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 void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void) 155 { 156 static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5}; 157 u32 *p; 158 u32 val = 0x12345678; 159 160 p = (u32 *)(data + 1); 161 if (*p == 0) 162 val = 0x87654321; 163 *p = val; 164 165 if (IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) 166 pr_err("XFAIL: arch has CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS\n"); 167 } 168 169 void lkdtm_SOFTLOCKUP(void) 170 { 171 preempt_disable(); 172 for (;;) 173 cpu_relax(); 174 } 175 176 void lkdtm_HARDLOCKUP(void) 177 { 178 local_irq_disable(); 179 for (;;) 180 cpu_relax(); 181 } 182 183 void lkdtm_SPINLOCKUP(void) 184 { 185 /* Must be called twice to trigger. */ 186 spin_lock(&lock_me_up); 187 /* Let sparse know we intended to exit holding the lock. */ 188 __release(&lock_me_up); 189 } 190 191 void lkdtm_HUNG_TASK(void) 192 { 193 set_current_state(TASK_UNINTERRUPTIBLE); 194 schedule(); 195 } 196 197 volatile unsigned int huge = INT_MAX - 2; 198 volatile unsigned int ignored; 199 200 void lkdtm_OVERFLOW_SIGNED(void) 201 { 202 int value; 203 204 value = huge; 205 pr_info("Normal signed addition ...\n"); 206 value += 1; 207 ignored = value; 208 209 pr_info("Overflowing signed addition ...\n"); 210 value += 4; 211 ignored = value; 212 } 213 214 215 void lkdtm_OVERFLOW_UNSIGNED(void) 216 { 217 unsigned int value; 218 219 value = huge; 220 pr_info("Normal unsigned addition ...\n"); 221 value += 1; 222 ignored = value; 223 224 pr_info("Overflowing unsigned addition ...\n"); 225 value += 4; 226 ignored = value; 227 } 228 229 /* Intentionally using old-style flex array definition of 1 byte. */ 230 struct array_bounds_flex_array { 231 int one; 232 int two; 233 char data[1]; 234 }; 235 236 struct array_bounds { 237 int one; 238 int two; 239 char data[8]; 240 int three; 241 }; 242 243 void lkdtm_ARRAY_BOUNDS(void) 244 { 245 struct array_bounds_flex_array *not_checked; 246 struct array_bounds *checked; 247 volatile int i; 248 249 not_checked = kmalloc(sizeof(*not_checked) * 2, GFP_KERNEL); 250 checked = kmalloc(sizeof(*checked) * 2, GFP_KERNEL); 251 252 pr_info("Array access within bounds ...\n"); 253 /* For both, touch all bytes in the actual member size. */ 254 for (i = 0; i < sizeof(checked->data); i++) 255 checked->data[i] = 'A'; 256 /* 257 * For the uninstrumented flex array member, also touch 1 byte 258 * beyond to verify it is correctly uninstrumented. 259 */ 260 for (i = 0; i < sizeof(not_checked->data) + 1; i++) 261 not_checked->data[i] = 'A'; 262 263 pr_info("Array access beyond bounds ...\n"); 264 for (i = 0; i < sizeof(checked->data) + 1; i++) 265 checked->data[i] = 'B'; 266 267 kfree(not_checked); 268 kfree(checked); 269 pr_err("FAIL: survived array bounds overflow!\n"); 270 pr_expected_config(CONFIG_UBSAN_BOUNDS); 271 } 272 273 void lkdtm_CORRUPT_LIST_ADD(void) 274 { 275 /* 276 * Initially, an empty list via LIST_HEAD: 277 * test_head.next = &test_head 278 * test_head.prev = &test_head 279 */ 280 LIST_HEAD(test_head); 281 struct lkdtm_list good, bad; 282 void *target[2] = { }; 283 void *redirection = ⌖ 284 285 pr_info("attempting good list addition\n"); 286 287 /* 288 * Adding to the list performs these actions: 289 * test_head.next->prev = &good.node 290 * good.node.next = test_head.next 291 * good.node.prev = test_head 292 * test_head.next = good.node 293 */ 294 list_add(&good.node, &test_head); 295 296 pr_info("attempting corrupted list addition\n"); 297 /* 298 * In simulating this "write what where" primitive, the "what" is 299 * the address of &bad.node, and the "where" is the address held 300 * by "redirection". 