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 (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 void lkdtm_PANIC(void) 72 { 73 panic("dumptest"); 74 } 75 76 void lkdtm_BUG(void) 77 { 78 BUG(); 79 } 80 81 static int warn_counter; 82 83 void lkdtm_WARNING(void) 84 { 85 WARN_ON(++warn_counter); 86 } 87 88 void lkdtm_WARNING_MESSAGE(void) 89 { 90 WARN(1, "Warning message trigger count: %d\n", ++warn_counter); 91 } 92 93 void lkdtm_EXCEPTION(void) 94 { 95 *((volatile int *) 0) = 0; 96 } 97 98 void lkdtm_LOOP(void) 99 { 100 for (;;) 101 ; 102 } 103 104 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 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 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 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 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 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 void lkdtm_SOFTLOCKUP(void) 249 { 250 preempt_disable(); 251 for (;;) 252 cpu_relax(); 253 } 254 255 void lkdtm_HARDLOCKUP(void) 256 { 257 local_irq_disable(); 258 for (;;) 259 cpu_relax(); 260 } 261 262 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 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 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 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[1]; 313 }; 314 315 struct array_bounds { 316 int one; 317 int two; 318 char data[8]; 319 int three; 320 }; 321 322 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 < sizeof(not_checked->data) + 1; 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 pr_expected_config(CONFIG_UBSAN_BOUNDS); 355 } 356 357 void lkdtm_CORRUPT_LIST_ADD(void) 358 { 359 /* 360 * Initially, an empty list via LIST_HEAD: 361 * test_head.next = &test_head 362 * test_head.prev = &test_head 363 */ 364 LIST_HEAD(test_head); 365 struct lkdtm_list good, bad; 366 void *target[2] = { }; 367 void *redirection = ⌖ 368 369 pr_info("attempting good list addition\n"); 370 371 /* 372 * Adding to the list performs these actions: 373 * test_head.next->prev = &good.node 374 * good.node.next = test_head.next 375 * good.node.prev = test_head 376 * test_head.next = good.node 377 */ 378 list_add(&good.node, &test_head); 379 380 pr_info("attempting corrupted list addition\n"); 381 /* 382 * In simulating this "write what where" primitive, the "what" is 383 * the address of &bad.node, and the "where" is the address held 384 * by "redirection". 385 */ 386 test_head.next = redirection; 387 list_add(&bad.node, &test_head); 388 389 if (target[0] == NULL && target[1] == NULL) 390 pr_err("Overwrite did not happen, but no BUG?!\n"); 391 else { 392 pr_err("list_add() corruption not detected!\n"); 393 pr_expected_config(CONFIG_DEBUG_LIST); 394 } 395 } 396 397 void lkdtm_CORRUPT_LIST_DEL(void) 398 { 399 LIST_HEAD(test_head); 400 struct lkdtm_list item; 401 void *target[2] = { }; 402 void *redirection = ⌖ 403 404 list_add(&item.node, &test_head); 405 406 pr_info("attempting good list removal\n"); 407 list_del(&item.node); 408 409 pr_info("attempting corrupted list removal\n"); 410 list_add(&item.node, &test_head); 411 412 /* As with the list_add() test above, this corrupts "next". */ 413 item.node.next = redirection; 414 list_del(&item.node); 415 416 if (target[0] == NULL && target[1] == NULL) 417 pr_err("Overwrite did not happen, but no BUG?!\n"); 418 else { 419 pr_err("list_del() corruption not detected!\n"); 420 pr_expected_config(CONFIG_DEBUG_LIST); 421 } 422 } 423 424 /* Test that VMAP_STACK is actually allocating with a leading guard page */ 425 void lkdtm_STACK_GUARD_PAGE_LEADING(void) 426 { 427 const unsigned char *stack = task_stack_page(current); 428 const unsigned char *ptr = stack - 1; 429 volatile unsigned char byte; 430 431 pr_info("attempting bad read from page below current stack\n"); 432 433 byte = *ptr; 434 435 pr_err("FAIL: accessed page before stack! (byte: %x)\n", byte); 436 } 437 438 /* Test that VMAP_STACK is actually allocating with a trailing guard page */ 439 void lkdtm_STACK_GUARD_PAGE_TRAILING(void) 440 { 441 const unsigned char *stack = task_stack_page(current); 442 const unsigned char *ptr = stack + THREAD_SIZE; 443 volatile unsigned char byte; 444 445 pr_info("attempting bad read from page above current stack\n"); 446 447 byte = *ptr; 448 449 pr_err("FAIL: accessed page after stack! (byte: %x)\n", byte); 450 } 451 452 void lkdtm_UNSET_SMEP(void) 453 { 454 #if IS_ENABLED(CONFIG_X86_64) && !IS_ENABLED(CONFIG_UML) 455 #define MOV_CR4_DEPTH 64 456 void (*direct_write_cr4)(unsigned long val); 457 unsigned char *insn; 458 unsigned long cr4; 459 int i; 460 461 cr4 = native_read_cr4(); 462 463 if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) { 464 pr_err("FAIL: SMEP not in use\n"); 465 return; 466 } 467 cr4 &= ~(X86_CR4_SMEP); 468 469 pr_info("trying to clear SMEP normally\n"); 470 native_write_cr4(cr4); 471 if (cr4 == native_read_cr4()) { 472 pr_err("FAIL: pinning SMEP failed!