// SPDX-License-Identifier: GPL-2.0
/*---------------------------------------------------------------------------+
 |  get_address.c                                                            |
 |                                                                           |
 | Get the effective address from an FPU instruction.                        |
 |                                                                           |
 | Copyright (C) 1992,1993,1994,1997                                         |
 |                       W. Metzenthen, 22 Parker St, Ormond, Vic 3163,      |
 |                       Australia.  E-mail   billm@suburbia.net             |
 |                                                                           |
 |                                                                           |
 +---------------------------------------------------------------------------*/

/*---------------------------------------------------------------------------+
 | Note:                                                                     |
 |    The file contains code which accesses user memory.                     |
 |    Emulator static data may change when user memory is accessed, due to   |
 |    other processes using the emulator while swapping is in progress.      |
 +---------------------------------------------------------------------------*/

#include <linux/stddef.h>

#include <linux/uaccess.h>
#include <asm/vm86.h>

#include "fpu_system.h"
#include "exception.h"
#include "fpu_emu.h"

#define FPU_WRITE_BIT 0x10

static int reg_offset[] = {
        offsetof(struct pt_regs, ax),
        offsetof(struct pt_regs, cx),
        offsetof(struct pt_regs, dx),
        offsetof(struct pt_regs, bx),
        offsetof(struct pt_regs, sp),
        offsetof(struct pt_regs, bp),
        offsetof(struct pt_regs, si),
        offsetof(struct pt_regs, di)
};

#define REG_(x) (*(long *)(reg_offset[(x)] + (u_char *)FPU_info->regs))

static int reg_offset_vm86[] = {
        offsetof(struct pt_regs, cs),
        offsetof(struct kernel_vm86_regs, ds),
        offsetof(struct kernel_vm86_regs, es),
        offsetof(struct kernel_vm86_regs, fs),
        offsetof(struct kernel_vm86_regs, gs),
        offsetof(struct pt_regs, ss),
        offsetof(struct kernel_vm86_regs, ds)
};

#define VM86_REG_(x) (*(unsigned short *) \
                (reg_offset_vm86[((unsigned)x)] + (u_char *)FPU_info->regs))

static int reg_offset_pm[] = {
        offsetof(struct pt_regs, cs),
        offsetof(struct pt_regs, ds),
        offsetof(struct pt_regs, es),
        offsetof(struct pt_regs, fs),
        offsetof(struct pt_regs, ds),   /* dummy, not saved on stack */
        offsetof(struct pt_regs, ss),
        offsetof(struct pt_regs, ds)
};

#define PM_REG_(x) (*(unsigned short *) \
                (reg_offset_pm[((unsigned)x)] + (u_char *)FPU_info->regs))

/* Decode the SIB byte. This function assumes mod != 0 */
static int sib(int mod, unsigned long *fpu_eip)
{
        u_char ss, index, base;
        long offset;

        RE_ENTRANT_CHECK_OFF;
        FPU_code_access_ok(1);
        FPU_get_user(base, (u_char __user *) (*fpu_eip));       /* The SIB byte */
        RE_ENTRANT_CHECK_ON;
        (*fpu_eip)++;
        ss = base >> 6;
        index = (base >> 3) & 7;
        base &= 7;

        if ((mod == 0) && (base == 5))
                offset = 0;     /* No base register */
        else
                offset = REG_(base);

        if (index == 4) {
                /* No index register */
                /* A non-zero ss is illegal */
                if (ss)
                        EXCEPTION(EX_Invalid);
        } else {
                offset += (REG_(index)) << ss;
        }

        if (mod == 1) {
                /* 8 bit signed displacement */
                long displacement;
                RE_ENTRANT_CHECK_OFF;
                FPU_code_access_ok(1);
                FPU_get_user(displacement, (signed char __user *)(*fpu_eip));
                offset += displacement;
                RE_ENTRANT_CHECK_ON;
                (*fpu_eip)++;
        } else if (mod == 2 || base == 5) {     /* The second condition also has mod==0 */
                /* 32 bit displacement */
                long displacement;
                RE_ENTRANT_CHECK_OFF;
                FPU_code_access_ok(4);
                FPU_get_user(displacement, (long __user *)(*fpu_eip));
                offset += displacement;
                RE_ENTRANT_CHECK_ON;
                (*fpu_eip) += 4;
        }

        return offset;
}

static unsigned long vm86_segment(u_char segment, struct address *addr)
{
        segment--;
#ifdef PARANOID
        if (segment > PREFIX_SS_) {
                EXCEPTION(EX_INTERNAL | 0x130);
                math_abort(FPU_info, SIGSEGV);
        }
#endif /* PARANOID */
        addr->selector = VM86_REG_(segment);
        return (unsigned long)VM86_REG_(segment) << 4;
}

