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 fortify_memset_chk(__kernel_size_t size, 204 const size_t p_size, 205 const size_t p_size_field) 206 { 207 if (__builtin_constant_p(size)) { 208 /* 209 * Length argument is a constant expression, so we 210 * can perform compile-time bounds checking where 211 * buffer sizes are known. 212 */ 213 214 /* Error when size is larger than enclosing struct. */ 215 if (p_size > p_size_field && p_size < size) 216 __write_overflow(); 217 218 /* Warn when write size is larger than dest field. */ 219 if (p_size_field < size) 220 __write_overflow_field(p_size_field, size); 221 } 222 /* 223 * At this point, length argument may not be a constant expression, 224 * so run-time bounds checking can be done where buffer sizes are 225 * known. (This is not an "else" because the above checks may only 226 * be compile-time warnings, and we want to still warn for run-time 227 * overflows.) 228 */ 229 230 /* 231 * Always stop accesses beyond the struct that contains the 232 * field, when the buffer's remaining size is known. 233 * (The -1 test is to optimize away checks where the buffer 234 * lengths are unknown.) 235 */ 236 if (p_size != (size_t)(-1) && p_size < size) 237 fortify_panic("memset"); 238 } 239 240 #define __fortify_memset_chk(p, c, size, p_size, p_size_field) ({ \ 241 size_t __fortify_size = (size_t)(size); \ 242 fortify_memset_chk(__fortify_size, p_size, p_size_field), \ 243 __underlying_memset(p, c, __fortify_size); \ 244 }) 245 246 /* 247 * __builtin_object_size() must be captured here to avoid evaluating argument 248 * side-effects further into the macro layers. 249 */ 250 #define memset(p, c, s) __fortify_memset_chk(p, c, s, \ 251 __builtin_object_size(p, 0), __builtin_object_size(p, 1)) 252 253 /* 254 * To make sure the compiler can enforce protection against buffer overflows, 255 * memcpy(), memmove(), and memset() must not be used beyond individual 256 * struct members. If you need to copy across multiple members, please use 257 * struct_group() to create a named mirror of an anonymous struct union. 258 * (e.g. see struct sk_buff.) Read overflow checking is currently only 259 * done when a write overflow is also present, or when building with W=1. 260 * 261 * Mitigation coverage matrix 262 * Bounds checking at: 263 * +-------+-------+-------+-------+ 264 * | Compile time | Run time | 265 * memcpy() argument sizes: | write | read | write | read | 266 * dest source length +-------+-------+-------+-------+ 267 * memcpy(known, known, constant) | y | y | n/a | n/a | 268 * memcpy(known, unknown, constant) | y | n | n/a | V | 269 * memcpy(known, known, dynamic) | n | n | B | B | 270 * memcpy(known, unknown, dynamic) | n | n | B | V | 271 * memcpy(unknown, known, constant) | n | y | V | n/a | 272 * memcpy(unknown, unknown, constant) | n | n | V | V | 273 * memcpy(unknown, known, dynamic) | n | n | V | B | 274 * memcpy(unknown, unknown, dynamic) | n | n | V | V | 275 * +-------+-------+-------+-------+ 276 * 277 * y = perform deterministic compile-time bounds checking 278 * n = cannot perform deterministic compile-time bounds checking 279 * n/a = no run-time bounds checking needed since compile-time deterministic 280 * B = can perform run-time bounds checking (currently unimplemented) 281 * V = vulnerable to run-time overflow (will need refactoring to solve) 282 * 283 */ 284 __FORTIFY_INLINE void fortify_memcpy_chk(__kernel_size_t size, 285 const size_t p_size, 286 const size_t q_size, 287 const size_t p_size_field, 288 const size_t q_size_field, 289 const char *func) 290 { 291 if (__builtin_constant_p(size)) { 292 /* 293 * Length argument is a constant expression, so we 294 * can perform compile-time bounds checking where 295 * buffer sizes are known. 296 */ 297 298 /* Error when size is larger than enclosing struct. */ 299 if (p_size > p_size_field && p_size < size) 300 __write_overflow(); 301 if (q_size > q_size_field && q_size < size) 302 __read_overflow2(); 303 304 /* Warn when write size argument larger than dest field. */ 305 if (p_size_field < size) 306 __write_overflow_field(p_size_field, size); 307 /* 308 * Warn for source field over-read when building with W=1 309 * or when an over-write happened, so both can be fixed at 310 * the same time. 311 */ 312 if ((IS_ENABLED(KBUILD_EXTRA_WARN1) || p_size_field < size) && 313 q_size_field < size) 314 __read_overflow2_field(q_size_field, size); 315 } 316 /* 317 * At this point, length argument may not be a constant expression, 318 * so run-time bounds checking can be done where buffer sizes are 319 * known. (This is not an "else" because the above checks may only 320 * be compile-time warnings, and we want to still warn for run-time 321 * overflows.) 