1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * This is for all the tests related to logic bugs (e.g. bad dereferences, 4 * bad alignment, bad loops, bad locking, bad scheduling, deep stacks, and 5 * lockups) along with other things that don't fit well into existing LKDTM 6 * test source files. 7 */ 8 #include "lkdtm.h" 9 #include <linux/list.h> 10 #include <linux/sched.h> 11 #include <linux/sched/signal.h> 12 #include <linux/sched/task_stack.h> 13 #include <linux/uaccess.h> 14 #include <linux/slab.h> 15 16 #if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML) 17 #include <asm/desc.h> 18 #endif 19 20 struct lkdtm_list { 21 struct list_head node; 22 }; 23 24 /* 25 * Make sure our attempts to over run the kernel stack doesn't trigger 26 * a compiler warning when CONFIG_FRAME_WARN is set. Then make sure we 27 * recurse past the end of THREAD_SIZE by default. 28 */ 29 #if defined(CONFIG_FRAME_WARN) && (CONFIG_FRAME_WARN > 0) 30 #define REC_STACK_SIZE (_AC(CONFIG_FRAME_WARN, UL) / 2) 31 #else 32 #define REC_STACK_SIZE (THREAD_SIZE / 8) 33 #endif 34 #define REC_NUM_DEFAULT ((THREAD_SIZE / REC_STACK_SIZE) * 2) 35 36 static int recur_count = REC_NUM_DEFAULT; 37 38 static DEFINE_SPINLOCK(lock_me_up); 39 40 /* 41 * Make sure compiler does not optimize this function or stack frame away: 42 * - function marked noinline 43 * - stack variables are marked volatile 44 * - stack variables are written (memset()) and read (pr_info()) 45 * - function has external effects (pr_info()) 46 * */ 47 static int noinline recursive_loop(int remaining) 48 { 49 volatile char buf[REC_STACK_SIZE]; 50 51 memset((void *)buf, remaining & 0xFF, sizeof(buf)); 52 pr_info("loop %d/%d ...\n", (int)buf[remaining % sizeof(buf)], 53 recur_count); 54 if (!remaining) 55 return 0; 56 else 57 return recursive_loop(remaining - 1); 58 } 59 60 /* If the depth is negative, use the default, otherwise keep parameter. */ 61 void __init lkdtm_bugs_init(int *recur_param) 62 { 63 if (*recur_param < 0) 64 *recur_param = recur_count; 65 else 66 recur_count = *recur_param; 67 } 68 69 void lkdtm_PANIC(void) 70 { 71 panic("dumptest"); 72 } 73 74 void lkdtm_BUG(void) 75 { 76 BUG(); 77 } 78 79 static int warn_counter; 80 81 void lkdtm_WARNING(void) 82 { 83 WARN_ON(++warn_counter); 84 } 85 86 void lkdtm_WARNING_MESSAGE(void) 87 { 88 WARN(1, "Warning message trigger count: %d\n", ++warn_counter); 89 } 90 91 void lkdtm_EXCEPTION(void) 92 { 93 *((volatile int *) 0) = 0; 94 } 95 96 void lkdtm_LOOP(void) 97 { 98 for (;;) 99 ; 100 } 101 102 void lkdtm_EXHAUST_STACK(void) 103 { 104 pr_info("Calling function with %lu frame size to depth %d ...\n", 105 REC_STACK_SIZE, recur_count); 106 recursive_loop(recur_count); 107 pr_info("FAIL: survived without exhausting stack?!\n"); 108 } 109 110 static noinline void __lkdtm_CORRUPT_STACK(void *stack) 111 { 112 memset(stack, '\xff', 64); 113 } 114 115 /* This should trip the stack canary, not corrupt the return address. */ 116 noinline void lkdtm_CORRUPT_STACK(void) 117 { 118 /* Use default char array length that triggers stack protection. */ 119 char data[8] __aligned(sizeof(void *)); 120 121 pr_info("Corrupting stack containing char array ...