1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * This is for all the tests relating directly to heap memory, including 4 * page allocation and slab allocations. 5 */ 6 #include "lkdtm.h" 7 #include <linux/kfence.h> 8 #include <linux/slab.h> 9 #include <linux/vmalloc.h> 10 #include <linux/sched.h> 11 12 static struct kmem_cache *double_free_cache; 13 static struct kmem_cache *a_cache; 14 static struct kmem_cache *b_cache; 15 16 /* 17 * Using volatile here means the compiler cannot ever make assumptions 18 * about this value. This means compile-time length checks involving 19 * this variable cannot be performed; only run-time checks. 20 */ 21 static volatile int __offset = 1; 22 23 /* 24 * If there aren't guard pages, it's likely that a consecutive allocation will 25 * let us overflow into the second allocation without overwriting something real. 26 * 27 * This should always be caught because there is an unconditional unmapped 28 * page after vmap allocations. 29 */ 30 static void lkdtm_VMALLOC_LINEAR_OVERFLOW(void) 31 { 32 char *one, *two; 33 34 one = vzalloc(PAGE_SIZE); 35 OPTIMIZER_HIDE_VAR(one); 36 two = vzalloc(PAGE_SIZE); 37 38 pr_info("Attempting vmalloc linear overflow ...\n"); 39 memset(one, 0xAA, PAGE_SIZE + __offset); 40 41 vfree(two); 42 vfree(one); 43 } 44 45 /* 46 * This tries to stay within the next largest power-of-2 kmalloc cache 47 * to avoid actually overwriting anything important if it's not detected 48 * correctly. 49 * 50 * This should get caught by either memory tagging, KASan, or by using 51 * CONFIG_SLUB_DEBUG=y and slub_debug=ZF (or CONFIG_SLUB_DEBUG_ON=y). 52 */ 53 static void lkdtm_SLAB_LINEAR_OVERFLOW(void) 54 { 55 size_t len = 1020; 56 u32 *data = kmalloc(len, GFP_KERNEL); 57 if (!data) 58 return; 59 60 pr_info("Attempting slab linear overflow ...\n"); 61 OPTIMIZER_HIDE_VAR(data); 62 data[1024 / sizeof(u32)] = 0x12345678; 63 kfree(data); 64 } 65 66 static void lkdtm_WRITE_AFTER_FREE(void) 67 { 68 int *base, *again; 69 size_t len = 1024; 70 /* 71 * The slub allocator uses the first word to store the free 72 * pointer in some configurations. Use the middle of the 73 * allocation to avoid running into the freelist 74 */ 75 size_t offset = (len / sizeof(*base)) / 2; 76 77 base = kmalloc(len, GFP_KERNEL); 78 if (!base) 79 return; 80 pr_info("Allocated memory %p-%p\n", base, &base[offset * 2]); 81 pr_info("Attempting bad write to freed memory at %p\n", 82 &base[offset]); 83 kfree(base); 84 base[offset] = 0x0abcdef0; 85 /* Attempt to notice the overwrite. */ 86 again = kmalloc(len, GFP_KERNEL); 87 kfree(again); 88 if (again != base) 89 pr_info("Hmm, didn't get the same memory range.\n"); 90 } 91 92 static void lkdtm_READ_AFTER_FREE(void) 93 { 94 int *base, *val, saw; 95 size_t len = 1024; 96 /* 97 * The slub allocator will use the either the first word or 98 * the middle of the allocation to store the free pointer, 99 * depending on configurations. Store in the second word to 100 * avoid running into the freelist. 101 */ 102 size_t offset = sizeof(*base); 103 104 base = kmalloc(len, GFP_KERNEL); 105 if (!base) { 106 pr_info("Unable to allocate base memory.\n"); 107 return; 108 } 109 110 val = kmalloc(len, GFP_KERNEL); 111 if (!val) { 112 pr_info("Unable to allocate val memory.\n"); 113 kfree(base); 114 return; 115 } 116 117 *val = 0x12345678; 118 base[offset] = *val; 119 pr_info("Value in memory before free: %x\n", base[offset]); 120 121 kfree(base); 122 123 pr_info("Attempting bad read from freed memory\n"); 124 saw = base[offset]; 125 if (saw != *val) { 126 /* Good! Poisoning happened, so declare a win. */ 127 pr_info("Memory correctly poisoned (%x)\n", saw); 128 } else { 129 pr_err("FAIL: Memory was not poisoned!