/* This should work for 16 and 32 bit protected mode. */
static long pm_address(u_char FPU_modrm, u_char segment,
                       struct address *addr, long offset)
{
        struct desc_struct descriptor;
        unsigned long base_address, limit, address, seg_top;

        segment--;

#ifdef PARANOID
        /* segment is unsigned, so this also detects if segment was 0: */
        if (segment > PREFIX_SS_) {
                EXCEPTION(EX_INTERNAL | 0x132);
                math_abort(FPU_info, SIGSEGV);
        }
#endif /* PARANOID */

        switch (segment) {
        case PREFIX_GS_ - 1:
                /* user gs handling can be lazy, use special accessors */
                savesegment(gs, addr->selector);
                break;
        default:
                addr->selector = PM_REG_(segment);
        }

        descriptor = FPU_get_ldt_descriptor(addr->selector);
        base_address = seg_get_base(&descriptor);
        address = base_address + offset;
        limit = seg_get_limit(&descriptor) + 1;
        limit *= seg_get_granularity(&descriptor);
        limit += base_address - 1;
        if (limit < base_address)
                limit = 0xffffffff;

        if (seg_expands_down(&descriptor)) {
                if (descriptor.g) {
                        seg_top = 0xffffffff;
                } else {
                        seg_top = base_address + (1 << 20);
                        if (seg_top < base_address)
                                seg_top = 0xffffffff;
                }
                access_limit =
                    (address <= limit) || (address >= seg_top) ? 0 :
                    ((seg_top - address) >= 255 ? 255 : seg_top - address);
        } else {
                access_limit =
                    (address > limit) || (address < base_address) ? 0 :
                    ((limit - address) >= 254 ? 255 : limit - address + 1);
        }
        if (seg_execute_only(&descriptor) ||
            (!seg_writable(&descriptor) && (FPU_modrm & FPU_WRITE_BIT))) {
                access_limit = 0;
        }
        return address;
}

/*
       MOD R/M byte:  MOD == 3 has a special use for the FPU
                      SIB byte used iff R/M = 100b

       7   6   5   4   3   2   1   0
       .....   .........   .........
        MOD    OPCODE(2)     R/M

       SIB byte

       7   6   5   4   3   2   1   0
       .....   .........   .........
        SS      INDEX        BASE

*/

void __user *FPU_get_address(u_char FPU_modrm, unsigned long *fpu_eip,
                             struct address *addr, fpu_addr_modes addr_modes)
{
        u_char mod;
        unsigned rm = FPU_modrm & 7;
        long *cpu_reg_ptr;
        int address = 0;        /* Initialized just to stop compiler warnings. */

        /* Memory accessed via the cs selector is write protected
           in `non-segmented' 32 bit protected mode. */
        if (!addr_modes.default_mode && (FPU_modrm & FPU_WRITE_BIT)
            && (addr_modes.override.segment == PREFIX_CS_)) {
                math_abort(FPU_info, SIGSEGV);
        }

        addr->selector = FPU_DS;        /* Default, for 32 bit non-segmented mode. */

        mod = (FPU_modrm >> 6) & 3;

        if (rm == 4 && mod != 3) {
                address = sib(mod, fpu_eip);
        } else {
                cpu_reg_ptr = &REG_(rm);
                switch (mod) {
                case 0:
                        if (rm == 5) {
                                /* Special case: disp32 */
                                RE_ENTRANT_CHECK_OFF;
                                FPU_code_access_ok(4);
                                FPU_get_user(address,
                                             (unsigned long __user
                                              *)(*fpu_eip));
                                (*fpu_eip) += 4;
                                RE_ENTRANT_CHECK_ON;
                                addr->offset = address;
                                return (void __user *)address;
                        } else {
                                address = *cpu_reg_ptr; /* Just return the contents
                                                           of the cpu register */
                                addr->offset = address;
                                return (void __user *)address;
                        }
                case 1:
                        /* 8 bit signed displacement */
                        RE_ENTRANT_CHECK_OFF;
                        FPU_code_access_ok(1);
                        FPU_get_user(address, (signed char __user *)(*fpu_eip));
                        RE_ENTRANT_CHECK_ON;
                        (*fpu_eip)++;
                        break;
                case 2:
                        /* 32 bit displacement */
                        RE_ENTRANT_CHECK_OFF;
                        FPU_code_access_ok(4);
                        FPU_get_user(address, (long __user *)(*fpu_eip));
                        (*fpu_eip) += 4;
                        RE_ENTRANT_CHECK_ON;
                        break;
                case 3:
                        /* Not legal for the FPU */
                        EXCEPTION(EX_Invalid);
                }
                address += *cpu_reg_ptr;
        }

