// SPDX-License-Identifier: GPL-2.0
/*
 *  Copyright (C) 1994  Linus Torvalds
 *
 *  29 dec 2001 - Fixed oopses caused by unchecked access to the vm86
 *                stack - Manfred Spraul <manfred@colorfullife.com>
 *
 *  22 mar 2002 - Manfred detected the stackfaults, but didn't handle
 *                them correctly. Now the emulation will be in a
 *                consistent state after stackfaults - Kasper Dupont
 *                <kasperd@daimi.au.dk>
 *
 *  22 mar 2002 - Added missing clear_IF in set_vflags_* Kasper Dupont
 *                <kasperd@daimi.au.dk>
 *
 *  ?? ??? 2002 - Fixed premature returns from handle_vm86_fault
 *                caused by Kasper Dupont's changes - Stas Sergeev
 *
 *   4 apr 2002 - Fixed CHECK_IF_IN_TRAP broken by Stas' changes.
 *                Kasper Dupont <kasperd@daimi.au.dk>
 *
 *   9 apr 2002 - Changed syntax of macros in handle_vm86_fault.
 *                Kasper Dupont <kasperd@daimi.au.dk>
 *
 *   9 apr 2002 - Changed stack access macros to jump to a label
 *                instead of returning to userspace. This simplifies
 *                do_int, and is needed by handle_vm6_fault. Kasper
 *                Dupont <kasperd@daimi.au.dk>
 *
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/capability.h>
#include <linux/errno.h>
#include <linux/interrupt.h>
#include <linux/syscalls.h>
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/highmem.h>
#include <linux/ptrace.h>
#include <linux/audit.h>
#include <linux/stddef.h>
#include <linux/slab.h>
#include <linux/security.h>

#include <linux/uaccess.h>
#include <asm/io.h>
#include <asm/tlbflush.h>
#include <asm/irq.h>
#include <asm/traps.h>
#include <asm/vm86.h>
#include <asm/switch_to.h>

/*
 * Known problems:
 *
 * Interrupt handling is not guaranteed:
 * - a real x86 will disable all interrupts for one instruction
 *   after a "mov ss,xx" to make stack handling atomic even without
 *   the 'lss' instruction. We can't guarantee this in v86 mode,
 *   as the next instruction might result in a page fault or similar.
 * - a real x86 will have interrupts disabled for one instruction
 *   past the 'sti' that enables them. We don't bother with all the
 *   details yet.
 *
 * Let's hope these problems do not actually matter for anything.
 */


/*
 * 8- and 16-bit register defines..
 */
#define AL(regs)        (((unsigned char *)&((regs)->pt.ax))[0])
#define AH(regs)        (((unsigned char *)&((regs)->pt.ax))[1])
#define IP(regs)        (*(unsigned short *)&((regs)->pt.ip))
#define SP(regs)        (*(unsigned short *)&((regs)->pt.sp))

/*
 * virtual flags (16 and 32-bit versions)
 */
#define VFLAGS  (*(unsigned short *)&(current->thread.vm86->veflags))
#define VEFLAGS (current->thread.vm86->veflags)

#define set_flags(X, new, mask) \
((X) = ((X) & ~(mask)) | ((new) & (mask)))

#define SAFE_MASK       (0xDD5)
#define RETURN_MASK     (0xDFF)

void save_v86_state(struct kernel_vm86_regs *regs, int retval)
{
        struct task_struct *tsk = current;
        struct vm86plus_struct __user *user;
        struct vm86 *vm86 = current->thread.vm86;

        /*
         * This gets called from entry.S with interrupts disabled, but
         * from process context. Enable interrupts here, before trying
         * to access user space.
         */
        local_irq_enable();

        if (!vm86 || !vm86->user_vm86) {
                pr_alert("no user_vm86: BAD\n");
                do_exit(SIGSEGV);
        }
        set_flags(regs->pt.flags, VEFLAGS, X86_EFLAGS_VIF | vm86->veflags_mask);
        user = vm86->user_vm86;

        if (!user_access_begin(user, vm86->vm86plus.is_vm86pus ?
                       sizeof(struct vm86plus_struct) :
                       sizeof(struct vm86_struct)))
                goto Efault;

