/* * 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 #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. */ /* * 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->v86flags)) #define VEFLAGS (current->thread.vm86->v86flags) #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 tss_struct *tss; struct task_struct *tsk = current; struct vm86plus_struct __user *user; struct vm86 *vm86 = current->thread.vm86; long err = 0; /* * 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 (!vm86 || !vm86->vm86_info) { pr_alert("no vm86_info: BAD\n"); do_exit(SIGSEGV); } set_flags(regs->pt.flags, VEFLAGS, X86_EFLAGS_VIF | vm86->v86mask); user = vm86->vm86_info; if (!access_ok(VERIFY_WRITE, user, vm86->vm86plus.is_vm86pus ? sizeof(struct vm86plus_struct) : sizeof(struct vm86_struct))) { pr_alert("could not access userspace vm86_info\n"); do_exit(SIGSEGV); } put_user_try { put_user_ex(regs->pt.bx, &user->regs.ebx); put_user_ex(regs->pt.cx, &user->regs.ecx); put_user_ex(regs->pt.dx, &user->regs.edx); put_user_ex(regs->pt.si, &user->regs.esi); put_user_ex(regs->pt.di, &user->regs.edi); put_user_ex(regs->pt.bp, &user->regs.ebp); put_user_ex(regs->pt.ax, &user->regs.eax); put_user_ex(regs->pt.ip, &user->regs.eip); put_user_ex(regs->pt.cs, &user->regs.cs); put_user_ex(regs->pt.flags, &user->regs.eflags); put_user_ex(regs->pt.sp, &user->regs.esp); put_user_ex(regs->pt.ss, &user->regs.ss); put_user_ex(regs->es, &user->regs.es); put_user_ex(regs->ds, &user->regs.ds); put_user_ex(regs->fs, &user->regs.fs); put_user_ex(regs->gs, &user->regs.gs); put_user_ex(vm86->screen_bitmap, &user->screen_bitmap); } put_user_catch(err); if (err) { pr_alert("could not access userspace vm86_info\n"); do_exit(SIGSEGV); } tss = &per_cpu(cpu_tss, get_cpu()); tsk->thread.sp0 = vm86->saved_sp0; tsk->thread.sysenter_cs = __KERNEL_CS; load_sp0(tss, &tsk->thread); vm86->saved_sp0 = 0; put_cpu(); memcpy(®s->pt, &vm86->regs32, sizeof(struct pt_regs)); lazy_load_gs(vm86->regs32.gs); regs->pt.ax = retval; } static void mark_screen_rdonly(struct mm_struct *mm) { pgd_t *pgd; pud_t *pud; pmd_t *pmd; pte_t *pte; spinlock_t *ptl; int i; down_write(&mm->mmap_sem); pgd = pgd_offset(mm, 0xA0000); if (pgd_none_or_clear_bad(pgd)) goto out; pud = pud_offset(pgd, 0xA0000); if (pud_none_or_clear_bad(pud)) goto out; pmd = pmd_offset(pud, 0xA0000); split_huge_page_pmd_mm(mm, 0xA0000, pmd); if (pmd_none_or_clear_bad(pmd)) goto out; pte = pte_offset_map_lock(mm, pmd, 0xA0000, &ptl); for (i = 0; i < 32; i++) { if (pte_present(*pte)) set_pte(pte, pte_wrprotect(*pte)); pte++; } pte_unmap_unlock(pte, ptl); out: up_write(&mm->mmap_sem); flush_tlb(); } static int do_vm86_irq_handling(int subfunction, int irqnumber); static long do_sys_vm86(struct vm86plus_struct __user *v86, bool plus); SYSCALL_DEFINE1(vm86old, struct vm86_struct __user *, v86) { return do_sys_vm86((struct vm86plus_struct __user *) v86, 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 *v86, bool plus) { struct tss_struct *tss; 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; if (!vm86) { if (!(vm86 = kzalloc(sizeof(*vm86), GFP_KERNEL))) return -ENOMEM; tsk->thread.vm86 = vm86; } if (vm86->saved_sp0) return -EPERM; if (!access_ok(VERIFY_READ, v86, plus ? sizeof(struct vm86_struct) : sizeof(struct vm86plus_struct))) return -EFAULT; memset(&vm86regs, 0, sizeof(vm86regs)); get_user_try { unsigned short seg; get_user_ex(vm86regs.pt.bx, &v86->regs.ebx); get_user_ex(vm86regs.pt.cx, &v86->regs.ecx); get_user_ex(vm86regs.pt.dx, &v86->regs.edx); get_user_ex(vm86regs.pt.si, &v86->regs.esi); get_user_ex(vm86regs.pt.di, &v86->regs.edi); get_user_ex(vm86regs.pt.bp, &v86->regs.ebp); get_user_ex(vm86regs.pt.ax, &v86->regs.eax); get_user_ex(vm86regs.pt.ip, &v86->regs.eip); get_user_ex(seg, &v86->regs.cs); vm86regs.pt.cs = seg; get_user_ex(vm86regs.pt.flags, &v86->regs.eflags); get_user_ex(vm86regs.pt.sp, &v86->regs.esp); get_user_ex(seg, &v86->regs.ss); vm86regs.pt.ss = seg; get_user_ex(vm86regs.es, &v86->regs.es); get_user_ex(vm86regs.ds, &v86->regs.ds); get_user_ex(vm86regs.fs, &v86->regs.fs); get_user_ex(vm86regs.gs, &v86->regs.gs); get_user_ex(vm86->flags, &v86->flags); get_user_ex(vm86->screen_bitmap, &v86->screen_bitmap); get_user_ex(vm86->cpu_type, &v86->cpu_type); } get_user_catch(err); if (err) return err; if (copy_from_user(&vm86->int_revectored, &v86->int_revectored, sizeof(struct revectored_struct))) return -EFAULT; if (copy_from_user(&vm86->int21_revectored, &v86->int21_revectored, sizeof(struct revectored_struct))) return -EFAULT; if (plus) { if (copy_from_user(&vm86->vm86plus, &v86->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->vm86_info = v86; /* * 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->v86mask = 0; break; case CPU_386: vm86->v86mask = X86_EFLAGS_NT | X86_EFLAGS_IOPL; break; case CPU_486: vm86->v86mask = X86_EFLAGS_AC | X86_EFLAGS_NT | X86_EFLAGS_IOPL; break; default: vm86->v86mask = 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); tss = &per_cpu(cpu_tss, get_cpu()); /* make room for real-mode segments */ tsk->thread.sp0 += 16; if (cpu_has_sep) tsk->thread.sysenter_cs = 0; load_sp0(tss, &tsk->thread); put_cpu(); if (vm86->flags & VM86_SCREEN_BITMAP) mark_screen_rdonly(tsk->mm); memcpy((struct kernel_vm86_regs *)regs, &vm86regs, sizeof(vm86regs)); force_iret(); 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->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.vm86->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.vm86->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; 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, 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; struct vm86plus_info_struct *vmpi = ¤t->thread.vm86->vm86plus; #define CHECK_IF_IN_TRAP \ if (vmpi->vm86dbg_active && vmpi->vm86dbg_TFpendig) \ newflags |= X86_EFLAGS_TF 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; 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) { 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; }