arch/x86/kernel/ioport_32.c

   1 /*
   2  * This contains the io-permission bitmap code - written by obz, with changes
   3  * by Linus.
   4  */
   5
   6 #include <linux/sched.h>
   7 #include <linux/kernel.h>
   8 #include <linux/capability.h>
   9 #include <linux/errno.h>
  10 #include <linux/types.h>
  11 #include <linux/ioport.h>
  12 #include <linux/smp.h>
  13 #include <linux/stddef.h>
  14 #include <linux/slab.h>
  15 #include <linux/thread_info.h>
  16 #include <linux/syscalls.h>
  17
  18 /* Set EXTENT bits starting at BASE in BITMAP to value TURN_ON. */
  19 static void set_bitmap(unsigned long *bitmap, unsigned int base, unsigned int extent, int new_value)
  20 {
  21         unsigned long mask;
  22         unsigned long *bitmap_base = bitmap + (base / BITS_PER_LONG);
  23         unsigned int low_index = base & (BITS_PER_LONG-1);
  24         int length = low_index + extent;
  25
  26         if (low_index != 0) {
  27                 mask = (~0UL << low_index);
  28                 if (length < BITS_PER_LONG)
  29                         mask &= ~(~0UL << length);
  30                 if (new_value)
  31                         *bitmap_base++ |= mask;
  32                 else
  33                         *bitmap_base++ &= ~mask;
  34                 length -= BITS_PER_LONG;
  35         }
  36
  37         mask = (new_value ? ~0UL : 0UL);
  38         while (length >= BITS_PER_LONG) {
  39                 *bitmap_base++ = mask;
  40                 length -= BITS_PER_LONG;
  41         }
  42
  43         if (length > 0) {
  44                 mask = ~(~0UL << length);
  45                 if (new_value)
  46                         *bitmap_base++ |= mask;
  47                 else
  48                         *bitmap_base++ &= ~mask;
  49         }
  50 }
  51
  52
  53 /*
  54  * this changes the io permissions bitmap in the current task.
  55  */
  56 asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
  57 {
  58         unsigned long i, max_long, bytes, bytes_updated;
  59         struct thread_struct * t = &current->thread;
  60         struct tss_struct * tss;
  61         unsigned long *bitmap;
  62
  63         if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
  64                 return -EINVAL;
  65         if (turn_on && !capable(CAP_SYS_RAWIO))
  66                 return -EPERM;
  67
  68         /*
  69          * If it's the first ioperm() call in this thread's lifetime, set the
  70          * IO bitmap up. ioperm() is much less timing critical than clone(),
  71          * this is why we delay this operation until now:
  72          */
  73         if (!t->io_bitmap_ptr) {
  74                 bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
  75                 if (!bitmap)
  76                         return -ENOMEM;
  77
  78                 memset(bitmap, 0xff, IO_BITMAP_BYTES);
  79                 t->io_bitmap_ptr = bitmap;
  80                 set_thread_flag(TIF_IO_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          * Reset the owner so that a process switch will not set
 112          * tss->io_bitmap_base to IO_BITMAP_OFFSET.
 113          */
 114         tss->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;
 115         tss->io_bitmap_owner = NULL;
 116
 117         put_cpu();
 118
 119         return 0;
 120 }
 121
 122 /*
 123  * sys_iopl has to be used when you want to access the IO ports
 124  * beyond the 0x3ff range: to get the full 65536 ports bitmapped
 125  * you'd need 8kB of bitmaps/process, which is a bit excessive.
 126  *
 127  * Here we just change the eflags value on the stack: we allow
 128  * only the super-user to do it. This depends on the stack-layout
 129  * on system-call entry - see also fork() and the signal handling
 130  * code.
 131  */
 132
 133 asmlinkage long sys_iopl(unsigned long unused)
 134 {
 135         volatile struct pt_regs * regs = (struct pt_regs *) &unused;
 136         unsigned int level = regs->ebx;
 137         unsigned int old = (regs->eflags >> 12) & 3;
 138         struct thread_struct *t = &current->thread;
 139
 140         if (level > 3)
 141                 return -EINVAL;
 142         /* Trying to gain more privileges? */
 143         if (level > old) {
 144                 if (!capable(CAP_SYS_RAWIO))
 145                         return -EPERM;
 146         }
 147         t->iopl = level << 12;
 148         regs->eflags = (regs->eflags & ~X86_EFLAGS_IOPL) | t->iopl;
 149         set_iopl_mask(t->iopl);
 150         return 0;
 151 }