322 */ 323 324 /* 325 * Always stop accesses beyond the struct that contains the 326 * field, when the buffer's remaining size is known. 327 * (The -1 test is to optimize away checks where the buffer 328 * lengths are unknown.) 329 */ 330 if ((p_size != (size_t)(-1) && p_size < size) || 331 (q_size != (size_t)(-1) && q_size < size)) 332 fortify_panic(func); 333 } 334 335 #define __fortify_memcpy_chk(p, q, size, p_size, q_size, \ 336 p_size_field, q_size_field, op) ({ \ 337 size_t __fortify_size = (size_t)(size); \ 338 fortify_memcpy_chk(__fortify_size, p_size, q_size, \ 339 p_size_field, q_size_field, #op); \ 340 __underlying_##op(p, q, __fortify_size); \ 341 }) 342 343 /* 344 * __builtin_object_size() must be captured here to avoid evaluating argument 345 * side-effects further into the macro layers. 346 */ 347 #define memcpy(p, q, s) __fortify_memcpy_chk(p, q, s, \ 348 __builtin_object_size(p, 0), __builtin_object_size(q, 0), \ 349 __builtin_object_size(p, 1), __builtin_object_size(q, 1), \ 350 memcpy) 351 #define memmove(p, q, s) __fortify_memcpy_chk(p, q, s, \ 352 __builtin_object_size(p, 0), __builtin_object_size(q, 0), \ 353 __builtin_object_size(p, 1), __builtin_object_size(q, 1), \ 354 memmove) 355 356 extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan); 357 __FORTIFY_INLINE void *memscan(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 __real_memscan(p, c, size); 366 } 367 368 __FORTIFY_INLINE int memcmp(const void *p, const void *q, __kernel_size_t size) 369 { 370 size_t p_size = __builtin_object_size(p, 0); 371 size_t q_size = __builtin_object_size(q, 0); 372 373 if (__builtin_constant_p(size)) { 374 if (p_size < size) 375 __read_overflow(); 376 if (q_size < size) 377 __read_overflow2(); 378 } 379 if (p_size < size || q_size < size) 380 fortify_panic(__func__); 381 return __underlying_memcmp(p, q, size); 382 } 383 384 __FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size) 385 { 386 size_t p_size = __builtin_object_size(p, 0); 387 388 if (__builtin_constant_p(size) && p_size < size) 389 __read_overflow(); 390 if (p_size < size) 391 fortify_panic(__func__); 392 return __underlying_memchr(p, c, size); 393 } 394 395 void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv); 396 __FORTIFY_INLINE void *memchr_inv(const void *p, int c, size_t size) 397 { 398 size_t p_size = __builtin_object_size(p, 0); 399 400 if (__builtin_constant_p(size) && p_size < size) 401 __read_overflow(); 402 if (p_size < size) 403 fortify_panic(__func__); 404 return __real_memchr_inv(p, c, size); 405 } 406 407 extern void *__real_kmemdup(const void *src, size_t len, gfp_t gfp) __RENAME(kmemdup); 408 __FORTIFY_INLINE void *kmemdup(const void *p, size_t size, gfp_t gfp) 409 { 410 size_t p_size = __builtin_object_size(p, 0); 411 412 if (__builtin_constant_p(size) && p_size < size) 413 __read_overflow(); 414 if (p_size < size) 415 fortify_panic(__func__); 416 return __real_kmemdup(p, size, gfp); 417 } 418 419 /* Defined after fortified strlen to reuse it. */ 420 __FORTIFY_INLINE char *strcpy(char *p, const char *q) 421 { 422 size_t p_size = __builtin_object_size(p, 1); 423 size_t q_size = __builtin_object_size(q, 1); 424 size_t size; 425 426 /* If neither buffer size is known, immediately give up. */ 427 if (p_size == (size_t)-1 && q_size == (size_t)-1) 428 return __underlying_strcpy(p, q); 429 size = strlen(q) + 1; 430 /* Compile-time check for const size overflow. */ 431 if (__builtin_constant_p(size) && p_size < size) 432 __write_overflow(); 433 /* Run-time check for dynamic size overflow. */ 434 if (p_size < size) 435 fortify_panic(__func__); 436 __underlying_memcpy(p, q, size); 437 return p; 438 } 439 440 /* Don't use these outside the FORITFY_SOURCE implementation */ 441 #undef __underlying_memchr 442 #undef __underlying_memcmp 443 #undef __underlying_strcat 444 #undef __underlying_strcpy 445 #undef __underlying_strlen 446 #undef __underlying_strncat 447 #undef __underlying_strncpy 448 449 #endif /* _LINUX_FORTIFY_STRING_H_ */ 450