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 __builtin_constant_p(*__p)) { \
24 size_t __p_len = __p_size - 1; \
25 if (__builtin_constant_p(__p[__p_len]) && \
26 __p[__p_len] == '\0') \
27 __ret = __builtin_strlen(__p); \
32 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
33 extern void *__underlying_memchr(const void *p, int c, __kernel_size_t size) __RENAME(memchr);
34 extern int __underlying_memcmp(const void *p, const void *q, __kernel_size_t size) __RENAME(memcmp);
35 extern void *__underlying_memcpy(void *p, const void *q, __kernel_size_t size) __RENAME(memcpy);
36 extern void *__underlying_memmove(void *p, const void *q, __kernel_size_t size) __RENAME(memmove);
37 extern void *__underlying_memset(void *p, int c, __kernel_size_t size) __RENAME(memset);
38 extern char *__underlying_strcat(char *p, const char *q) __RENAME(strcat);
39 extern char *__underlying_strcpy(char *p, const char *q) __RENAME(strcpy);
40 extern __kernel_size_t __underlying_strlen(const char *p) __RENAME(strlen);
41 extern char *__underlying_strncat(char *p, const char *q, __kernel_size_t count) __RENAME(strncat);
42 extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __RENAME(strncpy);
44 #define __underlying_memchr __builtin_memchr
45 #define __underlying_memcmp __builtin_memcmp
46 #define __underlying_memcpy __builtin_memcpy
47 #define __underlying_memmove __builtin_memmove
48 #define __underlying_memset __builtin_memset
49 #define __underlying_strcat __builtin_strcat
50 #define __underlying_strcpy __builtin_strcpy
51 #define __underlying_strlen __builtin_strlen
52 #define __underlying_strncat __builtin_strncat
53 #define __underlying_strncpy __builtin_strncpy
57 * unsafe_memcpy - memcpy implementation with no FORTIFY bounds checking
59 * @dst: Destination memory address to write to
60 * @src: Source memory address to read from
61 * @bytes: How many bytes to write to @dst from @src
62 * @justification: Free-form text or comment describing why the use is needed
64 * This should be used for corner cases where the compiler cannot do the
65 * right thing, or during transitions between APIs, etc. It should be used
66 * very rarely, and includes a place for justification detailing where bounds
67 * checking has happened, and why existing solutions cannot be employed.
69 #define unsafe_memcpy(dst, src, bytes, justification) \
70 __underlying_memcpy(dst, src, bytes)
73 * Clang's use of __builtin_object_size() within inlines needs hinting via
74 * __pass_object_size(). The preference is to only ever use type 1 (member
75 * size, rather than struct size), but there remain some stragglers using
76 * type 0 that will be converted in the future.
78 #define POS __pass_object_size(1)
79 #define POS0 __pass_object_size(0)
81 __FORTIFY_INLINE __diagnose_as(__builtin_strncpy, 1, 2, 3)
82 char *strncpy(char * const POS p, const char *q, __kernel_size_t size)
84 size_t p_size = __builtin_object_size(p, 1);
86 if (__builtin_constant_p(size) && p_size < size)
89 fortify_panic(__func__);
90 return __underlying_strncpy(p, q, size);
93 __FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2)
94 char *strcat(char * const POS p, const char *q)
96 size_t p_size = __builtin_object_size(p, 1);
98 if (p_size == (size_t)-1)
99 return __underlying_strcat(p, q);
100 if (strlcat(p, q, p_size) >= p_size)
101 fortify_panic(__func__);
105 extern __kernel_size_t __real_strnlen(const char *, __kernel_size_t) __RENAME(strnlen);
106 __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size_t maxlen)
108 size_t p_size = __builtin_object_size(p, 1);
109 size_t p_len = __compiletime_strlen(p);
112 /* We can take compile-time actions when maxlen is const. */
113 if (__builtin_constant_p(maxlen) && p_len != (size_t)-1) {
114 /* If p is const, we can use its compile-time-known len. */
115 if (maxlen >= p_size)
119 /* Do not check characters beyond the end of p. */
120 ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size);
121 if (p_size <= ret && maxlen != ret)
122 fortify_panic(__func__);
127 * Defined after fortified strnlen to reuse it. However, it must still be
128 * possible for strlen() to be used on compile-time strings for use in
129 * static initializers (i.e. as a constant expression).
