xref: /openbmc/linux/arch/x86/kernel/vm86_32.c (revision 68198dca)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  *  Copyright (C) 1994  Linus Torvalds
4  *
5  *  29 dec 2001 - Fixed oopses caused by unchecked access to the vm86
6  *                stack - Manfred Spraul <manfred@colorfullife.com>
7  *
8  *  22 mar 2002 - Manfred detected the stackfaults, but didn't handle
9  *                them correctly. Now the emulation will be in a
10  *                consistent state after stackfaults - Kasper Dupont
11  *                <kasperd@daimi.au.dk>
12  *
13  *  22 mar 2002 - Added missing clear_IF in set_vflags_* Kasper Dupont
14  *                <kasperd@daimi.au.dk>
15  *
16  *  ?? ??? 2002 - Fixed premature returns from handle_vm86_fault
17  *                caused by Kasper Dupont's changes - Stas Sergeev
18  *
19  *   4 apr 2002 - Fixed CHECK_IF_IN_TRAP broken by Stas' changes.
20  *                Kasper Dupont <kasperd@daimi.au.dk>
21  *
22  *   9 apr 2002 - Changed syntax of macros in handle_vm86_fault.
23  *                Kasper Dupont <kasperd@daimi.au.dk>
24  *
25  *   9 apr 2002 - Changed stack access macros to jump to a label
26  *                instead of returning to userspace. This simplifies
27  *                do_int, and is needed by handle_vm6_fault. Kasper
28  *                Dupont <kasperd@daimi.au.dk>
29  *
30  */
31 
32 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
33 
34 #include <linux/capability.h>
35 #include <linux/errno.h>
36 #include <linux/interrupt.h>
37 #include <linux/syscalls.h>
38 #include <linux/sched.h>
39 #include <linux/sched/task_stack.h>
40 #include <linux/kernel.h>
41 #include <linux/signal.h>
42 #include <linux/string.h>
43 #include <linux/mm.h>
44 #include <linux/smp.h>
45 #include <linux/highmem.h>
46 #include <linux/ptrace.h>
47 #include <linux/audit.h>
48 #include <linux/stddef.h>
49 #include <linux/slab.h>
50 #include <linux/security.h>
51 
52 #include <linux/uaccess.h>
53 #include <asm/io.h>
54 #include <asm/tlbflush.h>
55 #include <asm/irq.h>
56 #include <asm/traps.h>
57 #include <asm/vm86.h>
58 #include <asm/switch_to.h>
59 
60 /*
61  * Known problems:
62  *
63  * Interrupt handling is not guaranteed:
64  * - a real x86 will disable all interrupts for one instruction
65  *   after a "mov ss,xx" to make stack handling atomic even without
66  *   the 'lss' instruction. We can't guarantee this in v86 mode,
67  *   as the next instruction might result in a page fault or similar.
68  * - a real x86 will have interrupts disabled for one instruction
69  *   past the 'sti' that enables them. We don't bother with all the
70  *   details yet.
71  *
72  * Let's hope these problems do not actually matter for anything.
73  */
74 
75 
76 /*
77  * 8- and 16-bit register defines..
78  */
79 #define AL(regs)	(((unsigned char *)&((regs)->pt.ax))[0])
80 #define AH(regs)	(((unsigned char *)&((regs)->pt.ax))[1])
81 #define IP(regs)	(*(unsigned short *)&((regs)->pt.ip))
82 #define SP(regs)	(*(unsigned short *)&((regs)->pt.sp))
83 
84 /*
85  * virtual flags (16 and 32-bit versions)
86  */
87 #define VFLAGS	(*(unsigned short *)&(current->thread.vm86->veflags))
88 #define VEFLAGS	(current->thread.vm86->veflags)
89 
90 #define set_flags(X, new, mask) \
91 ((X) = ((X) & ~(mask)) | ((new) & (mask)))
92 
93 #define SAFE_MASK	(0xDD5)
94 #define RETURN_MASK	(0xDFF)
95 
96 void save_v86_state(struct kernel_vm86_regs *regs, int retval)
97 {
98 	struct task_struct *tsk = current;
99 	struct vm86plus_struct __user *user;
100 	struct vm86 *vm86 = current->thread.vm86;
101 	long err = 0;
102 
103 	/*
104 	 * This gets called from entry.S with interrupts disabled, but
105 	 * from process context. Enable interrupts here, before trying
106 	 * to access user space.
