WSL2-Linux-Kernel/arch/x86/kernel/vm86_32.c

/*
 *  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/sched.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 <asm/uaccess.h>
#include <asm/io.h>
#include <asm/tlbflush.h>
#include <asm/irq.h>
#include <asm/syscalls.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.
 */


#define KVM86	((struct kernel_vm86_struct *)regs)
#define VMPI	KVM86->vm86plus


/*
 * 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.v86flags))
#define VEFLAGS	(current->thread.v86flags)

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

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

/* convert kernel_vm86_regs to vm86_regs */
static int copy_vm86_regs_to_user(struct vm86_regs __user *user,
				  const struct kernel_vm86_regs *regs)
{
	int ret = 0;

	/*
	 * kernel_vm86_regs is missing gs, so copy everything up to
	 * (but not including) orig_eax, and then rest including orig_eax.
	 */
	ret += copy_to_user(user, regs, offsetof(struct kernel_vm86_regs, pt.orig_ax));
	ret += copy_to_user(&user->orig_eax, &regs->pt.orig_ax,
			    sizeof(struct kernel_vm86_regs) -
			    offsetof(struct kernel_vm86_regs, pt.orig_ax));

	return ret;
}

/* convert vm86_regs to kernel_vm86_regs */
static int copy_vm86_regs_from_user(struct kernel_vm86_regs *regs,
				    const struct vm86_regs __user *user,
				    unsigned extra)
{
	int ret = 0;

	/* copy ax-fs inclusive */
	ret += copy_from_user(regs, user, offsetof(struct kernel_vm86_regs, pt.orig_ax));
	/* copy orig_ax-__gsh+extra */
	ret += copy_from_user(&regs->pt.orig_ax, &user->orig_eax,
			      sizeof(struct kernel_vm86_regs) -
			      offsetof(struct kernel_vm86_regs, pt.orig_ax) +
			      extra);
	return ret;
}

struct pt_regs *save_v86_state(struct kernel_vm86_regs *regs)
{
	struct tss_struct *tss;
	struct pt_regs *ret;
	unsigned long tmp;

	/*
	 * 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 (!current->thread.vm86_info) {
		pr_alert("no vm86_info: BAD\n");
		do_exit(SIGSEGV);
	}
	set_flags(regs->pt.flags, VEFLAGS, X86_EFLAGS_VIF | current->thread.v86mask);
	tmp = copy_vm86_regs_to_user(&current->thread.vm86_info->regs, regs);
	tmp += put_user(current->thread.screen_bitmap, &current->thread.vm86_info->screen_bitmap);
	if (tmp) {
		pr_alert("could not access userspace vm86_info\n");
		do_exit(SIGSEGV);
	}

	tss = &per_cpu(init_tss, get_cpu());
	current->thread.sp0 = current->thread.saved_sp0;
	current->thread.sysenter_cs = __KERNEL_CS;
	load_sp0(tss, &current->thread);
	current->thread.saved_sp0 = 0;
	put_cpu();

	ret = KVM86->regs32;

	ret->fs = current->thread.saved_fs;
	set_user_gs(ret, current->thread.saved_gs);

	return ret;
}

static void mark_screen_rdonly(struct mm_struct *mm)
{
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;
	spinlock_t *ptl;
	int i;

	down_write(&mm->mmap_sem);
	pgd = pgd_offset(mm, 0xA0000);
	if (pgd_none_or_clear_bad(pgd))
		goto out;
	pud = pud_offset(pgd, 0xA0000);
	if (pud_none_or_clear_bad(pud))
		goto out;
	pmd = pmd_offset(pud, 0xA0000);
	split_huge_page_pmd_mm(mm, 0xA0000, pmd);
	if (pmd_none_or_clear_bad(pmd))
		goto out;
	pte = pte_offset_map_lock(mm, pmd, 0xA0000, &ptl);
	for (i = 0; i < 32; i++) {
		if (pte_present(*pte))
			set_pte(pte, pte_wrprotect(*pte));
		pte++;
	}
	pte_unmap_unlock(pte, ptl);
out:
	up_write(&mm->mmap_sem);
	flush_tlb();
}



