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 struct lkdtm_list { 16 struct list_head node; 17 }; 18 19 /* 20 * Make sure our attempts to over run the kernel stack doesn't trigger 21 * a compiler warning when CONFIG_FRAME_WARN is set. Then make sure we 22 * recurse past the end of THREAD_SIZE by default. 23 */ 24 #if defined(CONFIG_FRAME_WARN) && (CONFIG_FRAME_WARN > 0) 25 #define REC_STACK_SIZE (_AC(CONFIG_FRAME_WARN, UL) / 2) 26 #else 27 #define REC_STACK_SIZE (THREAD_SIZE / 8) 28 #endif 29 #define REC_NUM_DEFAULT ((THREAD_SIZE / REC_STACK_SIZE) * 2) 30 31 static int recur_count = REC_NUM_DEFAULT; 32 33 static DEFINE_SPINLOCK(lock_me_up); 34 35 /* 36 * Make sure compiler does not optimize this function or stack frame away: 37 * - function marked noinline 38 * - stack variables are marked volatile 39 * - stack variables are written (memset()) and read (pr_info()) 40 * - function has external effects (pr_info()) 41 * */ 42 static int noinline recursive_loop(int remaining) 43 { 44 volatile char buf[REC_STACK_SIZE]; 45 46 memset((void *)buf, remaining & 0xFF, sizeof(buf)); 47 pr_info("loop %d/%d ...\n", (int)buf[remaining % sizeof(buf)], 48 recur_count); 49 if (!remaining) 50 return 0; 51 else 52 return recursive_loop(remaining - 1); 53 } 54 55 /* If the depth is negative, use the default, otherwise keep parameter. */ 56 void __init lkdtm_bugs_init(int *recur_param) 57 { 58 if (*recur_param < 0) 59 *recur_param = recur_count; 60 else 61 recur_count = *recur_param; 62 } 63 64 void lkdtm_PANIC(void) 65 { 66 panic("dumptest"); 67 } 68 69 void lkdtm_BUG(void) 70 { 71 BUG(); 72 } 73 74 static int warn_counter; 75 76 void lkdtm_WARNING(void) 77 { 78 WARN_ON(++warn_counter); 79 } 80 81 void lkdtm_WARNING_MESSAGE(void) 82 { 83 WARN(1, "Warning message trigger count: %d\n", ++warn_counter); 84 } 85 86 void lkdtm_EXCEPTION(void) 87 { 88 *((volatile int *) 0) = 0; 89 } 90 91 void lkdtm_LOOP(void) 92 { 93 for (;;) 94 ; 95 } 96 97 void lkdtm_EXHAUST_STACK(void) 98 { 99 pr_info("Calling function with %lu frame size to depth %d ...\n", 100 REC_STACK_SIZE, recur_count); 101 recursive_loop(recur_count); 102 pr_info("FAIL: survived without exhausting stack?!\n"); 103 } 104 105 static noinline void __lkdtm_CORRUPT_STACK(void *stack) 106 { 107 memset(stack, '\xff', 64); 108 } 109 110 /* This should trip the stack canary, not corrupt the return address. */ 111 noinline void lkdtm_CORRUPT_STACK(void) 112 { 113 /* Use default char array length that triggers stack protection. */ 114 char data[8] __aligned(sizeof(void *)); 115 116 __lkdtm_CORRUPT_STACK(&data); 117 118 pr_info("Corrupted stack containing char array ...\n"); 119 } 120 121 /* Same as above but will only get a canary with -fstack-protector-strong */ 122 noinline void lkdtm_CORRUPT_STACK_STRONG(void) 123 { 124 union { 125 unsigned short shorts[4]; 126 unsigned long *ptr; 127 } data __aligned(sizeof(void *)); 128 129 __lkdtm_CORRUPT_STACK(&data); 130 131 pr_info("Corrupted stack containing union ...\n"); 132 } 133 134 void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void) 135 { 136 static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5}; 137 u32 *p; 138 u32 val = 0x12345678; 139 140 p = (u32 *)(data + 1); 141 if (*p == 0) 142 val = 0x87654321; 143 *p = val; 144 } 145 146 void lkdtm_SOFTLOCKUP(void) 147 { 148 preempt_disable(); 149 for (;;) 150 cpu_relax(); 151 } 152 153 void lkdtm_HARDLOCKUP(void) 154 { 155 local_irq_disable(); 156 for (;;) 157 cpu_relax(); 158 } 159 160 void lkdtm_SPINLOCKUP(void) 161 { 162 /* Must be called twice to trigger. */ 163 spin_lock(&lock_me_up); 164 /* Let sparse know we intended to exit holding the lock. */ 165 __release(&lock_me_up); 166 } 167 168 void lkdtm_HUNG_TASK(void) 169 { 170 set_current_state(TASK_UNINTERRUPTIBLE); 171 schedule(); 172 } 173 174 void lkdtm_CORRUPT_LIST_ADD(void) 175 { 176 /* 177 * Initially, an empty list via LIST_HEAD: 178 * test_head.next = &test_head 179 * test_head.prev = &test_head 180 */ 181 LIST_HEAD(test_head); 182 struct lkdtm_list good, bad; 183 void *target[2] = { }; 184 void *redirection = ⌖ 185 186 pr_info("attempting good list addition\n"); 187 188 /* 189 * Adding to the list performs these actions: 190 * test_head.next->prev = &good.node 191 * good.node.next = test_head.next 192 * good.node.prev = test_head 193 * test_head.next = good.node 194 */ 195 list_add(&good.node, &test_head); 196 197 pr_info("attempting corrupted list addition\n"); 198 /* 199 * In simulating this "write what where" primitive, the "what" is 200 * the address of &bad.node, and the "where" is the address held 201 * by "redirection". 