107 	 */
108 	local_irq_enable();
109 
110 	if (!vm86 || !vm86->user_vm86) {
111 		pr_alert("no user_vm86: BAD\n");
112 		do_exit(SIGSEGV);
113 	}
114 	set_flags(regs->pt.flags, VEFLAGS, X86_EFLAGS_VIF | vm86->veflags_mask);
115 	user = vm86->user_vm86;
116 
117 	if (!access_ok(VERIFY_WRITE, user, vm86->vm86plus.is_vm86pus ?
118 		       sizeof(struct vm86plus_struct) :
119 		       sizeof(struct vm86_struct))) {
120 		pr_alert("could not access userspace vm86 info\n");
121 		do_exit(SIGSEGV);
122 	}
123 
124 	put_user_try {
125 		put_user_ex(regs->pt.bx, &user->regs.ebx);
126 		put_user_ex(regs->pt.cx, &user->regs.ecx);
127 		put_user_ex(regs->pt.dx, &user->regs.edx);
128 		put_user_ex(regs->pt.si, &user->regs.esi);
129 		put_user_ex(regs->pt.di, &user->regs.edi);
130 		put_user_ex(regs->pt.bp, &user->regs.ebp);
131 		put_user_ex(regs->pt.ax, &user->regs.eax);
132 		put_user_ex(regs->pt.ip, &user->regs.eip);
133 		put_user_ex(regs->pt.cs, &user->regs.cs);
134 		put_user_ex(regs->pt.flags, &user->regs.eflags);
135 		put_user_ex(regs->pt.sp, &user->regs.esp);
136 		put_user_ex(regs->pt.ss, &user->regs.ss);
137 		put_user_ex(regs->es, &user->regs.es);
138 		put_user_ex(regs->ds, &user->regs.ds);
139 		put_user_ex(regs->fs, &user->regs.fs);
140 		put_user_ex(regs->gs, &user->regs.gs);
141 
142 		put_user_ex(vm86->screen_bitmap, &user->screen_bitmap);
143 	} put_user_catch(err);
144 	if (err) {
145 		pr_alert("could not access userspace vm86 info\n");
146 		do_exit(SIGSEGV);
147 	}
148 
149 	preempt_disable();
150 	tsk->thread.sp0 = vm86->saved_sp0;
151 	tsk->thread.sysenter_cs = __KERNEL_CS;
152 	update_sp0(tsk);
153 	refresh_sysenter_cs(&tsk->thread);
154 	vm86->saved_sp0 = 0;
155 	preempt_enable();
156 
157 	memcpy(&regs->pt, &vm86->regs32, sizeof(struct pt_regs));
158 
159 	lazy_load_gs(vm86->regs32.gs);
160 
161 	regs->pt.ax = retval;
162 }
163 
164 static void mark_screen_rdonly(struct mm_struct *mm)
165 {
166 	struct vm_area_struct *vma;
167 	spinlock_t *ptl;
168 	pgd_t *pgd;
169 	p4d_t *p4d;
170 	pud_t *pud;
171 	pmd_t *pmd;
172 	pte_t *pte;
173 	int i;
174 
175 	down_write(&mm->mmap_sem);
176 	pgd = pgd_offset(mm, 0xA0000);
177 	if (pgd_none_or_clear_bad(pgd))
178 		goto out;
179 	p4d = p4d_offset(pgd, 0xA0000);
180 	if (p4d_none_or_clear_bad(p4d))
181 		goto out;
182 	pud = pud_offset(p4d, 0xA0000);
183 	if (pud_none_or_clear_bad(pud))
184 		goto out;
185 	pmd = pmd_offset(pud, 0xA0000);
186 
187 	if (pmd_trans_huge(*pmd)) {
188 		vma = find_vma(mm, 0xA0000);
189 		split_huge_pmd(vma, pmd, 0xA0000);
190 	}
191 	if (pmd_none_or_clear_bad(pmd))
192 		goto out;
193 	pte = pte_offset_map_lock(mm, pmd, 0xA0000, &ptl);
194 	for (i = 0; i < 32; i++) {
195 		if (pte_present(*pte))
196 			set_pte(pte, pte_wrprotect(*pte));
197 		pte++;
198 	}
199 	pte_unmap_unlock(pte, ptl);
200 out:
201 	up_write(&mm->mmap_sem);
202 	flush_tlb_mm_range(mm, 0xA0000, 0xA0000 + 32*PAGE_SIZE, 0UL);
203 }
204 
205 
206 
207 static int do_vm86_irq_handling(int subfunction, int irqnumber);
208 static long do_sys_vm86(struct vm86plus_struct __user *user_vm86, bool plus);
209 
210 SYSCALL_DEFINE1(vm86old, struct vm86_struct __user *, user_vm86)
211 {
212 	return do_sys_vm86((struct vm86plus_struct __user *) user_vm86, false);
213 }
214 
215 
216 SYSCALL_DEFINE2(vm86, unsigned long, cmd, unsigned long, arg)
217 {
218 	switch (cmd) {
219 	case VM86_REQUEST_IRQ:
220 	case VM86_FREE_IRQ:
221 	case VM86_GET_IRQ_BITS:
222 	case VM86_GET_AND_RESET_IRQ:
223 		return do_vm86_irq_handling(cmd, (int)arg);
224 	case VM86_PLUS_INSTALL_CHECK:
225 		/*
226 		 * NOTE: on old vm86 stuff this will return the error
227 		 *  from access_ok(), because the subfunction is
228 		 *  interpreted as (invalid) address to vm86_struct.
