1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_FORTIFY_STRING_H_
3 #define _LINUX_FORTIFY_STRING_H_
5 #include <linux/const.h>
7 #define __FORTIFY_INLINE extern __always_inline __gnu_inline __overloadable
8 #define __RENAME(x) __asm__(#x)
10 void fortify_panic(const char *name) __noreturn __cold;
11 void __read_overflow(void) __compiletime_error("detected read beyond size of object (1st parameter)");
12 void __read_overflow2(void) __compiletime_error("detected read beyond size of object (2nd parameter)");
13 void __read_overflow2_field(size_t avail, size_t wanted) __compiletime_warning("detected read beyond size of field (2nd parameter); maybe use struct_group()?");
14 void __write_overflow(void) __compiletime_error("detected write beyond size of object (1st parameter)");
15 void __write_overflow_field(size_t avail, size_t wanted) __compiletime_warning("detected write beyond size of field (1st parameter); maybe use struct_group()?");
17 #define __compiletime_strlen(p) \
19 unsigned char *__p = (unsigned char *)(p); \
20 size_t __ret = (size_t)-1; \
21 size_t __p_size = __builtin_object_size(p, 1); \
22 if (__p_size != (size_t)-1) { \
23 size_t __p_len = __p_size - 1; \
24 if (__builtin_constant_p(__p[__p_len]) && \
25 __p[__p_len] == '\0') \
26 __ret = __builtin_strlen(__p); \
31 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
32 extern void *__underlying_memchr(const void *p, int c, __kernel_size_t size) __RENAME(memchr);
33 extern int __underlying_memcmp(const void *p, const void *q, __kernel_size_t size) __RENAME(memcmp);
34 extern void *__underlying_memcpy(void *p, const void *q, __kernel_size_t size) __RENAME(memcpy);
35 extern void *__underlying_memmove(void *p, const void *q, __kernel_size_t size) __RENAME(memmove);
36 extern void *__underlying_memset(void *p, int c, __kernel_size_t size) __RENAME(memset);
37 extern char *__underlying_strcat(char *p, const char *q) __RENAME(strcat);
38 extern char *__underlying_strcpy(char *p, const char *q) __RENAME(strcpy);
39 extern __kernel_size_t __underlying_strlen(const char *p) __RENAME(strlen);
40 extern char *__underlying_strncat(char *p, const char *q, __kernel_size_t count) __RENAME(strncat);
41 extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __RENAME(strncpy);
43 #define __underlying_memchr __builtin_memchr
44 #define __underlying_memcmp __builtin_memcmp
45 #define __underlying_memcpy __builtin_memcpy
46 #define __underlying_memmove __builtin_memmove
47 #define __underlying_memset __builtin_memset
48 #define __underlying_strcat __builtin_strcat
49 #define __underlying_strcpy __builtin_strcpy
50 #define __underlying_strlen __builtin_strlen
51 #define __underlying_strncat __builtin_strncat
52 #define __underlying_strncpy __builtin_strncpy
56 * unsafe_memcpy - memcpy implementation with no FORTIFY bounds checking
58 * @dst: Destination memory address to write to
59 * @src: Source memory address to read from
60 * @bytes: How many bytes to write to @dst from @src
61 * @justification: Free-form text or comment describing why the use is needed
63 * This should be used for corner cases where the compiler cannot do the
64 * right thing, or during transitions between APIs, etc. It should be used
65 * very rarely, and includes a place for justification detailing where bounds
66 * checking has happened, and why existing solutions cannot be employed.
68 #define unsafe_memcpy(dst, src, bytes, justification) \
69 __underlying_memcpy(dst, src, bytes)
72 * Clang's use of __builtin_object_size() within inlines needs hinting via
73 * __pass_object_size(). The preference is to only ever use type 1 (member
74 * size, rather than struct size), but there remain some stragglers using
75 * type 0 that will be converted in the future.