132 __builtin_choose_expr(__is_constexpr(__builtin_strlen(p)), \
133 __builtin_strlen(p), __fortify_strlen(p))
134 __FORTIFY_INLINE __diagnose_as(__builtin_strlen, 1)
135 __kernel_size_t __fortify_strlen(const char * const POS p)
138 size_t p_size = __builtin_object_size(p, 1);
140 /* Give up if we don't know how large p is. */
141 if (p_size == (size_t)-1)
142 return __underlying_strlen(p);
143 ret = strnlen(p, p_size);
145 fortify_panic(__func__);
149 /* defined after fortified strlen to reuse it */
150 extern size_t __real_strlcpy(char *, const char *, size_t) __RENAME(strlcpy);
151 __FORTIFY_INLINE size_t strlcpy(char * const POS p, const char * const POS q, size_t size)
153 size_t p_size = __builtin_object_size(p, 1);
154 size_t q_size = __builtin_object_size(q, 1);
155 size_t q_len; /* Full count of source string length. */
156 size_t len; /* Count of characters going into destination. */
158 if (p_size == (size_t)-1 && q_size == (size_t)-1)
159 return __real_strlcpy(p, q, size);
161 len = (q_len >= size) ? size - 1 : q_len;
162 if (__builtin_constant_p(size) && __builtin_constant_p(q_len) && size) {
163 /* Write size is always larger than destination. */
169 fortify_panic(__func__);
170 __underlying_memcpy(p, q, len);
176 /* defined after fortified strnlen to reuse it */
177 extern ssize_t __real_strscpy(char *, const char *, size_t) __RENAME(strscpy);
178 __FORTIFY_INLINE ssize_t strscpy(char * const POS p, const char * const POS q, size_t size)
181 /* Use string size rather than possible enclosing struct size. */
182 size_t p_size = __builtin_object_size(p, 1);
183 size_t q_size = __builtin_object_size(q, 1);
185 /* If we cannot get size of p and q default to call strscpy. */
186 if (p_size == (size_t) -1 && q_size == (size_t) -1)
187 return __real_strscpy(p, q, size);
190 * If size can be known at compile time and is greater than
191 * p_size, generate a compile time write overflow error.
193 if (__builtin_constant_p(size) && size > p_size)
197 * This call protects from read overflow, because len will default to q
198 * length if it smaller than size.
200 len = strnlen(q, size);
202 * If len equals size, we will copy only size bytes which leads to
203 * -E2BIG being returned.
204 * Otherwise we will copy len + 1 because of the final '\O'.
206 len = len == size ? size : len + 1;
209 * Generate a runtime write overflow error if len is greater than
213 fortify_panic(__func__);
216 * We can now safely call vanilla strscpy because we are protected from:
217 * 1. Read overflow thanks to call to strnlen().
218 * 2. Write overflow thanks to above ifs.
220 return __real_strscpy(p, q, len);
223 /* defined after fortified strlen and strnlen to reuse them */
224 __FORTIFY_INLINE __diagnose_as(__builtin_strncat, 1, 2, 3)
225 char *strncat(char * const POS p, const char * const POS q, __kernel_size_t count)
227 size_t p_len, copy_len;
228 size_t p_size = __builtin_object_size(p, 1);
229 size_t q_size = __builtin_object_size(q, 1);
231 if (p_size == (size_t)-1 && q_size == (size_t)-1)
232 return __underlying_strncat(p, q, count);
234 copy_len = strnlen(q, count);
235 if (p_size < p_len + copy_len + 1)
236 fortify_panic(__func__);
237 __underlying_memcpy(p + p_len, q, copy_len);
238 p[p_len + copy_len] = '\0';
242 __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size,
244 const size_t p_size_field)
246 if (__builtin_constant_p(size)) {
248 * Length argument is a constant expression, so we
249 * can perform compile-time bounds checking where
250 * buffer sizes are known.