229 		 *  So the installation check works.
230 		 */
231 		return 0;
232 	}
233 
234 	/* we come here only for functions VM86_ENTER, VM86_ENTER_NO_BYPASS */
235 	return do_sys_vm86((struct vm86plus_struct __user *) arg, true);
236 }
237 
238 
239 static long do_sys_vm86(struct vm86plus_struct __user *user_vm86, bool plus)
240 {
241 	struct task_struct *tsk = current;
242 	struct vm86 *vm86 = tsk->thread.vm86;
243 	struct kernel_vm86_regs vm86regs;
244 	struct pt_regs *regs = current_pt_regs();
245 	unsigned long err = 0;
246 
247 	err = security_mmap_addr(0);
248 	if (err) {
249 		/*
250 		 * vm86 cannot virtualize the address space, so vm86 users
251 		 * need to manage the low 1MB themselves using mmap.  Given
252 		 * that BIOS places important data in the first page, vm86
253 		 * is essentially useless if mmap_min_addr != 0.  DOSEMU,
254 		 * for example, won't even bother trying to use vm86 if it
255 		 * can't map a page at virtual address 0.
256 		 *
257 		 * To reduce the available kernel attack surface, simply
258 		 * disallow vm86(old) for users who cannot mmap at va 0.
259 		 *
260 		 * The implementation of security_mmap_addr will allow
261 		 * suitably privileged users to map va 0 even if
262 		 * vm.mmap_min_addr is set above 0, and we want this
263 		 * behavior for vm86 as well, as it ensures that legacy
264 		 * tools like vbetool will not fail just because of
265 		 * vm.mmap_min_addr.
266 		 */
267 		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",
268 			     current->comm, task_pid_nr(current),
269 			     from_kuid_munged(&init_user_ns, current_uid()));
270 		return -EPERM;
271 	}
272 
273 	if (!vm86) {
274 		if (!(vm86 = kzalloc(sizeof(*vm86), GFP_KERNEL)))
275 			return -ENOMEM;
276 		tsk->thread.vm86 = vm86;
277 	}
278 	if (vm86->saved_sp0)
279 		return -EPERM;
280 
281 	if (!access_ok(VERIFY_READ, user_vm86, plus ?
