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/capability.h>
  11 #include <linux/errno.h>
  12 #include <linux/types.h>
  13 #include <linux/ioport.h>
  14 #include <linux/smp.h>
  15 #include <linux/smp_lock.h>
  16 #include <linux/stddef.h>
  17 #include <linux/slab.h>
  18 #include <linux/thread_info.h>
  19 #include <linux/syscalls.h>
  20
  21 /* Set EXTENT bits starting at BASE in BITMAP to value TURN_ON. */
  22 static void set_bitmap(unsigned long *bitmap, unsigned int base, unsigned int extent, int new_value)
  23 {
  24         unsigned long mask;
  25         unsigned long *bitmap_base = bitmap + (base / BITS_PER_LONG);
  26         unsigned int low_index = base & (BITS_PER_LONG-1);
  27         int length = low_index + extent;
  28
  29         if (low_index != 0) {
  30                 mask = (~0UL << low_index);
  31                 if (length < BITS_PER_LONG)
  32                         mask &= ~(~0UL << length);
  33                 if (new_value)
  34                         *bitmap_base++ |= mask;
  35                 else
  36                         *bitmap_base++ &= ~mask;
  37                 length -= BITS_PER_LONG;
  38         }
  39
  40         mask = (new_value ? ~0UL : 0UL);
  41         while (length >= BITS_PER_LONG) {
  42                 *bitmap_base++ = mask;
  43                 length -= BITS_PER_LONG;
  44         }
  45
  46         if (length > 0) {
  47                 mask = ~(~0UL << length);
  48                 if (new_value)
  49                         *bitmap_base++ |= mask;
  50                 else
  51                         *bitmap_base++ &= ~mask;
  52         }
  53 }
  54
  55
  56 /*
  57  * this changes the io permissions bitmap in the current task.
  58  */
  59 asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
  60 {
  61         unsigned long i, max_long, bytes, bytes_updated;
  62         struct thread_struct * t = &current->thread;
  63         struct tss_struct * tss;
  64         unsigned long *bitmap;
  65
  66         if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
  67                 return -EINVAL;
  68         if (turn_on && !capable(CAP_SYS_RAWIO))
  69                 return -EPERM;
  70
  71         /*
  72          * If it's the first ioperm() call in this thread's lifetime, set the
  73          * IO bitmap up. ioperm() is much less timing critical than clone(),
  74          * this is why we delay this operation until now:
  75          */
  76         if (!t->io_bitmap_ptr) {
  77                 bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
  78                 if (!bitmap)
  79                         return -ENOMEM;
  80
  81                 memset(bitmap, 0xff, IO_BITMAP_BYTES);
  82                 t->io_bitmap_ptr = bitmap;
  83                 set_thread_flag(TIF_IO_BITMAP);
  84         }
  85
  86         /*
  87          * do it in the per-thread copy and in the TSS ...
  88          *
  89          * Disable preemption via get_cpu() - we must not switch away
  90          * because the ->io_bitmap_max value must match the bitmap
  91          * contents:
  92          */
  93         tss = &per_cpu(init_tss, get_cpu());
  94
  95         set_bitmap(t->io_bitmap_ptr, from, num, !turn_on);
  96
  97         /*
  98          * Search for a (possibly new) maximum. This is simple and stupid,
  99          * to keep it obviously correct:
 100          */
 101         max_long = 0;
 102         for (i = 0; i < IO_BITMAP_LONGS; i++)
 103                 if (t->io_bitmap_ptr[i] != ~0UL)
 104                         max_long = i;
 105
 106         bytes = (max_long + 1) * sizeof(long);
 107         bytes_updated = max(bytes, t->io_bitmap_max);
 108
 109         t->io_bitmap_max = bytes;
 110
 111         /*
 112          * Sets the lazy trigger so that the next I/O operation will
 113          * reload the correct bitmap.
 114          * Reset the owner so that a process switch will not set
 115          * tss->io_bitmap_base to IO_BITMAP_OFFSET.
 116          */
 117         tss->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;
 118         tss->io_bitmap_owner = NULL;
 119
 120         put_cpu();
 121
 122         return 0;
 123 }
 124
 125 /*
 126  * sys_iopl has to be used when you want to access the IO ports
 127  * beyond the 0x3ff range: to get the full 65536 ports bitmapped
 128  * you'd need 8kB of bitmaps/process, which is a bit excessive.
 129  *
 130  * Here we just change the eflags value on the stack: we allow
 131  * only the super-user to do it. This depends on the stack-layout
 132  * on system-call entry - see also fork() and the signal handling
 133  * code.
 134  */
 135
 136 asmlinkage long sys_iopl(unsigned long unused)
 137 {
 138         volatile struct pt_regs * regs = (struct pt_regs *) &unused;
 139         unsigned int level = regs->ebx;
 140         unsigned int old = (regs->eflags >> 12) & 3;
 141         struct thread_struct *t = &current->thread;
 142
 143         if (level > 3)
 144                 return -EINVAL;
 145         /* Trying to gain more privileges? */
 146         if (level > old) {
 147                 if (!capable(CAP_SYS_RAWIO))
 148                         return -EPERM;
 149         }
 150         t->iopl = level << 12;
 151         regs->eflags = (regs->eflags & ~X86_EFLAGS_IOPL) | t->iopl;
 152         set_iopl_mask(t->iopl);
 153         return 0;
 154 }