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