vm86.c

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/*
 *  linux/kernel/vm86.c
 *
 *  Copyright (C) 1994  Linus Torvalds
 */
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/string.h>
#include <linux/ptrace.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>

#include <asm/uaccess.h>
#include <asm/pgalloc.h>
#include <asm/io.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)->eax))[0])
#define AH(regs)	(((unsigned char *)&((regs)->eax))[1])
#define IP(regs)	(*(unsigned short *)&((regs)->eip))
#define SP(regs)	(*(unsigned short *)&((regs)->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)

#define VM86_REGS_PART2 orig_eax
#define VM86_REGS_SIZE1 \
        ( (unsigned)( & (((struct kernel_vm86_regs *)0)->VM86_REGS_PART2) ) )
#define VM86_REGS_SIZE2 (sizeof(struct kernel_vm86_regs) - VM86_REGS_SIZE1)

asmlinkage struct pt_regs * FASTCALL(save_v86_state(struct kernel_vm86_regs * regs));
struct pt_regs * save_v86_state(struct kernel_vm86_regs * regs)
{
	struct tss_struct *tss;
	struct pt_regs *ret;
	unsigned long tmp;

	if (!current->thread.vm86_info) {
		printk("no vm86_info: BAD\n");
		do_exit(SIGSEGV);
	}
	set_flags(regs->eflags, VEFLAGS, VIF_MASK | current->thread.v86mask);
	tmp = copy_to_user(&current->thread.vm86_info->regs,regs, VM86_REGS_SIZE1);
	tmp += copy_to_user(&current->thread.vm86_info->regs.VM86_REGS_PART2,
		&regs->VM86_REGS_PART2, VM86_REGS_SIZE2);
	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 = init_tss + smp_processor_id();
	tss->esp0 = current->thread.esp0 = current->thread.saved_esp0;
	current->thread.saved_esp0 = 0;
	ret = KVM86->regs32;
	return ret;
}

static void mark_screen_rdonly(struct task_struct * tsk)
{
	pgd_t *pgd;
	pmd_t *pmd;
	pte_t *pte;
	int i;

	pgd = pgd_offset(tsk->mm, 0xA0000);
	if (pgd_none(*pgd))
		return;
	if (pgd_bad(*pgd)) {
		pgd_ERROR(*pgd);
		pgd_clear(pgd);
		return;
	}
	pmd = pmd_offset(pgd, 0xA0000);
	if (pmd_none(*pmd))
		return;
	if (pmd_bad(*pmd)) {
		pmd_ERROR(*pmd);
		pmd_clear(pmd);
		return;
	}
	pte = pte_offset(pmd, 0xA0000);
	for (i = 0; i < 32; i++) {
		if (pte_present(*pte))
			set_pte(pte, pte_wrprotect(*pte));
		pte++;
	}
	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 vm86_struct * v86)
{
	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_from_user(&info, v86, VM86_REGS_SIZE1);
	tmp += copy_from_user(&info.regs.VM86_REGS_PART2, &v86->regs.VM86_REGS_PART2,
		(long)&info.vm86plus - (long)&info.regs.VM86_REGS_PART2);
	ret = -EFAULT;
	if (tmp)
		goto out;
	memset(&info.vm86plus, 0, (int)&info.regs32 - (int)&info.vm86plus);
	info.regs32 = (struct pt_regs *) &v86;
	tsk->thread.vm86_info = v86;
	do_sys_vm86(&info, tsk);
	ret = 0;	/* we never return here */
out:
	return ret;
}


asmlinkage int sys_vm86(unsigned long subfunction, struct vm86plus_struct * v86)
{
	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;

	tsk = current;
	switch (subfunction) {
		case VM86_REQUEST_IRQ:
		case VM86_FREE_IRQ:
		case VM86_GET_IRQ_BITS:
		case VM86_GET_AND_RESET_IRQ:
			ret = do_vm86_irq_handling(subfunction,(int)v86);
			goto out;
		case VM86_PLUS_INSTALL_CHECK:
			/* NOTE: on old vm86 stuff this will return the error
			   from verify_area(), 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;
	tmp  = copy_from_user(&info, v86, VM86_REGS_SIZE1);
	tmp += copy_from_user(&info.regs.VM86_REGS_PART2, &v86->regs.VM86_REGS_PART2,
		(long)&info.regs32 - (long)&info.regs.VM86_REGS_PART2);
	ret = -EFAULT;
	if (tmp)
		goto out;
	info.regs32 = (struct pt_regs *) &subfunction;
	info.vm86plus.is_vm86pus = 1;
	tsk->thread.vm86_info = (struct vm86_struct *)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.__null_ds = 0;
	info->regs.__null_es = 0;

/* we are clearing fs,gs later just before "jmp ret_from_sys_call",
 * because starting with Linux 2.1.x they aren't no longer 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.eflags;
	info->regs.eflags &= SAFE_MASK;
	info->regs.eflags |= info->regs32->eflags & ~SAFE_MASK;
	info->regs.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;
	tss = init_tss + smp_processor_id();
	tss->esp0 = tsk->thread.esp0 = (unsigned long) &info->VM86_TSS_ESP0;

	tsk->thread.screen_bitmap = info->screen_bitmap;
	if (info->flags & VM86_SCREEN_BITMAP)
		mark_screen_rdonly(tsk);
	__asm__ __volatile__(
		"xorl %%eax,%%eax; movl %%eax,%%fs; movl %%eax,%%gs\n\t"
		"movl %0,%%esp\n\t"
		"jmp ret_from_sys_call"
		: /* no outputs */
		:"r" (&info->regs), "b" (tsk) : "ax");
	/* 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"
		"jmp ret_from_sys_call"
		: : "r" (regs32), "b" (current));
}

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->eflags &= ~TF_MASK;
}

static inline void set_vflags_long(unsigned long eflags, struct kernel_vm86_regs * regs)
{
	set_flags(VEFLAGS, eflags, current->thread.v86mask);
	set_flags(regs->eflags, eflags, SAFE_MASK);
	if (eflags & IF_MASK)
		set_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->eflags, flags, SAFE_MASK);
	if (flags & IF_MASK)
		set_IF(regs);
}

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

	if (VEFLAGS & VIF_MASK)
		flags |= IF_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;
}

/*
 * Boy are these ugly, but we need to do the correct 16-bit arithmetic.
 * Gcc makes a mess of it, so we do it inline and use non-obvious calling
 * conventions..
 */
#define pushb(base, ptr, val) \
__asm__ __volatile__( \
	"decw %w0\n\t" \
	"movb %2,0(%1,%0)" \
	: "=r" (ptr) \
	: "r" (base), "q" (val), "0" (ptr))

#define pushw(base, ptr, val) \
__asm__ __volatile__( \
	"decw %w0\n\t" \