        addr->offset = address;

        switch (addr_modes.default_mode) {
        case 0:
                break;
        case VM86:
                address += vm86_segment(addr_modes.override.segment, addr);
                break;
        case PM16:
        case SEG32:
                address = pm_address(FPU_modrm, addr_modes.override.segment,
                                     addr, address);
                break;
        default:
                EXCEPTION(EX_INTERNAL | 0x133);
        }

        return (void __user *)address;
}

void __user *FPU_get_address_16(u_char FPU_modrm, unsigned long *fpu_eip,
                                struct address *addr, fpu_addr_modes addr_modes)
{
        u_char mod;
        unsigned rm = FPU_modrm & 7;
        int address = 0;        /* Default used for mod == 0 */

        /* Memory accessed via the cs selector is write protected
           in `non-segmented' 32 bit protected mode. */
        if (!addr_modes.default_mode && (FPU_modrm & FPU_WRITE_BIT)
            && (addr_modes.override.segment == PREFIX_CS_)) {
                math_abort(FPU_info, SIGSEGV);
        }

        addr->selector = FPU_DS;        /* Default, for 32 bit non-segmented mode. */

        mod = (FPU_modrm >> 6) & 3;

        switch (mod) {
        case 0:
                if (rm == 6) {
                        /* Special case: disp16 */
                        RE_ENTRANT_CHECK_OFF;
                        FPU_code_access_ok(2);
                        FPU_get_user(address,
                                     (unsigned short __user *)(*fpu_eip));
                        (*fpu_eip) += 2;
                        RE_ENTRANT_CHECK_ON;
                        goto add_segment;
                }
                break;
        case 1:
                /* 8 bit signed displacement */
                RE_ENTRANT_CHECK_OFF;
                FPU_code_access_ok(1);
                FPU_get_user(address, (signed char __user *)(*fpu_eip));
                RE_ENTRANT_CHECK_ON;
                (*fpu_eip)++;
                break;
        case 2:
                /* 16 bit displacement */
                RE_ENTRANT_CHECK_OFF;
                FPU_code_access_ok(2);
                FPU_get_user(address, (unsigned short __user *)(*fpu_eip));
                (*fpu_eip) += 2;
                RE_ENTRANT_CHECK_ON;
                break;
        case 3:
                /* Not legal for the FPU */
                EXCEPTION(EX_Invalid);
                break;
        }
        switch (rm) {
        case 0:
                address += FPU_info->regs->bx + FPU_info->regs->si;
                break;
        case 1:
                address += FPU_info->regs->bx + FPU_info->regs->di;
                break;
        case 2:
                address += FPU_info->regs->bp + FPU_info->regs->si;
                if (addr_modes.override.segment == PREFIX_DEFAULT)
                        addr_modes.override.segment = PREFIX_SS_;
                break;
        case 3:
                address += FPU_info->regs->bp + FPU_info->regs->di;
                if (addr_modes.override.segment == PREFIX_DEFAULT)
                        addr_modes.override.segment = PREFIX_SS_;
                break;
        case 4:
                address += FPU_info->regs->si;
                break;
        case 5:
                address += FPU_info->regs->di;
                break;
        case 6:
                address += FPU_info->regs->bp;
                if (addr_modes.override.segment == PREFIX_DEFAULT)
                        addr_modes.override.segment = PREFIX_SS_;
                break;
        case 7:
                address += FPU_info->regs->bx;
                break;
        }

      add_segment:
        address &= 0xffff;

        addr->offset = address;

        switch (addr_modes.default_mode) {
        case 0:
                break;
        case VM86:
                address += vm86_segment(addr_modes.override.segment, addr);
                break;
        case PM16:
        case SEG32:
                address = pm_address(FPU_modrm, addr_modes.override.segment,
                                     addr, address);
                break;
        default:
                EXCEPTION(EX_INTERNAL | 0x131);
        }

        return (void __user *)address;
}