arch/i386/kernel/ioport.c

   1 /*
   2  *      linux/arch/i386/kernel/ioport.c
   3  *
   4  * This contains the io-permission bitmap code - written by obz, with changes
   5  * by Linus.
   6  */
   7
   8 #include <linux/sched.h>
   9 #include <linux/kernel.h>
  10 #include <linux/errno.h>
  11 #include <linux/types.h>
  12 #include <linux/ioport.h>
  13 #include <linux/smp.h>
  14 #include <linux/smp_lock.h>
  15 #include <linux/stddef.h>
  16 #include <linux/slab.h>
  17 #include <linux/thread_info.h>
  18
  19 /* Set EXTENT bits starting at BASE in BITMAP to value TURN_ON. */
  20 static void set_bitmap(unsigned long *bitmap, unsigned int base, unsigned int extent, int new_value)
  21 {
  22         unsigned long mask;
  23         unsigned long *bitmap_base = bitmap + (base / BITS_PER_LONG);
  24         unsigned int low_index = base & (BITS_PER_LONG-1);
  25         int length = low_index + extent;
  26
  27         if (low_index != 0) {
  28                 mask = (~0UL << low_index);
  29                 if (length < BITS_PER_LONG)
  30                         mask &= ~(~0UL << length);
  31                 if (new_value)
  32                         *bitmap_base++ |= mask;
  33                 else
  34                         *bitmap_base++ &= ~mask;
  35                 length -= BITS_PER_LONG;
  36         }
  37
  38         mask = (new_value ? ~0UL : 0UL);
  39         while (length >= BITS_PER_LONG) {
  40                 *bitmap_base++ = mask;
  41                 length -= BITS_PER_LONG;
  42         }
  43
  44         if (length > 0) {
  45                 mask = ~(~0UL << length);
  46                 if (new_value)
  47                         *bitmap_base++ |= mask;
  48                 else
  49                         *bitmap_base++ &= ~mask;
  50         }
  51 }
  52
  53
  54 /*
  55  * this changes the io permissions bitmap in the current task.
  56  */
  57 asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
  58 {
  59         unsigned long i, max_long, bytes, bytes_updated;
  60         struct thread_struct * t = &current->thread;
  61         struct tss_struct * tss;
  62         unsigned long *bitmap;
  63
  64         if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
  65                 return -EINVAL;
  66         if (turn_on && !capable(CAP_SYS_RAWIO))
  67                 return -EPERM;
  68
  69         /*
  70          * If it's the first ioperm() call in this thread's lifetime, set the
  71          * IO bitmap up. ioperm() is much less timing critical than clone(),
  72          * this is why we delay this operation until now:
  73          */
  74         if (!t->io_bitmap_ptr) {
  75                 bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
  76                 if (!bitmap)
  77                         return -ENOMEM;
  78
  79                 memset(bitmap, 0xff, IO_BITMAP_BYTES);
  80                 t->io_bitmap_ptr = bitmap;
  81         }
  82
  83         /*
  84          * do it in the per-thread copy and in the TSS ...
  85          *
  86          * Disable preemption via get_cpu() - we must not switch away
  87          * because the ->io_bitmap_max value must match the bitmap
  88          * contents:
  89          */
  90         tss = &per_cpu(init_tss, get_cpu());
  91
  92         set_bitmap(t->io_bitmap_ptr, from, num, !turn_on);
  93
  94         /*
  95          * Search for a (possibly new) maximum. This is simple and stupid,
  96          * to keep it obviously correct:
  97          */
  98         max_long = 0;
  99         for (i = 0; i < IO_BITMAP_LONGS; i++)
 100                 if (t->io_bitmap_ptr[i] != ~0UL)
 101                         max_long = i;
 102
 103         bytes = (max_long + 1) * sizeof(long);
 104         bytes_updated = max(bytes, t->io_bitmap_max);
 105
 106         t->io_bitmap_max = bytes;
 107
 108         /*
 109          * Sets the lazy trigger so that the next I/O operation will
 110          * reload the correct bitmap.
 111          */
 112         tss->io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;
 113
 114         put_cpu();
 115
 116         return 0;
 117 }
 118
 119 /*
 120  * sys_iopl has to be used when you want to access the IO ports
 121  * beyond the 0x3ff range: to get the full 65536 ports bitmapped
 122  * you'd need 8kB of bitmaps/process, which is a bit excessive.
 123  *
 124  * Here we just change the eflags value on the stack: we allow
 125  * only the super-user to do it. This depends on the stack-layout
 126  * on system-call entry - see also fork() and the signal handling
 127  * code.
 128  */
 129
 130 asmlinkage long sys_iopl(unsigned long unused)
 131 {
 132         volatile struct pt_regs * regs = (struct pt_regs *) &unused;
 133         unsigned int level = regs->ebx;
 134         unsigned int old = (regs->eflags >> 12) & 3;
 135
 136         if (level > 3)
 137                 return -EINVAL;
 138         /* Trying to gain more privileges? */
 139         if (level > old) {
 140                 if (!capable(CAP_SYS_RAWIO))
 141                         return -EPERM;
 142         }
 143         regs->eflags = (regs->eflags &~ 0x3000UL) | (level << 12);
 144         /* Make sure we return the long way (not sysenter) */
 145         set_thread_flag(TIF_IRET);
 146         return 0;
 147 }