR_V_BIT */
        return cpsr & PSR_N_BIT;
}

static unsigned long __kprobes __check_gt(unsigned long cpsr)
{
        unsigned long temp = cpsr ^ (cpsr << 3); /* PSR_N_BIT ^= PSR_V_BIT */
        temp |= (cpsr << 1);                     /* PSR_N_BIT |= PSR_Z_BIT */
        return (~temp) & PSR_N_BIT;
}

static unsigned long __kprobes __check_le(unsigned long cpsr)
{
        unsigned long temp = cpsr ^ (cpsr << 3); /* PSR_N_BIT ^= PSR_V_BIT */
        temp |= (cpsr << 1);                     /* PSR_N_BIT |= PSR_Z_BIT */
        return temp & PSR_N_BIT;
}

static unsigned long __kprobes __check_al(unsigned long cpsr)
{
        return true;
}

probes_check_cc * const probes_condition_checks[16] = {
        &__check_eq, &__check_ne, &__check_cs, &__check_cc,
        &__check_mi, &__check_pl, &__check_vs, &__check_vc,
        &__check_hi, &__check_ls, &__check_ge, &__check_lt,
        &__check_gt, &__check_le, &__check_al, &__check_al
};


void __kprobes probes_simulate_nop(probes_opcode_t opcode,
        struct arch_probes_insn *asi,
        struct pt_regs *regs)
{
}

void __kprobes probes_emulate_none(probes_opcode_t opcode,
        struct arch_probes_insn *asi,
        struct pt_regs *regs)
{
        asi->insn_fn();
}

/*
 * Prepare an instruction slot to receive an instruction for emulating.
 * This is done by placing a subroutine return after the location where the
 * instruction will be placed. We also modify ARM instructions to be
 * unconditional as the condition code will already be checked before any
 * emulation handler is called.
 */
static probes_opcode_t __kprobes
prepare_emulated_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
                      bool thumb)
{
#ifdef CONFIG_THUMB2_KERNEL
        if (thumb) {
                u16 *thumb_insn = (u16 *)asi->insn;
                /* Thumb bx lr */
                thumb_insn[1] = __opcode_to_mem_thumb16(0x4770);
                thumb_insn[2] = __opcode_to_mem_thumb16(0x4770);
                return insn;
        }
        asi->insn[1] = __opcode_to_mem_arm(0xe12fff1e); /* ARM bx lr */
#else
        asi->insn[1] = __opcode_to_mem_arm(0xe1a0f00e); /* mov pc, lr */
#endif
        /* Make an ARM instruction unconditional */
        if (insn < 0xe0000000)
                insn = (insn | 0xe0000000) & ~0x10000000;
        return insn;
}

/*
 * Write a (probably modified) instruction into the slot previously prepared by
 * prepare_emulated_insn
 */
static void  __kprobes
set_emulated_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
                  bool thumb)
{
#ifdef CONFIG_THUMB2_KERNEL
        if (thumb) {
                u16 *ip = (u16 *)asi->insn;
                if (is_wide_instruction(insn))
                        *ip++ = __opcode_to_mem_thumb16(insn >> 16);
                *ip++ = __opcode_to_mem_thumb16(insn);
                return;
        }
#endif
        asi->insn[0] = __opcode_to_mem_arm(insn);
}

/*
 * When we modify the register numbers encoded in an instruction to be emulated,
 * the new values come from this define. For ARM and 32-bit Thumb instructions
 * this gives...
 *
 *      bit position      16  12   8   4   0
 *      ---------------+---+---+---+---+---+
 *      register         r2  r0  r1  --  r3
 */
#define INSN_NEW_BITS           0x00020103

/* Each nibble has same value as that at INSN_NEW_BITS bit 16 */
#define INSN_SAMEAS16_BITS      0x22222222