77 #define POS __pass_object_size(1)
78 #define POS0 __pass_object_size(0)
80 __FORTIFY_INLINE __diagnose_as(__builtin_strncpy, 1, 2, 3)
81 char *strncpy(char * const POS p, const char *q, __kernel_size_t size)
83 size_t p_size = __builtin_object_size(p, 1);
85 if (__builtin_constant_p(size) && p_size < size)
88 fortify_panic(__func__);
89 return __underlying_strncpy(p, q, size);
92 __FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2)
93 char *strcat(char * const POS p, const char *q)
95 size_t p_size = __builtin_object_size(p, 1);
97 if (p_size == (size_t)-1)
98 return __underlying_strcat(p, q);
99 if (strlcat(p, q, p_size) >= p_size)
100 fortify_panic(__func__);
104 extern __kernel_size_t __real_strnlen(const char *, __kernel_size_t) __RENAME(strnlen);
105 __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size_t maxlen)
107 size_t p_size = __builtin_object_size(p, 1);
108 size_t p_len = __compiletime_strlen(p);
111 /* We can take compile-time actions when maxlen is const. */
112 if (__builtin_constant_p(maxlen) && p_len != (size_t)-1) {
113 /* If p is const, we can use its compile-time-known len. */
114 if (maxlen >= p_size)
118 /* Do not check characters beyond the end of p. */
119 ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size);
120 if (p_size <= ret && maxlen != ret)
121 fortify_panic(__func__);
126 * Defined after fortified strnlen to reuse it. However, it must still be
127 * possible for strlen() to be used on compile-time strings for use in
128 * static initializers (i.e. as a constant expression).
131 __builtin_choose_expr(__is_constexpr(__builtin_strlen(p)), \
132 __builtin_strlen(p), __fortify_strlen(p))
133 __FORTIFY_INLINE __diagnose_as(__builtin_strlen, 1)
134 __kernel_size_t __fortify_strlen(const char * const POS p)
137 size_t p_size = __builtin_object_size(p, 1);
139 /* Give up if we don't know how large p is. */
140 if (p_size == (size_t)-1)
141 return __underlying_strlen(p);
142 ret = strnlen(p, p_size);
144 fortify_panic(__func__);
148 /* defined after fortified strlen to reuse it */
149 extern size_t __real_strlcpy(char *, const char *, size_t) __RENAME(strlcpy);
150 __FORTIFY_INLINE size_t strlcpy(char * const POS p, const char * const POS q, size_t size)
152 size_t p_size = __builtin_object_size(p, 1);
153 size_t q_size = __builtin_object_size(q, 1);
154 size_t q_len; /* Full count of source string length. */
155 size_t len; /* Count of characters going into destination. */
157 if (p_size == (size_t)-1 && q_size == (size_t)-1)
158 return __real_strlcpy(p, q, size);
160 len = (q_len >= size) ? size - 1 : q_len;
161 if (__builtin_constant_p(size) && __builtin_constant_p(q_len) && size) {
162 /* Write size is always larger than destination. */
168 fortify_panic(__func__);
169 __underlying_memcpy(p, q, len);
175 /* defined after fortified strnlen to reuse it */
176 extern ssize_t __real_strscpy(char *, const char *, size_t) __RENAME(strscpy);
177 __FORTIFY_INLINE ssize_t strscpy(char * const POS p, const char * const POS q, size_t size)
180 /* Use string size rather than possible enclosing struct size. */
181 size_t p_size = __builtin_object_size(p, 1);
182 size_t q_size = __builtin_object_size(q, 1);
184 /* If we cannot get size of p and q default to call strscpy. */
185 if (p_size == (size_t) -1 && q_size == (size_t) -1)
186 return __real_strscpy(p, q, size);
189 * If size can be known at compile time and is greater than
190 * p_size, generate a compile time write overflow error.
192 if (__builtin_constant_p(size) && size > p_size)
196 * This call protects from read overflow, because len will default to q
197 * length if it smaller than size.
199 len = strnlen(q, size);
201 * If len equals size, we will copy only size bytes which leads to
202 * -E2BIG being returned.
203 * Otherwise we will copy len + 1 because of the final '\O'.
205 len = len == size ? size : len + 1;
208 * Generate a runtime write overflow error if len is greater than
212 fortify_panic(__func__);
215 * We can now safely call vanilla strscpy because we are protected from:
216 * 1. Read overflow thanks to call to strnlen().
217 * 2. Write overflow thanks to above ifs.
