/*
       *	linux/arch/i386/kernel/ioport.c
       *
       * This contains the io-permission bitmap code - written by obz, with changes
       * by Linus.
       */
      
      #include <linux/sched.h>
      #include <linux/kernel.h>
      #include <linux/errno.h>
      #include <linux/types.h>
      #include <linux/ioport.h>
      #include <linux/mm.h>
      #include <linux/smp.h>
      #include <linux/smp_lock.h>
      #include <linux/stddef.h>
      
      /* Set EXTENT bits starting at BASE in BITMAP to value TURN_ON. */
  19  static void set_bitmap(unsigned long *bitmap, short base, short extent, int new_value)
      {
      	int mask;
      	unsigned long *bitmap_base = bitmap + (base >> 5);
      	unsigned short low_index = base & 0x1f;
      	int length = low_index + extent;
      
  26  	if (low_index != 0) {
      		mask = (~0 << low_index);
  28  		if (length < 32)
      				mask &= ~(~0 << length);
  30  		if (new_value)
      			*bitmap_base++ |= mask;
  32  		else
      			*bitmap_base++ &= ~mask;
      		length -= 32;
      	}
      
      	mask = (new_value ? ~0 : 0);
  38  	while (length >= 32) {
      		*bitmap_base++ = mask;
      		length -= 32;
      	}
      
  43  	if (length > 0) {
      		mask = ~(~0 << length);
  45  		if (new_value)
      			*bitmap_base++ |= mask;
  47  		else
      			*bitmap_base++ &= ~mask;
      	}
      }
      
      /*
       * this changes the io permissions bitmap in the current task.
       */
  55  asmlinkage int sys_ioperm(unsigned long from, unsigned long num, int turn_on)
      {
      	struct thread_struct * t = ¤t->thread;
      	struct tss_struct * tss = init_tss + smp_processor_id();
      
  60  	if ((from + num <= from) || (from + num > IO_BITMAP_SIZE*32))
  61  		return -EINVAL;
  62  	if (turn_on && !capable(CAP_SYS_RAWIO))
  63  		return -EPERM;
      	/*
      	 * If it's the first ioperm() call in this thread's lifetime, set the
      	 * IO bitmap up. ioperm() is much less timing critical than clone(),
      	 * this is why we delay this operation until now:
      	 */
  69  	if (!t->ioperm) {
      		/*
      		 * just in case ...
      		 */
      		memset(t->io_bitmap,0xff,(IO_BITMAP_SIZE+1)*4);
      		t->ioperm = 1;
      		/*
      		 * this activates it in the TSS
      		 */
      		tss->bitmap = IO_BITMAP_OFFSET;
      	}
      
      	/*
      	 * do it in the per-thread copy and in the TSS ...
      	 */
      	set_bitmap(t->io_bitmap, from, num, !turn_on);
      	set_bitmap(tss->io_bitmap, from, num, !turn_on);
      
  87  	return 0;
      }
      
      /*
       * sys_iopl has to be used when you want to access the IO ports
       * beyond the 0x3ff range: to get the full 65536 ports bitmapped
       * you'd need 8kB of bitmaps/process, which is a bit excessive.
       *
       * Here we just change the eflags value on the stack: we allow
       * only the super-user to do it. This depends on the stack-layout
       * on system-call entry - see also fork() and the signal handling
       * code.
       */
      
 101  asmlinkage int sys_iopl(unsigned long unused)
      {
      	struct pt_regs * regs = (struct pt_regs *) &unused;
      	unsigned int level = regs->ebx;
      	unsigned int old = (regs->eflags >> 12) & 3;
      
 107  	if (level > 3)
 108  		return -EINVAL;
      	/* Trying to gain more privileges? */
 110  	if (level > old) {
 111  		if (!capable(CAP_SYS_RAWIO))
 112  			return -EPERM;
      	}
      	regs->eflags = (regs->eflags & 0xffffcfff) | (level << 12);
 115  	return 0;
      }