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 15 #ifdef CONFIG_X86_32 16 #include <asm/desc.h> 17 #endif 18 19 struct lkdtm_list { 20 struct list_head node; 21 }; 22 23 /* 24 * Make sure our attempts to over run the kernel stack doesn't trigger 25 * a compiler warning when CONFIG_FRAME_WARN is set. Then make sure we 26 * recurse past the end of THREAD_SIZE by default. 27 */ 28 #if defined(CONFIG_FRAME_WARN) && (CONFIG_FRAME_WARN > 0) 29 #define REC_STACK_SIZE (_AC(CONFIG_FRAME_WARN, UL) / 2) 30 #else 31 #define REC_STACK_SIZE (THREAD_SIZE / 8) 32 #endif 33 #define REC_NUM_DEFAULT ((THREAD_SIZE / REC_STACK_SIZE) * 2) 34 35 static int recur_count = REC_NUM_DEFAULT; 36 37 static DEFINE_SPINLOCK(lock_me_up); 38 39 /* 40 * Make sure compiler does not optimize this function or stack frame away: 41 * - function marked noinline 42 * - stack variables are marked volatile 43 * - stack variables are written (memset()) and read (pr_info()) 44 * - function has external effects (pr_info()) 45 * */ 46 static int noinline recursive_loop(int remaining) 47 { 48 volatile char buf[REC_STACK_SIZE]; 49 50 memset((void *)buf, remaining & 0xFF, sizeof(buf)); 51 pr_info("loop %d/%d ...\n", (int)buf[remaining % sizeof(buf)], 52 recur_count); 53 if (!remaining) 54 return 0; 55 else 56 return recursive_loop(remaining - 1); 57 } 58 59 /* If the depth is negative, use the default, otherwise keep parameter. */ 60 void __init lkdtm_bugs_init(int *recur_param) 61 { 62 if (*recur_param < 0) 63 *recur_param = recur_count; 64 else 65 recur_count = *recur_param; 66 } 67 68 void lkdtm_PANIC(void) 69 { 70 panic("dumptest"); 71 } 72 73 void lkdtm_BUG(void) 74 { 75 BUG(); 76 } 77 78 static int warn_counter; 79 80 void lkdtm_WARNING(void) 81 { 82 WARN_ON(++warn_counter); 83 } 84 85 void lkdtm_WARNING_MESSAGE(void) 86 { 87 WARN(1, "Warning message trigger count: %d\n", ++warn_counter); 88 } 89 90 void lkdtm_EXCEPTION(void) 91 { 92 *((volatile int *) 0) = 0; 93 } 94 95 void lkdtm_LOOP(void) 96 { 97 for (;;) 98 ; 99 } 100 101 void lkdtm_EXHAUST_STACK(void) 102 { 103 pr_info("Calling function with %lu frame size to depth %d ...\n", 104 REC_STACK_SIZE, recur_count); 105 recursive_loop(recur_count); 106 pr_info("FAIL: survived without exhausting stack?!\n"); 107 } 108 109 static noinline void __lkdtm_CORRUPT_STACK(void *stack) 110 { 111 memset(stack, '\xff', 64); 112 } 113 114 /* This should trip the stack canary, not corrupt the return address. */ 115 noinline void lkdtm_CORRUPT_STACK(void) 116 { 117 /* Use default char array length that triggers stack protection. */ 118 char data[8] __aligned(sizeof(void *)); 119 120 __lkdtm_CORRUPT_STACK(&data); 121 122 pr_info("Corrupted stack containing char array ...\n"); 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 __lkdtm_CORRUPT_STACK(&data); 134 135 pr_info("Corrupted stack containing union ...