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1/*
2 * Access kernel memory without faulting.
3 */
4#include <linux/export.h>
5#include <linux/mm.h>
6#include <linux/uaccess.h>
7
8/**
9 * probe_kernel_read(): safely attempt to read from a location
10 * @dst: pointer to the buffer that shall take the data
11 * @src: address to read from
12 * @size: size of the data chunk
13 *
14 * Safely read from address @src to the buffer at @dst. If a kernel fault
15 * happens, handle that and return -EFAULT.
16 *
17 * We ensure that the copy_from_user is executed in atomic context so that
18 * do_page_fault() doesn't attempt to take mmap_sem. This makes
19 * probe_kernel_read() suitable for use within regions where the caller
20 * already holds mmap_sem, or other locks which nest inside mmap_sem.
21 */
22
23long __weak probe_kernel_read(void *dst, const void *src, size_t size)
24 __attribute__((alias("__probe_kernel_read")));
25
26long __probe_kernel_read(void *dst, const void *src, size_t size)
27{
28 long ret;
29 mm_segment_t old_fs = get_fs();
30
31 set_fs(KERNEL_DS);
32 pagefault_disable();
33 ret = __copy_from_user_inatomic(dst,
34 (__force const void __user *)src, size);
35 pagefault_enable();
36 set_fs(old_fs);
37
38 return ret ? -EFAULT : 0;
39}
40EXPORT_SYMBOL_GPL(probe_kernel_read);
41
42/**
43 * probe_kernel_write(): safely attempt to write to a location
44 * @dst: address to write to
45 * @src: pointer to the data that shall be written
46 * @size: size of the data chunk
47 *
48 * Safely write to address @dst from the buffer at @src. If a kernel fault
49 * happens, handle that and return -EFAULT.
50 */
51long __weak probe_kernel_write(void *dst, const void *src, size_t size)
52 __attribute__((alias("__probe_kernel_write")));
53
54long __probe_kernel_write(void *dst, const void *src, size_t size)
55{
56 long ret;
57 mm_segment_t old_fs = get_fs();
58
59 set_fs(KERNEL_DS);
60 pagefault_disable();
61 ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
62 pagefault_enable();
63 set_fs(old_fs);
64
65 return ret ? -EFAULT : 0;
66}
67EXPORT_SYMBOL_GPL(probe_kernel_write);
68
69/**
70 * strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address.
71 * @dst: Destination address, in kernel space. This buffer must be at
72 * least @count bytes long.
73 * @src: Unsafe address.
74 * @count: Maximum number of bytes to copy, including the trailing NUL.
75 *
76 * Copies a NUL-terminated string from unsafe address to kernel buffer.
77 *
78 * On success, returns the length of the string INCLUDING the trailing NUL.
79 *
80 * If access fails, returns -EFAULT (some data may have been copied
81 * and the trailing NUL added).
82 *
83 * If @count is smaller than the length of the string, copies @count-1 bytes,
84 * sets the last byte of @dst buffer to NUL and returns @count.
85 */
86long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
87{
88 mm_segment_t old_fs = get_fs();
89 const void *src = unsafe_addr;
90 long ret;
91
92 if (unlikely(count <= 0))
93 return 0;
94
95 set_fs(KERNEL_DS);
96 pagefault_disable();
97
98 do {
99 ret = __copy_from_user_inatomic(dst++,
100 (const void __user __force *)src++, 1);
101 } while (dst[-1] && ret == 0 && src - unsafe_addr < count);
102
103 dst[-1] = '\0';
104 pagefault_enable();
105 set_fs(old_fs);
106
107 return ret ? -EFAULT : src - unsafe_addr;
108}
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
9bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
10 size_t size)
11{
12 return true;
13}
14
15#define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) \
16 while (len >= sizeof(type)) { \
17 __get_kernel_nofault(dst, src, type, err_label); \
18 dst += sizeof(type); \
19 src += sizeof(type); \
20 len -= sizeof(type); \
21 }
22
23long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
24{
25 unsigned long align = 0;
26
27 if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
28 align = (unsigned long)dst | (unsigned long)src;
29
30 if (!copy_from_kernel_nofault_allowed(src, size))
31 return -ERANGE;
32
33 pagefault_disable();
34 if (!(align & 7))
35 copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
36 if (!(align & 3))
37 copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
38 if (!(align & 1))
39 copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
40 copy_from_kernel_nofault_loop(dst, src, size, u8, Efault);
41 pagefault_enable();
42 return 0;
43Efault:
44 pagefault_enable();
45 return -EFAULT;
46}
47EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
48
49#define copy_to_kernel_nofault_loop(dst, src, len, type, err_label) \
50 while (len >= sizeof(type)) { \
51 __put_kernel_nofault(dst, src, type, err_label); \
52 dst += sizeof(type); \
53 src += sizeof(type); \
54 len -= sizeof(type); \
55 }
56
57long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
58{
59 unsigned long align = 0;
60
61 if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
62 align = (unsigned long)dst | (unsigned long)src;
63
64 pagefault_disable();
65 if (!(align & 7))
66 copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
67 if (!(align & 3))
68 copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
69 if (!(align & 1))
70 copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
71 copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
72 pagefault_enable();
73 return 0;
74Efault:
75 pagefault_enable();
76 return -EFAULT;
77}
78
79long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
80{
81 const void *src = unsafe_addr;
82
83 if (unlikely(count <= 0))
84 return 0;
85 if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
86 return -ERANGE;
87
88 pagefault_disable();
89 do {
90 __get_kernel_nofault(dst, src, u8, Efault);
91 dst++;
92 src++;
93 } while (dst[-1] && src - unsafe_addr < count);
94 pagefault_enable();
95
96 dst[-1] = '\0';
97 return src - unsafe_addr;
98Efault:
99 pagefault_enable();
100 dst[0] = '\0';
101 return -EFAULT;
102}
103
104/**
105 * copy_from_user_nofault(): safely attempt to read from a user-space location
106 * @dst: pointer to the buffer that shall take the data
107 * @src: address to read from. This must be a user address.