282 		       sizeof(struct vm86_struct) :
283 		       sizeof(struct vm86plus_struct)))
284 		return -EFAULT;
285 
286 	memset(&vm86regs, 0, sizeof(vm86regs));
287 	get_user_try {
288 		unsigned short seg;
289 		get_user_ex(vm86regs.pt.bx, &user_vm86->regs.ebx);
290 		get_user_ex(vm86regs.pt.cx, &user_vm86->regs.ecx);
291 		get_user_ex(vm86regs.pt.dx, &user_vm86->regs.edx);
292 		get_user_ex(vm86regs.pt.si, &user_vm86->regs.esi);
293 		get_user_ex(vm86regs.pt.di, &user_vm86->regs.edi);
294 		get_user_ex(vm86regs.pt.bp, &user_vm86->regs.ebp);
295 		get_user_ex(vm86regs.pt.ax, &user_vm86->regs.eax);
296 		get_user_ex(vm86regs.pt.ip, &user_vm86->regs.eip);
297 		get_user_ex(seg, &user_vm86->regs.cs);
298 		vm86regs.pt.cs = seg;
299 		get_user_ex(vm86regs.pt.flags, &user_vm86->regs.eflags);
300 		get_user_ex(vm86regs.pt.sp, &user_vm86->regs.esp);
301 		get_user_ex(seg, &user_vm86->regs.ss);
302 		vm86regs.pt.ss = seg;
303 		get_user_ex(vm86regs.es, &user_vm86->regs.es);
304 		get_user_ex(vm86regs.ds, &user_vm86->regs.ds);
305 		get_user_ex(vm86regs.fs, &user_vm86->regs.fs);
306 		get_user_ex(vm86regs.gs, &user_vm86->regs.gs);
307 
308 		get_user_ex(vm86->flags, &user_vm86->flags);
309 		get_user_ex(vm86->screen_bitmap, &user_vm86->screen_bitmap);
310 		get_user_ex(vm86->cpu_type, &user_vm86->cpu_type);
311 	} get_user_catch(err);
312 	if (err)
313 		return err;
314 
315 	if (copy_from_user(&vm86->int_revectored,
316 			   &user_vm86->int_revectored,
317 			   sizeof(struct revectored_struct)))
318 		return -EFAULT;
319 	if (copy_from_user(&vm86->int21_revectored,
320 			   &user_vm86->int21_revectored,
321 			   sizeof(struct revectored_struct)))
322 		return -EFAULT;
323 	if (plus) {
324 		if (copy_from_user(&vm86->vm86plus, &user_vm86->vm86plus,
325 				   sizeof(struct vm86plus_info_struct)))
326 			return -EFAULT;
327 		vm86->vm86plus.is_vm86pus = 1;
328 	} else
329 		memset(&vm86->vm86plus, 0,
330 		       sizeof(struct vm86plus_info_struct));
331 
332 	memcpy(&vm86->regs32, regs, sizeof(struct pt_regs));
333 	vm86->user_vm86 = user_vm86;
334 
335 /*
336  * The flags register is also special: we cannot trust that the user
337  * has set it up safely, so this makes sure interrupt etc flags are
338  * inherited from protected mode.
339  */
340 	VEFLAGS = vm86regs.pt.flags;
341 	vm86regs.pt.flags &= SAFE_MASK;
342 	vm86regs.pt.flags |= regs->flags & ~SAFE_MASK;
343 	vm86regs.pt.flags |= X86_VM_MASK;
344 
345 	vm86regs.pt.orig_ax = regs->orig_ax;
346 
347 	switch (vm86->cpu_type) {
348 	case CPU_286:
349 		vm86->veflags_mask = 0;
350 		break;
351 	case CPU_386:
352 		vm86->veflags_mask = X86_EFLAGS_NT | X86_EFLAGS_IOPL;
353 		break;
354 	case CPU_486:
355 		vm86->veflags_mask = X86_EFLAGS_AC | X86_EFLAGS_NT | X86_EFLAGS_IOPL;
356 		break;
357 	default:
358 		vm86->veflags_mask = X86_EFLAGS_ID | X86_EFLAGS_AC | X86_EFLAGS_NT | X86_EFLAGS_IOPL;
359 		break;
360 	}
361 
362 /*
363  * Save old state
364  */
365 	vm86->saved_sp0 = tsk->thread.sp0;
366 	lazy_save_gs(vm86->regs32.gs);
367 
368 	/* make room for real-mode segments */
369 	preempt_disable();
370 	tsk->thread.sp0 += 16;
371 
372 	if (static_cpu_has(X86_FEATURE_SEP)) {
373 		tsk->thread.sysenter_cs = 0;
374 		refresh_sysenter_cs(&tsk->thread);
375 	}
376 
377 	update_sp0(tsk);
378 	preempt_enable();
379 
380 	if (vm86->flags & VM86_SCREEN_BITMAP)
381 		mark_screen_rdonly(tsk->mm);
382 
383 	memcpy((struct kernel_vm86_regs *)regs, &vm86regs, sizeof(vm86regs));
384 	force_iret();
385 	return regs->ax;
386 }
387 
388 static inline void set_IF(struct kernel_vm86_regs *regs)
389 {
390 	VEFLAGS |= X86_EFLAGS_VIF;
391 }
392 
393 static inline void clear_IF(struct kernel_vm86_regs *regs)
394 {
395 	VEFLAGS &= ~X86_EFLAGS_VIF;
396 }
397 
398 static inline void clear_TF(struct kernel_vm86_regs *regs)
399 {
400 	regs->pt.flags &= ~X86_EFLAGS_TF;
401 }
402 
403 static inline void clear_AC(struct kernel_vm86_regs *regs)
404 {
405 	regs->pt.flags &= ~X86_EFLAGS_AC;
406 }
407 
408 /*
409  * It is correct to call set_IF(regs) from the set_vflags_*
410  * functions. However someone forgot to call clear_IF(regs)
411  * in the opposite case.