\n"); 122 __lkdtm_CORRUPT_STACK((void *)&data); 123 } 124 125 /* Same as above but will only get a canary with -fstack-protector-strong */ 126 noinline void lkdtm_CORRUPT_STACK_STRONG(void) 127 { 128 union { 129 unsigned short shorts[4]; 130 unsigned long *ptr; 131 } data __aligned(sizeof(void *)); 132 133 pr_info("Corrupting stack containing union ...\n"); 134 __lkdtm_CORRUPT_STACK((void *)&data); 135 } 136 137 static pid_t stack_pid; 138 static unsigned long stack_addr; 139 140 void lkdtm_REPORT_STACK(void) 141 { 142 volatile uintptr_t magic; 143 pid_t pid = task_pid_nr(current); 144 145 if (pid != stack_pid) { 146 pr_info("Starting stack offset tracking for pid %d\n", pid); 147 stack_pid = pid; 148 stack_addr = (uintptr_t)&magic; 149 } 150 151 pr_info("Stack offset: %d\n", (int)(stack_addr - (uintptr_t)&magic)); 152 } 153 154 static pid_t stack_canary_pid; 155 static unsigned long stack_canary; 156 static unsigned long stack_canary_offset; 157 158 static noinline void __lkdtm_REPORT_STACK_CANARY(void *stack) 159 { 160 int i = 0; 161 pid_t pid = task_pid_nr(current); 162 unsigned long *canary = (unsigned long *)stack; 163 unsigned long current_offset = 0, init_offset = 0; 164 165 /* Do our best to find the canary in a 16 word window ... */ 166 for (i = 1; i < 16; i++) { 167 canary = (unsigned long *)stack + i; 168 #ifdef CONFIG_STACKPROTECTOR 169 if (*canary == current->stack_canary) 170 current_offset = i; 171 if (*canary == init_task.stack_canary) 172 init_offset = i; 173 #endif 174 } 175 176 if (current_offset == 0) { 177 /* 178 * If the canary doesn't match what's in the task_struct, 179 * we're either using a global canary or the stack frame 180 * layout changed. 181 */ 182 if (init_offset != 0) { 183 pr_err("FAIL: global stack canary found at offset %ld (canary for pid %d matches init_task's)!\n", 184 init_offset, pid); 185 } else { 186 pr_warn("FAIL: did not correctly locate stack canary :(\n"); 187 pr_expected_config(CONFIG_STACKPROTECTOR); 188 } 189 190 return; 191 } else if (init_offset != 0) { 192 pr_warn("WARNING: found both current and init_task canaries nearby?!\n"); 193 } 194 195 canary = (unsigned long *)stack + current_offset; 196 if (stack_canary_pid == 0) { 197 stack_canary = *canary; 198 stack_canary_pid = pid; 199 stack_canary_offset = current_offset; 200 pr_info("Recorded stack canary for pid %d at offset %ld\n", 201 stack_canary_pid, stack_canary_offset); 202 } else if (pid == stack_canary_pid) { 203 pr_warn("ERROR: saw pid %d again -- please use a new pid\n", pid); 204 } else { 205 if (current_offset != stack_canary_offset) { 206 pr_warn("ERROR: canary offset changed from %ld to %ld!?\n", 207 stack_canary_offset, current_offset); 208 return; 209 } 210 211 if (*canary == stack_canary) { 212 pr_warn("FAIL: canary identical for pid %d and pid %d at offset %ld!\n", 213 stack_canary_pid, pid, current_offset); 214 } else { 215 pr_info("ok: stack canaries differ between pid %d and pid %d at offset %ld.