        unsafe_put_user(regs->pt.bx, &user->regs.ebx, Efault_end);
        unsafe_put_user(regs->pt.cx, &user->regs.ecx, Efault_end);
        unsafe_put_user(regs->pt.dx, &user->regs.edx, Efault_end);
        unsafe_put_user(regs->pt.si, &user->regs.esi, Efault_end);
        unsafe_put_user(regs->pt.di, &user->regs.edi, Efault_end);
        unsafe_put_user(regs->pt.bp, &user->regs.ebp, Efault_end);
        unsafe_put_user(regs->pt.ax, &user->regs.eax, Efault_end);
        unsafe_put_user(regs->pt.ip, &user->regs.eip, Efault_end);
        unsafe_put_user(regs->pt.cs, &user->regs.cs, Efault_end);
        unsafe_put_user(regs->pt.flags, &user->regs.eflags, Efault_end);
        unsafe_put_user(regs->pt.sp, &user->regs.esp, Efault_end);
        unsafe_put_user(regs->pt.ss, &user->regs.ss, Efault_end);
        unsafe_put_user(regs->es, &user->regs.es, Efault_end);
        unsafe_put_user(regs->ds, &user->regs.ds, Efault_end);
        unsafe_put_user(regs->fs, &user->regs.fs, Efault_end);
        unsafe_put_user(regs->gs, &user->regs.gs, Efault_end);

        /*
         * Don't write screen_bitmap in case some user had a value there
         * and expected it to remain unchanged.
         */

        user_access_end();

        preempt_disable();
        tsk->thread.sp0 = vm86->saved_sp0;
        tsk->thread.sysenter_cs = __KERNEL_CS;
        update_task_stack(tsk);
        refresh_sysenter_cs(&tsk->thread);
        vm86->saved_sp0 = 0;
        preempt_enable();

        memcpy(&regs->pt, &vm86->regs32, sizeof(struct pt_regs));

        lazy_load_gs(vm86->regs32.gs);

        regs->pt.ax = retval;
        return;

Efault_end:
        user_access_end();
Efault:
        pr_alert("could not access userspace vm86 info\n");
        do_exit(SIGSEGV);
}

static int do_vm86_irq_handling(int subfunction, int irqnumber);
static long do_sys_vm86(struct vm86plus_struct __user *user_vm86, bool plus);

SYSCALL_DEFINE1(vm86old, struct vm86_struct __user *, user_vm86)
{
        return do_sys_vm86((struct vm86plus_struct __user *) user_vm86, false);
}


SYSCALL_DEFINE2(vm86, unsigned long, cmd, unsigned long, arg)
{
        switch (cmd) {
        case VM86_REQUEST_IRQ:
        case VM86_FREE_IRQ:
        case VM86_GET_IRQ_BITS:
        case VM86_GET_AND_RESET_IRQ:
                return do_vm86_irq_handling(cmd, (int)arg);
        case VM86_PLUS_INSTALL_CHECK:
                /*
                 * NOTE: on old vm86 stuff this will return the error
                 *  from access_ok(), because the subfunction is
                 *  interpreted as (invalid) address to vm86_struct.
                 *  So the installation check works.
                 */
                return 0;
        }

        /* we come here only for functions VM86_ENTER, VM86_ENTER_NO_BYPASS */
        return do_sys_vm86((struct vm86plus_struct __user *) arg, true);
}


static long do_sys_vm86(struct vm86plus_struct __user *user_vm86, bool plus)
{
        struct task_struct *tsk = current;
        struct vm86 *vm86 = tsk->thread.vm86;
        struct kernel_vm86_regs vm86regs;
        struct pt_regs *regs = current_pt_regs();
        unsigned long err = 0;
        struct vm86_struct v;

