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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>
 *
 */

#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>

/*
 * 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.eax))[0])
#define AH(regs)  (((unsigned char *)&((regs)->pt.eax))[1])
#define IP(regs)  (*(unsigned short *)&((regs)->pt.eip))
#define SP(regs)  (*(unsigned short *)&((regs)->pt.esp))

/*
 * 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 xgs, 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_eax));
      ret += copy_to_user(&user->orig_eax, &regs->pt.orig_eax,
                      sizeof(struct kernel_vm86_regs) -
                      offsetof(struct kernel_vm86_regs, pt.orig_eax));

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

struct pt_regs * FASTCALL(save_v86_state(struct kernel_vm86_regs * regs));
struct pt_regs * fastcall 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) {
            printk("no vm86_info: BAD\n");
            do_exit(SIGSEGV);
      }
      set_flags(regs->pt.eflags, VEFLAGS, VIF_MASK | 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) {
            printk("vm86: could not access userspace vm86_info\n");
            do_exit(SIGSEGV);
      }

      tss = &per_cpu(init_tss, get_cpu());
      current->thread.esp0 = current->thread.saved_esp0;
      current->thread.sysenter_cs = __KERNEL_CS;
      load_esp0(tss, &current->thread);
      current->thread.saved_esp0 = 0;
      put_cpu();

      ret = KVM86->regs32;

      ret->xfs = current->thread.saved_fs;
      loadsegment(gs, 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;

      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);
      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:
      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);

asmlinkage int sys_vm86old(struct pt_regs regs)
{
      struct vm86_struct __user *v86 = (struct vm86_struct __user *)regs.ebx;
      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_esp0)
            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 = &regs;
      tsk->thread.vm86_info = v86;
      do_sys_vm86(&info, tsk);
      ret = 0;    /* we never return here */
out:
      return ret;
}


asmlinkage int sys_vm86(struct pt_regs regs)
{
      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 (regs.ebx) {
            case VM86_REQUEST_IRQ:
            case VM86_FREE_IRQ:
            case VM86_GET_IRQ_BITS:
            case VM86_GET_AND_RESET_IRQ:
                  ret = do_vm86_irq_handling(regs.ebx, (int)regs.ecx);
                  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_esp0)
            goto out;
      v86 = (struct vm86plus_struct __user *)regs.ecx;
      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 = &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.xds = 0;
      info->regs.pt.xes = 0;
      info->regs.pt.xfs = 0;

/* we are clearing gs later just before "jmp resume_userspace",
 * because it is not saved/restored.
 */

/*
 * The eflags 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.eflags;
      info->regs.pt.eflags &= SAFE_MASK;
      info->regs.pt.eflags |= info->regs32->eflags & ~SAFE_MASK;
      info->regs.pt.eflags |= VM_MASK;

      switch (info->cpu_type) {
            case CPU_286:
                  tsk->thread.v86mask = 0;
                  break;
            case CPU_386:
                  tsk->thread.v86mask = NT_MASK | IOPL_MASK;
                  break;
            case CPU_486:
                  tsk->thread.v86mask = AC_MASK | NT_MASK | IOPL_MASK;
                  break;
            default:
                  tsk->thread.v86mask = ID_MASK | AC_MASK | NT_MASK | IOPL_MASK;
                  break;
      }

/*
 * Save old state, set default return value (%eax) to 0
 */
      info->regs32->eax = 0;
      tsk->thread.saved_esp0 = tsk->thread.esp0;
      tsk->thread.saved_fs = info->regs32->xfs;
      savesegment(gs, tsk->thread.saved_gs);

      tss = &per_cpu(init_tss, get_cpu());
      tsk->thread.esp0 = (unsigned long) &info->VM86_TSS_ESP0;
      if (cpu_has_sep)
            tsk->thread.sysenter_cs = 0;
      load_esp0(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 */
      if (unlikely(current->audit_context))
            audit_syscall_exit(AUDITSC_RESULT(0), 0);

      __asm__ __volatile__(
            "movl %0,%%esp\n\t"
            "movl %1,%%ebp\n\t"
            "mov  %2, %%gs\n\t"
            "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->eax = 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 |= VIF_MASK;
      if (VEFLAGS & VIP_MASK)
            return_to_32bit(regs, VM86_STI);
}

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

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

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

/* 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 interrups 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 eflags, struct kernel_vm86_regs * regs)
{
      set_flags(VEFLAGS, eflags, current->thread.v86mask);
      set_flags(regs->pt.eflags, eflags, SAFE_MASK);
      if (eflags & IF_MASK)
            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.eflags, flags, SAFE_MASK);
      if (flags & IF_MASK)
            set_IF(regs);
      else
            clear_IF(regs);
}

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

      if (VEFLAGS & VIF_MASK)
            flags |= IF_MASK;
      flags |= IOPL_MASK;
      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.xcs == 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.xcs, cannot_handle);
      pushw(ssp, sp, IP(regs), cannot_handle);
      regs->pt.xcs = 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) )
                  return_to_32bit(regs, VM86_TRAP + (trapno << 8));
            do_int(regs, trapno, (unsigned char __user *) (regs->pt.xss << 4), SP(regs));
            return 0;
      }
      if (trapno !=1)
            return 1; /* we let this handle by the calling routine */
      if (current->ptrace & PT_PTRACED) {
            unsigned long flags;
            spin_lock_irqsave(&current->sighand->siglock, flags);
            sigdelset(&current->blocked, SIGTRAP);
            recalc_sigpending();
            spin_unlock_irqrestore(&current->sighand->siglock, flags);
      }
      send_sig(SIGTRAP, current, 1);
      current->thread.trap_no = trapno;
      current->thread.error_code = error_code;
      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 |= TF_MASK
#define VM86_FAULT_RETURN do { \
      if (VMPI.force_return_for_pic  && (VEFLAGS & (IF_MASK | VIF_MASK))) \
            return_to_32bit(regs, VM86_PICRETURN); \
      if (orig_flags & TF_MASK) \
            handle_vm86_trap(regs, 0, 1); \
      return; } while (0)

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

      csp = (unsigned char __user *) (regs->pt.xcs << 4);
      ssp = (unsigned char __user *) (regs->pt.xss << 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.xcs = 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;
}


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