summaryrefslogtreecommitdiffstats
path: root/arch/x86/lib/usercopy.c
blob: 2e4e4b02c37a62cd593f3a59645898d946d95ffb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
/*
 * User address space access functions.
 *
 *  For licencing details see kernel-base/COPYING
 */

#include <linux/highmem.h>
#include <linux/module.h>

#include <asm/word-at-a-time.h>

/*
 * best effort, GUP based copy_from_user() that is NMI-safe
 */
unsigned long
copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
{
	unsigned long offset, addr = (unsigned long)from;
	unsigned long size, len = 0;
	struct page *page;
	void *map;
	int ret;

	do {
		ret = __get_user_pages_fast(addr, 1, 0, &page);
		if (!ret)
			break;

		offset = addr & (PAGE_SIZE - 1);
		size = min(PAGE_SIZE - offset, n - len);

		map = kmap_atomic(page);
		memcpy(to, map+offset, size);
		kunmap_atomic(map);
		put_page(page);

		len  += size;
		to   += size;
		addr += size;

	} while (len < n);

	return len;
}
EXPORT_SYMBOL_GPL(copy_from_user_nmi);

/*
 * Do a strncpy, return length of string without final '\0'.
 * 'count' is the user-supplied count (return 'count' if we
 * hit it), 'max' is the address space maximum (and we return
 * -EFAULT if we hit it).
 */
static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max)
{
	long res = 0;

	/*
	 * Truncate 'max' to the user-specified limit, so that
	 * we only have one limit we need to check in the loop
	 */
	if (max > count)
		max = count;

	while (max >= sizeof(unsigned long)) {
		unsigned long c, mask;

		/* Fall back to byte-at-a-time if we get a page fault */
		if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
			break;
		mask = has_zero(c);
		if (mask) {
			mask = (mask - 1) & ~mask;
			mask >>= 7;
			*(unsigned long *)(dst+res) = c & mask;
			return res + count_masked_bytes(mask);
		}
		*(unsigned long *)(dst+res) = c;
		res += sizeof(unsigned long);
		max -= sizeof(unsigned long);
	}

	while (max) {
		char c;

		if (unlikely(__get_user(c,src+res)))
			return -EFAULT;
		dst[res] = c;
		if (!c)
			return res;
		res++;
		max--;
	}

	/*
	 * Uhhuh. We hit 'max'. But was that the user-specified maximum
	 * too? If so, that's ok - we got as much as the user asked for.
	 */
	if (res >= count)
		return res;

	/*
	 * Nope: we hit the address space limit, and we still had more
	 * characters the caller would have wanted. That's an EFAULT.
	 */
	return -EFAULT;
}

/**
 * strncpy_from_user: - Copy a NUL terminated string from userspace.
 * @dst:   Destination address, in kernel space.  This buffer must be at
 *         least @count bytes long.
 * @src:   Source address, in user space.
 * @count: Maximum number of bytes to copy, including the trailing NUL.
 *
 * Copies a NUL-terminated string from userspace to kernel space.
 *
 * On success, returns the length of the string (not including the trailing
 * NUL).
 *
 * If access to userspace fails, returns -EFAULT (some data may have been
 * copied).
 *
 * If @count is smaller than the length of the string, copies @count bytes
 * and returns @count.
 */
long
strncpy_from_user(char *dst, const char __user *src, long count)
{
	unsigned long max_addr, src_addr;

	if (unlikely(count <= 0))
		return 0;

	max_addr = current_thread_info()->addr_limit.seg;
	src_addr = (unsigned long)src;
	if (likely(src_addr < max_addr)) {
		unsigned long max = max_addr - src_addr;
		return do_strncpy_from_user(dst, src, count, max);
	}
	return -EFAULT;
}
EXPORT_SYMBOL(strncpy_from_user);