1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Access kernel or user memory without faulting.
4 */
5 #include <linux/export.h>
6 #include <linux/mm.h>
7 #include <linux/uaccess.h>
8
copy_from_kernel_nofault_allowed(const void * unsafe_src,size_t size)9 bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
10 size_t size)
11 {
12 return true;
13 }
14
15 #ifdef HAVE_GET_KERNEL_NOFAULT
16
17 #define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) \
18 while (len >= sizeof(type)) { \
19 __get_kernel_nofault(dst, src, type, err_label); \
20 dst += sizeof(type); \
21 src += sizeof(type); \
22 len -= sizeof(type); \
23 }
24
copy_from_kernel_nofault(void * dst,const void * src,size_t size)25 long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
26 {
27 if (!copy_from_kernel_nofault_allowed(src, size))
28 return -ERANGE;
29
30 pagefault_disable();
31 copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
32 copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
33 copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
34 copy_from_kernel_nofault_loop(dst, src, size, u8, Efault);
35 pagefault_enable();
36 return 0;
37 Efault:
38 pagefault_enable();
39 return -EFAULT;
40 }
41 EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
42
43 #define copy_to_kernel_nofault_loop(dst, src, len, type, err_label) \
44 while (len >= sizeof(type)) { \
45 __put_kernel_nofault(dst, src, type, err_label); \
46 dst += sizeof(type); \
47 src += sizeof(type); \
48 len -= sizeof(type); \
49 }
50
copy_to_kernel_nofault(void * dst,const void * src,size_t size)51 long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
52 {
53 pagefault_disable();
54 copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
55 copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
56 copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
57 copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
58 pagefault_enable();
59 return 0;
60 Efault:
61 pagefault_enable();
62 return -EFAULT;
63 }
64
strncpy_from_kernel_nofault(char * dst,const void * unsafe_addr,long count)65 long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
66 {
67 const void *src = unsafe_addr;
68
69 if (unlikely(count <= 0))
70 return 0;
71 if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
72 return -ERANGE;
73
74 pagefault_disable();
75 do {
76 __get_kernel_nofault(dst, src, u8, Efault);
77 dst++;
78 src++;
79 } while (dst[-1] && src - unsafe_addr < count);
80 pagefault_enable();
81
82 dst[-1] = '\0';
83 return src - unsafe_addr;
84 Efault:
85 pagefault_enable();
86 dst[-1] = '\0';
87 return -EFAULT;
88 }
89 #else /* HAVE_GET_KERNEL_NOFAULT */
90 /**
91 * copy_from_kernel_nofault(): safely attempt to read from kernel-space
92 * @dst: pointer to the buffer that shall take the data
93 * @src: address to read from
94 * @size: size of the data chunk
95 *
96 * Safely read from kernel address @src to the buffer at @dst. If a kernel
97 * fault happens, handle that and return -EFAULT. If @src is not a valid kernel
98 * address, return -ERANGE.
99 *
100 * We ensure that the copy_from_user is executed in atomic context so that
101 * do_page_fault() doesn't attempt to take mmap_lock. This makes
102 * copy_from_kernel_nofault() suitable for use within regions where the caller
103 * already holds mmap_lock, or other locks which nest inside mmap_lock.
104 */
copy_from_kernel_nofault(void * dst,const void * src,size_t size)105 long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
106 {
107 long ret;
108 mm_segment_t old_fs = get_fs();
109
110 if (!copy_from_kernel_nofault_allowed(src, size))
111 return -ERANGE;
112
113 set_fs(KERNEL_DS);
114 pagefault_disable();
115 ret = __copy_from_user_inatomic(dst, (__force const void __user *)src,
116 size);
117 pagefault_enable();
118 set_fs(old_fs);
119
120 if (ret)
121 return -EFAULT;
122 return 0;
123 }
124 EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
125
126 /**
127 * copy_to_kernel_nofault(): safely attempt to write to a location
128 * @dst: address to write to
129 * @src: pointer to the data that shall be written
130 * @size: size of the data chunk
131 *
132 * Safely write to address @dst from the buffer at @src. If a kernel fault
133 * happens, handle that and return -EFAULT.
134 */
copy_to_kernel_nofault(void * dst,const void * src,size_t size)135 long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
136 {
137 long ret;
138 mm_segment_t old_fs = get_fs();
139
140 set_fs(KERNEL_DS);
141 pagefault_disable();
142 ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
143 pagefault_enable();
144 set_fs(old_fs);
145
146 if (ret)
147 return -EFAULT;
148 return 0;
149 }
150
151 /**
152 * strncpy_from_kernel_nofault: - Copy a NUL terminated string from unsafe
153 * address.
154 * @dst: Destination address, in kernel space. This buffer must be at
155 * least @count bytes long.
156 * @unsafe_addr: Unsafe address.
157 * @count: Maximum number of bytes to copy, including the trailing NUL.
158 *
159 * Copies a NUL-terminated string from unsafe address to kernel buffer.
160 *
161 * On success, returns the length of the string INCLUDING the trailing NUL.
162 *
163 * If access fails, returns -EFAULT (some data may have been copied and the
164 * trailing NUL added). If @unsafe_addr is not a valid kernel address, return
165 * -ERANGE.
166 *
167 * If @count is smaller than the length of the string, copies @count-1 bytes,
168 * sets the last byte of @dst buffer to NUL and returns @count.
