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
copy_from_user_nmi(void * to,const void __user * from,unsigned long n)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