\n"); 136 } 137 138 void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void) 139 { 140 static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5}; 141 u32 *p; 142 u32 val = 0x12345678; 143 144 p = (u32 *)(data + 1); 145 if (*p == 0) 146 val = 0x87654321; 147 *p = val; 148 } 149 150 void lkdtm_SOFTLOCKUP(void) 151 { 152 preempt_disable(); 153 for (;;) 154 cpu_relax(); 155 } 156 157 void lkdtm_HARDLOCKUP(void) 158 { 159 local_irq_disable(); 160 for (;;) 161 cpu_relax(); 162 } 163 164 void lkdtm_SPINLOCKUP(void) 165 { 166 /* Must be called twice to trigger. */ 167 spin_lock(&lock_me_up); 168 /* Let sparse know we intended to exit holding the lock. */ 169 __release(&lock_me_up); 170 } 171 172 void lkdtm_HUNG_TASK(void) 173 { 174 set_current_state(TASK_UNINTERRUPTIBLE); 175 schedule(); 176 } 177 178 void lkdtm_CORRUPT_LIST_ADD(void) 179 { 180 /* 181 * Initially, an empty list via LIST_HEAD: 182 * test_head.next = &test_head 183 * test_head.prev = &test_head 184 */ 185 LIST_HEAD(test_head); 186 struct lkdtm_list good, bad; 187 void *target[2] = { }; 188 void *redirection = ⌖ 189 190 pr_info("attempting good list addition\n"); 191 192 /* 193 * Adding to the list performs these actions: 194 * test_head.next->prev = &good.node 195 * good.node.next = test_head.next 196 * good.node.prev = test_head 197 * test_head.next = good.node 198 */ 199 list_add(&good.node, &test_head); 200 201 pr_info("attempting corrupted list addition\n"); 202 /* 203 * In simulating this "write what where" primitive, the "what" is 204 * the address of &bad.node, and the "where" is the address held 205 * by "redirection". 206 */ 207 test_head.next = redirection; 208 list_add(&bad.node, &test_head); 209 210 if (target[0] == NULL && target[1] == NULL) 211 pr_err("Overwrite did not happen, but no BUG?!\n"); 212 else 213 pr_err("list_add() corruption not detected!\n"); 214 } 215 216 void lkdtm_CORRUPT_LIST_DEL(void) 217 { 218 LIST_HEAD(test_head); 219 struct lkdtm_list item; 220 void *target[2] = { }; 221 void *redirection = ⌖ 222 223 list_add(&item.node, &test_head); 224 225 pr_info("attempting good list removal\n"); 226 list_del(&item.node); 227 228 pr_info("attempting corrupted list removal\n"); 229 list_add(&item.node, &test_head); 230 231 /* As with the list_add() test above, this corrupts "next". */ 232 item.node.next = redirection; 233 list_del(&item.node); 234 235 if (target[0] == NULL && target[1] == NULL) 236 pr_err("Overwrite did not happen, but no BUG?!\n"); 237 else 238 pr_err("list_del() corruption not detected!\n"); 239 } 240 241 /* Test if unbalanced set_fs(KERNEL_DS)/set_fs(USER_DS) check exists. */ 242 void lkdtm_CORRUPT_USER_DS(void) 243 { 244 pr_info("setting bad task size limit\n"); 245 set_fs(KERNEL_DS); 246 247 /* Make sure we do not keep running with a KERNEL_DS! */ 248 force_sig(SIGKILL); 249 } 250 251 /* Test that VMAP_STACK is actually allocating with a leading guard page */ 252 void lkdtm_STACK_GUARD_PAGE_LEADING(void) 253 { 254 const unsigned char *stack = task_stack_page(current); 255 const unsigned char *ptr = stack - 1; 256 volatile unsigned char byte; 257 258 pr_info("attempting bad read from page below current stack\n"); 259 260 byte = *ptr; 261 262 pr_err("FAIL: accessed page before stack!\n"); 263 } 264 265 /* Test that VMAP_STACK is actually allocating with a trailing guard page */ 266 void lkdtm_STACK_GUARD_PAGE_TRAILING(void) 267 { 268 const unsigned char *stack = task_stack_page(current); 269 const unsigned char *ptr = stack + THREAD_SIZE; 270 volatile unsigned char byte; 271 272 pr_info("attempting bad read from page above current stack\n"); 273 274 byte = *ptr; 275 276 pr_err("FAIL: accessed page after stack!