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 / 8UL) 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 (buf[..] passed as arg) 45 * - function may have external effects (memzero_explicit()) 46 * - no tail recursion possible 47 */ 48 static int noinline recursive_loop(int remaining) 49 { 50 volatile char buf[REC_STACK_SIZE]; 51 volatile int ret; 52 53 memset((void *)buf, remaining & 0xFF, sizeof(buf)); 54 if (!remaining) 55 ret = 0; 56 else 57 ret = recursive_loop((int)buf[remaining % sizeof(buf)] - 1); 58 memzero_explicit((void *)buf, sizeof(buf)); 59 return ret; 60 } 61 62 /* If the depth is negative, use the default, otherwise keep parameter. */ 63 void __init lkdtm_bugs_init(int *recur_param) 64 { 65 if (*recur_param < 0) 66 *recur_param = recur_count; 67 else 68 recur_count = *recur_param; 69 } 70 71 static void lkdtm_PANIC(void) 72 { 73 panic("dumptest"); 74 } 75 76 static void lkdtm_BUG(void) 77 { 78 BUG(); 79 } 80 81 static int warn_counter; 82 83 static void lkdtm_WARNING(void) 84 { 85 WARN_ON(++warn_counter); 86 } 87 88 static void lkdtm_WARNING_MESSAGE(void) 89 { 90 WARN(1, "Warning message trigger count: %d\n", ++warn_counter); 91 } 92 93 static void lkdtm_EXCEPTION(void) 94 { 95 *((volatile int *) 0) = 0; 96 } 97 98 static void lkdtm_LOOP(void) 99 { 100 for (;;) 101 ; 102 } 103 104 static void lkdtm_EXHAUST_STACK(void) 105 { 106 pr_info("Calling function with %lu frame size to depth %d ...\n", 107 REC_STACK_SIZE, recur_count); 108 recursive_loop(recur_count); 109 pr_info("FAIL: survived without exhausting stack?!\n"); 110 } 111 112 static noinline void __lkdtm_CORRUPT_STACK(void *stack) 113 { 114 memset(stack, '\xff', 64); 115 } 116 117 /* This should trip the stack canary, not corrupt the return address. */ 118 static noinline void lkdtm_CORRUPT_STACK(void) 119 { 120 /* Use default char array length that triggers stack protection. */ 121 char data[8] __aligned(sizeof(void *)); 122 123 pr_info("Corrupting stack containing char array ...\n"); 124 __lkdtm_CORRUPT_STACK((void *)&data); 125 } 126 127 /* Same as above but will only get a canary with -fstack-protector-strong */ 128 static noinline void lkdtm_CORRUPT_STACK_STRONG(void) 129 { 130 union { 131 unsigned short shorts[4]; 132 unsigned long *ptr; 133 } data __aligned(sizeof(void *)); 134 135 pr_info("Corrupting stack containing union ...\n"); 136 __lkdtm_CORRUPT_STACK((void *)&data); 137 } 138 139 static pid_t stack_pid; 140 static unsigned long stack_addr; 141 142 static void lkdtm_REPORT_STACK(void) 143 { 144 volatile uintptr_t magic; 145 pid_t pid = task_pid_nr(current); 146 147 if (pid != stack_pid) { 148 pr_info("Starting stack offset tracking for pid %d\n", pid); 149 stack_pid = pid; 150 stack_addr = (uintptr_t)&magic; 151 } 152 153 pr_info("Stack offset: %d\n", (int)(stack_addr - (uintptr_t)&magic)); 154 } 155 156 static pid_t stack_canary_pid; 157 static unsigned long stack_canary; 158 static unsigned long stack_canary_offset; 159 160 static noinline void __lkdtm_REPORT_STACK_CANARY(void *stack) 161 { 162 int i = 0; 163 pid_t pid = task_pid_nr(current); 164 unsigned long *canary = (unsigned long *)stack; 165 unsigned long current_offset = 0, init_offset = 0; 166 167 /* Do our best to find the canary in a 16 word window ... */ 168 for (i = 1; i < 16; i++) { 169 canary = (unsigned long *)stack + i; 170 #ifdef CONFIG_STACKPROTECTOR 171 if (*canary == current->stack_canary) 172 current_offset = i; 173 if (*canary == init_task.stack_canary) 174 init_offset = i; 175 #endif 176 } 177 178 if (current_offset == 0) { 179 /* 180 * If the canary doesn't match what's in the task_struct, 181 * we're either using a global canary or the stack frame 182 * layout changed. 