static int do_vm86_irq_handling(int subfunction, int irqnumber);
static void do_sys_vm86(struct kernel_vm86_struct *info, struct task_struct *tsk);

int sys_vm86old(struct vm86_struct __user *v86)
{
	struct kernel_vm86_struct info; /* declare this _on top_,
					 * this avoids wasting of stack space.
					 * This remains on the stack until we
					 * return to 32 bit user space.
					 */
	struct task_struct *tsk;
	int tmp, ret = -EPERM;

	tsk = current;
	if (tsk->thread.saved_sp0)
		goto out;
	tmp = copy_vm86_regs_from_user(&info.regs, &v86->regs,
				       offsetof(struct kernel_vm86_struct, vm86plus) -
				       sizeof(info.regs));
	ret = -EFAULT;
	if (tmp)
		goto out;
	memset(&info.vm86plus, 0, (int)&info.regs32 - (int)&info.vm86plus);
	info.regs32 = current_pt_regs();
	tsk->thread.vm86_info = v86;
	do_sys_vm86(&info, tsk);
	ret = 0;	/* we never return here */
out:
	return ret;
}


int sys_vm86(unsigned long cmd, unsigned long arg)
{
	struct kernel_vm86_struct info; /* declare this _on top_,
					 * this avoids wasting of stack space.
					 * This remains on the stack until we
					 * return to 32 bit user space.
					 */
	struct task_struct *tsk;
	int tmp, ret;
	struct vm86plus_struct __user *v86;

	tsk = current;
	switch (cmd) {
	case VM86_REQUEST_IRQ:
	case VM86_FREE_IRQ:
	case VM86_GET_IRQ_BITS:
	case VM86_GET_AND_RESET_IRQ:
		ret = do_vm86_irq_handling(cmd, (int)arg);
		goto out;
	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.
		 */
		ret = 0;
		goto out;
	}

	/* we come here only for functions VM86_ENTER, VM86_ENTER_NO_BYPASS */
	ret = -EPERM;
	if (tsk->thread.saved_sp0)
		goto out;
	v86 = (struct vm86plus_struct __user *)arg;
	tmp = copy_vm86_regs_from_user(&info.regs, &v86->regs,
				       offsetof(struct kernel_vm86_struct, regs32) -
				       sizeof(info.regs));
	ret = -EFAULT;
	if (tmp)
		goto out;
	info.regs32 = current_pt_regs();
	info.vm86plus.is_vm86pus = 1;
	tsk->thread.vm86_info = (struct vm86_struct __user *)v86;
	do_sys_vm86(&info, tsk);
	ret = 0;	/* we never return here */
out:
	return ret;
}


static void do_sys_vm86(struct kernel_vm86_struct *info, struct task_struct *tsk)
{
	struct tss_struct *tss;
/*
 * make sure the vm86() system call doesn't try to do anything silly
 */
	info->regs.pt.ds = 0;
	info->regs.pt.es = 0;
	info->regs.pt.fs = 0;
#ifndef CONFIG_X86_32_LAZY_GS
	info->regs.pt.gs = 0;
#endif

/*
 * 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 = info->regs.pt.flags;
	info->regs.pt.flags &= SAFE_MASK;
	info->regs.pt.flags |= info->regs32->flags & ~SAFE_MASK;
	info->regs.pt.flags |= X86_VM_MASK;

	switch (info->cpu_type) {
	case CPU_286:
		tsk->thread.v86mask = 0;
		break;
	case CPU_386:
		tsk->thread.v86mask = X86_EFLAGS_NT | X86_EFLAGS_IOPL;
		break;
	case CPU_486:
		tsk->thread.v86mask = X86_EFLAGS_AC | X86_EFLAGS_NT | X86_EFLAGS_IOPL;
		break;
	default:
		tsk->thread.v86mask = X86_EFLAGS_ID | X86_EFLAGS_AC | X86_EFLAGS_NT | X86_EFLAGS_IOPL;
		break;
	}

