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 void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void) 138 { 139 static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5}; 140 u32 *p; 141 u32 val = 0x12345678; 142 143 p = (u32 *)(data + 1); 144 if (*p == 0) 145 val = 0x87654321; 146 *p = val; 147 } 148 149 void lkdtm_SOFTLOCKUP(void) 150 { 151 preempt_disable(); 152 for (;;) 153 cpu_relax(); 154 } 155 156 void lkdtm_HARDLOCKUP(void) 157 { 158 local_irq_disable(); 159 for (;;) 160 cpu_relax(); 161 } 162 163 void lkdtm_SPINLOCKUP(void) 164 { 165 /* Must be called twice to trigger. */ 166 spin_lock(&lock_me_up); 167 /* Let sparse know we intended to exit holding the lock. */ 168 __release(&lock_me_up); 169 } 170 171 void lkdtm_HUNG_TASK(void) 172 { 173 set_current_state(TASK_UNINTERRUPTIBLE); 174 schedule(); 175 } 176 177 volatile unsigned int huge = INT_MAX - 2; 178 volatile unsigned int ignored; 179 180 void lkdtm_OVERFLOW_SIGNED(void) 181 { 182 int value; 183 184 value = huge; 185 pr_info("Normal signed addition ...\n"); 186 value += 1; 187 ignored = value; 188 189 pr_info("Overflowing signed addition ...\n"); 190 value += 4; 191 ignored = value; 192 } 193 194 195 void lkdtm_OVERFLOW_UNSIGNED(void) 196 { 197 unsigned int value; 198 199 value = huge; 200 pr_info("Normal unsigned addition ...\n"); 201 value += 1; 202 ignored = value; 203 204 pr_info("Overflowing unsigned addition ...\n"); 205 value += 4; 206 ignored = value; 207 } 208 209 /* Intentionally using old-style flex array definition of 1 byte. */ 210 struct array_bounds_flex_array { 211 int one; 212 int two; 213 char data[1]; 214 }; 215 216 struct array_bounds { 217 int one; 218 int two; 219 char data[8]; 220 int three; 221 }; 222 223 void lkdtm_ARRAY_BOUNDS(void) 224 { 225 struct array_bounds_flex_array *not_checked; 226 struct array_bounds *checked; 227 volatile int i; 228 229 not_checked = kmalloc(sizeof(*not_checked) * 2, GFP_KERNEL); 230 checked = kmalloc(sizeof(*checked) * 2, GFP_KERNEL); 231 232 pr_info("Array access within bounds ...\n"); 233 /* For both, touch all bytes in the actual member size. */ 234 for (i = 0; i < sizeof(checked->data); i++) 235 checked->data[i] = 'A'; 236 /* 237 * For the uninstrumented flex array member, also touch 1 byte 238 * beyond to verify it is correctly uninstrumented. 239 */ 240 for (i = 0; i < sizeof(not_checked->data) + 1; i++) 241 not_checked->data[i] = 'A'; 242 243 pr_info("Array access beyond bounds ...\n"); 244 for (i = 0; i < sizeof(checked->data) + 1; i++) 245 checked->data[i] = 'B'; 246 247 kfree(not_checked); 248 kfree(checked); 249 pr_err("FAIL: survived array bounds overflow!\n"); 250 } 251 252 void lkdtm_CORRUPT_LIST_ADD(void) 253 { 254 /* 255 * Initially, an empty list via LIST_HEAD: 256 * test_head.next = &test_head 257 * test_head.prev = &test_head 258 */ 259 LIST_HEAD(test_head); 260 struct lkdtm_list good, bad; 261 void *target[2] = { }; 262 void *redirection = ⌖ 263 264 pr_info("attempting good list addition\n"); 265 266 /* 267 * Adding to the list performs these actions: 268 * test_head.next->prev = &good.node 269 * good.node.next = test_head.next 270 * good.node.prev = test_head 271 * test_head.next = good.node 272 */ 273 list_add(&good.node, &test_head); 274 275 pr_info("attempting corrupted list addition\n"); 276 /* 277 * In simulating this "write what where" primitive, the "what" is 278 * the address of &bad.node, and the "where" is the address held 279 * by "redirection". 