/*
 * Validate and modify each of the registers encoded in an instruction.
 *
 * Each nibble in regs contains a value from enum decode_reg_type. For each
 * non-zero value, the corresponding nibble in pinsn is validated and modified
 * according to the type.
 */
static bool __kprobes decode_regs(probes_opcode_t *pinsn, u32 regs, bool modify)
{
        probes_opcode_t insn = *pinsn;
        probes_opcode_t mask = 0xf; /* Start at least significant nibble */

        for (; regs != 0; regs >>= 4, mask <<= 4) {

                probes_opcode_t new_bits = INSN_NEW_BITS;

                switch (regs & 0xf) {

                case REG_TYPE_NONE:
                        /* Nibble not a register, skip to next */
                        continue;

                case REG_TYPE_ANY:
                        /* Any register is allowed */
                        break;

                case REG_TYPE_SAMEAS16:
                        /* Replace register with same as at bit position 16 */
                        new_bits = INSN_SAMEAS16_BITS;
                        break;

                case REG_TYPE_SP:
                        /* Only allow SP (R13) */
                        if ((insn ^ 0xdddddddd) & mask)
                                goto reject;
                        break;

                case REG_TYPE_PC:
                        /* Only allow PC (R15) */
                        if ((insn ^ 0xffffffff) & mask)
                                goto reject;
                        break;

                case REG_TYPE_NOSP:
                        /* Reject SP (R13) */
                        if (((insn ^ 0xdddddddd) & mask) == 0)
                                goto reject;
                        break;

                case REG_TYPE_NOSPPC:
                case REG_TYPE_NOSPPCX:
                        /* Reject SP and PC (R13 and R15) */
                        if (((insn ^ 0xdddddddd) & 0xdddddddd & mask) == 0)
                                goto reject;
                        break;

                case REG_TYPE_NOPCWB:
                        if (!is_writeback(insn))
                                break; /* No writeback, so any register is OK */
                        /* fall through... */
                case REG_TYPE_NOPC:
                case REG_TYPE_NOPCX:
                        /* Reject PC (R15) */
                        if (((insn ^ 0xffffffff) & mask) == 0)
                                goto reject;
                        break;
                }

                /* Replace value of nibble with new register number... */
                insn &= ~mask;
                insn |= new_bits & mask;
        }

        if (modify)
                *pinsn = insn;

        return true;

reject:
        return false;
}

static const int decode_struct_sizes[NUM_DECODE_TYPES] = {
        [DECODE_TYPE_TABLE]     = sizeof(struct decode_table),
        [DECODE_TYPE_CUSTOM]    = sizeof(struct decode_custom),
        [DECODE_TYPE_SIMULATE]  = sizeof(struct decode_simulate),
        [DECODE_TYPE_EMULATE]   = sizeof(struct decode_emulate),
        [DECODE_TYPE_OR]        = sizeof(struct decode_or),
        [DECODE_TYPE_REJECT]    = sizeof(struct decode_reject)
};

static int run_checkers(const struct decode_checker *checkers[],
                int action, probes_opcode_t insn,
                struct arch_probes_insn *asi,
                const struct decode_header *h)
{
        const struct decode_checker **p;

        if (!checkers)
                return INSN_GOOD;

        p = checkers;
        while (*p != NULL) {
                int retval;
                probes_check_t *checker_func = (*p)[action].checker;

                retval = INSN_GOOD;
                if (checker_func)
                        retval = checker_func(insn, asi, h);
                if (retval == INSN_REJECTED)
                        return retval;
                p++;
        }
        return INSN_GOOD;
}