        err = security_mmap_addr(0);
        if (err) {
                /*
                 * vm86 cannot virtualize the address space, so vm86 users
                 * need to manage the low 1MB themselves using mmap.  Given
                 * that BIOS places important data in the first page, vm86
                 * is essentially useless if mmap_min_addr != 0.  DOSEMU,
                 * for example, won't even bother trying to use vm86 if it
                 * can't map a page at virtual address 0.
                 *
                 * To reduce the available kernel attack surface, simply
                 * disallow vm86(old) for users who cannot mmap at va 0.
                 *
                 * The implementation of security_mmap_addr will allow
                 * suitably privileged users to map va 0 even if
                 * vm.mmap_min_addr is set above 0, and we want this
                 * behavior for vm86 as well, as it ensures that legacy
                 * tools like vbetool will not fail just because of
                 * vm.mmap_min_addr.
                 */
                pr_info_once("Denied a call to vm86(old) from %s[%d] (uid: %d).  Set the vm.mmap_min_addr sysctl to 0 and/or adjust LSM mmap_min_addr policy to enable vm86 if you are using a vm86-based DOS emulator.\n",
                             current->comm, task_pid_nr(current),
                             from_kuid_munged(&init_user_ns, current_uid()));
                return -EPERM;
        }

        if (!vm86) {
                if (!(vm86 = kzalloc(sizeof(*vm86), GFP_KERNEL)))
                        return -ENOMEM;
                tsk->thread.vm86 = vm86;
        }
        if (vm86->saved_sp0)
                return -EPERM;

        if (copy_from_user(&v, user_vm86,
                        offsetof(struct vm86_struct, int_revectored)))
                return -EFAULT;


        /* VM86_SCREEN_BITMAP had numerous bugs and appears to have no users. */
        if (v.flags & VM86_SCREEN_BITMAP) {
                char comm[TASK_COMM_LEN];

                pr_info_once("vm86: '%s' uses VM86_SCREEN_BITMAP, which is no longer supported\n", get_task_comm(comm, current));
                return -EINVAL;
        }

        memset(&vm86regs, 0, sizeof(vm86regs));

        vm86regs.pt.bx = v.regs.ebx;
        vm86regs.pt.cx = v.regs.ecx;
        vm86regs.pt.dx = v.regs.edx;
        vm86regs.pt.si = v.regs.esi;
        vm86regs.pt.di = v.regs.edi;
        vm86regs.pt.bp = v.regs.ebp;
        vm86regs.pt.ax = v.regs.eax;
        vm86regs.pt.ip = v.regs.eip;
        vm86regs.pt.cs = v.regs.cs;
        vm86regs.pt.flags = v.regs.eflags;
        vm86regs.pt.sp = v.regs.esp;
        vm86regs.pt.ss = v.regs.ss;
        vm86regs.es = v.regs.es;
        vm86regs.ds = v.regs.ds;
        vm86regs.fs = v.regs.fs;
        vm86regs.gs = v.regs.gs;

        vm86->flags = v.flags;
        vm86->cpu_type = v.cpu_type;

        if (copy_from_user(&vm86->int_revectored,
                           &user_vm86->int_revectored,
                           sizeof(struct revectored_struct)))
                return -EFAULT;
        if (copy_from_user(&vm86->int21_revectored,
                           &user_vm86->int21_revectored,
                           sizeof(struct revectored_struct)))
                return -EFAULT;
        if (plus) {
                if (copy_from_user(&vm86->vm86plus, &user_vm86->vm86plus,
                                   sizeof(struct vm86plus_info_struct)))
                        return -EFAULT;
                vm86->vm86plus.is_vm86pus = 1;
        } else
                memset(&vm86->vm86plus, 0,
                       sizeof(struct vm86plus_info_struct));

        memcpy(&vm86->regs32, regs, sizeof(struct pt_regs));
        vm86->user_vm86 = user_vm86;

/*
 * The flags register is also special: we cannot trust that the user
 * has set it up safely, so this makes sure interrupt etc flags are
 * inherited from protected mode.
 */
        VEFLAGS = vm86regs.pt.flags;
        vm86regs.pt.flags &= SAFE_MASK;
        vm86regs.pt.flags |= regs->flags & ~SAFE_MASK;
        vm86regs.pt.flags |= X86_VM_MASK;

        vm86regs.pt.orig_ax = regs->orig_ax;

        switch (vm86->cpu_type) {
        case CPU_286:
                vm86->veflags_mask = 0;
                break;
        case CPU_386:
                vm86->veflags_mask = X86_EFLAGS_NT | X86_EFLAGS_IOPL;
                break;
        case CPU_486:
                vm86->veflags_mask = X86_EFLAGS_AC | X86_EFLAGS_NT | X86_EFLAGS_IOPL;
                break;
        default:
                vm86->veflags_mask = X86_EFLAGS_ID | X86_EFLAGS_AC | X86_EFLAGS_NT | X86_EFLAGS_IOPL;
                break;
        }