219 return __real_strscpy(p, q, len);
222 /* defined after fortified strlen and strnlen to reuse them */
223 __FORTIFY_INLINE __diagnose_as(__builtin_strncat, 1, 2, 3)
224 char *strncat(char * const POS p, const char * const POS q, __kernel_size_t count)
226 size_t p_len, copy_len;
227 size_t p_size = __builtin_object_size(p, 1);
228 size_t q_size = __builtin_object_size(q, 1);
230 if (p_size == (size_t)-1 && q_size == (size_t)-1)
231 return __underlying_strncat(p, q, count);
233 copy_len = strnlen(q, count);
234 if (p_size < p_len + copy_len + 1)
235 fortify_panic(__func__);
236 __underlying_memcpy(p + p_len, q, copy_len);
237 p[p_len + copy_len] = '\0';
241 __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size,
243 const size_t p_size_field)
245 if (__builtin_constant_p(size)) {
247 * Length argument is a constant expression, so we
248 * can perform compile-time bounds checking where
249 * buffer sizes are known.
252 /* Error when size is larger than enclosing struct. */
253 if (p_size > p_size_field && p_size < size)
256 /* Warn when write size is larger than dest field. */
257 if (p_size_field < size)
258 __write_overflow_field(p_size_field, size);
261 * At this point, length argument may not be a constant expression,
262 * so run-time bounds checking can be done where buffer sizes are
263 * known. (This is not an "else" because the above checks may only
264 * be compile-time warnings, and we want to still warn for run-time
269 * Always stop accesses beyond the struct that contains the
270 * field, when the buffer's remaining size is known.
271 * (The -1 test is to optimize away checks where the buffer
272 * lengths are unknown.)
274 if (p_size != (size_t)(-1) && p_size < size)
275 fortify_panic("memset");
278 #define __fortify_memset_chk(p, c, size, p_size, p_size_field) ({ \
279 size_t __fortify_size = (size_t)(size); \
280 fortify_memset_chk(__fortify_size, p_size, p_size_field), \
281 __underlying_memset(p, c, __fortify_size); \
285 * __builtin_object_size() must be captured here to avoid evaluating argument
286 * side-effects further into the macro layers.
288 #define memset(p, c, s) __fortify_memset_chk(p, c, s, \
289 __builtin_object_size(p, 0), __builtin_object_size(p, 1))
292 * To make sure the compiler can enforce protection against buffer overflows,
293 * memcpy(), memmove(), and memset() must not be used beyond individual
294 * struct members. If you need to copy across multiple members, please use
295 * struct_group() to create a named mirror of an anonymous struct union.
296 * (e.g. see struct sk_buff.) Read overflow checking is currently only
297 * done when a write overflow is also present, or when building with W=1.
299 * Mitigation coverage matrix
300 * Bounds checking at:
301 * +-------+-------+-------+-------+
302 * | Compile time | Run time |
303 * memcpy() argument sizes: | write | read | write | read |
304 * dest source length +-------+-------+-------+-------+
305 * memcpy(known, known, constant) | y | y | n/a | n/a |
306 * memcpy(known, unknown, constant) | y | n | n/a | V |
307 * memcpy(known, known, dynamic) | n | n | B | B |
308 * memcpy(known, unknown, dynamic) | n | n | B | V |
309 * memcpy(unknown, known, constant) | n | y | V | n/a |
310 * memcpy(unknown, unknown, constant) | n | n | V | V |
311 * memcpy(unknown, known, dynamic) | n | n | V | B |
312 * memcpy(unknown, unknown, dynamic) | n | n | V | V |
313 * +-------+-------+-------+-------+
315 * y = perform deterministic compile-time bounds checking
316 * n = cannot perform deterministic compile-time bounds checking
317 * n/a = no run-time bounds checking needed since compile-time deterministic
318 * B = can perform run-time bounds checking (currently unimplemented)
319 * V = vulnerable to run-time overflow (will need refactoring to solve)
322 __FORTIFY_INLINE void fortify_memcpy_chk(__kernel_size_t size,
325 const size_t p_size_field,
326 const size_t q_size_field,
329 if (__builtin_constant_p(size)) {
331 * Length argument is a constant expression, so we
332 * can perform compile-time bounds checking where
333 * buffer sizes are known.
336 /* Error when size is larger than enclosing struct. */
337 if (p_size > p_size_field && p_size < size)
339 if (q_size > q_size_field && q_size < size)
342 /* Warn when write size argument larger than dest field. */
343 if (p_size_field < size)
344 __write_overflow_field(p_size_field, size);
346 * Warn for source field over-read when building with W=1
347 * or when an over-write happened, so both can be fixed at
350 if ((IS_ENABLED(KBUILD_EXTRA_WARN1) || p_size_field < size) &&
352 __read_overflow2_field(q_size_field, size);
355 * At this point, length argument may not be a constant expression,
356 * so run-time bounds checking can be done where buffer sizes are
357 * known. (This is not an "else" because the above checks may only
358 * be compile-time warnings, and we want to still warn for run-time
363 * Always stop accesses beyond the struct that contains the
364 * field, when the buffer's remaining size is known.
