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 <linux/module.h>
  19 #include <asm/syscalls.h>
  20
  21 /*
  22  * this changes the io permissions bitmap in the current task.
  23  */
  24 asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
  25 {
  26         struct thread_struct *t = &current->thread;
  27         struct tss_struct *tss;
  28         unsigned int i, max_long, bytes, bytes_updated;
  29
  30         if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
  31                 return -EINVAL;
  32         if (turn_on && (!capable(CAP_SYS_RAWIO) || secure_modules()))
  33                 return -EPERM;
  34
  35         /*
  36          * If it's the first ioperm() call in this thread's lifetime, set the
  37          * IO bitmap up. ioperm() is much less timing critical than clone(),
  38          * this is why we delay this operation until now:
  39          */
  40         if (!t->io_bitmap_ptr) {
  41                 unsigned long *bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
  42
  43                 if (!bitmap)
  44                         return -ENOMEM;
  45
  46                 memset(bitmap, 0xff, IO_BITMAP_BYTES);
  47                 t->io_bitmap_ptr = bitmap;
  48                 set_thread_flag(TIF_IO_BITMAP);
  49         }
  50
  51         /*
  52          * do it in the per-thread copy and in the TSS ...
  53          *
  54          * Disable preemption via get_cpu() - we must not switch away
  55          * because the ->io_bitmap_max value must match the bitmap
  56          * contents:
  57          */
  58         tss = &per_cpu(cpu_tss, get_cpu());
  59
  60         if (turn_on)
  61                 bitmap_clear(t->io_bitmap_ptr, from, num);
  62         else
  63                 bitmap_set(t->io_bitmap_ptr, from, num);
  64
  65         /*
  66          * Search for a (possibly new) maximum. This is simple and stupid,
  67          * to keep it obviously correct:
  68          */
  69         max_long = 0;
  70         for (i = 0; i < IO_BITMAP_LONGS; i++)
  71                 if (t->io_bitmap_ptr[i] != ~0UL)
  72                         max_long = i;
  73
  74         bytes = (max_long + 1) * sizeof(unsigned long);
  75         bytes_updated = max(bytes, t->io_bitmap_max);
  76
  77         t->io_bitmap_max = bytes;
  78
  79         /* Update the TSS: */
  80         memcpy(tss->io_bitmap, t->io_bitmap_ptr, bytes_updated);
  81
  82         put_cpu();
  83
  84         return 0;
  85 }
  86
  87 /*
  88  * sys_iopl has to be used when you want to access the IO ports
  89  * beyond the 0x3ff range: to get the full 65536 ports bitmapped
  90  * you'd need 8kB of bitmaps/process, which is a bit excessive.
  91  *
  92  * Here we just change the flags value on the stack: we allow
  93  * only the super-user to do it. This depends on the stack-layout
  94  * on system-call entry - see also fork() and the signal handling
  95  * code.
  96  */
  97 SYSCALL_DEFINE1(iopl, unsigned int, level)
  98 {
  99         struct pt_regs *regs = current_pt_regs();
 100         struct thread_struct *t = &current->thread;
 101
 102         /*
 103          * Careful: the IOPL bits in regs->flags are undefined under Xen PV
 104          * and changing them has no effect.
 105          */
 106         unsigned int old = t->iopl >> X86_EFLAGS_IOPL_BIT;
 107
 108         if (level > 3)
 109                 return -EINVAL;
 110         /* Trying to gain more privileges? */
 111         if (level > old) {
 112                 if (!capable(CAP_SYS_RAWIO) || secure_modules())
 113                         return -EPERM;
 114         }
 115         regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
 116                 (level << X86_EFLAGS_IOPL_BIT);
 117         t->iopl = level << X86_EFLAGS_IOPL_BIT;
 118         set_iopl_mask(t->iopl);
 119
 120         return 0;
 121 }