arch/x86_64/kernel/ioport.c

   1 /*
   2  *      linux/arch/x86_64/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         int i;
  24                 if (new_value)
  25                 for (i = base; i < base + extent; i++)
  26                         __set_bit(i, bitmap);
  27                 else
  28                 for (i = base; i < base + extent; i++)
  29                         clear_bit(i, bitmap);
  30 }
  31
  32 /*
  33  * this changes the io permissions bitmap in the current task.
  34  */
  35 asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
  36 {
  37         unsigned int i, max_long, bytes, bytes_updated;
  38         struct thread_struct * t = &current->thread;
  39         struct tss_struct * tss;
  40         unsigned long *bitmap;
  41
  42         if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
  43                 return -EINVAL;
  44         if (turn_on && !capable(CAP_SYS_RAWIO))
  45                 return -EPERM;
  46
  47         /*
  48          * If it's the first ioperm() call in this thread's lifetime, set the
  49          * IO bitmap up. ioperm() is much less timing critical than clone(),
  50          * this is why we delay this operation until now:
  51          */
  52         if (!t->io_bitmap_ptr) {
  53                 bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
  54                 if (!bitmap)
  55                         return -ENOMEM;
  56
  57                 memset(bitmap, 0xff, IO_BITMAP_BYTES);
  58                 t->io_bitmap_ptr = bitmap;
  59                 set_thread_flag(TIF_IO_BITMAP);
  60         }
  61
  62         /*
  63          * do it in the per-thread copy and in the TSS ...
  64          *
  65          * Disable preemption via get_cpu() - we must not switch away
  66          * because the ->io_bitmap_max value must match the bitmap
  67          * contents:
  68          */
  69         tss = &per_cpu(init_tss, get_cpu());
  70
  71         set_bitmap(t->io_bitmap_ptr, from, num, !turn_on);
  72
  73         /*
  74          * Search for a (possibly new) maximum. This is simple and stupid,
  75          * to keep it obviously correct:
  76          */
  77         max_long = 0;
  78         for (i = 0; i < IO_BITMAP_LONGS; i++)
  79                 if (t->io_bitmap_ptr[i] != ~0UL)
  80                         max_long = i;
  81
  82         bytes = (max_long + 1) * sizeof(long);
  83         bytes_updated = max(bytes, t->io_bitmap_max);
  84
  85         t->io_bitmap_max = bytes;
  86
  87         /* Update the TSS: */
  88         memcpy(tss->io_bitmap, t->io_bitmap_ptr, bytes_updated);
  89
  90         put_cpu();
  91
  92         return 0;
  93 }
  94
  95 /*
  96  * sys_iopl has to be used when you want to access the IO ports
  97  * beyond the 0x3ff range: to get the full 65536 ports bitmapped
  98  * you'd need 8kB of bitmaps/process, which is a bit excessive.
  99  *
 100  * Here we just change the eflags value on the stack: we allow
 101  * only the super-user to do it. This depends on the stack-layout
 102  * on system-call entry - see also fork() and the signal handling
 103  * code.
 104  */
 105
 106 asmlinkage long sys_iopl(unsigned int level, struct pt_regs *regs)
 107 {
 108         unsigned int old = (regs->eflags >> 12) & 3;
 109
 110         if (level > 3)
 111                 return -EINVAL;
 112         /* Trying to gain more privileges? */
 113         if (level > old) {
 114                 if (!capable(CAP_SYS_RAWIO))
 115                         return -EPERM;
 116         }
 117         regs->eflags = (regs->eflags &~ X86_EFLAGS_IOPL) | (level << 12);
 118         return 0;
 119 }