365 * (The -1 test is to optimize away checks where the buffer
366 * lengths are unknown.)
368 if ((p_size != (size_t)(-1) && p_size < size) ||
369 (q_size != (size_t)(-1) && q_size < size))
373 #define __fortify_memcpy_chk(p, q, size, p_size, q_size, \
374 p_size_field, q_size_field, op) ({ \
375 size_t __fortify_size = (size_t)(size); \
376 fortify_memcpy_chk(__fortify_size, p_size, q_size, \
377 p_size_field, q_size_field, #op); \
378 __underlying_##op(p, q, __fortify_size); \
382 * __builtin_object_size() must be captured here to avoid evaluating argument
383 * side-effects further into the macro layers.
385 #define memcpy(p, q, s) __fortify_memcpy_chk(p, q, s, \
386 __builtin_object_size(p, 0), __builtin_object_size(q, 0), \
387 __builtin_object_size(p, 1), __builtin_object_size(q, 1), \
389 #define memmove(p, q, s) __fortify_memcpy_chk(p, q, s, \
390 __builtin_object_size(p, 0), __builtin_object_size(q, 0), \
391 __builtin_object_size(p, 1), __builtin_object_size(q, 1), \
394 extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan);
395 __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size)
397 size_t p_size = __builtin_object_size(p, 0);
399 if (__builtin_constant_p(size) && p_size < size)
402 fortify_panic(__func__);
403 return __real_memscan(p, c, size);
406 __FORTIFY_INLINE __diagnose_as(__builtin_memcmp, 1, 2, 3)
407 int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t size)
409 size_t p_size = __builtin_object_size(p, 0);
410 size_t q_size = __builtin_object_size(q, 0);
412 if (__builtin_constant_p(size)) {
418 if (p_size < size || q_size < size)
419 fortify_panic(__func__);
420 return __underlying_memcmp(p, q, size);
423 __FORTIFY_INLINE __diagnose_as(__builtin_memchr, 1, 2, 3)
424 void *memchr(const void * const POS0 p, int c, __kernel_size_t size)
426 size_t p_size = __builtin_object_size(p, 0);
428 if (__builtin_constant_p(size) && p_size < size)
431 fortify_panic(__func__);
432 return __underlying_memchr(p, c, size);
435 void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv);
436 __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size)
438 size_t p_size = __builtin_object_size(p, 0);
440 if (__builtin_constant_p(size) && p_size < size)
443 fortify_panic(__func__);
444 return __real_memchr_inv(p, c, size);
447 extern void *__real_kmemdup(const void *src, size_t len, gfp_t gfp) __RENAME(kmemdup);
448 __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp)
450 size_t p_size = __builtin_object_size(p, 0);
452 if (__builtin_constant_p(size) && p_size < size)
455 fortify_panic(__func__);
456 return __real_kmemdup(p, size, gfp);
459 /* Defined after fortified strlen to reuse it. */
460 __FORTIFY_INLINE __diagnose_as(__builtin_strcpy, 1, 2)
461 char *strcpy(char * const POS p, const char * const POS q)
463 size_t p_size = __builtin_object_size(p, 1);
464 size_t q_size = __builtin_object_size(q, 1);
467 /* If neither buffer size is known, immediately give up. */
468 if (p_size == (size_t)-1 && q_size == (size_t)-1)
469 return __underlying_strcpy(p, q);
470 size = strlen(q) + 1;
471 /* Compile-time check for const size overflow. */
472 if (__builtin_constant_p(size) && p_size < size)
474 /* Run-time check for dynamic size overflow. */
476 fortify_panic(__func__);
477 __underlying_memcpy(p, q, size);
481 /* Don't use these outside the FORITFY_SOURCE implementation */
482 #undef __underlying_memchr
483 #undef __underlying_memcmp
484 #undef __underlying_strcat
485 #undef __underlying_strcpy
486 #undef __underlying_strlen
487 #undef __underlying_strncat
488 #undef __underlying_strncpy
493 #endif /* _LINUX_FORTIFY_STRING_H_ */