/* * Copyright (C) 1994 Linus Torvalds * * 29 dec 2001 - Fixed oopses caused by unchecked access to the vm86 * stack - Manfred Spraul * * 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 * * * 22 mar 2002 - Added missing clear_IF in set_vflags_* Kasper Dupont * * * ?? ??? 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 * * 9 apr 2002 - Changed syntax of macros in handle_vm86_fault. * Kasper Dupont * * 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 * */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* * 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, ®s->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(®s->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(¤t->thread.vm86_info->regs, regs); tmp += put_user(current->thread.screen_bitmap, ¤t->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, ¤t->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, 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 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 = -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 = 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 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 (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 = 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 call save_v86_state() and change the stack pointer to KVM86->regs32 */ set_thread_flag(TIF_IRET); 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 *)®s->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; }