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457c8996 | 1 | // SPDX-License-Identifier: GPL-2.0-only |
c33fa9f5 | 2 | /* |
3f0acb1e | 3 | * Access kernel or user memory without faulting. |
c33fa9f5 | 4 | */ |
b95f1b31 | 5 | #include <linux/export.h> |
c33fa9f5 | 6 | #include <linux/mm.h> |
7c7fcf76 | 7 | #include <linux/uaccess.h> |
c33fa9f5 | 8 | |
98a23609 | 9 | bool __weak probe_kernel_read_allowed(const void *unsafe_src, size_t size) |
eab0c608 CH |
10 | { |
11 | return true; | |
12 | } | |
13 | ||
c33fa9f5 | 14 | /** |
98a23609 | 15 | * probe_kernel_read(): safely attempt to read from kernel-space |
4f6de12b CH |
16 | * @dst: pointer to the buffer that shall take the data |
17 | * @src: address to read from | |
18 | * @size: size of the data chunk | |
19 | * | |
20 | * Safely read from kernel address @src to the buffer at @dst. If a kernel | |
21 | * fault happens, handle that and return -EFAULT. | |
0ab32b6f AM |
22 | * |
23 | * We ensure that the copy_from_user is executed in atomic context so that | |
c1e8d7c6 | 24 | * do_page_fault() doesn't attempt to take mmap_lock. This makes |
0ab32b6f | 25 | * probe_kernel_read() suitable for use within regions where the caller |
c1e8d7c6 | 26 | * already holds mmap_lock, or other locks which nest inside mmap_lock. |
c33fa9f5 | 27 | */ |
98a23609 | 28 | long probe_kernel_read(void *dst, const void *src, size_t size) |
c33fa9f5 IM |
29 | { |
30 | long ret; | |
b4b8ac52 | 31 | mm_segment_t old_fs = get_fs(); |
c33fa9f5 | 32 | |
98a23609 | 33 | if (!probe_kernel_read_allowed(src, size)) |
eab0c608 CH |
34 | return -EFAULT; |
35 | ||
b4b8ac52 | 36 | set_fs(KERNEL_DS); |
cd030905 CH |
37 | pagefault_disable(); |
38 | ret = __copy_from_user_inatomic(dst, (__force const void __user *)src, | |
39 | size); | |
40 | pagefault_enable(); | |
b4b8ac52 | 41 | set_fs(old_fs); |
c33fa9f5 | 42 | |
cd030905 CH |
43 | if (ret) |
44 | return -EFAULT; | |
45 | return 0; | |
c33fa9f5 | 46 | } |
98a23609 | 47 | EXPORT_SYMBOL_GPL(probe_kernel_read); |
c33fa9f5 IM |
48 | |
49 | /** | |
50 | * probe_kernel_write(): safely attempt to write to a location | |
51 | * @dst: address to write to | |
52 | * @src: pointer to the data that shall be written | |
53 | * @size: size of the data chunk | |
54 | * | |
55 | * Safely write to address @dst from the buffer at @src. If a kernel fault | |
56 | * happens, handle that and return -EFAULT. | |
57 | */ | |
48c49c0e | 58 | long probe_kernel_write(void *dst, const void *src, size_t size) |
c33fa9f5 IM |
59 | { |
60 | long ret; | |
b4b8ac52 | 61 | mm_segment_t old_fs = get_fs(); |
c33fa9f5 | 62 | |
b4b8ac52 | 63 | set_fs(KERNEL_DS); |
cd030905 CH |
64 | pagefault_disable(); |
65 | ret = __copy_to_user_inatomic((__force void __user *)dst, src, size); | |
66 | pagefault_enable(); | |
b4b8ac52 | 67 | set_fs(old_fs); |
c33fa9f5 | 68 | |
cd030905 CH |
69 | if (ret) |
70 | return -EFAULT; | |
71 | return 0; | |
c33fa9f5 | 72 | } |
dbb7ee0e | 73 | |
4f6de12b | 74 | /** |
c4cb1644 | 75 | * strncpy_from_kernel_nofault: - Copy a NUL terminated string from unsafe |
4f6de12b CH |
76 | * address. |
77 | * @dst: Destination address, in kernel space. This buffer must be at | |
78 | * least @count bytes long. | |
79 | * @unsafe_addr: Unsafe address. | |
80 | * @count: Maximum number of bytes to copy, including the trailing NUL. | |
81 | * | |
82 | * Copies a NUL-terminated string from unsafe address to kernel buffer. | |
83 | * | |
84 | * On success, returns the length of the string INCLUDING the trailing NUL. | |
85 | * | |
86 | * If access fails, returns -EFAULT (some data may have been copied | |
87 | * and the trailing NUL added). | |
88 | * | |
89 | * If @count is smaller than the length of the string, copies @count-1 bytes, | |
90 | * sets the last byte of @dst buffer to NUL and returns @count. | |
91 | */ | |
eab0c608 | 92 | long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count) |
dbb7ee0e AS |
93 | { |
94 | mm_segment_t old_fs = get_fs(); | |
95 | const void *src = unsafe_addr; | |
96 | long ret; | |
97 | ||
98 | if (unlikely(count <= 0)) | |
99 | return 0; | |
98a23609 | 100 | if (!probe_kernel_read_allowed(unsafe_addr, count)) |
eab0c608 | 101 | return -EFAULT; |
dbb7ee0e AS |
102 | |
103 | set_fs(KERNEL_DS); | |
104 | pagefault_disable(); | |
105 | ||
106 | do { | |
bd28b145 | 107 | ret = __get_user(*dst++, (const char __user __force *)src++); |
dbb7ee0e AS |
108 | } while (dst[-1] && ret == 0 && src - unsafe_addr < count); |
109 | ||
110 | dst[-1] = '\0'; | |
111 | pagefault_enable(); | |
112 | set_fs(old_fs); | |
113 | ||
9dd861d5 | 114 | return ret ? -EFAULT : src - unsafe_addr; |
