root/arch/x86/kernel/ioport.c

DEFINITIONS

1. ksys_ioperm
2. SYSCALL_DEFINE3
3. SYSCALL_DEFINE1

   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/security.h>
  15 #include <linux/smp.h>
  16 #include <linux/stddef.h>
  17 #include <linux/slab.h>
  18 #include <linux/thread_info.h>
  19 #include <linux/syscalls.h>
  20 #include <linux/bitmap.h>
  21 #include <asm/syscalls.h>
  22 #include <asm/desc.h>
  23 
  24 /*
  25  * this changes the io permissions bitmap in the current task.
  26  */
  27 long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
  28 {
  29         struct thread_struct *t = &current->thread;
  30         struct tss_struct *tss;
  31         unsigned int i, max_long, bytes, bytes_updated;
  32 
  33         if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
  34                 return -EINVAL;
  35         if (turn_on && (!capable(CAP_SYS_RAWIO) ||
  36                         security_locked_down(LOCKDOWN_IOPORT)))
  37                 return -EPERM;
  38 
  39         /*
  40          * If it's the first ioperm() call in this thread's lifetime, set the
  41          * IO bitmap up. ioperm() is much less timing critical than clone(),
  42          * this is why we delay this operation until now:
  43          */
  44         if (!t->io_bitmap_ptr) {
  45                 unsigned long *bitmap = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
  46 
  47                 if (!bitmap)
  48                         return -ENOMEM;
  49 
  50                 memset(bitmap, 0xff, IO_BITMAP_BYTES);
  51                 t->io_bitmap_ptr = bitmap;
  52                 set_thread_flag(TIF_IO_BITMAP);
  53 
  54                 /*
  55                  * Now that we have an IO bitmap, we need our TSS limit to be
  56                  * correct.  It's fine if we are preempted after doing this:
  57                  * with TIF_IO_BITMAP set, context switches will keep our TSS
  58                  * limit correct.
  59                  */
  60                 preempt_disable();
  61                 refresh_tss_limit();
  62                 preempt_enable();
  63         }
  64 
  65         /*
  66          * do it in the per-thread copy and in the TSS ...
  67          *
  68          * Disable preemption via get_cpu() - we must not switch away
  69          * because the ->io_bitmap_max value must match the bitmap
  70          * contents:
  71          */
  72         tss = &per_cpu(cpu_tss_rw, get_cpu());
  73 
  74         if (turn_on)
  75                 bitmap_clear(t->io_bitmap_ptr, from, num);
  76         else
  77                 bitmap_set(t->io_bitmap_ptr, from, num);
  78 
  79         /*
  80          * Search for a (possibly new) maximum. This is simple and stupid,
  81          * to keep it obviously correct:
  82          */
  83         max_long = 0;
  84         for (i = 0; i < IO_BITMAP_LONGS; i++)
  85                 if (t->io_bitmap_ptr[i] != ~0UL)
  86                         max_long = i;
  87 
  88         bytes = (max_long + 1) * sizeof(unsigned long);
  89         bytes_updated = max(bytes, t->io_bitmap_max);
  90 
  91         t->io_bitmap_max = bytes;
  92 
  93         /* Update the TSS: */
  94         memcpy(tss->io_bitmap, t->io_bitmap_ptr, bytes_updated);
  95 
  96         put_cpu();
  97 
  98         return 0;
  99 }
 100 
 101 SYSCALL_DEFINE3(ioperm, unsigned long, from, unsigned long, num, int, turn_on)
 102 {
 103         return ksys_ioperm(from, num, turn_on);
 104 }
 105 
 106 /*
 107  * sys_iopl has to be used when you want to access the IO ports
 108  * beyond the 0x3ff range: to get the full 65536 ports bitmapped
 109  * you'd need 8kB of bitmaps/process, which is a bit excessive.
 110  *
 111  * Here we just change the flags value on the stack: we allow
 112  * only the super-user to do it. This depends on the stack-layout
 113  * on system-call entry - see also fork() and the signal handling
 114  * code.
 115  */
 116 SYSCALL_DEFINE1(iopl, unsigned int, level)
 117 {
 118         struct pt_regs *regs = current_pt_regs();
 119         struct thread_struct *t = &current->thread;
 120 
 121         /*
 122          * Careful: the IOPL bits in regs->flags are undefined under Xen PV
 123          * and changing them has no effect.
 124          */
 125         unsigned int old = t->iopl >> X86_EFLAGS_IOPL_BIT;
 126 
 127         if (level > 3)
 128                 return -EINVAL;
 129         /* Trying to gain more privileges? */
 130         if (level > old) {
 131                 if (!capable(CAP_SYS_RAWIO) ||
 132                     security_locked_down(LOCKDOWN_IOPORT))
 133                         return -EPERM;
 134         }
 135         regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
 136                 (level << X86_EFLAGS_IOPL_BIT);
 137         t->iopl = level << X86_EFLAGS_IOPL_BIT;
 138         set_iopl_mask(t->iopl);
 139 
 140         return 0;
 141 }