183 */ 184 if (init_offset != 0) { 185 pr_err("FAIL: global stack canary found at offset %ld (canary for pid %d matches init_task's)!\n", 186 init_offset, pid); 187 } else { 188 pr_warn("FAIL: did not correctly locate stack canary :(\n"); 189 pr_expected_config(CONFIG_STACKPROTECTOR); 190 } 191 192 return; 193 } else if (init_offset != 0) { 194 pr_warn("WARNING: found both current and init_task canaries nearby?!\n"); 195 } 196 197 canary = (unsigned long *)stack + current_offset; 198 if (stack_canary_pid == 0) { 199 stack_canary = *canary; 200 stack_canary_pid = pid; 201 stack_canary_offset = current_offset; 202 pr_info("Recorded stack canary for pid %d at offset %ld\n", 203 stack_canary_pid, stack_canary_offset); 204 } else if (pid == stack_canary_pid) { 205 pr_warn("ERROR: saw pid %d again -- please use a new pid\n", pid); 206 } else { 207 if (current_offset != stack_canary_offset) { 208 pr_warn("ERROR: canary offset changed from %ld to %ld!?\n", 209 stack_canary_offset, current_offset); 210 return; 211 } 212 213 if (*canary == stack_canary) { 214 pr_warn("FAIL: canary identical for pid %d and pid %d at offset %ld!\n", 215 stack_canary_pid, pid, current_offset); 216 } else { 217 pr_info("ok: stack canaries differ between pid %d and pid %d at offset %ld.\n", 218 stack_canary_pid, pid, current_offset); 219 /* Reset the test. */ 220 stack_canary_pid = 0; 221 } 222 } 223 } 224 225 static void lkdtm_REPORT_STACK_CANARY(void) 226 { 227 /* Use default char array length that triggers stack protection. */ 228 char data[8] __aligned(sizeof(void *)) = { }; 229 230 __lkdtm_REPORT_STACK_CANARY((void *)&data); 231 } 232 233 static void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void) 234 { 235 static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5}; 236 u32 *p; 237 u32 val = 0x12345678; 238 239 p = (u32 *)(data + 1); 240 if (*p == 0) 241 val = 0x87654321; 242 *p = val; 243 244 if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) 245 pr_err("XFAIL: arch has CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS\n"); 246 } 247 248 static void lkdtm_SOFTLOCKUP(void) 249 { 250 preempt_disable(); 251 for (;;) 252 cpu_relax(); 253 } 254 255 static void lkdtm_HARDLOCKUP(void) 256 { 257 local_irq_disable(); 258 for (;;) 259 cpu_relax(); 260 } 261 262 static void lkdtm_SPINLOCKUP(void) 263 { 264 /* Must be called twice to trigger. */ 265 spin_lock(&lock_me_up); 266 /* Let sparse know we intended to exit holding the lock. */ 267 __release(&lock_me_up); 268 } 269 270 static void lkdtm_HUNG_TASK(void) 271 { 272 set_current_state(TASK_UNINTERRUPTIBLE); 273 schedule(); 274 } 275 276 volatile unsigned int huge = INT_MAX - 2; 277 volatile unsigned int ignored; 278 279 static void lkdtm_OVERFLOW_SIGNED(void) 280 { 281 int value; 282 283 value = huge; 284 pr_info("Normal signed addition ...\n"); 285 value += 1; 286 ignored = value; 287 288 pr_info("Overflowing signed addition ...