dbb7ee0e | 115 | } |
3d708182 | 116 | |
fc3562d7 CH |
117 | /** |
118 | * probe_user_read(): safely attempt to read from a user-space location | |
119 | * @dst: pointer to the buffer that shall take the data | |
120 | * @src: address to read from. This must be a user address. | |
121 | * @size: size of the data chunk | |
122 | * | |
123 | * Safely read from user address @src to the buffer at @dst. If a kernel fault | |
124 | * happens, handle that and return -EFAULT. | |
125 | */ | |
126 | long probe_user_read(void *dst, const void __user *src, size_t size) | |
127 | { | |
128 | long ret = -EFAULT; | |
129 | mm_segment_t old_fs = get_fs(); | |
130 | ||
131 | set_fs(USER_DS); | |
132 | if (access_ok(src, size)) { | |
133 | pagefault_disable(); | |
134 | ret = __copy_from_user_inatomic(dst, src, size); | |
135 | pagefault_enable(); | |
136 | } | |
137 | set_fs(old_fs); | |
138 | ||
139 | if (ret) | |
140 | return -EFAULT; | |
141 | return 0; | |
142 | } | |
143 | EXPORT_SYMBOL_GPL(probe_user_read); | |
144 | ||
145 | /** | |
146 | * probe_user_write(): safely attempt to write to a user-space location | |
147 | * @dst: address to write to | |
148 | * @src: pointer to the data that shall be written | |
149 | * @size: size of the data chunk | |
150 | * | |
151 | * Safely write to address @dst from the buffer at @src. If a kernel fault | |
152 | * happens, handle that and return -EFAULT. | |
153 | */ | |
154 | long probe_user_write(void __user *dst, const void *src, size_t size) | |
155 | { | |
156 | long ret = -EFAULT; | |
157 | mm_segment_t old_fs = get_fs(); | |
158 | ||
159 | set_fs(USER_DS); | |
160 | if (access_ok(dst, size)) { | |
161 | pagefault_disable(); | |
162 | ret = __copy_to_user_inatomic(dst, src, size); | |
163 | pagefault_enable(); | |
164 | } | |
165 | set_fs(old_fs); | |
166 | ||
167 | if (ret) | |
168 | return -EFAULT; | |
169 | return 0; | |
170 | } | |
171 | EXPORT_SYMBOL_GPL(probe_user_write); | |
172 | ||
3d708182 | 173 | /** |
bd88bb5d | 174 | * strncpy_from_user_nofault: - Copy a NUL terminated string from unsafe user |
3d708182 MH |
175 | * address. |
176 | * @dst: Destination address, in kernel space. This buffer must be at | |
177 | * least @count bytes long. | |
178 | * @unsafe_addr: Unsafe user address. | |
179 | * @count: Maximum number of bytes to copy, including the trailing NUL. | |
180 | * | |
181 | * Copies a NUL-terminated string from unsafe user address to kernel buffer. | |
182 | * | |
183 | * On success, returns the length of the string INCLUDING the trailing NUL. | |
184 | * | |
185 | * If access fails, returns -EFAULT (some data may have been copied | |
186 | * and the trailing NUL added). | |
187 | * | |
188 | * If @count is smaller than the length of the string, copies @count-1 bytes, | |
189 | * sets the last byte of @dst buffer to NUL and returns @count. | |
190 | */ | |
bd88bb5d | 191 | long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr, |
3d708182 MH |
192 | long count) |
193 | { | |
194 | mm_segment_t old_fs = get_fs(); | |
195 | long ret; | |
196 | ||
197 | if (unlikely(count <= 0)) | |
198 | return 0; | |
199 | ||
200 | set_fs(USER_DS); | |
201 | pagefault_disable(); | |
202 | ret = strncpy_from_user(dst, unsafe_addr, count); | |
203 | pagefault_enable(); | |
204 | set_fs(old_fs); | |
205 | ||
206 | if (ret >= count) { | |
207 | ret = count; | |
208 | dst[ret - 1] = '\0'; | |
209 | } else if (ret > 0) { | |
210 | ret++; | |
211 | } | |
212 | ||
213 | return ret; | |
214 | } | |
215 | ||
216 | /** | |
02dddb16 | 217 | * strnlen_user_nofault: - Get the size of a user string INCLUDING final NUL. |
3d708182 MH |
218 | * @unsafe_addr: The string to measure. |
219 | * @count: Maximum count (including NUL) | |
220 | * | |
221 | * Get the size of a NUL-terminated string in user space without pagefault. | |
222 | * | |
223 | * Returns the size of the string INCLUDING the terminating NUL. | |
224 | * | |
225 | * If the string is too long, returns a number larger than @count. User | |
226 | * has to check the return value against "> count". | |
227 | * On exception (or invalid count), returns 0. | |
228 | * | |
229 | * Unlike strnlen_user, this can be used from IRQ handler etc. because | |
230 | * it disables pagefaults. | |
231 | */ | |
02dddb16 | 232 | long strnlen_user_nofault(const void __user *unsafe_addr, long count) |
3d708182 MH |
233 | { |
234 | mm_segment_t old_fs = get_fs(); | |
235 | int ret; | |
236 | ||
237 | set_fs(USER_DS); | |
238 | pagefault_disable(); | |
239 | ret = strnlen_user(unsafe_addr, count); | |
240 | pagefault_enable(); | |
241 | set_fs(old_fs); | |
242 | ||
243 | return ret; | |
244 | } |