1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _LINUX_FORTIFY_STRING_H_ 3 #define _LINUX_FORTIFY_STRING_H_ 4 5 #define __FORTIFY_INLINE extern __always_inline __attribute__((gnu_inline)) 6 #define __RENAME(x) __asm__(#x) 7 8 void fortify_panic(const char *name) __noreturn __cold; 9 void __read_overflow(void) __compiletime_error("detected read beyond size of object (1st parameter)"); 10 void __read_overflow2(void) __compiletime_error("detected read beyond size of object (2nd parameter)"); 11 void __read_overflow2_field(size_t avail, size_t wanted) __compiletime_warning("detected read beyond size of field (2nd parameter); maybe use struct_group()?"); 12 void __write_overflow(void) __compiletime_error("detected write beyond size of object (1st parameter)"); 13 void __write_overflow_field(size_t avail, size_t wanted) __compiletime_warning("detected write beyond size of field (1st parameter); maybe use struct_group()?"); 14 15 #define __compiletime_strlen(p) \ 16 ({ \ 17 unsigned char *__p = (unsigned char *)(p); \ 18 size_t __ret = (size_t)-1; \ 19 size_t __p_size = __builtin_object_size(p, 1); \ 20 if (__p_size != (size_t)-1) { \ 21 size_t __p_len = __p_size - 1; \ 22 if (__builtin_constant_p(__p[__p_len]) && \ 23 __p[__p_len] == '\0') \ 24 __ret = __builtin_strlen(__p); \ 25 } \ 26 __ret; \ 27 }) 28 29 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS) 30 extern void *__underlying_memchr(const void *p, int c, __kernel_size_t size) __RENAME(memchr); 31 extern int __underlying_memcmp(const void *p, const void *q, __kernel_size_t size) __RENAME(memcmp); 32 extern void *__underlying_memcpy(void *p, const void *q, __kernel_size_t size) __RENAME(memcpy); 33 extern void *__underlying_memmove(void *p, const void *q, __kernel_size_t size) __RENAME(memmove); 34 extern void *__underlying_memset(void *p, int c, __kernel_size_t size) __RENAME(memset); 35 extern char *__underlying_strcat(char *p, const char *q) __RENAME(strcat); 36 extern char *__underlying_strcpy(char *p, const char *q) __RENAME(strcpy); 37 extern __kernel_size_t __underlying_strlen(const char *p) __RENAME(strlen); 38 extern char *__underlying_strncat(char *p, const char *q, __kernel_size_t count) __RENAME(strncat); 39 extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __RENAME(strncpy); 40 #else 41 #define __underlying_memchr __builtin_memchr 42 #define __underlying_memcmp __builtin_memcmp 43 #define __underlying_memcpy __builtin_memcpy 44 #define __underlying_memmove __builtin_memmove 45 #define __underlying_memset __builtin_memset 46 #define __underlying_strcat __builtin_strcat 47 #define __underlying_strcpy __builtin_strcpy 48 #define __underlying_strlen __builtin_strlen 49 #define __underlying_strncat __builtin_strncat 50 #define __underlying_strncpy __builtin_strncpy 51 #endif 52 53 __FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size) 54 { 55 size_t p_size = __builtin_object_size(p, 1); 56 57 if (__builtin_constant_p(size) && p_size < size) 58 __write_overflow(); 59 if (p_size < size) 60 fortify_panic(__func__); 61 return __underlying_strncpy(p, q, size); 62 } 63 64 __FORTIFY_INLINE char *strcat(char *p, const char *q) 65 { 66 size_t p_size = __builtin_object_size(p, 1); 67 68 if (p_size == (size_t)-1) 69 return __underlying_strcat(p, q); 70 if (strlcat(p, q, p_size) >= p_size) 71 fortify_panic(__func__); 72 return p; 73 } 74 75 extern __kernel_size_t __real_strnlen(const char *, __kernel_size_t) __RENAME(strnlen); 76 __FORTIFY_INLINE __kernel_size_t strnlen(const char *p, __kernel_size_t maxlen) 77 { 78 size_t p_size = __builtin_object_size(p, 1); 79 size_t p_len = __compiletime_strlen(p); 80 size_t ret; 81 82 /* We can take compile-time actions when maxlen is const. */ 83 if (__builtin_constant_p(maxlen) && p_len != (size_t)-1) { 84 /* If p is const, we can use its compile-time-known len. */ 85 if (maxlen >= p_size) 86 return p_len; 87 } 88 89 /* Do not check characters beyond the end of p. */ 90 ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size); 91 if (p_size <= ret && maxlen != ret) 92 fortify_panic(__func__); 93 return ret; 94 } 95 96 /* defined after fortified strnlen to reuse it. */ 97 __FORTIFY_INLINE __kernel_size_t strlen(const char *p) 98 { 99 __kernel_size_t ret; 100 size_t p_size = __builtin_object_size(p, 1); 101 102 /* Give up if we don't know how large p is. */ 103 if (p_size == (size_t)-1) 104 return __underlying_strlen(p); 105 ret = strnlen(p, p_size); 106 if (p_size <= ret) 107 fortify_panic(__func__); 108 return ret; 109 } 110 111 /* defined after fortified strlen to reuse it */ 112 extern size_t __real_strlcpy(char *, const char *, size_t) __RENAME(strlcpy); 113 __FORTIFY_INLINE size_t strlcpy(char *p, const char *q, size_t size) 114 { 115 size_t p_size = __builtin_object_size(p, 1); 116 size_t q_size = __builtin_object_size(q, 1); 117 size_t q_len; /* Full count of source string length. */ 118 size_t len; /* Count of characters going into destination. */ 119 120 if (p_size == (size_t)-1 && q_size == (size_t)-1) 121 return __real_strlcpy(p, q, size); 122 q_len = strlen(q); 123 len = (q_len >= size) ? size - 1 : q_len; 124 if (__builtin_constant_p(size) && __builtin_constant_p(q_len) && size) { 125 /* Write size is always larger than destination. */ 126 if (len >= p_size) 127 __write_overflow(); 128 } 129 if (size) { 130 if (len >= p_size) 131 fortify_panic(__func__); 132 __underlying_memcpy(p, q, len); 133 p[len] = '\0'; 134 } 135 return q_len; 136 } 137 138 /* defined after fortified strnlen to reuse it */ 139 extern ssize_t __real_strscpy(char *, const char *, size_t) __RENAME(strscpy); 140 __FORTIFY_INLINE ssize_t strscpy(char *p, const char *q, size_t size) 141 { 142 size_t len; 143 /* Use string size rather than possible enclosing struct size. */ 144 size_t p_size = __builtin_object_size(p, 1); 145 size_t q_size = __builtin_object_size(q, 1); 146 147 /* If we cannot get size of p and q default to call strscpy. */ 148 if (p_size == (size_t) -1 && q_size == (size_t) -1) 149 return __real_strscpy(p, q, size); 150 151 /* 152 * If size can be known at compile time and is greater than 153 * p_size, generate a compile time write overflow error. 154 */ 155 if (__builtin_constant_p(size) && size > p_size) 156 __write_overflow(); 157 158 /* 159 * This call protects from read overflow, because len will default to q 160 * length if it smaller than size. 161 */ 162 len = strnlen(q, size); 163 /* 164 * If len equals size, we will copy only size bytes which leads to 165 * -E2BIG being returned. 166 * Otherwise we will copy len + 1 because of the final '\O'. 167 */ 168 len = len == size ? size : len + 1; 169 170 /* 171 * Generate a runtime write overflow error if len is greater than 172 * p_size. 173 */ 174 if (len > p_size) 175 fortify_panic(__func__); 176 177 /* 178 * We can now safely call vanilla strscpy because we are protected from: 179 * 1. Read overflow thanks to call to strnlen(). 180 * 2. Write overflow thanks to above ifs. 181 */ 182 return __real_strscpy(p, q, len); 183 } 184 185 /* defined after fortified strlen and strnlen to reuse them */ 186 __FORTIFY_INLINE char *strncat(char *p, const char *q, __kernel_size_t count) 187 { 188 size_t p_len, copy_len; 189 size_t p_size = __builtin_object_size(p, 1); 190 size_t q_size = __builtin_object_size(q, 1); 191 192 if (p_size == (size_t)-1 && q_size == (size_t)-1) 193 return __underlying_strncat(p, q, count); 194 p_len = strlen(p); 195 copy_len = strnlen(q, count); 196 if (p_size < p_len + copy_len + 1) 197 fortify_panic(__func__); 198 __underlying_memcpy(p + p_len, q, copy_len); 199 p[p_len + copy_len] = '\0'; 200 return p; 201 } 202 203 __FORTIFY_INLINE void *memset(void *p, int c, __kernel_size_t size) 204 { 205 size_t p_size = __builtin_object_size(p, 0); 206 207 if (__builtin_constant_p(size) && p_size < size) 208 __write_overflow(); 209 if (p_size < size) 210 fortify_panic(__func__); 211 return __underlying_memset(p, c, size); 212 } 213 214 /* 215 * To make sure the compiler can enforce protection against buffer overflows, 216 * memcpy(), memmove(), and memset() must not be used beyond individual 217 * struct members. If you need to copy across multiple members, please use 218 * struct_group() to create a named mirror of an anonymous struct union. 