\n"); 473 cr4 |= X86_CR4_SMEP; 474 pr_info("restoring SMEP\n"); 475 native_write_cr4(cr4); 476 return; 477 } 478 pr_info("ok: SMEP did not get cleared\n"); 479 480 /* 481 * To test the post-write pinning verification we need to call 482 * directly into the middle of native_write_cr4() where the 483 * cr4 write happens, skipping any pinning. This searches for 484 * the cr4 writing instruction. 485 */ 486 insn = (unsigned char *)native_write_cr4; 487 for (i = 0; i < MOV_CR4_DEPTH; i++) { 488 /* mov %rdi, %cr4 */ 489 if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7) 490 break; 491 /* mov %rdi,%rax; mov %rax, %cr4 */ 492 if (insn[i] == 0x48 && insn[i+1] == 0x89 && 493 insn[i+2] == 0xf8 && insn[i+3] == 0x0f && 494 insn[i+4] == 0x22 && insn[i+5] == 0xe0) 495 break; 496 } 497 if (i >= MOV_CR4_DEPTH) { 498 pr_info("ok: cannot locate cr4 writing call gadget\n"); 499 return; 500 } 501 direct_write_cr4 = (void *)(insn + i); 502 503 pr_info("trying to clear SMEP with call gadget\n"); 504 direct_write_cr4(cr4); 505 if (native_read_cr4() & X86_CR4_SMEP) { 506 pr_info("ok: SMEP removal was reverted\n"); 507 } else { 508 pr_err("FAIL: cleared SMEP not detected!\n"); 509 cr4 |= X86_CR4_SMEP; 510 pr_info("restoring SMEP\n"); 511 native_write_cr4(cr4); 512 } 513 #else 514 pr_err("XFAIL: this test is x86_64-only\n"); 515 #endif 516 } 517 518 void lkdtm_DOUBLE_FAULT(void) 519 { 520 #if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML) 521 /* 522 * Trigger #DF by setting the stack limit to zero. This clobbers 523 * a GDT TLS slot, which is okay because the current task will die 524 * anyway due to the double fault. 525 */ 526 struct desc_struct d = { 527 .type = 3, /* expand-up, writable, accessed data */ 528 .p = 1, /* present */ 529 .d = 1, /* 32-bit */ 530 .g = 0, /* limit in bytes */ 531 .s = 1, /* not system */ 532 }; 533 534 local_irq_disable(); 535 write_gdt_entry(get_cpu_gdt_rw(smp_processor_id()), 536 GDT_ENTRY_TLS_MIN, &d, DESCTYPE_S); 537 538 /* 539 * Put our zero-limit segment in SS and then trigger a fault. The 540 * 4-byte access to (%esp) will fault with #SS, and the attempt to 541 * deliver the fault will recursively cause #SS and result in #DF. 542 * This whole process happens while NMIs and MCEs are blocked by the 543 * MOV SS window. This is nice because an NMI with an invalid SS 544 * would also double-fault, resulting in the NMI or MCE being lost. 545 */ 546 asm volatile ("movw %0, %%ss; addl $0, (%%esp)" :: 547 "r" ((unsigned short)(GDT_ENTRY_TLS_MIN << 3))); 548 549 pr_err("FAIL: tried to double fault but didn't die\n"); 550 #else 551 pr_err("XFAIL: this test is ia32-only\n"); 552 #endif 553 } 554 555 #ifdef CONFIG_ARM64 556 static noinline void change_pac_parameters(void) 557 { 558 if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) { 559 /* Reset the keys of current task */ 560 ptrauth_thread_init_kernel(current); 561 ptrauth_thread_switch_kernel(current); 562 } 563 } 564 #endif 565 566 noinline void lkdtm_CORRUPT_PAC(void) 567 { 568 #ifdef CONFIG_ARM64 569 #define CORRUPT_PAC_ITERATE 10 570 int i; 571 572 if (!IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) 573 pr_err("FAIL: kernel not built with CONFIG_ARM64_PTR_AUTH_KERNEL\n"); 574 575 if (!system_supports_address_auth()) { 576 pr_err("FAIL: CPU lacks pointer authentication feature\n"); 577 return; 578 } 579 580 pr_info("changing PAC parameters to force function return failure...\n"); 581 /* 582 * PAC is a hash value computed from input keys, return address and 583 * stack pointer. As pac has fewer bits so there is a chance of 584 * collision, so iterate few times to reduce the collision probability. 585 */ 586 for (i = 0; i < CORRUPT_PAC_ITERATE; i++) 587 change_pac_parameters(); 588 589 pr_err("FAIL: survived PAC changes! Kernel may be unstable from here\n"); 590 #else 591 pr_err("XFAIL: this test is arm64-only\n"); 592 #endif 593 } 594