301 */ 302 test_head.next = redirection; 303 list_add(&bad.node, &test_head); 304 305 if (target[0] == NULL && target[1] == NULL) 306 pr_err("Overwrite did not happen, but no BUG?!\n"); 307 else { 308 pr_err("list_add() corruption not detected!\n"); 309 pr_expected_config(CONFIG_DEBUG_LIST); 310 } 311 } 312 313 void lkdtm_CORRUPT_LIST_DEL(void) 314 { 315 LIST_HEAD(test_head); 316 struct lkdtm_list item; 317 void *target[2] = { }; 318 void *redirection = ⌖ 319 320 list_add(&item.node, &test_head); 321 322 pr_info("attempting good list removal\n"); 323 list_del(&item.node); 324 325 pr_info("attempting corrupted list removal\n"); 326 list_add(&item.node, &test_head); 327 328 /* As with the list_add() test above, this corrupts "next". */ 329 item.node.next = redirection; 330 list_del(&item.node); 331 332 if (target[0] == NULL && target[1] == NULL) 333 pr_err("Overwrite did not happen, but no BUG?!\n"); 334 else { 335 pr_err("list_del() corruption not detected!\n"); 336 pr_expected_config(CONFIG_DEBUG_LIST); 337 } 338 } 339 340 /* Test that VMAP_STACK is actually allocating with a leading guard page */ 341 void lkdtm_STACK_GUARD_PAGE_LEADING(void) 342 { 343 const unsigned char *stack = task_stack_page(current); 344 const unsigned char *ptr = stack - 1; 345 volatile unsigned char byte; 346 347 pr_info("attempting bad read from page below current stack\n"); 348 349 byte = *ptr; 350 351 pr_err("FAIL: accessed page before stack! (byte: %x)\n", byte); 352 } 353 354 /* Test that VMAP_STACK is actually allocating with a trailing guard page */ 355 void lkdtm_STACK_GUARD_PAGE_TRAILING(void) 356 { 357 const unsigned char *stack = task_stack_page(current); 358 const unsigned char *ptr = stack + THREAD_SIZE; 359 volatile unsigned char byte; 360 361 pr_info("attempting bad read from page above current stack\n"); 362 363 byte = *ptr; 364 365 pr_err("FAIL: accessed page after stack! (byte: %x)\n", byte); 366 } 367 368 void lkdtm_UNSET_SMEP(void) 369 { 370 #if IS_ENABLED(CONFIG_X86_64) && !IS_ENABLED(CONFIG_UML) 371 #define MOV_CR4_DEPTH 64 372 void (*direct_write_cr4)(unsigned long val); 373 unsigned char *insn; 374 unsigned long cr4; 375 int i; 376 377 cr4 = native_read_cr4(); 378 379 if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) { 380 pr_err("FAIL: SMEP not in use\n"); 381 return; 382 } 383 cr4 &= ~(X86_CR4_SMEP); 384 385 pr_info("trying to clear SMEP normally\n"); 386 native_write_cr4(cr4); 387 if (cr4 == native_read_cr4()) { 388 pr_err("FAIL: pinning SMEP failed!\n"); 389 cr4 |= X86_CR4_SMEP; 390 pr_info("restoring SMEP\n"); 391 native_write_cr4(cr4); 392 return; 393 } 394 pr_info("ok: SMEP did not get cleared\n"); 395 396 /* 397 * To test the post-write pinning verification we need to call 398 * directly into the middle of native_write_cr4() where the 399 * cr4 write happens, skipping any pinning. This searches for 400 * the cr4 writing instruction. 