219 * (e.g. see struct sk_buff.) Read overflow checking is currently only 220 * done when a write overflow is also present, or when building with W=1. 221 * 222 * Mitigation coverage matrix 223 * Bounds checking at: 224 * +-------+-------+-------+-------+ 225 * | Compile time | Run time | 226 * memcpy() argument sizes: | write | read | write | read | 227 * dest source length +-------+-------+-------+-------+ 228 * memcpy(known, known, constant) | y | y | n/a | n/a | 229 * memcpy(known, unknown, constant) | y | n | n/a | V | 230 * memcpy(known, known, dynamic) | n | n | B | B | 231 * memcpy(known, unknown, dynamic) | n | n | B | V | 232 * memcpy(unknown, known, constant) | n | y | V | n/a | 233 * memcpy(unknown, unknown, constant) | n | n | V | V | 234 * memcpy(unknown, known, dynamic) | n | n | V | B | 235 * memcpy(unknown, unknown, dynamic) | n | n | V | V | 236 * +-------+-------+-------+-------+ 237 * 238 * y = perform deterministic compile-time bounds checking 239 * n = cannot perform deterministic compile-time bounds checking 240 * n/a = no run-time bounds checking needed since compile-time deterministic 241 * B = can perform run-time bounds checking (currently unimplemented) 242 * V = vulnerable to run-time overflow (will need refactoring to solve) 243 * 244 */ 245 __FORTIFY_INLINE void fortify_memcpy_chk(__kernel_size_t size, 246 const size_t p_size, 247 const size_t q_size, 248 const size_t p_size_field, 249 const size_t q_size_field, 250 const char *func) 251 { 252 if (__builtin_constant_p(size)) { 253 /* 254 * Length argument is a constant expression, so we 255 * can perform compile-time bounds checking where 256 * buffer sizes are known. 257 */ 258 259 /* Error when size is larger than enclosing struct. */ 260 if (p_size > p_size_field && p_size < size) 261 __write_overflow(); 262 if (q_size > q_size_field && q_size < size) 263 __read_overflow2(); 264 265 /* Warn when write size argument larger than dest field. */ 266 if (p_size_field < size) 267 __write_overflow_field(p_size_field, size); 268 /* 269 * Warn for source field over-read when building with W=1 270 * or when an over-write happened, so both can be fixed at 271 * the same time. 272 */ 273 if ((IS_ENABLED(KBUILD_EXTRA_WARN1) || p_size_field < size) && 274 q_size_field < size) 275 __read_overflow2_field(q_size_field, size); 276 } 277 /* 278 * At this point, length argument may not be a constant expression, 279 * so run-time bounds checking can be done where buffer sizes are 280 * known. (This is not an "else" because the above checks may only 281 * be compile-time warnings, and we want to still warn for run-time 282 * overflows.) 283 */ 284 285 /* 286 * Always stop accesses beyond the struct that contains the 287 * field, when the buffer's remaining size is known. 288 * (The -1 test is to optimize away checks where the buffer 289 * lengths are unknown.) 290 */ 291 if ((p_size != (size_t)(-1) && p_size < size) || 292 (q_size != (size_t)(-1) && q_size < size)) 293 fortify_panic(func); 294 } 295 296 #define __fortify_memcpy_chk(p, q, size, p_size, q_size, \ 297 p_size_field, q_size_field, op) ({ \ 298 size_t __fortify_size = (size_t)(size); \ 299 fortify_memcpy_chk(__fortify_size, p_size, q_size, \ 300 p_size_field, q_size_field, #op); \ 301 __underlying_##op(p, q, __fortify_size); \ 302 }) 303 304 /* 305 * __builtin_object_size() must be captured here to avoid evaluating argument 306 * side-effects further into the macro layers. 