412  * After the command sequence CLI PUSHF STI POPF you should
413  * end up with interrupts disabled, but you ended up with
414  * interrupts enabled.
415  *  ( I was testing my own changes, but the only bug I
416  *    could find was in a function I had not changed. )
417  * [KD]
418  */
419 
420 static inline void set_vflags_long(unsigned long flags, struct kernel_vm86_regs *regs)
421 {
422 	set_flags(VEFLAGS, flags, current->thread.vm86->veflags_mask);
423 	set_flags(regs->pt.flags, flags, SAFE_MASK);
424 	if (flags & X86_EFLAGS_IF)
425 		set_IF(regs);
426 	else
427 		clear_IF(regs);
428 }
429 
430 static inline void set_vflags_short(unsigned short flags, struct kernel_vm86_regs *regs)
431 {
432 	set_flags(VFLAGS, flags, current->thread.vm86->veflags_mask);
433 	set_flags(regs->pt.flags, flags, SAFE_MASK);
434 	if (flags & X86_EFLAGS_IF)
435 		set_IF(regs);
436 	else
437 		clear_IF(regs);
438 }
439 
440 static inline unsigned long get_vflags(struct kernel_vm86_regs *regs)
441 {
442 	unsigned long flags = regs->pt.flags & RETURN_MASK;
443 
444 	if (VEFLAGS & X86_EFLAGS_VIF)
445 		flags |= X86_EFLAGS_IF;
446 	flags |= X86_EFLAGS_IOPL;
447 	return flags | (VEFLAGS & current->thread.vm86->veflags_mask);
448 }
449 
450 static inline int is_revectored(int nr, struct revectored_struct *bitmap)
451 {
452 	return test_bit(nr, bitmap->__map);
453 }
454 
455 #define val_byte(val, n) (((__u8 *)&val)[n])
456 
457 #define pushb(base, ptr, val, err_label) \
458 	do { \
459 		__u8 __val = val; \
460 		ptr--; \
461 		if (put_user(__val, base + ptr) < 0) \
462 			goto err_label; \
463 	} while (0)
464 
465 #define pushw(base, ptr, val, err_label) \
466 	do { \
467 		__u16 __val = val; \
468 		ptr--; \
469 		if (put_user(val_byte(__val, 1), base + ptr) < 0) \
470 			goto err_label; \
471 		ptr--; \
472 		if (put_user(val_byte(__val, 0), base + ptr) < 0) \
473 			goto err_label; \
474 	} while (0)
475 
476 #define pushl(base, ptr, val, err_label) \
477 	do { \
478 		__u32 __val = val; \
479 		ptr--; \
480 		if (put_user(val_byte(__val, 3), base + ptr) < 0) \
481 			goto err_label; \
482 		ptr--; \
483 		if (put_user(val_byte(__val, 2), base + ptr) < 0) \
484 			goto err_label; \
485 		ptr--; \
486 		if (put_user(val_byte(__val, 1), base + ptr) < 0) \
487 			goto err_label; \
488 		ptr--; \
489 		if (put_user(val_byte(__val, 0), base + ptr) < 0) \
490 			goto err_label; \
491 	} while (0)
492 
493 #define popb(base, ptr, err_label) \
494 	({ \
495 		__u8 __res; \
496 		if (get_user(__res, base + ptr) < 0) \
497 			goto err_label; \
498 		ptr++; \
499 		__res; \
500 	})
501 
502 #define popw(base, ptr, err_label) \
503 	({ \
504 		__u16 __res; \
505 		if (get_user(val_byte(__res, 0), base + ptr) < 0) \
506 			goto err_label; \
507 		ptr++; \
508 		if (get_user(val_byte(__res, 1), base + ptr) < 0) \
509 			goto err_label; \
510 		ptr++; \
511 		__res; \
512 	})
513 
514 #define popl(base, ptr, err_label) \
515 	({ \
516 		__u32 __res; \
517 		if (get_user(val_byte(__res, 0), base + ptr) < 0) \
518 			goto err_label; \
519 		ptr++; \
520 		if (get_user(val_byte(__res, 1), base + ptr) < 0) \
521 			goto err_label; \
522 		ptr++; \
523 		if (get_user(val_byte(__res, 2), base + ptr) < 0) \
524 			goto err_label; \
525 		ptr++; \
526 		if (get_user(val_byte(__res, 3), base + ptr) < 0) \
