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); 56