\n"); 130 pr_expected_config_param(CONFIG_INIT_ON_FREE_DEFAULT_ON, "init_on_free"); 131 } 132 133 kfree(val); 134 } 135 136 static void lkdtm_KFENCE_READ_AFTER_FREE(void) 137 { 138 int *base, val, saw; 139 unsigned long timeout, resched_after; 140 size_t len = 1024; 141 /* 142 * The slub allocator will use the either the first word or 143 * the middle of the allocation to store the free pointer, 144 * depending on configurations. Store in the second word to 145 * avoid running into the freelist. 146 */ 147 size_t offset = sizeof(*base); 148 149 /* 150 * 100x the sample interval should be more than enough to ensure we get 151 * a KFENCE allocation eventually. 152 */ 153 timeout = jiffies + msecs_to_jiffies(100 * kfence_sample_interval); 154 /* 155 * Especially for non-preemption kernels, ensure the allocation-gate 156 * timer can catch up: after @resched_after, every failed allocation 157 * attempt yields, to ensure the allocation-gate timer is scheduled. 158 */ 159 resched_after = jiffies + msecs_to_jiffies(kfence_sample_interval); 160 do { 161 base = kmalloc(len, GFP_KERNEL); 162 if (!base) { 163 pr_err("FAIL: Unable to allocate kfence memory!\n"); 164 return; 165 } 166 167 if (is_kfence_address(base)) { 168 val = 0x12345678; 169 base[offset] = val; 170 pr_info("Value in memory before free: %x\n", base[offset]); 171 172 kfree(base); 173 174 pr_info("Attempting bad read from freed memory\n"); 175 saw = base[offset]; 176 if (saw != val) { 177 /* Good! Poisoning happened, so declare a win. */ 178 pr_info("Memory correctly poisoned (%x)\n", saw); 179 } else { 180 pr_err("FAIL: Memory was not poisoned!\n"); 181 pr_expected_config_param(CONFIG_INIT_ON_FREE_DEFAULT_ON, "init_on_free"); 182 } 183 return; 184 } 185 186 kfree(base); 187 if (time_after(jiffies, resched_after)) 188 cond_resched(); 189 } while (time_before(jiffies, timeout)); 190 191 pr_err("FAIL: kfence memory never allocated!\n"); 192 } 193 194 static void lkdtm_WRITE_BUDDY_AFTER_FREE(void) 195 { 196 unsigned long p = __get_free_page(GFP_KERNEL); 197 if (!p) { 198 pr_info("Unable to allocate free page\n"); 199 return; 200 } 201 202 pr_info("Writing to the buddy page before free\n"); 203 memset((void *)p, 0x3, PAGE_SIZE); 204 free_page(p); 205 schedule(); 206 pr_info("Attempting bad write to the buddy page after free\n"); 207 memset((void *)p, 0x78, PAGE_SIZE); 208 /* Attempt to notice the overwrite. */ 209 p = __get_free_page(GFP_KERNEL); 210 free_page(p); 211 schedule(); 212 } 213 214 static void lkdtm_READ_BUDDY_AFTER_FREE(void) 215 { 216 unsigned long p = __get_free_page(GFP_KERNEL); 217 int saw, *val; 218 int *base; 219 220 if (!p) { 221 pr_info("Unable to allocate free page\n"); 222 return; 223 } 224 225 val = kmalloc(1024, GFP_KERNEL); 226 if (!val) { 227 pr_info("Unable to allocate val memory.\n"); 228 free_page(p); 229 return; 230 } 231 232 base = (int *)p; 233 234 *val = 0x12345678; 235 base[0] = *val; 236 pr_info("Value in memory before free: %x\n", base[0]); 237 free_page(p); 238 pr_info("Attempting to read from freed memory\n"); 239 saw = base[0]; 240 if (saw != *val) { 241 /* Good! Poisoning happened, so declare a win. */ 242 pr_info("Memory correctly poisoned (%x)\n", saw); 243 } else { 244 pr_err("FAIL: Buddy page was not poisoned!\n"); 245 pr_expected_config_param(CONFIG_INIT_ON_FREE_DEFAULT_ON, "init_on_free"); 246 } 247 248 kfree(val); 249 } 250 251 static void lkdtm_SLAB_INIT_ON_ALLOC(void) 252 { 253 u8 *first; 254 u8 *val; 255 256 first = kmalloc(512, GFP_KERNEL); 257 if (!first) { 258 pr_info("Unable to allocate 512 bytes the first time.\n"); 259 return; 260 } 261 262 memset(first, 0xAB, 512); 263 kfree(first); 264 265 val = kmalloc(512, GFP_KERNEL); 266 if (!val) { 267 pr_info("Unable to allocate 512 bytes the second time.