527 			goto err_label; \
528 		ptr++; \
529 		__res; \
530 	})
531 
532 /* There are so many possible reasons for this function to return
533  * VM86_INTx, so adding another doesn't bother me. We can expect
534  * userspace programs to be able to handle it. (Getting a problem
535  * in userspace is always better than an Oops anyway.) [KD]
536  */
537 static void do_int(struct kernel_vm86_regs *regs, int i,
538     unsigned char __user *ssp, unsigned short sp)
539 {
540 	unsigned long __user *intr_ptr;
541 	unsigned long segoffs;
542 	struct vm86 *vm86 = current->thread.vm86;
543 
544 	if (regs->pt.cs == BIOSSEG)
545 		goto cannot_handle;
546 	if (is_revectored(i, &vm86->int_revectored))
547 		goto cannot_handle;
548 	if (i == 0x21 && is_revectored(AH(regs), &vm86->int21_revectored))
549 		goto cannot_handle;
550 	intr_ptr = (unsigned long __user *) (i << 2);
551 	if (get_user(segoffs, intr_ptr))
552 		goto cannot_handle;
553 	if ((segoffs >> 16) == BIOSSEG)
554 		goto cannot_handle;
555 	pushw(ssp, sp, get_vflags(regs), cannot_handle);
556 	pushw(ssp, sp, regs->pt.cs, cannot_handle);
557 	pushw(ssp, sp, IP(regs), cannot_handle);
558 	regs->pt.cs = segoffs >> 16;
559 	SP(regs) -= 6;
560 	IP(regs) = segoffs & 0xffff;
561 	clear_TF(regs);
562 	clear_IF(regs);
563 	clear_AC(regs);
564 	return;
565 
566 cannot_handle:
567 	save_v86_state(regs, VM86_INTx + (i << 8));
568 }
569 
570 int handle_vm86_trap(struct kernel_vm86_regs *regs, long error_code, int trapno)
571 {
572 	struct vm86 *vm86 = current->thread.vm86;
573 
574 	if (vm86->vm86plus.is_vm86pus) {
575 		if ((trapno == 3) || (trapno == 1)) {
576 			save_v86_state(regs, VM86_TRAP + (trapno << 8));
577 			return 0;
578 		}
579 		do_int(regs, trapno, (unsigned char __user *) (regs->pt.ss << 4), SP(regs));
580 		return 0;
581 	}
582 	if (trapno != 1)
583 		return 1; /* we let this handle by the calling routine */
584 	current->thread.trap_nr = trapno;
585 	current->thread.error_code = error_code;
586 	force_sig(SIGTRAP, current);
587 	return 0;
588 }
589 
590 void handle_vm86_fault(struct kernel_vm86_regs *regs, long error_code)
591 {
592 	unsigned char opcode;
593 	unsigned char __user *csp;
594 	unsigned char __user *ssp;
595 	unsigned short ip, sp, orig_flags;
596 	int data32, pref_done;
597 	struct vm86plus_info_struct *vmpi = &current->thread.vm86->vm86plus;
598 
599 #define CHECK_IF_IN_TRAP \
600 	if (vmpi->vm86dbg_active && vmpi->vm86dbg_TFpendig) \
601 		newflags |= X86_EFLAGS_TF
602 
603 	orig_flags = *(unsigned short *)&regs->pt.flags;
604 
605 	csp = (unsigned char __user *) (regs->pt.cs << 4);
606 	ssp = (unsigned char __user *) (regs->pt.ss << 4);
607 	sp = SP(regs);
608 	ip = IP(regs);
609 
610 	data32 = 0;
611 	pref_done = 0;
612 	do {
613 		switch (opcode = popb(csp, ip, simulate_sigsegv)) {
614 		case 0x66:      /* 32-bit data */     data32 = 1; break;
615 		case 0x67:      /* 32-bit address */  break;
616 		case 0x2e:      /* CS */              break;
617 		case 0x3e:      /* DS */              break;
618 		case 0x26:      /* ES */              break;
619 		case 0x36:      /* SS */              break;
620 		case 0x65:      /* GS */              break;
621 		case 0x64:      /* FS */              break;
622 		case 0xf2:      /* repnz */       break;
