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ioport_32.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/capability.h>
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/ioport.h>
#include <linux/smp.h>
#include <linux/stddef.h>
#include <linux/slab.h>
#include <linux/thread_info.h>
#include <linux/syscalls.h>

/* Set EXTENT bits starting at BASE in BITMAP to value TURN_ON. */
static void set_bitmap(unsigned long *bitmap, unsigned int base, unsigned int extent, int new_value)
{
      unsigned long mask;
      unsigned long *bitmap_base = bitmap + (base / BITS_PER_LONG);
      unsigned int low_index = base & (BITS_PER_LONG-1);
      int length = low_index + extent;

      if (low_index != 0) {
            mask = (~0UL << low_index);
            if (length < BITS_PER_LONG)
                  mask &= ~(~0UL << length);
            if (new_value)
                  *bitmap_base++ |= mask;
            else
                  *bitmap_base++ &= ~mask;
            length -= BITS_PER_LONG;
      }

      mask = (new_value ? ~0UL : 0UL);
      while (length >= BITS_PER_LONG) {
            *bitmap_base++ = mask;
            length -= BITS_PER_LONG;
      }

      if (length > 0) {
            mask = ~(~0UL << length);
            if (new_value)
                  *bitmap_base++ |= mask;
            else
                  *bitmap_base++ &= ~mask;
      }
}


/*
 * this changes the io permissions bitmap in the current task.
 */
asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
{
      unsigned long i, max_long, bytes, bytes_updated;
      struct thread_struct * t = &current->thread;
      struct tss_struct * tss;
      unsigned long *bitmap;

      if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
            return -EINVAL;
      if (turn_on && !capable(CAP_SYS_RAWIO))
            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:
       */
      if (!t->io_bitmap_ptr) {
            bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
            if (!bitmap)
                  return -ENOMEM;

            memset(bitmap, 0xff, IO_BITMAP_BYTES);
            t->io_bitmap_ptr = bitmap;
            set_thread_flag(TIF_IO_BITMAP);
      }

      /*
       * do it in the per-thread copy and in the TSS ...
       *
       * Disable preemption via get_cpu() - we must not switch away
       * because the ->io_bitmap_max value must match the bitmap
       * contents:
       */
      tss = &per_cpu(init_tss, get_cpu());

      set_bitmap(t->io_bitmap_ptr, from, num, !turn_on);

      /*
       * Search for a (possibly new) maximum. This is simple and stupid,
       * to keep it obviously correct:
       */
      max_long = 0;
      for (i = 0; i < IO_BITMAP_LONGS; i++)
            if (t->io_bitmap_ptr[i] != ~0UL)
                  max_long = i;

      bytes = (max_long + 1) * sizeof(long);
      bytes_updated = max(bytes, t->io_bitmap_max);

      t->io_bitmap_max = bytes;

      /*
       * Sets the lazy trigger so that the next I/O operation will
       * reload the correct bitmap.
       * Reset the owner so that a process switch will not set
       * tss->io_bitmap_base to IO_BITMAP_OFFSET.
       */
      tss->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;
      tss->io_bitmap_owner = NULL;

      put_cpu();

      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.
 */

asmlinkage long sys_iopl(unsigned long unused)
{
      volatile struct pt_regs * regs = (struct pt_regs *) &unused;
      unsigned int level = regs->ebx;
      unsigned int old = (regs->eflags >> 12) & 3;
      struct thread_struct *t = &current->thread;

      if (level > 3)
            return -EINVAL;
      /* Trying to gain more privileges? */
      if (level > old) {
            if (!capable(CAP_SYS_RAWIO))
                  return -EPERM;
      }
      t->iopl = level << 12;
      regs->eflags = (regs->eflags & ~X86_EFLAGS_IOPL) | t->iopl;
      set_iopl_mask(t->iopl);
      return 0;
}

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