280 */ 281 test_head.next = redirection; 282 list_add(&bad.node, &test_head); 283 284 if (target[0] == NULL && target[1] == NULL) 285 pr_err("Overwrite did not happen, but no BUG?!\n"); 286 else 287 pr_err("list_add() corruption not detected!\n"); 288 } 289 290 void lkdtm_CORRUPT_LIST_DEL(void) 291 { 292 LIST_HEAD(test_head); 293 struct lkdtm_list item; 294 void *target[2] = { }; 295 void *redirection = ⌖ 296 297 list_add(&item.node, &test_head); 298 299 pr_info("attempting good list removal\n"); 300 list_del(&item.node); 301 302 pr_info("attempting corrupted list removal\n"); 303 list_add(&item.node, &test_head); 304 305 /* As with the list_add() test above, this corrupts "next". */ 306 item.node.next = redirection; 307 list_del(&item.node); 308 309 if (target[0] == NULL && target[1] == NULL) 310 pr_err("Overwrite did not happen, but no BUG?!\n"); 311 else 312 pr_err("list_del() corruption not detected!\n"); 313 } 314 315 /* Test if unbalanced set_fs(KERNEL_DS)/set_fs(USER_DS) check exists. */ 316 void lkdtm_CORRUPT_USER_DS(void) 317 { 318 pr_info("setting bad task size limit\n"); 319 set_fs(KERNEL_DS); 320 321 /* Make sure we do not keep running with a KERNEL_DS! */ 322 force_sig(SIGKILL); 323 } 324 325 /* Test that VMAP_STACK is actually allocating with a leading guard page */ 326 void lkdtm_STACK_GUARD_PAGE_LEADING(void) 327 { 328 const unsigned char *stack = task_stack_page(current); 329 const unsigned char *ptr = stack - 1; 330 volatile unsigned char byte; 331 332 pr_info("attempting bad read from page below current stack\n"); 333 334 byte = *ptr; 335 336 pr_err("FAIL: accessed page before stack! (byte: %x)\n", byte); 337 } 338 339 /* Test that VMAP_STACK is actually allocating with a trailing guard page */ 340 void lkdtm_STACK_GUARD_PAGE_TRAILING(void) 341 { 342 const unsigned char *stack = task_stack_page(current); 343 const unsigned char *ptr = stack + THREAD_SIZE; 344 volatile unsigned char byte; 345 346 pr_info("attempting bad read from page above current stack\n"); 347 348 byte = *ptr; 349 350 pr_err("FAIL: accessed page after stack! (byte: %x)\n", byte); 351 } 352 353 void lkdtm_UNSET_SMEP(void) 354 { 355 #if IS_ENABLED(CONFIG_X86_64) && !IS_ENABLED(CONFIG_UML) 356 #define MOV_CR4_DEPTH 64 357 void (*direct_write_cr4)(unsigned long val); 358 unsigned char *insn; 359 unsigned long cr4; 360 int i; 361 362 cr4 = native_read_cr4(); 363 364 if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) { 365 pr_err("FAIL: SMEP not in use\n"); 366 return; 367 } 368 cr4 &= ~(X86_CR4_SMEP); 369 370 pr_info("trying to clear SMEP normally\n"); 371 native_write_cr4(cr4); 372 if (cr4 == native_read_cr4()) { 373 pr_err("FAIL: pinning SMEP failed!\n"); 374 cr4 |= X86_CR4_SMEP; 375 pr_info("restoring SMEP\n"); 376 native_write_cr4(cr4); 377 return; 378 } 379 pr_info("ok: SMEP did not get cleared\n"); 380 381 /* 382 * To test the post-write pinning verification we need to call 383 * directly into the middle of native_write_cr4() where the 384 * cr4 write happens, skipping any pinning. This searches for 385 * the cr4 writing instruction. 