401 */ 402 insn = (unsigned char *)native_write_cr4; 403 for (i = 0; i < MOV_CR4_DEPTH; i++) { 404 /* mov %rdi, %cr4 */ 405 if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7) 406 break; 407 /* mov %rdi,%rax; mov %rax, %cr4 */ 408 if (insn[i] == 0x48 && insn[i+1] == 0x89 && 409 insn[i+2] == 0xf8 && insn[i+3] == 0x0f && 410 insn[i+4] == 0x22 && insn[i+5] == 0xe0) 411 break; 412 } 413 if (i >= MOV_CR4_DEPTH) { 414 pr_info("ok: cannot locate cr4 writing call gadget\n"); 415 return; 416 } 417 direct_write_cr4 = (void *)(insn + i); 418 419 pr_info("trying to clear SMEP with call gadget\n"); 420 direct_write_cr4(cr4); 421 if (native_read_cr4() & X86_CR4_SMEP) { 422 pr_info("ok: SMEP removal was reverted\n"); 423 } else { 424 pr_err("FAIL: cleared SMEP not detected!\n"); 425 cr4 |= X86_CR4_SMEP; 426 pr_info("restoring SMEP\n"); 427 native_write_cr4(cr4); 428 } 429 #else 430 pr_err("XFAIL: this test is x86_64-only\n"); 431 #endif 432 } 433 434 void lkdtm_DOUBLE_FAULT(void) 435 { 436 #if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML) 437 /* 438 * Trigger #DF by setting the stack limit to zero. This clobbers 439 * a GDT TLS slot, which is okay because the current task will die 440 * anyway due to the double fault. 441 */ 442 struct desc_struct d = { 443 .type = 3, /* expand-up, writable, accessed data */ 444 .p = 1, /* present */ 445 .d = 1, /* 32-bit */ 446 .g = 0, /* limit in bytes */ 447 .s = 1, /* not system */ 448 }; 449 450 local_irq_disable(); 451 write_gdt_entry(get_cpu_gdt_rw(smp_processor_id()), 452 GDT_ENTRY_TLS_MIN, &d, DESCTYPE_S); 453 454 /* 455 * Put our zero-limit segment in SS and then trigger a fault. The 456 * 4-byte access to (%esp) will fault with #SS, and the attempt to 457 * deliver the fault will recursively cause #SS and result in #DF. 458 * This whole process happens while NMIs and MCEs are blocked by the 459 * MOV SS window. This is nice because an NMI with an invalid SS 460 * would also double-fault, resulting in the NMI or MCE being lost. 461 */ 462 asm volatile ("movw %0, %%ss; addl $0, (%%esp)" :: 463 "r" ((unsigned short)(GDT_ENTRY_TLS_MIN << 3))); 464 465 pr_err("FAIL: tried to double fault but didn't die\n"); 466 #else 467 pr_err("XFAIL: this test is ia32-only\n"); 468 #endif 469 } 470 471 #ifdef CONFIG_ARM64 472 static noinline void change_pac_parameters(void) 473 { 474 if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) { 475 /* Reset the keys of current task */ 476 ptrauth_thread_init_kernel(current); 477 ptrauth_thread_switch_kernel(current); 478 } 479 } 480 #endif 481 482 noinline void lkdtm_CORRUPT_PAC(void) 483 { 484 #ifdef CONFIG_ARM64 485 #define CORRUPT_PAC_ITERATE 10 486 int i; 487 488 if (!IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) 489 pr_err("FAIL: kernel not built with CONFIG_ARM64_PTR_AUTH_KERNEL\n"); 490 491 if (!system_supports_address_auth()) { 492 pr_err("FAIL: CPU lacks pointer authentication feature\n"); 493 return; 494 } 495 496 pr_info("changing PAC parameters to force function return failure...\n"); 497 /* 498 * PAC is a hash value computed from input keys, return address and 499 * stack pointer. As pac has fewer bits so there is a chance of 500 * collision, so iterate few times to reduce the collision probability. 501 */ 502 for (i = 0; i < CORRUPT_PAC_ITERATE; i++) 503 change_pac_parameters(); 504 505 pr_err("FAIL: survived PAC changes! Kernel may be unstable from here\n"); 506 #else 507 pr_err("XFAIL: this test is arm64-only\n"); 508 #endif 509 } 510