\n"); 289 value += 4; 290 ignored = value; 291 } 292 293 294 static void lkdtm_OVERFLOW_UNSIGNED(void) 295 { 296 unsigned int value; 297 298 value = huge; 299 pr_info("Normal unsigned addition ...\n"); 300 value += 1; 301 ignored = value; 302 303 pr_info("Overflowing unsigned addition ...\n"); 304 value += 4; 305 ignored = value; 306 } 307 308 /* Intentionally using old-style flex array definition of 1 byte. */ 309 struct array_bounds_flex_array { 310 int one; 311 int two; 312 char data[]; 313 }; 314 315 struct array_bounds { 316 int one; 317 int two; 318 char data[8]; 319 int three; 320 }; 321 322 static void lkdtm_ARRAY_BOUNDS(void) 323 { 324 struct array_bounds_flex_array *not_checked; 325 struct array_bounds *checked; 326 volatile int i; 327 328 not_checked = kmalloc(sizeof(*not_checked) * 2, GFP_KERNEL); 329 checked = kmalloc(sizeof(*checked) * 2, GFP_KERNEL); 330 if (!not_checked || !checked) { 331 kfree(not_checked); 332 kfree(checked); 333 return; 334 } 335 336 pr_info("Array access within bounds ...\n"); 337 /* For both, touch all bytes in the actual member size. */ 338 for (i = 0; i < sizeof(checked->data); i++) 339 checked->data[i] = 'A'; 340 /* 341 * For the uninstrumented flex array member, also touch 1 byte 342 * beyond to verify it is correctly uninstrumented. 343 */ 344 for (i = 0; i < 2; i++) 345 not_checked->data[i] = 'A'; 346 347 pr_info("Array access beyond bounds ...\n"); 348 for (i = 0; i < sizeof(checked->data) + 1; i++) 349 checked->data[i] = 'B'; 350 351 kfree(not_checked); 352 kfree(checked); 353 pr_err("FAIL: survived array bounds overflow!\n"); 354 if (IS_ENABLED(CONFIG_UBSAN_BOUNDS)) 355 pr_expected_config(CONFIG_UBSAN_TRAP); 356 else 357 pr_expected_config(CONFIG_UBSAN_BOUNDS); 358 } 359 360 static void lkdtm_CORRUPT_LIST_ADD(void) 361 { 362 /* 363 * Initially, an empty list via LIST_HEAD: 364 * test_head.next = &test_head 365 * test_head.prev = &test_head 366 */ 367 LIST_HEAD(test_head); 368 struct lkdtm_list good, bad; 369 void *target[2] = { }; 370 void *redirection = ⌖ 371 372 pr_info("attempting good list addition\n"); 373 374 /* 375 * Adding to the list performs these actions: 376 * test_head.next->prev = &good.node 377 * good.node.next = test_head.next 378 * good.node.prev = test_head 379 * test_head.next = good.node 380 */ 381 list_add(&good.node, &test_head); 382 383 pr_info("attempting corrupted list addition\n"); 384 /* 385 * In simulating this "write what where" primitive, the "what" is 386 * the address of &bad.node, and the "where" is the address held 387 * by "redirection". 388 */ 389 test_head.next = redirection; 390 list_add(&bad.node, &test_head); 391 392 if (target[0] == NULL && target[1] == NULL) 393 pr_err("Overwrite did not happen, but no BUG?!\n"); 394 else { 395 pr_err("list_add() corruption not detected!\n"); 396 pr_expected_config(CONFIG_DEBUG_LIST); 397 } 398 } 399 400 static void lkdtm_CORRUPT_LIST_DEL(void) 401 { 402 LIST_HEAD(test_head); 403 struct lkdtm_list item; 404 void *target[2] = { }; 405 void *redirection = ⌖ 406 407 list_add(&item.node, &test_head); 408 409 pr_info("attempting good list removal\n"); 410 list_del(&item.node); 411 412 pr_info("attempting corrupted list removal\n"); 413 list_add(&item.node, &test_head); 414 415 /* As with the list_add() test above, this corrupts "next". */ 416 item.node.next = redirection; 417 list_del(&item.node); 418 419 if (target[0] == NULL && target[1] == NULL) 420 pr_err("Overwrite did not happen, but no BUG?!