\n", 216 stack_canary_pid, pid, current_offset); 217 /* Reset the test. */ 218 stack_canary_pid = 0; 219 } 220 } 221 } 222 223 void lkdtm_REPORT_STACK_CANARY(void) 224 { 225 /* Use default char array length that triggers stack protection. */ 226 char data[8] __aligned(sizeof(void *)) = { }; 227 228 __lkdtm_REPORT_STACK_CANARY((void *)&data); 229 } 230 231 void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void) 232 { 233 static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5}; 234 u32 *p; 235 u32 val = 0x12345678; 236 237 p = (u32 *)(data + 1); 238 if (*p == 0) 239 val = 0x87654321; 240 *p = val; 241 242 if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) 243 pr_err("XFAIL: arch has CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS\n"); 244 } 245 246 void lkdtm_SOFTLOCKUP(void) 247 { 248 preempt_disable(); 249 for (;;) 250 cpu_relax(); 251 } 252 253 void lkdtm_HARDLOCKUP(void) 254 { 255 local_irq_disable(); 256 for (;;) 257 cpu_relax(); 258 } 259 260 void lkdtm_SPINLOCKUP(void) 261 { 262 /* Must be called twice to trigger. */ 263 spin_lock(&lock_me_up); 264 /* Let sparse know we intended to exit holding the lock. */ 265 __release(&lock_me_up); 266 } 267 268 void lkdtm_HUNG_TASK(void) 269 { 270 set_current_state(TASK_UNINTERRUPTIBLE); 271 schedule(); 272 } 273 274 volatile unsigned int huge = INT_MAX - 2; 275 volatile unsigned int ignored; 276 277 void lkdtm_OVERFLOW_SIGNED(void) 278 { 279 int value; 280 281 value = huge; 282 pr_info("Normal signed addition ...\n"); 283 value += 1; 284 ignored = value; 285 286 pr_info("Overflowing signed addition ...\n"); 287 value += 4; 288 ignored = value; 289 } 290 291 292 void lkdtm_OVERFLOW_UNSIGNED(void) 293 { 294 unsigned int value; 295 296 value = huge; 297 pr_info("Normal unsigned addition ...\n"); 298 value += 1; 299 ignored = value; 300 301 pr_info("Overflowing unsigned addition ...\n"); 302 value += 4; 303 ignored = value; 304 } 305 306 /* Intentionally using old-style flex array definition of 1 byte. */ 307 struct array_bounds_flex_array { 308 int one; 309 int two; 310 char data[1]; 311 }; 312 313 struct array_bounds { 314 int one; 315 int two; 316 char data[8]; 317 int three; 318 }; 319 320 void lkdtm_ARRAY_BOUNDS(void) 321 { 322 struct array_bounds_flex_array *not_checked; 323 struct array_bounds *checked; 324 volatile int i; 325 326 not_checked = kmalloc(sizeof(*not_checked) * 2, GFP_KERNEL); 327 checked = kmalloc(sizeof(*checked) * 2, GFP_KERNEL); 328 329 pr_info("Array access within bounds ...\n"); 330 /* For both, touch all bytes in the actual member size. */ 331 for (i = 0; i < sizeof(checked->data); i++) 332 checked->data[i] = 'A'; 333 /* 334 * For the uninstrumented flex array member, also touch 1 byte 335 * beyond to verify it is correctly uninstrumented. 336 */ 337 for (i = 0; i < sizeof(not_checked->data) + 1; i++) 338 not_checked->data[i] = 'A'; 339 340 pr_info("Array access beyond bounds ...\n"); 341 for (i = 0; i < sizeof(checked->data) + 1; i++) 342 checked->data[i] = 'B'; 343 344 kfree(not_checked); 345 kfree(checked); 346 pr_err("FAIL: survived array bounds overflow!\n"); 347 pr_expected_config(CONFIG_UBSAN_BOUNDS); 348 } 349 350 void lkdtm_CORRUPT_LIST_ADD(void) 351 { 352 /* 353 * Initially, an empty list via LIST_HEAD: 354 * test_head.next = &test_head 355 * test_head.prev = &test_head 356 */ 357 LIST_HEAD(test_head); 358 struct lkdtm_list good, bad; 359 void *target[2] = { }; 360 void *redirection = ⌖ 361 362 pr_info("attempting good list addition\n"); 363 364 /* 365 * Adding to the list performs these actions: 366 * test_head.next->prev = &good.node 367 * good.node.next = test_head.next 368 * good.node.prev = test_head 369 * test_head.next = good.node 370 */ 371 list_add(&good.node, &test_head); 372 373 pr_info("attempting corrupted list addition\n"); 374 /* 375 * In simulating this "write what where" primitive, the "what" is 376 * the address of &bad.node, and the "where" is the address held 377 * by "redirection". 