drivers/misc/lkdtm/heap.c

   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 slab_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 };