aboutsummaryrefslogtreecommitdiffstats
path: root/mm/maccess.c
blob: 3bd70405f2d848d15ee90897e7e267eb3de2ebda (plain) (blame)
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
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Access kernel or user memory without faulting.
 */
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/uaccess.h>

bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
		size_t size)
{
	return true;
}

#ifdef HAVE_GET_KERNEL_NOFAULT

#define copy_from_kernel_nofault_loop(dst, src, len, type, err_label)	\
	while (len >= sizeof(type)) {					\
		__get_kernel_nofault(dst, src, type, err_label);		\
		dst += sizeof(type);					\
		src += sizeof(type);					\
		len -= sizeof(type);					\
	}

long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
{
	if (!copy_from_kernel_nofault_allowed(src, size))
		return -ERANGE;

	pagefault_disable();
	copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
	copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
	copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
	copy_from_kernel_nofault_loop(dst, src, size, u8, Efault);
	pagefault_enable();
	return 0;
Efault:
	pagefault_enable();
	return -EFAULT;
}
EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);

#define copy_to_kernel_nofault_loop(dst, src, len, type, err_label)	\
	while (len >= sizeof(type)) {					\
		__put_kernel_nofault(dst, src, type, err_label);		\
		dst += sizeof(type);					\
		src += sizeof(type);					\
		len -= sizeof(type);					\
	}

long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
{
	pagefault_disable();
	copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
	copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
	copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
	copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
	pagefault_enable();
	return 0;
Efault:
	pagefault_enable();
	return -EFAULT;
}

long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
{
	const void *src = unsafe_addr;

	if (unlikely(count <= 0))
		return 0;
	if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
		return -ERANGE;

	pagefault_disable();
	do {
		__get_kernel_nofault(dst, src, u8, Efault);
		dst++;
		src++;
	} while (dst[-1] && src - unsafe_addr < count);
	pagefault_enable();

	dst[-1] = '\0';
	return src - unsafe_addr;
Efault:
	pagefault_enable();
	dst[-1] = '\0';
	return -EFAULT;
}
#else /* HAVE_GET_KERNEL_NOFAULT */
/**
 * copy_from_kernel_nofault(): safely attempt to read from kernel-space
 * @dst: pointer to the buffer that shall take the data
 * @src: address to read from
 * @size: size of the data chunk
 *
 * Safely read from kernel address @src to the buffer at @dst.  If a kernel
 * fault happens, handle that and return -EFAULT.  If @src is not a valid kernel
 * address, return -ERANGE.
 *
 * We ensure that the copy_from_user is executed in atomic context so that
 * do_page_fault() doesn't attempt to take mmap_lock.  This makes
 * copy_from_kernel_nofault() suitable for use within regions where the caller
 * already holds mmap_lock, or other locks which nest inside mmap_lock.
 */
long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
{
	long ret;
	mm_segment_t old_fs = get_fs();

	if (!copy_from_kernel_nofault_allowed(src, size))
		return -ERANGE;

	set_fs(KERNEL_DS);
	pagefault_disable();
	ret = __copy_from_user_inatomic(dst, (__force const void __user *)src,
			size);
	pagefault_enable();
	set_fs(old_fs);

	if (ret)
		return -EFAULT;
	return 0;
}
EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);

/**
 * copy_to_kernel_nofault(): safely attempt to write to a location
 * @dst: address to write to
 * @src: pointer to the data that shall be written
 * @size: size of the data chunk
 *
 * Safely write to address @dst from the buffer at @src.  If a kernel fault
 * happens, handle that and return -EFAULT.
 */
long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
{
	long ret;
	mm_segment_t old_fs = get_fs();

	set_fs(KERNEL_DS);
	pagefault_disable();
	ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
	pagefault_enable();
	set_fs(old_fs);

	if (ret)
		return -EFAULT;
	return 0;
}

/**
 * strncpy_from_kernel_nofault: - Copy a NUL terminated string from unsafe
 *				 address.
 * @dst:   Destination address, in kernel space.  This buffer must be at
 *         least @count bytes long.
 * @unsafe_addr: Unsafe address.
 * @count: Maximum number of bytes to copy, including the trailing NUL.
 *
 * Copies a NUL-terminated string from unsafe address to kernel buffer.
 *
 * On success, returns the length of the string INCLUDING the trailing NUL.
 *
 * If access fails, returns -EFAULT (some data may have been copied and the
 * trailing NUL added).  If @unsafe_addr is not a valid kernel address, return
 * -ERANGE.
 *
 * If @count is smaller than the length of the string, copies @count-1 bytes,
 * sets the last byte of @dst buffer to NUL and returns @count.
 */
long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
{
	mm_segment_t old_fs = get_fs();
	const void *src = unsafe_addr;
	long ret;