\n"); 268 return; 269 } 270 if (val != first) { 271 pr_warn("Reallocation missed clobbered memory.\n"); 272 } 273 274 if (memchr(val, 0xAB, 512) == NULL) { 275 pr_info("Memory appears initialized (%x, no earlier values)\n", *val); 276 } else { 277 pr_err("FAIL: Slab was not initialized\n"); 278 pr_expected_config_param(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, "init_on_alloc"); 279 } 280 kfree(val); 281 } 282 283 static void lkdtm_BUDDY_INIT_ON_ALLOC(void) 284 { 285 u8 *first; 286 u8 *val; 287 288 first = (u8 *)__get_free_page(GFP_KERNEL); 289 if (!first) { 290 pr_info("Unable to allocate first free page\n"); 291 return; 292 } 293 294 memset(first, 0xAB, PAGE_SIZE); 295 free_page((unsigned long)first); 296 297 val = (u8 *)__get_free_page(GFP_KERNEL); 298 if (!val) { 299 pr_info("Unable to allocate second free page\n"); 300 return; 301 } 302 303 if (val != first) { 304 pr_warn("Reallocation missed clobbered memory.\n"); 305 } 306 307 if (memchr(val, 0xAB, PAGE_SIZE) == NULL) { 308 pr_info("Memory appears initialized (%x, no earlier values)\n", *val); 309 } else { 310 pr_err("FAIL: Slab was not initialized\n"); 311 pr_expected_config_param(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, "init_on_alloc"); 312 } 313 free_page((unsigned long)val); 314 } 315 316 static void lkdtm_SLAB_FREE_DOUBLE(void) 317 { 318 int *val; 319 320 val = kmem_cache_alloc(double_free_cache, GFP_KERNEL); 321 if (!val) { 322 pr_info("Unable to allocate double_free_cache memory.\n"); 323 return; 324 } 325 326 /* Just make sure we got real memory. */ 327 *val = 0x12345678; 328 pr_info("Attempting double slab free ...\n"); 329 kmem_cache_free(double_free_cache, val); 330 kmem_cache_free(double_free_cache, val); 331 } 332 333 static void lkdtm_SLAB_FREE_CROSS(void) 334 { 335 int *val; 336 337 val = kmem_cache_alloc(a_cache, GFP_KERNEL); 338 if (!val) { 339 pr_info("Unable to allocate a_cache memory.\n"); 340 return; 341 } 342 343 /* Just make sure we got real memory. */ 344 *val = 0x12345679; 345 pr_info("Attempting cross-cache slab free ...\n"); 346 kmem_cache_free(b_cache, val); 347 } 348 349 static void lkdtm_SLAB_FREE_PAGE(void) 350 { 351 unsigned long p = __get_free_page(GFP_KERNEL); 352 353 pr_info("Attempting non-Slab slab free ...\n"); 354 kmem_cache_free(NULL, (void *)p); 355 free_page(p); 356 } 357 358 /* 359 * We have constructors to keep the caches distinctly separated without 360 * needing to boot with "slab_nomerge". 361 */ 362 static void ctor_double_free(void *region) 363 { } 364 static void ctor_a(void *region) 365 { } 366 static void ctor_b(void *region) 367 { } 368 369 void __init lkdtm_heap_init(void) 370 { 371 double_free_cache = kmem_cache_create("lkdtm-heap-double_free", 372 64, 0, 0, ctor_double_free); 373 a_cache = kmem_cache_create("lkdtm-heap-a", 64, 0, 0, ctor_a); 374 b_cache = kmem_cache_create("lkdtm-heap-b", 64, 0, 0, ctor_b); 375 } 376 377 void __exit lkdtm_heap_exit(void) 378 { 379 kmem_cache_destroy(double_free_cache); 380 kmem_cache_destroy(a_cache); 381 kmem_cache_destroy(b_cache); 382 } 383 384 static struct crashtype crashtypes[] = { 385 CRASHTYPE(SLAB_LINEAR_OVERFLOW), 386 CRASHTYPE(VMALLOC_LINEAR_OVERFLOW), 387 CRASHTYPE(WRITE_AFTER_FREE), 388 CRASHTYPE(READ_AFTER_FREE), 389 CRASHTYPE(KFENCE_READ_AFTER_FREE), 390 CRASHTYPE(WRITE_BUDDY_AFTER_FREE), 391 CRASHTYPE(READ_BUDDY_AFTER_FREE), 392 CRASHTYPE(SLAB_INIT_ON_ALLOC), 393 CRASHTYPE(BUDDY_INIT_ON_ALLOC), 394 CRASHTYPE(SLAB_FREE_DOUBLE), 395 CRASHTYPE(SLAB_FREE_CROSS), 396 CRASHTYPE(SLAB_FREE_PAGE), 397 }; 398 399 struct crashtype_category heap_crashtypes = { 400 .crashtypes = crashtypes, 401 .len = ARRAY_SIZE(crashtypes), 402 }; 403