arch/x86/kernel/ioport.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * This contains the io-permission bitmap code - written by obz, with changes
   4  * by Linus. 32/64 bits code unification by Miguel Botón.
   5  */
   6
   7 #include <linux/sched.h>
   8 #include <linux/sched/task_stack.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 #include <linux/bitmap.h>
  20 #include <asm/syscalls.h>
  21 #include <asm/desc.h>
  22
  23 /*
  24  * this changes the io permissions bitmap in the current task.
  25  */
  26 asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
  27 {
  28         struct thread_struct *t = &current->thread;
  29         struct tss_struct *tss;
  30         unsigned int i, max_long, bytes, bytes_updated;
  31
  32         if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
  33                 return -EINVAL;
  34         if (turn_on && !capable(CAP_SYS_RAWIO))
  35                 return -EPERM;
  36
  37         /*
  38          * If it's the first ioperm() call in this thread's lifetime, set the
  39          * IO bitmap up. ioperm() is much less timing critical than clone(),
  40          * this is why we delay this operation until now:
  41          */
  42         if (!t->io_bitmap_ptr) {
  43                 unsigned long *bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
  44
  45                 if (!bitmap)
  46                         return -ENOMEM;
  47
  48                 memset(bitmap, 0xff, IO_BITMAP_BYTES);
  49                 t->io_bitmap_ptr = bitmap;
  50                 set_thread_flag(TIF_IO_BITMAP);
  51
  52                 /*
  53                  * Now that we have an IO bitmap, we need our TSS limit to be
  54                  * correct.  It's fine if we are preempted after doing this:
  55                  * with TIF_IO_BITMAP set, context switches will keep our TSS
  56                  * limit correct.
  57                  */
  58                 preempt_disable();
  59                 refresh_tss_limit();
  60                 preempt_enable();
  61         }
  62
  63         /*
  64          * do it in the per-thread copy and in the TSS ...
  65          *
  66          * Disable preemption via get_cpu() - we must not switch away
  67          * because the ->io_bitmap_max value must match the bitmap
  68          * contents:
  69          */
  70         tss = &per_cpu(cpu_tss, get_cpu());
  71
  72         if (turn_on)
  73                 bitmap_clear(t->io_bitmap_ptr, from, num);
  74         else
  75                 bitmap_set(t->io_bitmap_ptr, from, num);
  76
  77         /*
  78          * Search for a (possibly new) maximum. This is simple and stupid,
  79          * to keep it obviously correct:
  80          */
  81         max_long = 0;
  82         for (i = 0; i < IO_BITMAP_LONGS; i++)
  83                 if (t->io_bitmap_ptr[i] != ~0UL)
  84                         max_long = i;
  85
  86         bytes = (max_long + 1) * sizeof(unsigned long);
  87         bytes_updated = max(bytes, t->io_bitmap_max);
  88
  89         t->io_bitmap_max = bytes;
  90
  91         /* Update the TSS: */
  92         memcpy(tss->io_bitmap, t->io_bitmap_ptr, bytes_updated);
  93
  94         put_cpu();
  95
  96         return 0;
  97 }
  98
  99 /*
 100  * sys_iopl has to be used when you want to access the IO ports
 101  * beyond the 0x3ff range: to get the full 65536 ports bitmapped
 102  * you'd need 8kB of bitmaps/process, which is a bit excessive.
 103  *
 104  * Here we just change the flags value on the stack: we allow
 105  * only the super-user to do it. This depends on the stack-layout
 106  * on system-call entry - see also fork() and the signal handling
 107  * code.
 108  */
 109 SYSCALL_DEFINE1(iopl, unsigned int, level)
 110 {
 111         struct pt_regs *regs = current_pt_regs();
 112         struct thread_struct *t = &current->thread;
 113
 114         /*
 115          * Careful: the IOPL bits in regs->flags are undefined under Xen PV
 116          * and changing them has no effect.
 117          */
 118         unsigned int old = t->iopl >> X86_EFLAGS_IOPL_BIT;
 119
 120         if (level > 3)
 121                 return -EINVAL;
 122         /* Trying to gain more privileges? */
 123         if (level > old) {
 124                 if (!capable(CAP_SYS_RAWIO))
 125                         return -EPERM;
 126         }
 127         regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
 128                 (level << X86_EFLAGS_IOPL_BIT);
 129         t->iopl = level << X86_EFLAGS_IOPL_BIT;
 130         set_iopl_mask(t->iopl);
 131
 132         return 0;
 133 }