\n"); 421 else { 422 pr_err("list_del() corruption not detected!\n"); 423 pr_expected_config(CONFIG_DEBUG_LIST); 424 } 425 } 426 427 /* Test that VMAP_STACK is actually allocating with a leading guard page */ 428 static void lkdtm_STACK_GUARD_PAGE_LEADING(void) 429 { 430 const unsigned char *stack = task_stack_page(current); 431 const unsigned char *ptr = stack - 1; 432 volatile unsigned char byte; 433 434 pr_info("attempting bad read from page below current stack\n"); 435 436 byte = *ptr; 437 438 pr_err("FAIL: accessed page before stack! (byte: %x)\n", byte); 439 } 440 441 /* Test that VMAP_STACK is actually allocating with a trailing guard page */ 442 static void lkdtm_STACK_GUARD_PAGE_TRAILING(void) 443 { 444 const unsigned char *stack = task_stack_page(current); 445 const unsigned char *ptr = stack + THREAD_SIZE; 446 volatile unsigned char byte; 447 448 pr_info("attempting bad read from page above current stack\n"); 449 450 byte = *ptr; 451 452 pr_err("FAIL: accessed page after stack! (byte: %x)\n", byte); 453 } 454 455 static void lkdtm_UNSET_SMEP(void) 456 { 457 #if IS_ENABLED(CONFIG_X86_64) && !IS_ENABLED(CONFIG_UML) 458 #define MOV_CR4_DEPTH 64 459 void (*direct_write_cr4)(unsigned long val); 460 unsigned char *insn; 461 unsigned long cr4; 462 int i; 463 464 cr4 = native_read_cr4(); 465 466 if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) { 467 pr_err("FAIL: SMEP not in use\n"); 468 return; 469 } 470 cr4 &= ~(X86_CR4_SMEP); 471 472 pr_info("trying to clear SMEP normally\n"); 473 native_write_cr4(cr4); 474 if (cr4 == native_read_cr4()) { 475 pr_err("FAIL: pinning SMEP failed!\n"); 476 cr4 |= X86_CR4_SMEP; 477 pr_info("restoring SMEP\n"); 478 native_write_cr4(cr4); 479 return; 480 } 481 pr_info("ok: SMEP did not get cleared\n"); 482 483 /* 484 * To test the post-write pinning verification we need to call 485 * directly into the middle of native_write_cr4() where the 486 * cr4 write happens, skipping any pinning. This searches for 487 * the cr4 writing instruction. 488 */ 489 insn = (unsigned char *)native_write_cr4; 490 OPTIMIZER_HIDE_VAR(insn); 491 for (i = 0; i < MOV_CR4_DEPTH; i++) { 492 /* mov %rdi, %cr4 */ 493 if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7) 494 break; 495 /* mov %rdi,%rax; mov %rax, %cr4 */ 496 if (insn[i] == 0x48 && insn[i+1] == 0x89 && 497 insn[i+2] == 0xf8 && insn[i+3] == 0x0f && 498 insn[i+4] == 0x22 && insn[i+5] == 0xe0) 499 break; 500 } 501 if (i >= MOV_CR4_DEPTH) { 502 pr_info("ok: cannot locate cr4 writing call gadget\n"); 503 return; 504 } 505 direct_write_cr4 = (void *)(insn + i); 506 507 pr_info("trying to clear SMEP with call gadget\n"); 508 direct_write_cr4(cr4); 509 if (native_read_cr4() & X86_CR4_SMEP) { 510 pr_info("ok: SMEP removal was reverted\n"); 511 } else { 512 pr_err("FAIL: cleared SMEP not detected!\n"); 513 cr4 |= X86_CR4_SMEP; 514 pr_info("restoring SMEP\n"); 515 native_write_cr4(cr4); 516 } 517 #else 518 pr_err("XFAIL: this test is x86_64-only\n"); 519 #endif 520 } 521 522 static void lkdtm_DOUBLE_FAULT(void) 523 { 524 #if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML) 525 /* 526 * Trigger #DF by setting the stack limit to zero. This clobbers 527 * a GDT TLS slot, which is okay because the current task will die 528 * anyway due to the double fault. 