/*
 * Save old state, set default return value (%ax) to 0 (VM86_SIGNAL)
 */
	info->regs32->ax = VM86_SIGNAL;
	tsk->thread.saved_sp0 = tsk->thread.sp0;
	tsk->thread.saved_fs = info->regs32->fs;
	tsk->thread.saved_gs = get_user_gs(info->regs32);

	tss = &per_cpu(init_tss, get_cpu());
	tsk->thread.sp0 = (unsigned long) &info->VM86_TSS_ESP0;
	if (cpu_has_sep)
		tsk->thread.sysenter_cs = 0;
	load_sp0(tss, &tsk->thread);
	put_cpu();

	tsk->thread.screen_bitmap = info->screen_bitmap;
	if (info->flags & VM86_SCREEN_BITMAP)
		mark_screen_rdonly(tsk->mm);

	/*call __audit_syscall_exit since we do not exit via the normal paths */
#ifdef CONFIG_AUDITSYSCALL
	if (unlikely(current->audit_context))
		__audit_syscall_exit(1, 0);
#endif

	__asm__ __volatile__(
		"movl %0,%%esp\n\t"
		"movl %1,%%ebp\n\t"
#ifdef CONFIG_X86_32_LAZY_GS
		"mov  %2, %%gs\n\t"
#endif
		"jmp resume_userspace"
		: /* no outputs */
		:"r" (&info->regs), "r" (task_thread_info(tsk)), "r" (0));
	/* we never return here */
}

static inline void return_to_32bit(struct kernel_vm86_regs *regs16, int retval)
{
	struct pt_regs *regs32;

	regs32 = save_v86_state(regs16);
	regs32->ax = retval;
	__asm__ __volatile__("movl %0,%%esp\n\t"
		"movl %1,%%ebp\n\t"
		"jmp resume_userspace"
		: : "r" (regs32), "r" (current_thread_info()));
}

static inline void set_IF(struct kernel_vm86_regs *regs)
{
	VEFLAGS |= X86_EFLAGS_VIF;
	if (VEFLAGS & X86_EFLAGS_VIP)
		return_to_32bit(regs, VM86_STI);
}

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.v86mask);
	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.v86mask);
	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.v86mask);
}

static inline int is_revectored(int nr, struct revectored_struct *bitmap)
{
	__asm__ __volatile__("btl %2,%1\n\tsbbl %0,%0"
		:"=r" (nr)
		:"m" (*bitmap), "r" (nr));
	return nr;
}

#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;

	if (regs->pt.cs == BIOSSEG)
		goto cannot_handle;
	if (is_revectored(i, &KVM86->int_revectored))
		goto cannot_handle;
	if (i == 0x21 && is_revectored(AH(regs), &KVM86->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:
	return_to_32bit(regs, VM86_INTx + (i << 8));
}

int handle_vm86_trap(struct kernel_vm86_regs *regs, long error_code, int trapno)
{
	if (VMPI.is_vm86pus) {
		if ((trapno == 3) || (trapno == 1)) {
			KVM86->regs32->ax = VM86_TRAP + (trapno << 8);
			/* setting this flag forces the code in entry_32.S to
			   the path where we call save_v86_state() and change
			   the stack pointer to KVM86->regs32 */
			set_thread_flag(TIF_NOTIFY_RESUME);
			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, current);
	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;

#define CHECK_IF_IN_TRAP \
	if (VMPI.vm86dbg_active && VMPI.vm86dbg_TFpendig) \
		newflags |= X86_EFLAGS_TF
#define VM86_FAULT_RETURN do { \
	if (VMPI.force_return_for_pic  && (VEFLAGS & (X86_EFLAGS_IF | X86_EFLAGS_VIF))) \
		return_to_32bit(regs, VM86_PICRETURN); \
	if (orig_flags & X86_EFLAGS_TF) \
		handle_vm86_trap(regs, 0, 1); \
	return; } while (0)

	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;
		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);

		VM86_FAULT_RETURN;
		}

	/* 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])
				return_to_32bit(regs, VM86_INTx + (intno << 8));
		}
		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);
		}
		VM86_FAULT_RETURN;
		}

	/* cli */
	case 0xfa:
		IP(regs) = ip;
		clear_IF(regs);
		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);
		VM86_FAULT_RETURN;

	default:
		return_to_32bit(regs, VM86_UNKNOWN);
	}

	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]
	 */
	return_to_32bit(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;
}