\n"); 277 } 278 279 void lkdtm_UNSET_SMEP(void) 280 { 281 #ifdef CONFIG_X86_64 282 #define MOV_CR4_DEPTH 64 283 void (*direct_write_cr4)(unsigned long val); 284 unsigned char *insn; 285 unsigned long cr4; 286 int i; 287 288 cr4 = native_read_cr4(); 289 290 if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) { 291 pr_err("FAIL: SMEP not in use\n"); 292 return; 293 } 294 cr4 &= ~(X86_CR4_SMEP); 295 296 pr_info("trying to clear SMEP normally\n"); 297 native_write_cr4(cr4); 298 if (cr4 == native_read_cr4()) { 299 pr_err("FAIL: pinning SMEP failed!\n"); 300 cr4 |= X86_CR4_SMEP; 301 pr_info("restoring SMEP\n"); 302 native_write_cr4(cr4); 303 return; 304 } 305 pr_info("ok: SMEP did not get cleared\n"); 306 307 /* 308 * To test the post-write pinning verification we need to call 309 * directly into the middle of native_write_cr4() where the 310 * cr4 write happens, skipping any pinning. This searches for 311 * the cr4 writing instruction. 312 */ 313 insn = (unsigned char *)native_write_cr4; 314 for (i = 0; i < MOV_CR4_DEPTH; i++) { 315 /* mov %rdi, %cr4 */ 316 if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7) 317 break; 318 /* mov %rdi,%rax; mov %rax, %cr4 */ 319 if (insn[i] == 0x48 && insn[i+1] == 0x89 && 320 insn[i+2] == 0xf8 && insn[i+3] == 0x0f && 321 insn[i+4] == 0x22 && insn[i+5] == 0xe0) 322 break; 323 } 324 if (i >= MOV_CR4_DEPTH) { 325 pr_info("ok: cannot locate cr4 writing call gadget\n"); 326 return; 327 } 328 direct_write_cr4 = (void *)(insn + i); 329 330 pr_info("trying to clear SMEP with call gadget\n"); 331 direct_write_cr4(cr4); 332 if (native_read_cr4() & X86_CR4_SMEP) { 333 pr_info("ok: SMEP removal was reverted\n"); 334 } else { 335 pr_err("FAIL: cleared SMEP not detected!\n"); 336 cr4 |= X86_CR4_SMEP; 337 pr_info("restoring SMEP\n"); 338 native_write_cr4(cr4); 339 } 340 #else 341 pr_err("FAIL: this test is x86_64-only\n"); 342 #endif 343 } 344 345 #ifdef CONFIG_X86_32 346 void lkdtm_DOUBLE_FAULT(void) 347 { 348 /* 349 * Trigger #DF by setting the stack limit to zero. This clobbers 350 * a GDT TLS slot, which is okay because the current task will die 351 * anyway due to the double fault. 352 */ 353 struct desc_struct d = { 354 .type = 3, /* expand-up, writable, accessed data */ 355 .p = 1, /* present */ 356 .d = 1, /* 32-bit */ 357 .g = 0, /* limit in bytes */ 358 .s = 1, /* not system */ 359 }; 360 361 local_irq_disable(); 362 write_gdt_entry(get_cpu_gdt_rw(smp_processor_id()), 363 GDT_ENTRY_TLS_MIN, &d, DESCTYPE_S); 364 365 /* 366 * Put our zero-limit segment in SS and then trigger a fault. The 367 * 4-byte access to (%esp) will fault with #SS, and the attempt to 368 * deliver the fault will recursively cause #SS and result in #DF. 369 * This whole process happens while NMIs and MCEs are blocked by the 370 * MOV SS window. This is nice because an NMI with an invalid SS 371 * would also double-fault, resulting in the NMI or MCE being lost. 372 */ 373 asm volatile ("movw %0, %%ss; addl $0, (%%esp)" :: 374 "r" ((unsigned short)(GDT_ENTRY_TLS_MIN << 3))); 375 376 panic("tried to double fault but didn't die\n"); 377 } 378 #endif 379