307 */ 308 #define memcpy(p, q, s) __fortify_memcpy_chk(p, q, s, \ 309 __builtin_object_size(p, 0), __builtin_object_size(q, 0), \ 310 __builtin_object_size(p, 1), __builtin_object_size(q, 1), \ 311 memcpy) 312 313 __FORTIFY_INLINE void *memmove(void *p, const void *q, __kernel_size_t size) 314 { 315 size_t p_size = __builtin_object_size(p, 0); 316 size_t q_size = __builtin_object_size(q, 0); 317 318 if (__builtin_constant_p(size)) { 319 if (p_size < size) 320 __write_overflow(); 321 if (q_size < size) 322 __read_overflow2(); 323 } 324 if (p_size < size || q_size < size) 325 fortify_panic(__func__); 326 return __underlying_memmove(p, q, size); 327 } 328 329 extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan); 330 __FORTIFY_INLINE void *memscan(void *p, int c, __kernel_size_t size) 331 { 332 size_t p_size = __builtin_object_size(p, 0); 333 334 if (__builtin_constant_p(size) && p_size < size) 335 __read_overflow(); 336 if (p_size < size) 337 fortify_panic(__func__); 338 return __real_memscan(p, c, size); 339 } 340 341 __FORTIFY_INLINE int memcmp(const void *p, const void *q, __kernel_size_t size) 342 { 343 size_t p_size = __builtin_object_size(p, 0); 344 size_t q_size = __builtin_object_size(q, 0); 345 346 if (__builtin_constant_p(size)) { 347 if (p_size < size) 348 __read_overflow(); 349 if (q_size < size) 350 __read_overflow2(); 351 } 352 if (p_size < size || q_size < size) 353 fortify_panic(__func__); 354 return __underlying_memcmp(p, q, size); 355 } 356 357 __FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size) 358 { 359 size_t p_size = __builtin_object_size(p, 0); 360 361 if (__builtin_constant_p(size) && p_size < size) 362 __read_overflow(); 363 if (p_size < size) 364 fortify_panic(__func__); 365 return __underlying_memchr(p, c, size); 366 } 367 368 void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv); 369 __FORTIFY_INLINE void *memchr_inv(const void *p, int c, size_t size) 370 { 371 size_t p_size = __builtin_object_size(p, 0); 372 373 if (__builtin_constant_p(size) && p_size < size) 374 __read_overflow(); 375 if (p_size < size) 376 fortify_panic(__func__); 377 return __real_memchr_inv(p, c, size); 378 } 379 380 extern void *__real_kmemdup(const void *src, size_t len, gfp_t gfp) __RENAME(kmemdup); 381 __FORTIFY_INLINE void *kmemdup(const void *p, size_t size, gfp_t gfp) 382 { 383 size_t p_size = __builtin_object_size(p, 0); 384 385 if (__builtin_constant_p(size) && p_size < size) 386 __read_overflow(); 387 if (p_size < size) 388 fortify_panic(__func__); 389 return __real_kmemdup(p, size, gfp); 390 } 391 392 /* Defined after fortified strlen to reuse it. */ 393 __FORTIFY_INLINE char *strcpy(char *p, const char *q) 394 { 395 size_t p_size = __builtin_object_size(p, 1); 396 size_t q_size = __builtin_object_size(q, 1); 397 size_t size; 398 399 /* If neither buffer size is known, immediately give up. */ 400 if (p_size == (size_t)-1 && q_size == (size_t)-1) 401 return __underlying_strcpy(p, q); 402 size = strlen(q) + 1; 403 /* Compile-time check for const size overflow. */ 404 if (__builtin_constant_p(size) && p_size < size) 405 __write_overflow(); 406 /* Run-time check for dynamic size overflow. */ 407 if (p_size < size) 408 fortify_panic(__func__); 409 __underlying_memcpy(p, q, size); 410 return p; 411 } 412 413 /* Don't use these outside the FORITFY_SOURCE implementation */ 414 #undef __underlying_memchr 415 #undef __underlying_memcmp 416 #undef __underlying_memmove 417 #undef __underlying_memset 418 #undef __underlying_strcat 419 #undef __underlying_strcpy 420 #undef __underlying_strlen 421 #undef __underlying_strncat 422 #undef __underlying_strncpy 423 424 #endif /* _LINUX_FORTIFY_STRING_H_ */ 425