386 */ 387 insn = (unsigned char *)native_write_cr4; 388 for (i = 0; i < MOV_CR4_DEPTH; i++) { 389 /* mov %rdi, %cr4 */ 390 if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7) 391 break; 392 /* mov %rdi,%rax; mov %rax, %cr4 */ 393 if (insn[i] == 0x48 && insn[i+1] == 0x89 && 394 insn[i+2] == 0xf8 && insn[i+3] == 0x0f && 395 insn[i+4] == 0x22 && insn[i+5] == 0xe0) 396 break; 397 } 398 if (i >= MOV_CR4_DEPTH) { 399 pr_info("ok: cannot locate cr4 writing call gadget\n"); 400 return; 401 } 402 direct_write_cr4 = (void *)(insn + i); 403 404 pr_info("trying to clear SMEP with call gadget\n"); 405 direct_write_cr4(cr4); 406 if (native_read_cr4() & X86_CR4_SMEP) { 407 pr_info("ok: SMEP removal was reverted\n"); 408 } else { 409 pr_err("FAIL: cleared SMEP not detected!\n"); 410 cr4 |= X86_CR4_SMEP; 411 pr_info("restoring SMEP\n"); 412 native_write_cr4(cr4); 413 } 414 #else 415 pr_err("XFAIL: this test is x86_64-only\n"); 416 #endif 417 } 418 419 void lkdtm_DOUBLE_FAULT(void) 420 { 421 #if IS_ENABLED(CONFIG_X86_32) && !IS_ENABLED(CONFIG_UML) 422 /* 423 * Trigger #DF by setting the stack limit to zero. This clobbers 424 * a GDT TLS slot, which is okay because the current task will die 425 * anyway due to the double fault. 426 */ 427 struct desc_struct d = { 428 .type = 3, /* expand-up, writable, accessed data */ 429 .p = 1, /* present */ 430 .d = 1, /* 32-bit */ 431 .g = 0, /* limit in bytes */ 432 .s = 1, /* not system */ 433 }; 434 435 local_irq_disable(); 436 write_gdt_entry(get_cpu_gdt_rw(smp_processor_id()), 437 GDT_ENTRY_TLS_MIN, &d, DESCTYPE_S); 438 439 /* 440 * Put our zero-limit segment in SS and then trigger a fault. The 441 * 4-byte access to (%esp) will fault with #SS, and the attempt to 442 * deliver the fault will recursively cause #SS and result in #DF. 443 * This whole process happens while NMIs and MCEs are blocked by the 444 * MOV SS window. This is nice because an NMI with an invalid SS 445 * would also double-fault, resulting in the NMI or MCE being lost. 446 */ 447 asm volatile ("movw %0, %%ss; addl $0, (%%esp)" :: 448 "r" ((unsigned short)(GDT_ENTRY_TLS_MIN << 3))); 449 450 pr_err("FAIL: tried to double fault but didn't die\n"); 451 #else 452 pr_err("XFAIL: this test is ia32-only\n"); 453 #endif 454 } 455 456 #ifdef CONFIG_ARM64 457 static noinline void change_pac_parameters(void) 458 { 459 if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH)) { 460 /* Reset the keys of current task */ 461 ptrauth_thread_init_kernel(current); 462 ptrauth_thread_switch_kernel(current); 463 } 464 } 465 #endif 466 467 noinline void lkdtm_CORRUPT_PAC(void) 468 { 469 #ifdef CONFIG_ARM64 470 #define CORRUPT_PAC_ITERATE 10 471 int i; 472 473 if (!IS_ENABLED(CONFIG_ARM64_PTR_AUTH)) 474 pr_err("FAIL: kernel not built with CONFIG_ARM64_PTR_AUTH\n"); 475 476 if (!system_supports_address_auth()) { 477 pr_err("FAIL: CPU lacks pointer authentication feature\n"); 478 return; 479 } 480 481 pr_info("changing PAC parameters to force function return failure...\n"); 482 /* 483 * PAC is a hash value computed from input keys, return address and 484 * stack pointer. As pac has fewer bits so there is a chance of 485 * collision, so iterate few times to reduce the collision probability. 486 */ 487 for (i = 0; i < CORRUPT_PAC_ITERATE; i++) 488 change_pac_parameters(); 489 490 pr_err("FAIL: survived PAC changes! Kernel may be unstable from here\n"); 491 #else 492 pr_err("XFAIL: this test is arm64-only\n"); 493 #endif 494 } 495