529 */ 530 struct desc_struct d = { 531 .type = 3, /* expand-up, writable, accessed data */ 532 .p = 1, /* present */ 533 .d = 1, /* 32-bit */ 534 .g = 0, /* limit in bytes */ 535 .s = 1, /* not system */ 536 }; 537 538 local_irq_disable(); 539 write_gdt_entry(get_cpu_gdt_rw(smp_processor_id()), 540 GDT_ENTRY_TLS_MIN, &d, DESCTYPE_S); 541 542 /* 543 * Put our zero-limit segment in SS and then trigger a fault. The 544 * 4-byte access to (%esp) will fault with #SS, and the attempt to 545 * deliver the fault will recursively cause #SS and result in #DF. 546 * This whole process happens while NMIs and MCEs are blocked by the 547 * MOV SS window. This is nice because an NMI with an invalid SS 548 * would also double-fault, resulting in the NMI or MCE being lost. 549 */ 550 asm volatile ("movw %0, %%ss; addl $0, (%%esp)" :: 551 "r" ((unsigned short)(GDT_ENTRY_TLS_MIN << 3))); 552 553 pr_err("FAIL: tried to double fault but didn't die\n"); 554 #else 555 pr_err("XFAIL: this test is ia32-only\n"); 556 #endif 557 } 558 559 #ifdef CONFIG_ARM64 560 static noinline void change_pac_parameters(void) 561 { 562 if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) { 563 /* Reset the keys of current task */ 564 ptrauth_thread_init_kernel(current); 565 ptrauth_thread_switch_kernel(current); 566 } 567 } 568 #endif 569 570 static noinline void lkdtm_CORRUPT_PAC(void) 571 { 572 #ifdef CONFIG_ARM64 573 #define CORRUPT_PAC_ITERATE 10 574 int i; 575 576 if (!IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) 577 pr_err("FAIL: kernel not built with CONFIG_ARM64_PTR_AUTH_KERNEL\n"); 578 579 if (!system_supports_address_auth()) { 580 pr_err("FAIL: CPU lacks pointer authentication feature\n"); 581 return; 582 } 583 584 pr_info("changing PAC parameters to force function return failure...\n"); 585 /* 586 * PAC is a hash value computed from input keys, return address and 587 * stack pointer. As pac has fewer bits so there is a chance of 588 * collision, so iterate few times to reduce the collision probability. 589 */ 590 for (i = 0; i < CORRUPT_PAC_ITERATE; i++) 591 change_pac_parameters(); 592 593 pr_err("FAIL: survived PAC changes! Kernel may be unstable from here\n"); 594 #else 595 pr_err("XFAIL: this test is arm64-only\n"); 596 #endif 597 } 598 599 static struct crashtype crashtypes[] = { 600 CRASHTYPE(PANIC), 601 CRASHTYPE(BUG), 602 CRASHTYPE(WARNING), 603 CRASHTYPE(WARNING_MESSAGE), 604 CRASHTYPE(EXCEPTION), 605 CRASHTYPE(LOOP), 606 CRASHTYPE(EXHAUST_STACK), 607 CRASHTYPE(CORRUPT_STACK), 608 CRASHTYPE(CORRUPT_STACK_STRONG), 609 CRASHTYPE(REPORT_STACK), 610 CRASHTYPE(REPORT_STACK_CANARY), 611 CRASHTYPE(UNALIGNED_LOAD_STORE_WRITE), 612 CRASHTYPE(SOFTLOCKUP), 613 CRASHTYPE(HARDLOCKUP), 614 CRASHTYPE(SPINLOCKUP), 615 CRASHTYPE(HUNG_TASK), 616 CRASHTYPE(OVERFLOW_SIGNED), 617 CRASHTYPE(OVERFLOW_UNSIGNED), 618 CRASHTYPE(ARRAY_BOUNDS), 619 CRASHTYPE(CORRUPT_LIST_ADD), 620 CRASHTYPE(CORRUPT_LIST_DEL), 621 CRASHTYPE(STACK_GUARD_PAGE_LEADING), 622 CRASHTYPE(STACK_GUARD_PAGE_TRAILING), 623 CRASHTYPE(UNSET_SMEP), 624 CRASHTYPE(DOUBLE_FAULT), 625 CRASHTYPE(CORRUPT_PAC), 626 }; 627 628 struct crashtype_category bugs_crashtypes = { 629 .crashtypes = crashtypes, 630 .len = ARRAY_SIZE(crashtypes), 631 }; 632