378 */ 379 test_head.next = redirection; 380 list_add(&bad.node, &test_head); 381 382 if (target[0] == NULL && target[1] == NULL) 383 pr_err("Overwrite did not happen, but no BUG?!\n"); 384 else { 385 pr_err("list_add() corruption not detected!\n"); 386 pr_expected_config(CONFIG_DEBUG_LIST); 387 } 388 } 389 390 void lkdtm_CORRUPT_LIST_DEL(void) 391 { 392 LIST_HEAD(test_head); 393 struct lkdtm_list item; 394 void *target[2] = { }; 395 void *redirection = ⌖ 396 397 list_add(&item.node, &test_head); 398 399 pr_info("attempting good list removal\n"); 400 list_del(&item.node); 401 402 pr_info("attempting corrupted list removal\n"); 403 list_add(&item.node, &test_head); 404 405 /* As with the list_add() test above, this corrupts "next". */ 406 item.node.next = redirection; 407 list_del(&item.node); 408 409 if (target[0] == NULL && target[1] == NULL) 410 pr_err("Overwrite did not happen, but no BUG?!\n"); 411 else { 412 pr_err("list_del() corruption not detected!\n"); 413 pr_expected_config(CONFIG_DEBUG_LIST); 414 } 415 } 416 417 /* Test that VMAP_STACK is actually allocating with a leading guard page */ 418 void lkdtm_STACK_GUARD_PAGE_LEADING(void) 419 { 420 const unsigned char *stack = task_stack_page(current); 421 const unsigned char *ptr = stack - 1; 422 volatile unsigned char byte; 423 424 pr_info("attempting bad read from page below current stack\n"); 425 426 byte = *ptr; 427 428 pr_err("FAIL: accessed page before stack! (byte: %x)\n", byte); 429 } 430 431 /* Test that VMAP_STACK is actually allocating with a trailing guard page */ 432 void lkdtm_STACK_GUARD_PAGE_TRAILING(void) 433 { 434 const unsigned char *stack = task_stack_page(current); 435 const unsigned char *ptr = stack + THREAD_SIZE; 436 volatile unsigned char byte; 437 438 pr_info("attempting bad read from page above current stack\n"); 439 440 byte = *ptr; 441 442 pr_err("FAIL: accessed page after stack! (byte: %x)\n", byte); 443 } 444 445 void lkdtm_UNSET_SMEP(void) 446 { 447 #if IS_ENABLED(CONFIG_X86_64) && !IS_ENABLED(CONFIG_UML) 448 #define MOV_CR4_DEPTH 64 449 void (*direct_write_cr4)(unsigned long val); 450 unsigned char *insn; 451 unsigned long cr4; 452 int i; 453 454 cr4 = native_read_cr4(); 455 456 if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) { 457 pr_err("FAIL: SMEP not in use\n"); 458 return; 459 } 460 cr4 &= ~(X86_CR4_SMEP); 461 462 pr_info("trying to clear SMEP normally\n"); 463 native_write_cr4(cr4); 464 if (cr4 == native_read_cr4()) { 465 pr_err("FAIL: pinning SMEP failed!\n"); 466 cr4 |= X86_CR4_SMEP; 467 pr_info("restoring SMEP\n"); 468 native_write_cr4(cr4); 469 return; 470 } 471 pr_info("ok: SMEP did not get cleared\n"); 472 473 /* 474 * To test the post-write pinning verification we need to call 475 * directly into the middle of native_write_cr4() where the 476 * cr4 write happens, skipping any pinning. This searches for 477 * the cr4 writing instruction. 