summaryrefslogtreecommitdiff
path: root/arch/x86/kernel/vm86_32.c
blob: cce1c89cb7dfd4897c9256ba1d24516303031e96 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
// 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();

	BUG_ON(!vm86);

	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();

exit_vm86:
	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");
	force_fatal_sig(SIGSEGV);
	goto exit_vm86;
}

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;
}