623 		case 0xf3:      /* rep */             break;
624 		default: pref_done = 1;
625 		}
626 	} while (!pref_done);
627 
628 	switch (opcode) {
629 
630 	/* pushf */
631 	case 0x9c:
632 		if (data32) {
633 			pushl(ssp, sp, get_vflags(regs), simulate_sigsegv);
634 			SP(regs) -= 4;
635 		} else {
636 			pushw(ssp, sp, get_vflags(regs), simulate_sigsegv);
637 			SP(regs) -= 2;
638 		}
639 		IP(regs) = ip;
640 		goto vm86_fault_return;
641 
642 	/* popf */
643 	case 0x9d:
644 		{
645 		unsigned long newflags;
646 		if (data32) {
647 			newflags = popl(ssp, sp, simulate_sigsegv);
648 			SP(regs) += 4;
649 		} else {
650 			newflags = popw(ssp, sp, simulate_sigsegv);
651 			SP(regs) += 2;
652 		}
653 		IP(regs) = ip;
654 		CHECK_IF_IN_TRAP;
655 		if (data32)
656 			set_vflags_long(newflags, regs);
657 		else
658 			set_vflags_short(newflags, regs);
659 
660 		goto check_vip;
661 		}
662 
663 	/* int xx */
664 	case 0xcd: {
665 		int intno = popb(csp, ip, simulate_sigsegv);
666 		IP(regs) = ip;
667 		if (vmpi->vm86dbg_active) {
668 			if ((1 << (intno & 7)) & vmpi->vm86dbg_intxxtab[intno >> 3]) {
669 				save_v86_state(regs, VM86_INTx + (intno << 8));
670 				return;
671 			}
672 		}
673 		do_int(regs, intno, ssp, sp);
674 		return;
675 	}
676 
677 	/* iret */
678 	case 0xcf:
679 		{
680 		unsigned long newip;
681 		unsigned long newcs;
682 		unsigned long newflags;
683 		if (data32) {
684 			newip = popl(ssp, sp, simulate_sigsegv);
685 			newcs = popl(ssp, sp, simulate_sigsegv);
686 			newflags = popl(ssp, sp, simulate_sigsegv);
687 			SP(regs) += 12;
688 		} else {
689 			newip = popw(ssp, sp, simulate_sigsegv);
690 			newcs = popw(ssp, sp, simulate_sigsegv);
691 			newflags = popw(ssp, sp, simulate_sigsegv);
692 			SP(regs) += 6;
693 		}
694 		IP(regs) = newip;
695 		regs->pt.cs = newcs;
696 		CHECK_IF_IN_TRAP;
697 		if (data32) {
698 			set_vflags_long(newflags, regs);
699 		} else {
700 			set_vflags_short(newflags, regs);
701 		}
702 		goto check_vip;
703 		}
704 
705 	/* cli */
706 	case 0xfa:
707 		IP(regs) = ip;
708 		clear_IF(regs);
709 		goto vm86_fault_return;
710 
711 	/* sti */
712 	/*
713 	 * Damn. This is incorrect: the 'sti' instruction should actually
714 	 * enable interrupts after the /next/ instruction. Not good.
715 	 *
716 	 * Probably needs some horsing around with the TF flag. Aiee..
717 	 */
718 	case 0xfb:
719 		IP(regs) = ip;
720 		set_IF(regs);
721 		goto check_vip;
722 
723 	default:
724 		save_v86_state(regs, VM86_UNKNOWN);
725 	}
726 
727 	return;
728 
729 check_vip:
730 	if (VEFLAGS & X86_EFLAGS_VIP) {
731 		save_v86_state(regs, VM86_STI);
732 		return;
733 	}
734 
735 vm86_fault_return:
736 	if (vmpi->force_return_for_pic  && (VEFLAGS & (X86_EFLAGS_IF | X86_EFLAGS_VIF))) {
737 		save_v86_state(regs, VM86_PICRETURN);
738 		return;
739 	}
740 	if (orig_flags & X86_EFLAGS_TF)
741 		handle_vm86_trap(regs, 0, X86_TRAP_DB);
742 	return;
743 
744 simulate_sigsegv:
745 	/* FIXME: After a long discussion with Stas we finally
746 	 *        agreed, that this is wrong. Here we should
747 	 *        really send a SIGSEGV to the user program.
748 	 *        But how do we create the correct context? We
749 	 *        are inside a general protection fault handler
750 	 *        and has just returned from a page fault handler.