478 */ 479 insn = (unsigned char *)native_write_cr4; 480 for (i = 0; i < MOV_CR4_DEPTH; i++) { 481 /* mov %rdi, %cr4 */ 482 if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7) 483 break; 484 /* mov %rdi,%rax; mov %rax, %cr4 */ 485 if (insn[i] == 0x48 && insn[i+1] == 0x89 && 486 insn[i+2] == 0xf8 && insn[i+3] == 0x0f && 487 insn[i+4] == 0x22 && insn[i+5] == 0xe0) 488 break; 489 } 490 if (i >= MOV_CR4_DEPTH) { 491 pr_info("ok: cannot locate cr4 writing call gadget\n"); 492 return; 493 } 494 direct_write_cr4 = (void *)(insn + i); 495 496 pr_info("trying to clear SMEP with call gadget\n"); 497 direct_write_cr4(cr4); 498 if (native_read_cr4() & X86_CR4_SMEP) { 499 pr_info("ok: SMEP removal was reverted\n"); 500 } else { 501 pr_err("FAIL: cleared SMEP not detected!\n"); 502 cr4 |= X86_CR4_SMEP; 503 pr_info("restoring SMEP\n"); 504 native_write_cr4(cr4); 505 } 506 #else 507 pr_err("XFAIL: this test is x86_64-only\n"); 508 #endif 509 } 510 511 void lkdtm_DOUBLE_FAULT(void) 512 { 513 #if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML) 514 /* 515 * Trigger #DF by setting the stack limit to zero. This clobbers 516 * a GDT TLS slot, which is okay because the current task will die 517 * anyway due to the double fault. 518 */ 519 struct desc_struct d = { 520 .type = 3, /* expand-up, writable, accessed data */ 521 .p = 1, /* present */ 522 .d = 1, /* 32-bit */ 523 .g = 0, /* limit in bytes */ 524 .s = 1, /* not system */ 525 }; 526 527 local_irq_disable(); 528 write_gdt_entry(get_cpu_gdt_rw(smp_processor_id()), 529 GDT_ENTRY_TLS_MIN, &d, DESCTYPE_S); 530 531 /* 532 * Put our zero-limit segment in SS and then trigger a fault. The 533 * 4-byte access to (%esp) will fault with #SS, and the attempt to 534 * deliver the fault will recursively cause #SS and result in #DF. 535 * This whole process happens while NMIs and MCEs are blocked by the 536 * MOV SS window. This is nice because an NMI with an invalid SS 537 * would also double-fault, resulting in the NMI or MCE being lost. 538 */ 539 asm volatile ("movw %0, %%ss; addl $0, (%%esp)" :: 540 "r" ((unsigned short)(GDT_ENTRY_TLS_MIN << 3))); 541 542 pr_err("FAIL: tried to double fault but didn't die\n"); 543 #else 544 pr_err("XFAIL: this test is ia32-only\n"); 545 #endif 546 } 547 548 #ifdef CONFIG_ARM64 549 static noinline void change_pac_parameters(void) 550 { 551 if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) { 552 /* Reset the keys of current task */ 553 ptrauth_thread_init_kernel(current); 554 ptrauth_thread_switch_kernel(current); 555 } 556 } 557 #endif 558 559 noinline void lkdtm_CORRUPT_PAC(void) 560 { 561 #ifdef CONFIG_ARM64 562 #define CORRUPT_PAC_ITERATE 10 563 int i; 564 565 if (!IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) 566 pr_err("FAIL: kernel not built with CONFIG_ARM64_PTR_AUTH_KERNEL\n"); 567 568 if (!system_supports_address_auth()) { 569 pr_err("FAIL: CPU lacks pointer authentication feature\n"); 570 return; 571 } 572 573 pr_info("changing PAC parameters to force function return failure...\n"); 574 /* 575 * PAC is a hash value computed from input keys, return address and 576 * stack pointer. As pac has fewer bits so there is a chance of 577 * collision, so iterate few times to reduce the collision probability. 578 */ 579 for (i = 0; i < CORRUPT_PAC_ITERATE; i++) 580 change_pac_parameters(); 581 582 pr_err("FAIL: survived PAC changes! Kernel may be unstable from here\n"); 583 #else 584 pr_err("XFAIL: this test is arm64-only\n"); 585 #endif 586 } 587