169 */
strncpy_from_kernel_nofault(char * dst,const void * unsafe_addr,long count)170 long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
171 {
172 mm_segment_t old_fs = get_fs();
173 const void *src = unsafe_addr;
174 long ret;
175
176 if (unlikely(count <= 0))
177 return 0;
178 if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
179 return -ERANGE;
180
181 set_fs(KERNEL_DS);
182 pagefault_disable();
183
184 do {
185 ret = __get_user(*dst++, (const char __user __force *)src++);
186 } while (dst[-1] && ret == 0 && src - unsafe_addr < count);
187
188 dst[-1] = '\0';
189 pagefault_enable();
190 set_fs(old_fs);
191
192 return ret ? -EFAULT : src - unsafe_addr;
193 }
194 #endif /* HAVE_GET_KERNEL_NOFAULT */
195
196 /**
197 * copy_from_user_nofault(): safely attempt to read from a user-space location
198 * @dst: pointer to the buffer that shall take the data
199 * @src: address to read from. This must be a user address.
200 * @size: size of the data chunk
201 *
202 * Safely read from user address @src to the buffer at @dst. If a kernel fault
203 * happens, handle that and return -EFAULT.
204 */
copy_from_user_nofault(void * dst,const void __user * src,size_t size)205 long copy_from_user_nofault(void *dst, const void __user *src, size_t size)
206 {
207 long ret = -EFAULT;
208 mm_segment_t old_fs = force_uaccess_begin();
209
210 if (access_ok(src, size)) {
211 pagefault_disable();
212 ret = __copy_from_user_inatomic(dst, src, size);
213 pagefault_enable();
214 }
215 force_uaccess_end(old_fs);
216
217 if (ret)
218 return -EFAULT;
219 return 0;
220 }
221 EXPORT_SYMBOL_GPL(copy_from_user_nofault);
222
223 /**
224 * copy_to_user_nofault(): safely attempt to write to a user-space location
225 * @dst: address to write to
226 * @src: pointer to the data that shall be written
227 * @size: size of the data chunk
228 *
229 * Safely write to address @dst from the buffer at @src. If a kernel fault
230 * happens, handle that and return -EFAULT.
231 */
copy_to_user_nofault(void __user * dst,const void * src,size_t size)232 long copy_to_user_nofault(void __user *dst, const void *src, size_t size)
233 {
234 long ret = -EFAULT;
235 mm_segment_t old_fs = force_uaccess_begin();
236
237 if (access_ok(dst, size)) {
238 pagefault_disable();
239 ret = __copy_to_user_inatomic(dst, src, size);
240 pagefault_enable();
241 }
242 force_uaccess_end(old_fs);
243
244 if (ret)
245 return -EFAULT;
246 return 0;
247 }
248 EXPORT_SYMBOL_GPL(copy_to_user_nofault);
249
250 /**
251 * strncpy_from_user_nofault: - Copy a NUL terminated string from unsafe user
252 * address.
253 * @dst: Destination address, in kernel space. This buffer must be at
254 * least @count bytes long.
255 * @unsafe_addr: Unsafe user address.
256 * @count: Maximum number of bytes to copy, including the trailing NUL.
257 *
258 * Copies a NUL-terminated string from unsafe user address to kernel buffer.
259 *
260 * On success, returns the length of the string INCLUDING the trailing NUL.
261 *
262 * If access fails, returns -EFAULT (some data may have been copied
263 * and the trailing NUL added).
264 *
265 * If @count is smaller than the length of the string, copies @count-1 bytes,
266 * sets the last byte of @dst buffer to NUL and returns @count.
267 */
strncpy_from_user_nofault(char * dst,const void __user * unsafe_addr,long count)268 long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
269 long count)
270 {
271 mm_segment_t old_fs;
272 long ret;
273
274 if (unlikely(count <= 0))
275 return 0;
276
277 old_fs = force_uaccess_begin();
278 pagefault_disable();
279 ret = strncpy_from_user(dst, unsafe_addr, count);
280 pagefault_enable();
281 force_uaccess_end(old_fs);
282
283 if (ret >= count) {
284 ret = count;
285 dst[ret - 1] = '\0';
286 } else if (ret > 0) {
287 ret++;
288 }
289
290 return ret;
291 }
292
293 /**
294 * strnlen_user_nofault: - Get the size of a user string INCLUDING final NUL.
295 * @unsafe_addr: The string to measure.
296 * @count: Maximum count (including NUL)
297 *
298 * Get the size of a NUL-terminated string in user space without pagefault.
299 *
300 * Returns the size of the string INCLUDING the terminating NUL.
301 *
302 * If the string is too long, returns a number larger than @count. User
303 * has to check the return value against "> count".
304 * On exception (or invalid count), returns 0.
305 *
306 * Unlike strnlen_user, this can be used from IRQ handler etc. because
307 * it disables pagefaults.
308 */
strnlen_user_nofault(const void __user * unsafe_addr,long count)309 long strnlen_user_nofault(const void __user *unsafe_addr, long count)
310 {
311 mm_segment_t old_fs;
312 int ret;
313
314 old_fs = force_uaccess_begin();
315 pagefault_disable();
316 ret = strnlen_user(unsafe_addr, count);
317 pagefault_enable();
318 force_uaccess_end(old_fs);
319
320 return ret;
321 }
322