/*
 * probes_decode_insn operates on data tables in order to decode an ARM
 * architecture instruction onto which a kprobe has been placed.
 *
 * These instruction decoding tables are a concatenation of entries each
 * of which consist of one of the following structs:
 *
 *      decode_table
 *      decode_custom
 *      decode_simulate
 *      decode_emulate
 *      decode_or
 *      decode_reject
 *
 * Each of these starts with a struct decode_header which has the following
 * fields:
 *
 *      type_regs
 *      mask
 *      value
 *
 * The least significant DECODE_TYPE_BITS of type_regs contains a value
 * from enum decode_type, this indicates which of the decode_* structs
 * the entry contains. The value DECODE_TYPE_END indicates the end of the
 * table.
 *
 * When the table is parsed, each entry is checked in turn to see if it
 * matches the instruction to be decoded using the test:
 *
 *      (insn & mask) == value
 *
 * If no match is found before the end of the table is reached then decoding
 * fails with INSN_REJECTED.
 *
 * When a match is found, decode_regs() is called to validate and modify each
 * of the registers encoded in the instruction; the data it uses to do this
 * is (type_regs >> DECODE_TYPE_BITS). A validation failure will cause decoding
 * to fail with INSN_REJECTED.
 *
 * Once the instruction has passed the above tests, further processing
 * depends on the type of the table entry's decode struct.
 *
 */
int __kprobes
probes_decode_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
                   const union decode_item *table, bool thumb,
                   bool emulate, const union decode_action *actions,
                   const struct decode_checker *checkers[])
{
        const struct decode_header *h = (struct decode_header *)table;
        const struct decode_header *next;
        bool matched = false;
        /*
         * @insn can be modified by decode_regs. Save its original
         * value for checkers.
         */
        probes_opcode_t origin_insn = insn;

        /*
         * stack_space is initialized to 0 here. Checker functions
         * should update is value if they find this is a stack store
         * instruction: positive value means bytes of stack usage,
         * negitive value means unable to determine stack usage
         * statically. For instruction doesn't store to stack, checker
         * do nothing with it.
         */
        asi->stack_space = 0;

        /*
         * Similarly to stack_space, register_usage_flags is filled by
         * checkers. Its default value is set to ~0, which is 'all
         * registers are used', to prevent any potential optimization.
         */
        asi->register_usage_flags = ~0UL;

        if (emulate)
                insn = prepare_emulated_insn(insn, asi, thumb);

        for (;; h = next) {
                enum decode_type type = h->type_regs.bits & DECODE_TYPE_MASK;
                u32 regs = h->type_regs.bits >> DECODE_TYPE_BITS;

                if (type == DECODE_TYPE_END)
                        return INSN_REJECTED;

                next = (struct decode_header *)
                                ((uintptr_t)h + decode_struct_sizes[type]);

                if (!matched && (insn & h->mask.bits) != h->value.bits)
                        continue;

                if (!decode_regs(&insn, regs, emulate))
                        return INSN_REJECTED;

                switch (type) {

                case DECODE_TYPE_TABLE: {
                        struct decode_table *d = (struct decode_table *)h;
                        next = (struct decode_header *)d->table.table;
                        break;
                }

                case DECODE_TYPE_CUSTOM: {
                        int err;
                        struct decode_custom *d = (struct decode_custom *)h;
                        int action = d->decoder.action;

                        err = run_checkers(checkers, action, origin_insn, asi, h);
                        if (err == INSN_REJECTED)
                                return INSN_REJECTED;
                        return actions[action].decoder(insn, asi, h);
                }

                case DECODE_TYPE_SIMULATE: {
                        int err;
                        struct decode_simulate *d = (struct decode_simulate *)h;
                        int action = d->handler.action;

                        err = run_checkers(checkers, action, origin_insn, asi, h);
                        if (err == INSN_REJECTED)
                                return INSN_REJECTED;
                        asi->insn_handler = actions[action].handler;
                        return INSN_GOOD_NO_SLOT;
                }

                case DECODE_TYPE_EMULATE: {
                        int err;
                        struct decode_emulate *d = (struct decode_emulate *)h;
                        int action = d->handler.action;

                        err = run_checkers(checkers, action, origin_insn, asi, h);
                        if (err == INSN_REJECTED)
                                return INSN_REJECTED;

                        if (!emulate)
                                return actions[action].decoder(insn, asi, h);

                        asi->insn_handler = actions[action].handler;
                        set_emulated_insn(insn, asi, thumb);
                        return INSN_GOOD;
                }

                case DECODE_TYPE_OR:
                        matched = true;
                        break;

                case DECODE_TYPE_REJECT:
                default:
                        return INSN_REJECTED;
                }
        }
}