arch/x86/lib/usercopy.c

   1 /*
   2  * User address space access functions.
   3  *
   4  *  For licencing details see kernel-base/COPYING
   5  */
   6
   7 #include <linux/uaccess.h>
   8 #include <linux/export.h>
   9 #include <linux/instrumented.h>
  10
  11 #include <asm/tlbflush.h>
  12
  13 /**
  14  * copy_from_user_nmi - NMI safe copy from user
  15  * @to:         Pointer to the destination buffer
  16  * @from:       Pointer to a user space address of the current task
  17  * @n:          Number of bytes to copy
  18  *
  19  * Returns: The number of not copied bytes. 0 is success, i.e. all bytes copied
  20  *
  21  * Contrary to other copy_from_user() variants this function can be called
  22  * from NMI context. Despite the name it is not restricted to be called
  23  * from NMI context. It is safe to be called from any other context as
  24  * well. It disables pagefaults across the copy which means a fault will
  25  * abort the copy.
  26  *
  27  * For NMI context invocations this relies on the nested NMI work to allow
  28  * atomic faults from the NMI path; the nested NMI paths are careful to
  29  * preserve CR2.
  30  */
  31 unsigned long
  32 copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
  33 {
  34         unsigned long ret;
  35
  36         if (!__access_ok(from, n))
  37                 return n;
  38
  39         if (!nmi_uaccess_okay())
  40                 return n;
  41
  42         /*
  43          * Even though this function is typically called from NMI/IRQ context
  44          * disable pagefaults so that its behaviour is consistent even when
  45          * called from other contexts.
  46          */
  47         pagefault_disable();
  48         instrument_copy_from_user_before(to, from, n);
  49         ret = raw_copy_from_user(to, from, n);
  50         instrument_copy_from_user_after(to, from, n, ret);
  51         pagefault_enable();
  52
  53         return ret;
  54 }
  55 EXPORT_SYMBOL_GPL(copy_from_user_nmi);