arch/x86/kernel/ioport_32.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/stddef.h>
  16 #include <linux/slab.h>
  17 #include <linux/thread_info.h>
  18 #include <linux/syscalls.h>
  19
  20 /* Set EXTENT bits starting at BASE in BITMAP to value TURN_ON. */
  21 static void set_bitmap(unsigned long *bitmap, unsigned int base, unsigned int extent, int new_value)
  22 {
  23         unsigned long mask;
  24         unsigned long *bitmap_base = bitmap + (base / BITS_PER_LONG);
  25         unsigned int low_index = base & (BITS_PER_LONG-1);
  26         int length = low_index + extent;
  27
  28         if (low_index != 0) {
  29                 mask = (~0UL << low_index);
  30                 if (length < BITS_PER_LONG)
  31                         mask &= ~(~0UL << length);
  32                 if (new_value)
  33                         *bitmap_base++ |= mask;
  34                 else
  35                         *bitmap_base++ &= ~mask;
  36                 length -= BITS_PER_LONG;
  37         }
  38
  39         mask = (new_value ? ~0UL : 0UL);
  40         while (length >= BITS_PER_LONG) {
  41                 *bitmap_base++ = mask;
  42                 length -= BITS_PER_LONG;
  43         }
  44
  45         if (length > 0) {
  46                 mask = ~(~0UL << length);
  47                 if (new_value)
  48                         *bitmap_base++ |= mask;
  49                 else
  50                         *bitmap_base++ &= ~mask;
  51         }
  52 }
  53
  54
  55 /*
  56  * this changes the io permissions bitmap in the current task.
  57  */
  58 asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
  59 {
  60         unsigned long i, max_long, bytes, bytes_updated;
  61         struct thread_struct * t = &current->thread;
  62         struct tss_struct * tss;
  63         unsigned long *bitmap;
  64
  65         if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
  66                 return -EINVAL;
  67         if (turn_on && !capable(CAP_SYS_RAWIO))
  68                 return -EPERM;
  69
  70         /*
  71          * If it's the first ioperm() call in this thread's lifetime, set the
  72          * IO bitmap up. ioperm() is much less timing critical than clone(),
  73          * this is why we delay this operation until now:
  74          */
  75         if (!t->io_bitmap_ptr) {
  76                 bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
  77                 if (!bitmap)
  78                         return -ENOMEM;
  79
  80                 memset(bitmap, 0xff, IO_BITMAP_BYTES);
  81                 t->io_bitmap_ptr = bitmap;
  82                 set_thread_flag(TIF_IO_BITMAP);
  83         }
  84
  85         /*
  86          * do it in the per-thread copy and in the TSS ...
  87          *
  88          * Disable preemption via get_cpu() - we must not switch away
  89          * because the ->io_bitmap_max value must match the bitmap
  90          * contents:
  91          */
  92         tss = &per_cpu(init_tss, get_cpu());
  93
  94         set_bitmap(t->io_bitmap_ptr, from, num, !turn_on);
  95
  96         /*
  97          * Search for a (possibly new) maximum. This is simple and stupid,
  98          * to keep it obviously correct:
  99          */
 100         max_long = 0;
 101         for (i = 0; i < IO_BITMAP_LONGS; i++)
 102                 if (t->io_bitmap_ptr[i] != ~0UL)
 103                         max_long = i;
 104
 105         bytes = (max_long + 1) * sizeof(long);
 106         bytes_updated = max(bytes, t->io_bitmap_max);
 107
 108         t->io_bitmap_max = bytes;
 109
 110         /*
 111          * Sets the lazy trigger so that the next I/O operation will
 112          * reload the correct bitmap.
 113          * Reset the owner so that a process switch will not set
 114          * tss->io_bitmap_base to IO_BITMAP_OFFSET.
 115          */
 116         tss->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;
 117         tss->io_bitmap_owner = NULL;
 118
 119         put_cpu();
 120
 121         return 0;
 122 }
 123
 124 /*
 125  * sys_iopl has to be used when you want to access the IO ports
 126  * beyond the 0x3ff range: to get the full 65536 ports bitmapped
 127  * you'd need 8kB of bitmaps/process, which is a bit excessive.
 128  *
 129  * Here we just change the eflags value on the stack: we allow
 130  * only the super-user to do it. This depends on the stack-layout
 131  * on system-call entry - see also fork() and the signal handling
 132  * code.
 133  */
 134
 135 asmlinkage long sys_iopl(unsigned long unused)
 136 {
 137         volatile struct pt_regs * regs = (struct pt_regs *) &unused;
 138         unsigned int level = regs->ebx;
 139         unsigned int old = (regs->eflags >> 12) & 3;
 140         struct thread_struct *t = &current->thread;
 141
 142         if (level > 3)
 143                 return -EINVAL;
 144         /* Trying to gain more privileges? */
 145         if (level > old) {
 146                 if (!capable(CAP_SYS_RAWIO))
 147                         return -EPERM;
 148         }
 149         t->iopl = level << 12;
 150         regs->eflags = (regs->eflags & ~X86_EFLAGS_IOPL) | t->iopl;
 151         set_iopl_mask(t->iopl);
 152         return 0;
 153 }