	if (unlikely(count <= 0))
		return 0;
	if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
		return -ERANGE;

	set_fs(KERNEL_DS);
	pagefault_disable();

	do {
		ret = __get_user(*dst++, (const char __user __force *)src++);
	} while (dst[-1] && ret == 0 && src - unsafe_addr < count);

	dst[-1] = '\0';
	pagefault_enable();
	set_fs(old_fs);

	return ret ? -EFAULT : src - unsafe_addr;
}
#endif /* HAVE_GET_KERNEL_NOFAULT */

/**
 * copy_from_user_nofault(): safely attempt to read from a user-space location
 * @dst: pointer to the buffer that shall take the data
 * @src: address to read from. This must be a user address.
 * @size: size of the data chunk
 *
 * Safely read from user address @src to the buffer at @dst. If a kernel fault
 * happens, handle that and return -EFAULT.
 */
long copy_from_user_nofault(void *dst, const void __user *src, size_t size)
{
	long ret = -EFAULT;
	mm_segment_t old_fs = force_uaccess_begin();

	if (access_ok(src, size)) {
		pagefault_disable();
		ret = __copy_from_user_inatomic(dst, src, size);
		pagefault_enable();
	}
	force_uaccess_end(old_fs);

	if (ret)
		return -EFAULT;
	return 0;
}
EXPORT_SYMBOL_GPL(copy_from_user_nofault);

/**
 * copy_to_user_nofault(): safely attempt to write to a user-space location
 * @dst: address to write to
 * @src: pointer to the data that shall be written
 * @size: size of the data chunk
 *
 * Safely write to address @dst from the buffer at @src.  If a kernel fault
 * happens, handle that and return -EFAULT.
 */
long copy_to_user_nofault(void __user *dst, const void *src, size_t size)
{
	long ret = -EFAULT;
	mm_segment_t old_fs = force_uaccess_begin();

	if (access_ok(dst, size)) {
		pagefault_disable();
		ret = __copy_to_user_inatomic(dst, src, size);
		pagefault_enable();
	}
	force_uaccess_end(old_fs);

	if (ret)
		return -EFAULT;
	return 0;
}
EXPORT_SYMBOL_GPL(copy_to_user_nofault);

/**
 * strncpy_from_user_nofault: - Copy a NUL terminated string from unsafe user
 *				address.
 * @dst:   Destination address, in kernel space.  This buffer must be at
 *         least @count bytes long.
 * @unsafe_addr: Unsafe user address.
 * @count: Maximum number of bytes to copy, including the trailing NUL.
 *
 * Copies a NUL-terminated string from unsafe user address to kernel buffer.
 *
 * On success, returns the length of the string INCLUDING the trailing NUL.
 *
 * If access fails, returns -EFAULT (some data may have been copied
 * and the trailing NUL added).
 *
 * If @count is smaller than the length of the string, copies @count-1 bytes,
 * sets the last byte of @dst buffer to NUL and returns @count.
 */
long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
			      long count)
{
	mm_segment_t old_fs;
	long ret;

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

	old_fs = force_uaccess_begin();
	pagefault_disable();
	ret = strncpy_from_user(dst, unsafe_addr, count);
	pagefault_enable();
	force_uaccess_end(old_fs);

	if (ret >= count) {
		ret = count;
		dst[ret - 1] = '\0';
	} else if (ret > 0) {
		ret++;
	}

	return ret;
}

/**
 * strnlen_user_nofault: - Get the size of a user string INCLUDING final NUL.
 * @unsafe_addr: The string to measure.
 * @count: Maximum count (including NUL)
 *
 * Get the size of a NUL-terminated string in user space without pagefault.
 *
 * Returns the size of the string INCLUDING the terminating NUL.
 *
 * If the string is too long, returns a number larger than @count. User
 * has to check the return value against "> count".
 * On exception (or invalid count), returns 0.
 *
 * Unlike strnlen_user, this can be used from IRQ handler etc. because
 * it disables pagefaults.
 */
long strnlen_user_nofault(const void __user *unsafe_addr, long count)
{
	mm_segment_t old_fs;
	int ret;

	old_fs = force_uaccess_begin();
	pagefault_disable();
	ret = strnlen_user(unsafe_addr, count);
	pagefault_enable();
	force_uaccess_end(old_fs);

	return ret;
}