253 /* Error when size is larger than enclosing struct. */
254 if (p_size > p_size_field && p_size < size)
257 /* Warn when write size is larger than dest field. */
258 if (p_size_field < size)
259 __write_overflow_field(p_size_field, size);
262 * At this point, length argument may not be a constant expression,
263 * so run-time bounds checking can be done where buffer sizes are
264 * known. (This is not an "else" because the above checks may only
265 * be compile-time warnings, and we want to still warn for run-time
270 * Always stop accesses beyond the struct that contains the
271 * field, when the buffer's remaining size is known.
272 * (The -1 test is to optimize away checks where the buffer
273 * lengths are unknown.)
275 if (p_size != (size_t)(-1) && p_size < size)
276 fortify_panic("memset");
279 #define __fortify_memset_chk(p, c, size, p_size, p_size_field) ({ \
280 size_t __fortify_size = (size_t)(size); \
281 fortify_memset_chk(__fortify_size, p_size, p_size_field), \
282 __underlying_memset(p, c, __fortify_size); \
286 * __builtin_object_size() must be captured here to avoid evaluating argument
287 * side-effects further into the macro layers.
289 #define memset(p, c, s) __fortify_memset_chk(p, c, s, \
290 __builtin_object_size(p, 0), __builtin_object_size(p, 1))
293 * To make sure the compiler can enforce protection against buffer overflows,
294 * memcpy(), memmove(), and memset() must not be used beyond individual
295 * struct members. If you need to copy across multiple members, please use
296 * struct_group() to create a named mirror of an anonymous struct union.
297 * (e.g. see struct sk_buff.) Read overflow checking is currently only
298 * done when a write overflow is also present, or when building with W=1.
300 * Mitigation coverage matrix
301 * Bounds checking at:
302 * +-------+-------+-------+-------+
303 * | Compile time | Run time |
304 * memcpy() argument sizes: | write | read | write | read |
305 * dest source length +-------+-------+-------+-------+
306 * memcpy(known, known, constant) | y | y | n/a | n/a |
307 * memcpy(known, unknown, constant) | y | n | n/a | V |
308 * memcpy(known, known, dynamic) | n | n | B | B |
309 * memcpy(known, unknown, dynamic) | n | n | B | V |
310 * memcpy(unknown, known, constant) | n | y | V | n/a |
311 * memcpy(unknown, unknown, constant) | n | n | V | V |
312 * memcpy(unknown, known, dynamic) | n | n | V | B |
313 * memcpy(unknown, unknown, dynamic) | n | n | V | V |
314 * +-------+-------+-------+-------+
316 * y = perform deterministic compile-time bounds checking
317 * n = cannot perform deterministic compile-time bounds checking
318 * n/a = no run-time bounds checking needed since compile-time deterministic
319 * B = can perform run-time bounds checking (currently unimplemented)
320 * V = vulnerable to run-time overflow (will need refactoring to solve)
323 __FORTIFY_INLINE void fortify_memcpy_chk(__kernel_size_t size,
326 const size_t p_size_field,
327 const size_t q_size_field,
330 if (__builtin_constant_p(size)) {
332 * Length argument is a constant expression, so we
333 * can perform compile-time bounds checking where
334 * buffer sizes are known.
337 /* Error when size is larger than enclosing struct. */
338 if (p_size > p_size_field && p_size < size)
340 if (q_size > q_size_field && q_size < size)
343 /* Warn when write size argument larger than dest field. */
344 if (p_size_field < size)
345 __write_overflow_field(p_size_field, size);
347 * Warn for source field over-read when building with W=1
348 * or when an over-write happened, so both can be fixed at
351 if ((IS_ENABLED(KBUILD_EXTRA_WARN1) || p_size_field < size) &&
353 __read_overflow2_field(q_size_field, size);
356 * At this point, length argument may not be a constant expression,
357 * so run-time bounds checking can be done where buffer sizes are
358 * known. (This is not an "else" because the above checks may only
359 * be compile-time warnings, and we want to still warn for run-time
364 * Always stop accesses beyond the struct that contains the
365 * field, when the buffer's remaining size is known.