/*
 * Save old state
 */
        vm86->saved_sp0 = tsk->thread.sp0;
        lazy_save_gs(vm86->regs32.gs);

        /* make room for real-mode segments */
        preempt_disable();
        tsk->thread.sp0 += 16;

        if (boot_cpu_has(X86_FEATURE_SEP)) {
                tsk->thread.sysenter_cs = 0;
                refresh_sysenter_cs(&tsk->thread);
        }

        update_task_stack(tsk);
        preempt_enable();

        memcpy((struct kernel_vm86_regs *)regs, &vm86regs, sizeof(vm86regs));
        return regs->ax;
}

static inline void set_IF(struct kernel_vm86_regs *regs)
{
        VEFLAGS |= X86_EFLAGS_VIF;
}

static inline void clear_IF(struct kernel_vm86_regs *regs)
{
        VEFLAGS &= ~X86_EFLAGS_VIF;
}

static inline void clear_TF(struct kernel_vm86_regs *regs)
{
        regs->pt.flags &= ~X86_EFLAGS_TF;
}

static inline void clear_AC(struct kernel_vm86_regs *regs)
{
        regs->pt.flags &= ~X86_EFLAGS_AC;
}

/*
 * It is correct to call set_IF(regs) from the set_vflags_*
 * functions. However someone forgot to call clear_IF(regs)
 * in the opposite case.
 * After the command sequence CLI PUSHF STI POPF you should
 * end up with interrupts disabled, but you ended up with
 * interrupts enabled.
 *  ( I was testing my own changes, but the only bug I
 *    could find was in a function I had not changed. )
 * [KD]
 */

static inline void set_vflags_long(unsigned long flags, struct kernel_vm86_regs *regs)
{
        set_flags(VEFLAGS, flags, current->thread.vm86->veflags_mask);
        set_flags(regs->pt.flags, flags, SAFE_MASK);
        if (flags & X86_EFLAGS_IF)
                set_IF(regs);
        else
                clear_IF(regs);
}

static inline void set_vflags_short(unsigned short flags, struct kernel_vm86_regs *regs)
{
        set_flags(VFLAGS, flags, current->thread.vm86->veflags_mask);
        set_flags(regs->pt.flags, flags, SAFE_MASK);
        if (flags & X86_EFLAGS_IF)
                set_IF(regs);
        else
                clear_IF(regs);
}

static inline unsigned long get_vflags(struct kernel_vm86_regs *regs)
{
        unsigned long flags = regs->pt.flags & RETURN_MASK;

        if (VEFLAGS & X86_EFLAGS_VIF)
                flags |= X86_EFLAGS_IF;
        flags |= X86_EFLAGS_IOPL;
        return flags | (VEFLAGS & current->thread.vm86->veflags_mask);
}

static inline int is_revectored(int nr, struct revectored_struct *bitmap)
{
        return test_bit(nr, bitmap->__map);
}

#define val_byte(val, n) (((__u8 *)&val)[n])

#define pushb(base, ptr, val, err_label) \
        do { \
                __u8 __val = val; \
                ptr--; \
                if (put_user(__val, base + ptr) < 0) \
                        goto err_label; \
        } while (0)

#define pushw(base, ptr, val, err_label) \
        do { \
                __u16 __val = val; \
                ptr--; \
                if (put_user(val_byte(__val, 1), base + ptr) < 0) \
                        goto err_label; \
                ptr--; \
                if (put_user(val_byte(__val, 0), base + ptr) < 0) \
                        goto err_label; \
        } while (0)

#define pushl(base, ptr, val, err_label) \
        do { \
                __u32 __val = val; \
                ptr--; \
                if (put_user(val_byte(__val, 3), base + ptr) < 0) \
                        goto err_label; \
                ptr--; \
                if (put_user(val_byte(__val, 2), base + ptr) < 0) \
                        goto err_label; \
                ptr--; \
                if (put_user(val_byte(__val, 1), base + ptr) < 0) \
                        goto err_label; \
                ptr--; \
                if (put_user(val_byte(__val, 0), base + ptr) < 0) \
                        goto err_label; \
        } while (0)

