arch/x86/kernel/ioport.c

   1 /*
   2  * This contains the io-permission bitmap code - written by obz, with changes
   3  * by Linus. 32/64 bits code unification by Miguel Botón.
   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 #include <linux/bitmap.h>
  18 #include <asm/syscalls.h>
  19
  20 /*
  21  * this changes the io permissions bitmap in the current task.
  22  */
  23 asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
  24 {
  25         struct thread_struct *t = &current->thread;
  26         struct tss_struct *tss;
  27         unsigned int i, max_long, bytes, bytes_updated;
  28
  29         if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
  30                 return -EINVAL;
  31         if (turn_on && !capable(CAP_SYS_RAWIO))
  32                 return -EPERM;
  33
  34         /*
  35          * If it's the first ioperm() call in this thread's lifetime, set the
  36          * IO bitmap up. ioperm() is much less timing critical than clone(),
  37          * this is why we delay this operation until now:
  38          */
  39         if (!t->io_bitmap_ptr) {
  40                 unsigned long *bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
  41
  42                 if (!bitmap)
  43                         return -ENOMEM;
  44
  45                 memset(bitmap, 0xff, IO_BITMAP_BYTES);
  46                 t->io_bitmap_ptr = bitmap;
  47                 set_thread_flag(TIF_IO_BITMAP);
  48         }
  49
  50         /*
  51          * do it in the per-thread copy and in the TSS ...
  52          *
  53          * Disable preemption via get_cpu() - we must not switch away
  54          * because the ->io_bitmap_max value must match the bitmap
  55          * contents:
  56          */
  57         tss = &per_cpu(cpu_tss, get_cpu());
  58
  59         if (turn_on)
  60                 bitmap_clear(t->io_bitmap_ptr, from, num);
  61         else
  62                 bitmap_set(t->io_bitmap_ptr, from, num);
  63
  64         /*
  65          * Search for a (possibly new) maximum. This is simple and stupid,
  66          * to keep it obviously correct:
  67          */
  68         max_long = 0;
  69         for (i = 0; i < IO_BITMAP_LONGS; i++)
  70                 if (t->io_bitmap_ptr[i] != ~0UL)
  71                         max_long = i;
  72
  73         bytes = (max_long + 1) * sizeof(unsigned long);
  74         bytes_updated = max(bytes, t->io_bitmap_max);
  75
  76         t->io_bitmap_max = bytes;
  77
  78         /* Update the TSS: */
  79         memcpy(tss->io_bitmap, t->io_bitmap_ptr, bytes_updated);
  80
  81         put_cpu();
  82
  83         return 0;
  84 }
  85
  86 /*
  87  * sys_iopl has to be used when you want to access the IO ports
  88  * beyond the 0x3ff range: to get the full 65536 ports bitmapped
  89  * you'd need 8kB of bitmaps/process, which is a bit excessive.
  90  *
  91  * Here we just change the flags value on the stack: we allow
  92  * only the super-user to do it. This depends on the stack-layout
  93  * on system-call entry - see also fork() and the signal handling
  94  * code.
  95  */
  96 SYSCALL_DEFINE1(iopl, unsigned int, level)
  97 {
  98         struct pt_regs *regs = current_pt_regs();
  99         struct thread_struct *t = &current->thread;
 100
 101         /*
 102          * Careful: the IOPL bits in regs->flags are undefined under Xen PV
 103          * and changing them has no effect.
 104          */
 105         unsigned int old = t->iopl >> X86_EFLAGS_IOPL_BIT;
 106
 107         if (level > 3)
 108                 return -EINVAL;
 109         /* Trying to gain more privileges? */
 110         if (level > old) {
 111                 if (!capable(CAP_SYS_RAWIO))
 112                         return -EPERM;
 113         }
 114         regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
 115                 (level << X86_EFLAGS_IOPL_BIT);
 116         t->iopl = level << X86_EFLAGS_IOPL_BIT;
 117         set_iopl_mask(t->iopl);
 118
 119         return 0;
 120 }