751 	 *        The correct context for the signal handler
752 	 *        should be a mixture of the two, but how do we
753 	 *        get the information? [KD]
754 	 */
755 	save_v86_state(regs, VM86_UNKNOWN);
756 }
757 
758 /* ---------------- vm86 special IRQ passing stuff ----------------- */
759 
760 #define VM86_IRQNAME		"vm86irq"
761 
762 static struct vm86_irqs {
763 	struct task_struct *tsk;
764 	int sig;
765 } vm86_irqs[16];
766 
767 static DEFINE_SPINLOCK(irqbits_lock);
768 static int irqbits;
769 
770 #define ALLOWED_SIGS (1 /* 0 = don't send a signal */ \
771 	| (1 << SIGUSR1) | (1 << SIGUSR2) | (1 << SIGIO)  | (1 << SIGURG) \
772 	| (1 << SIGUNUSED))
773 
774 static irqreturn_t irq_handler(int intno, void *dev_id)
775 {
776 	int irq_bit;
777 	unsigned long flags;
778 
779 	spin_lock_irqsave(&irqbits_lock, flags);
780 	irq_bit = 1 << intno;
781 	if ((irqbits & irq_bit) || !vm86_irqs[intno].tsk)
782 		goto out;
783 	irqbits |= irq_bit;
784 	if (vm86_irqs[intno].sig)
785 		send_sig(vm86_irqs[intno].sig, vm86_irqs[intno].tsk, 1);
786 	/*
787 	 * IRQ will be re-enabled when user asks for the irq (whether
788 	 * polling or as a result of the signal)
789 	 */
790 	disable_irq_nosync(intno);
791 	spin_unlock_irqrestore(&irqbits_lock, flags);
792 	return IRQ_HANDLED;
793 
794 out:
795 	spin_unlock_irqrestore(&irqbits_lock, flags);
796 	return IRQ_NONE;
797 }
798 
799 static inline void free_vm86_irq(int irqnumber)
800 {
801 	unsigned long flags;
802 
803 	free_irq(irqnumber, NULL);
804 	vm86_irqs[irqnumber].tsk = NULL;
805 
806 	spin_lock_irqsave(&irqbits_lock, flags);
807 	irqbits &= ~(1 << irqnumber);
808 	spin_unlock_irqrestore(&irqbits_lock, flags);
809 }
810 
811 void release_vm86_irqs(struct task_struct *task)
812 {
813 	int i;
814 	for (i = FIRST_VM86_IRQ ; i <= LAST_VM86_IRQ; i++)
815 	    if (vm86_irqs[i].tsk == task)
816 		free_vm86_irq(i);
817 }
818 
819 static inline int get_and_reset_irq(int irqnumber)
820 {
821 	int bit;
822 	unsigned long flags;
823 	int ret = 0;
824 
825 	if (invalid_vm86_irq(irqnumber)) return 0;
826 	if (vm86_irqs[irqnumber].tsk != current) return 0;
827 	spin_lock_irqsave(&irqbits_lock, flags);
828 	bit = irqbits & (1 << irqnumber);
829 	irqbits &= ~bit;
830 	if (bit) {
831 		enable_irq(irqnumber);
832 		ret = 1;
833 	}
834 
835 	spin_unlock_irqrestore(&irqbits_lock, flags);
836 	return ret;
837 }
838 
839 
840 static int do_vm86_irq_handling(int subfunction, int irqnumber)
841 {
842 	int ret;
843 	switch (subfunction) {
844 		case VM86_GET_AND_RESET_IRQ: {
845 			return get_and_reset_irq(irqnumber);
846 		}
847 		case VM86_GET_IRQ_BITS: {
848 			return irqbits;
849 		}
850 		case VM86_REQUEST_IRQ: {
851 			int sig = irqnumber >> 8;
852 			int irq = irqnumber & 255;
853 			if (!capable(CAP_SYS_ADMIN)) return -EPERM;
854 			if (!((1 << sig) & ALLOWED_SIGS)) return -EPERM;
855 			if (invalid_vm86_irq(irq)) return -EPERM;
856 			if (vm86_irqs[irq].tsk) return -EPERM;
857 			ret = request_irq(irq, &irq_handler, 0, VM86_IRQNAME, NULL);
858 			if (ret) return ret;
859 			vm86_irqs[irq].sig = sig;
860 			vm86_irqs[irq].tsk = current;
861 			return irq;
862 		}
863 		case  VM86_FREE_IRQ: {
864 			if (invalid_vm86_irq(irqnumber)) return -EPERM;
865 			if (!vm86_irqs[irqnumber].tsk) return 0;
866 			if (vm86_irqs[irqnumber].tsk != current) return -EPERM;
867 			free_vm86_irq(irqnumber);
868 			return 0;
869 		}
870 	}
871 	return -EINVAL;
872 }
873 
874