#define popb(base, ptr, err_label) \
        ({ \
                __u8 __res; \
                if (get_user(__res, base + ptr) < 0) \
                        goto err_label; \
                ptr++; \
                __res; \
        })

#define popw(base, ptr, err_label) \
        ({ \
                __u16 __res; \
                if (get_user(val_byte(__res, 0), base + ptr) < 0) \
                        goto err_label; \
                ptr++; \
                if (get_user(val_byte(__res, 1), base + ptr) < 0) \
                        goto err_label; \
                ptr++; \
                __res; \
        })

#define popl(base, ptr, err_label) \
        ({ \
                __u32 __res; \
                if (get_user(val_byte(__res, 0), base + ptr) < 0) \
                        goto err_label; \
                ptr++; \
                if (get_user(val_byte(__res, 1), base + ptr) < 0) \
                        goto err_label; \
                ptr++; \
                if (get_user(val_byte(__res, 2), base + ptr) < 0) \
                        goto err_label; \
                ptr++; \
                if (get_user(val_byte(__res, 3), base + ptr) < 0) \
                        goto err_label; \
                ptr++; \
                __res; \
        })

/* There are so many possible reasons for this function to return
 * VM86_INTx, so adding another doesn't bother me. We can expect
 * userspace programs to be able to handle it. (Getting a problem
 * in userspace is always better than an Oops anyway.) [KD]
 */
static void do_int(struct kernel_vm86_regs *regs, int i,
    unsigned char __user *ssp, unsigned short sp)
{
        unsigned long __user *intr_ptr;
        unsigned long segoffs;
        struct vm86 *vm86 = current->thread.vm86;

        if (regs->pt.cs == BIOSSEG)
                goto cannot_handle;
        if (is_revectored(i, &vm86->int_revectored))
                goto cannot_handle;
        if (i == 0x21 && is_revectored(AH(regs), &vm86->int21_revectored))
                goto cannot_handle;
        intr_ptr = (unsigned long __user *) (i << 2);
        if (get_user(segoffs, intr_ptr))
                goto cannot_handle;
        if ((segoffs >> 16) == BIOSSEG)
                goto cannot_handle;
        pushw(ssp, sp, get_vflags(regs), cannot_handle);
        pushw(ssp, sp, regs->pt.cs, cannot_handle);
        pushw(ssp, sp, IP(regs), cannot_handle);
        regs->pt.cs = segoffs >> 16;
        SP(regs) -= 6;
        IP(regs) = segoffs & 0xffff;
        clear_TF(regs);
        clear_IF(regs);
        clear_AC(regs);
        return;

cannot_handle:
        save_v86_state(regs, VM86_INTx + (i << 8));
}

int handle_vm86_trap(struct kernel_vm86_regs *regs, long error_code, int trapno)
{
        struct vm86 *vm86 = current->thread.vm86;

        if (vm86->vm86plus.is_vm86pus) {
                if ((trapno == 3) || (trapno == 1)) {
                        save_v86_state(regs, VM86_TRAP + (trapno << 8));
                        return 0;
                }
                do_int(regs, trapno, (unsigned char __user *) (regs->pt.ss << 4), SP(regs));
                return 0;
        }
        if (trapno != 1)
                return 1; /* we let this handle by the calling routine */
        current->thread.trap_nr = trapno;
        current->thread.error_code = error_code;
        force_sig(SIGTRAP);
        return 0;
}

void handle_vm86_fault(struct kernel_vm86_regs *regs, long error_code)
{
        unsigned char opcode;
        unsigned char __user *csp;
        unsigned char __user *ssp;
        unsigned short ip, sp, orig_flags;
        int data32, pref_done;
        struct vm86plus_info_struct *vmpi = &current->thread.vm86->vm86plus;