366 * (The -1 test is to optimize away checks where the buffer
367 * lengths are unknown.)
369 if ((p_size != (size_t)(-1) && p_size < size) ||
370 (q_size != (size_t)(-1) && q_size < size))
374 #define __fortify_memcpy_chk(p, q, size, p_size, q_size, \
375 p_size_field, q_size_field, op) ({ \
376 size_t __fortify_size = (size_t)(size); \
377 fortify_memcpy_chk(__fortify_size, p_size, q_size, \
378 p_size_field, q_size_field, #op); \
379 __underlying_##op(p, q, __fortify_size); \
383 * __builtin_object_size() must be captured here to avoid evaluating argument
384 * side-effects further into the macro layers.
386 #define memcpy(p, q, s) __fortify_memcpy_chk(p, q, s, \
387 __builtin_object_size(p, 0), __builtin_object_size(q, 0), \
388 __builtin_object_size(p, 1), __builtin_object_size(q, 1), \
390 #define memmove(p, q, s) __fortify_memcpy_chk(p, q, s, \
391 __builtin_object_size(p, 0), __builtin_object_size(q, 0), \
392 __builtin_object_size(p, 1), __builtin_object_size(q, 1), \
395 extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan);
396 __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size)
398 size_t p_size = __builtin_object_size(p, 0);
400 if (__builtin_constant_p(size) && p_size < size)
403 fortify_panic(__func__);
404 return __real_memscan(p, c, size);
407 __FORTIFY_INLINE __diagnose_as(__builtin_memcmp, 1, 2, 3)
408 int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t size)
410 size_t p_size = __builtin_object_size(p, 0);
411 size_t q_size = __builtin_object_size(q, 0);
413 if (__builtin_constant_p(size)) {
419 if (p_size < size || q_size < size)
420 fortify_panic(__func__);
421 return __underlying_memcmp(p, q, size);
424 __FORTIFY_INLINE __diagnose_as(__builtin_memchr, 1, 2, 3)
425 void *memchr(const void * const POS0 p, int c, __kernel_size_t size)
427 size_t p_size = __builtin_object_size(p, 0);
429 if (__builtin_constant_p(size) && p_size < size)
432 fortify_panic(__func__);
433 return __underlying_memchr(p, c, size);
436 void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv);
437 __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size)
439 size_t p_size = __builtin_object_size(p, 0);
441 if (__builtin_constant_p(size) && p_size < size)
444 fortify_panic(__func__);
445 return __real_memchr_inv(p, c, size);
448 extern void *__real_kmemdup(const void *src, size_t len, gfp_t gfp) __RENAME(kmemdup);
449 __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp)
451 size_t p_size = __builtin_object_size(p, 0);
453 if (__builtin_constant_p(size) && p_size < size)
456 fortify_panic(__func__);
457 return __real_kmemdup(p, size, gfp);
460 /* Defined after fortified strlen to reuse it. */
461 __FORTIFY_INLINE __diagnose_as(__builtin_strcpy, 1, 2)
462 char *strcpy(char * const POS p, const char * const POS q)
464 size_t p_size = __builtin_object_size(p, 1);
465 size_t q_size = __builtin_object_size(q, 1);
468 /* If neither buffer size is known, immediately give up. */
469 if (p_size == (size_t)-1 && q_size == (size_t)-1)
470 return __underlying_strcpy(p, q);
471 size = strlen(q) + 1;
472 /* Compile-time check for const size overflow. */
473 if (__builtin_constant_p(size) && p_size < size)
475 /* Run-time check for dynamic size overflow. */
477 fortify_panic(__func__);
478 __underlying_memcpy(p, q, size);
482 /* Don't use these outside the FORITFY_SOURCE implementation */
483 #undef __underlying_memchr
484 #undef __underlying_memcmp
485 #undef __underlying_strcat
486 #undef __underlying_strcpy
487 #undef __underlying_strlen
488 #undef __underlying_strncat
489 #undef __underlying_strncpy
494 #endif /* _LINUX_FORTIFY_STRING_H_ */