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