#define CHECK_IF_IN_TRAP \
        if (vmpi->vm86dbg_active && vmpi->vm86dbg_TFpendig) \
                newflags |= X86_EFLAGS_TF

        orig_flags = *(unsigned short *)&regs->pt.flags;

        csp = (unsigned char __user *) (regs->pt.cs << 4);
        ssp = (unsigned char __user *) (regs->pt.ss << 4);
        sp = SP(regs);
        ip = IP(regs);

        data32 = 0;
        pref_done = 0;
        do {
                switch (opcode = popb(csp, ip, simulate_sigsegv)) {
                case 0x66:      /* 32-bit data */     data32 = 1; break;
                case 0x67:      /* 32-bit address */  break;
                case 0x2e:      /* CS */              break;
                case 0x3e:      /* DS */              break;
                case 0x26:      /* ES */              break;
                case 0x36:      /* SS */              break;
                case 0x65:      /* GS */              break;
                case 0x64:      /* FS */              break;
                case 0xf2:      /* repnz */       break;
                case 0xf3:      /* rep */             break;
                default: pref_done = 1;
                }
        } while (!pref_done);

        switch (opcode) {

        /* pushf */
        case 0x9c:
                if (data32) {
                        pushl(ssp, sp, get_vflags(regs), simulate_sigsegv);
                        SP(regs) -= 4;
                } else {
                        pushw(ssp, sp, get_vflags(regs), simulate_sigsegv);
                        SP(regs) -= 2;
                }
                IP(regs) = ip;
                goto vm86_fault_return;

        /* popf */
        case 0x9d:
                {
                unsigned long newflags;
                if (data32) {
                        newflags = popl(ssp, sp, simulate_sigsegv);
                        SP(regs) += 4;
                } else {
                        newflags = popw(ssp, sp, simulate_sigsegv);
                        SP(regs) += 2;
                }
                IP(regs) = ip;
                CHECK_IF_IN_TRAP;
                if (data32)
                        set_vflags_long(newflags, regs);
                else
                        set_vflags_short(newflags, regs);

                goto check_vip;
                }

        /* int xx */
        case 0xcd: {
                int intno = popb(csp, ip, simulate_sigsegv);
                IP(regs) = ip;
                if (vmpi->vm86dbg_active) {
                        if ((1 << (intno & 7)) & vmpi->vm86dbg_intxxtab[intno >> 3]) {
                                save_v86_state(regs, VM86_INTx + (intno << 8));
                                return;
                        }
                }
                do_int(regs, intno, ssp, sp);
                return;
        }

        /* iret */
        case 0xcf:
                {
                unsigned long newip;
                unsigned long newcs;
                unsigned long newflags;
                if (data32) {
                        newip = popl(ssp, sp, simulate_sigsegv);
                        newcs = popl(ssp, sp, simulate_sigsegv);
                        newflags = popl(ssp, sp, simulate_sigsegv);
                        SP(regs) += 12;
                } else {
                        newip = popw(ssp, sp, simulate_sigsegv);
                        newcs = popw(ssp, sp, simulate_sigsegv);
                        newflags = popw(ssp, sp, simulate_sigsegv);
                        SP(regs) += 6;
                }
                IP(regs) = newip;
                regs->pt.cs = newcs;
                CHECK_IF_IN_TRAP;
                if (data32) {
                        set_vflags_long(newflags, regs);
                } else {
                        set_vflags_short(newflags, regs);
                }
                goto check_vip;
                }

        /* cli */
        case 0xfa:
                IP(regs) = ip;
                clear_IF(regs);
                goto vm86_fault_return;

        /* sti */
        /*
         * Damn. This is incorrect: the 'sti' instruction should actually
         * enable interrupts after the /next/ instruction. Not good.
         *
         * Probably needs some horsing around with the TF flag. Aiee..
         */
        case 0xfb:
                IP(regs) = ip;
                set_IF(regs);
                goto check_vip;

        default:
                save_v86_state(regs, VM86_UNKNOWN);
        }

        return;

check_vip:
        if ((VEFLAGS & (X86_EFLAGS_VIP | X86_EFLAGS_VIF)) ==
            (X86_EFLAGS_VIP | X86_EFLAGS_VIF)) {
                save_v86_state(regs, VM86_STI);
                return;
        }

vm86_fault_return:
        if (vmpi->force_return_for_pic  && (VEFLAGS & (X86_EFLAGS_IF | X86_EFLAGS_VIF))) {
                save_v86_state(regs, VM86_PICRETURN);
                return;
        }
        if (orig_flags & X86_EFLAGS_TF)
                handle_vm86_trap(regs, 0, X86_TRAP_DB);
        return;

simulate_sigsegv:
        /* FIXME: After a long discussion with Stas we finally
         *        agreed, that this is wrong. Here we should
         *        really send a SIGSEGV to the user program.
         *        But how do we create the correct context? We
         *        are inside a general protection fault handler
         *        and has just returned from a page fault handler.
         *        The correct context for the signal handler
         *        should be a mixture of the two, but how do we
         *        get the information? [KD]
         */
        save_v86_state(regs, VM86_UNKNOWN);
}