108 * @size: size of the data chunk
109 *
110 * Safely read from user address @src to the buffer at @dst. If a kernel fault
111 * happens, handle that and return -EFAULT.
112 */
113long copy_from_user_nofault(void *dst, const void __user *src, size_t size)
114{
115 long ret = -EFAULT;
116 if (access_ok(src, size)) {
117 pagefault_disable();
118 ret = __copy_from_user_inatomic(dst, src, size);
119 pagefault_enable();
120 }
121
122 if (ret)
123 return -EFAULT;
124 return 0;
125}
126EXPORT_SYMBOL_GPL(copy_from_user_nofault);
127
128/**
129 * copy_to_user_nofault(): safely attempt to write to a user-space location
130 * @dst: address to write to
131 * @src: pointer to the data that shall be written
132 * @size: size of the data chunk
133 *
134 * Safely write to address @dst from the buffer at @src. If a kernel fault
135 * happens, handle that and return -EFAULT.
136 */
137long copy_to_user_nofault(void __user *dst, const void *src, size_t size)
138{
139 long ret = -EFAULT;
140
141 if (access_ok(dst, size)) {
142 pagefault_disable();
143 ret = __copy_to_user_inatomic(dst, src, size);
144 pagefault_enable();
145 }
146
147 if (ret)
148 return -EFAULT;
149 return 0;
150}
151EXPORT_SYMBOL_GPL(copy_to_user_nofault);
152
153/**
154 * strncpy_from_user_nofault: - Copy a NUL terminated string from unsafe user
155 * address.
156 * @dst: Destination address, in kernel space. This buffer must be at
157 * least @count bytes long.
158 * @unsafe_addr: Unsafe user address.
159 * @count: Maximum number of bytes to copy, including the trailing NUL.
160 *
161 * Copies a NUL-terminated string from unsafe user address to kernel buffer.
162 *
163 * On success, returns the length of the string INCLUDING the trailing NUL.
164 *
165 * If access fails, returns -EFAULT (some data may have been copied
166 * and the trailing NUL added).
167 *
168 * If @count is smaller than the length of the string, copies @count-1 bytes,
169 * sets the last byte of @dst buffer to NUL and returns @count.
170 */
171long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
172 long count)
173{
174 long ret;
175
176 if (unlikely(count <= 0))
177 return 0;
178
179 pagefault_disable();
180 ret = strncpy_from_user(dst, unsafe_addr, count);
181 pagefault_enable();
182
183 if (ret >= count) {
184 ret = count;
185 dst[ret - 1] = '\0';
186 } else if (ret > 0) {
187 ret++;
188 }
189
190 return ret;
191}
192
193/**
194 * strnlen_user_nofault: - Get the size of a user string INCLUDING final NUL.
195 * @unsafe_addr: The string to measure.
196 * @count: Maximum count (including NUL)
197 *
198 * Get the size of a NUL-terminated string in user space without pagefault.
199 *
200 * Returns the size of the string INCLUDING the terminating NUL.
201 *
202 * If the string is too long, returns a number larger than @count. User
203 * has to check the return value against "> count".
204 * On exception (or invalid count), returns 0.
205 *
206 * Unlike strnlen_user, this can be used from IRQ handler etc. because
207 * it disables pagefaults.
208 */
209long strnlen_user_nofault(const void __user *unsafe_addr, long count)
210{
211 int ret;
212
213 pagefault_disable();
214 ret = strnlen_user(unsafe_addr, count);
215 pagefault_enable();
216
217 return ret;
218}
219
220void __copy_overflow(int size, unsigned long count)
221{
222 WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
223}
224EXPORT_SYMBOL(__copy_overflow);