/* ---------------- vm86 special IRQ passing stuff ----------------- */

#define VM86_IRQNAME            "vm86irq"

static struct vm86_irqs {
        struct task_struct *tsk;
        int sig;
} vm86_irqs[16];

static DEFINE_SPINLOCK(irqbits_lock);
static int irqbits;

#define ALLOWED_SIGS (1 /* 0 = don't send a signal */ \
        | (1 << SIGUSR1) | (1 << SIGUSR2) | (1 << SIGIO)  | (1 << SIGURG) \
        | (1 << SIGUNUSED))

static irqreturn_t irq_handler(int intno, void *dev_id)
{
        int irq_bit;
        unsigned long flags;

        spin_lock_irqsave(&irqbits_lock, flags);
        irq_bit = 1 << intno;
        if ((irqbits & irq_bit) || !vm86_irqs[intno].tsk)
                goto out;
        irqbits |= irq_bit;
        if (vm86_irqs[intno].sig)
                send_sig(vm86_irqs[intno].sig, vm86_irqs[intno].tsk, 1);
        /*
         * IRQ will be re-enabled when user asks for the irq (whether
         * polling or as a result of the signal)
         */
        disable_irq_nosync(intno);
        spin_unlock_irqrestore(&irqbits_lock, flags);
        return IRQ_HANDLED;

out:
        spin_unlock_irqrestore(&irqbits_lock, flags);
        return IRQ_NONE;
}

static inline void free_vm86_irq(int irqnumber)
{
        unsigned long flags;

        free_irq(irqnumber, NULL);
        vm86_irqs[irqnumber].tsk = NULL;

        spin_lock_irqsave(&irqbits_lock, flags);
        irqbits &= ~(1 << irqnumber);
        spin_unlock_irqrestore(&irqbits_lock, flags);
}

void release_vm86_irqs(struct task_struct *task)
{
        int i;
        for (i = FIRST_VM86_IRQ ; i <= LAST_VM86_IRQ; i++)
            if (vm86_irqs[i].tsk == task)
                free_vm86_irq(i);
}

static inline int get_and_reset_irq(int irqnumber)
{
        int bit;
        unsigned long flags;
        int ret = 0;

        if (invalid_vm86_irq(irqnumber)) return 0;
        if (vm86_irqs[irqnumber].tsk != current) return 0;
        spin_lock_irqsave(&irqbits_lock, flags);
        bit = irqbits & (1 << irqnumber);
        irqbits &= ~bit;
        if (bit) {
                enable_irq(irqnumber);
                ret = 1;
        }

        spin_unlock_irqrestore(&irqbits_lock, flags);
        return ret;
}


static int do_vm86_irq_handling(int subfunction, int irqnumber)
{
        int ret;
        switch (subfunction) {
                case VM86_GET_AND_RESET_IRQ: {
                        return get_and_reset_irq(irqnumber);
                }
                case VM86_GET_IRQ_BITS: {
                        return irqbits;
                }
                case VM86_REQUEST_IRQ: {
                        int sig = irqnumber >> 8;
                        int irq = irqnumber & 255;
                        if (!capable(CAP_SYS_ADMIN)) return -EPERM;
                        if (!((1 << sig) & ALLOWED_SIGS)) return -EPERM;
                        if (invalid_vm86_irq(irq)) return -EPERM;
                        if (vm86_irqs[irq].tsk) return -EPERM;
                        ret = request_irq(irq, &irq_handler, 0, VM86_IRQNAME, NULL);
                        if (ret) return ret;
                        vm86_irqs[irq].sig = sig;
                        vm86_irqs[irq].tsk = current;
                        return irq;
                }
                case  VM86_FREE_IRQ: {
                        if (invalid_vm86_irq(irqnumber)) return -EPERM;
                        if (!vm86_irqs[irqnumber].tsk) return 0;
                        if (vm86_irqs[irqnumber].tsk != current) return -EPERM;
                        free_vm86_irq(irqnumber);
                        return 0;
                }
        }
        return -EINVAL;
}