202 */ 203 test_head.next = redirection; 204 list_add(&bad.node, &test_head); 205 206 if (target[0] == NULL && target[1] == NULL) 207 pr_err("Overwrite did not happen, but no BUG?!\n"); 208 else 209 pr_err("list_add() corruption not detected!\n"); 210 } 211 212 void lkdtm_CORRUPT_LIST_DEL(void) 213 { 214 LIST_HEAD(test_head); 215 struct lkdtm_list item; 216 void *target[2] = { }; 217 void *redirection = ⌖ 218 219 list_add(&item.node, &test_head); 220 221 pr_info("attempting good list removal\n"); 222 list_del(&item.node); 223 224 pr_info("attempting corrupted list removal\n"); 225 list_add(&item.node, &test_head); 226 227 /* As with the list_add() test above, this corrupts "next". */ 228 item.node.next = redirection; 229 list_del(&item.node); 230 231 if (target[0] == NULL && target[1] == NULL) 232 pr_err("Overwrite did not happen, but no BUG?!\n"); 233 else 234 pr_err("list_del() corruption not detected!\n"); 235 } 236 237 /* Test if unbalanced set_fs(KERNEL_DS)/set_fs(USER_DS) check exists. */ 238 void lkdtm_CORRUPT_USER_DS(void) 239 { 240 pr_info("setting bad task size limit\n"); 241 set_fs(KERNEL_DS); 242 243 /* Make sure we do not keep running with a KERNEL_DS! */ 244 force_sig(SIGKILL); 245 } 246 247 /* Test that VMAP_STACK is actually allocating with a leading guard page */ 248 void lkdtm_STACK_GUARD_PAGE_LEADING(void) 249 { 250 const unsigned char *stack = task_stack_page(current); 251 const unsigned char *ptr = stack - 1; 252 volatile unsigned char byte; 253 254 pr_info("attempting bad read from page below current stack\n"); 255 256 byte = *ptr; 257 258 pr_err("FAIL: accessed page before stack!\n"); 259 } 260 261 /* Test that VMAP_STACK is actually allocating with a trailing guard page */ 262 void lkdtm_STACK_GUARD_PAGE_TRAILING(void) 263 { 264 const unsigned char *stack = task_stack_page(current); 265 const unsigned char *ptr = stack + THREAD_SIZE; 266 volatile unsigned char byte; 267 268 pr_info("attempting bad read from page above current stack\n"); 269 270 byte = *ptr; 271 272 pr_err("FAIL: accessed page after stack!\n"); 273 } 274 275 void lkdtm_UNSET_SMEP(void) 276 { 277 #ifdef CONFIG_X86_64 278 #define MOV_CR4_DEPTH 64 279 void (*direct_write_cr4)(unsigned long val); 280 unsigned char *insn; 281 unsigned long cr4; 282 int i; 283 284 cr4 = native_read_cr4(); 285 286 if ((cr4 & X86_CR4_SMEP) != X86_CR4_SMEP) { 287 pr_err("FAIL: SMEP not in use\n"); 288 return; 289 } 290 cr4 &= ~(X86_CR4_SMEP); 291 292 pr_info("trying to clear SMEP normally\n"); 293 native_write_cr4(cr4); 294 if (cr4 == native_read_cr4()) { 295 pr_err("FAIL: pinning SMEP failed!\n"); 296 cr4 |= X86_CR4_SMEP; 297 pr_info("restoring SMEP\n"); 298 native_write_cr4(cr4); 299 return; 300 } 301 pr_info("ok: SMEP did not get cleared\n"); 302 303 /* 304 * To test the post-write pinning verification we need to call 305 * directly into the middle of native_write_cr4() where the 306 * cr4 write happens, skipping any pinning. This searches for 307 * the cr4 writing instruction. 308 */ 309 insn = (unsigned char *)native_write_cr4; 310 for (i = 0; i < MOV_CR4_DEPTH; i++) { 311 /* mov %rdi, %cr4 */ 312 if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7) 313 break; 314 /* mov %rdi,%rax; mov %rax, %cr4 */ 315 if (insn[i] == 0x48 && insn[i+1] == 0x89 && 316 insn[i+2] == 0xf8 && insn[i+3] == 0x0f && 317 insn[i+4] == 0x22 && insn[i+5] == 0xe0) 318 break; 319 } 320 if (i >= MOV_CR4_DEPTH) { 321 pr_info("ok: cannot locate cr4 writing call gadget\n"); 322 return; 323 } 324 direct_write_cr4 = (void *)(insn + i); 325 326 pr_info("trying to clear SMEP with call gadget\n"); 327 direct_write_cr4(cr4); 328 if (native_read_cr4() & X86_CR4_SMEP) { 329 pr_info("ok: SMEP removal was reverted\n"); 330 } else { 331 pr_err("FAIL: cleared SMEP not detected!\n"); 332 cr4 |= X86_CR4_SMEP; 333 pr_info("restoring SMEP\n"); 334 native_write_cr4(cr4); 335 } 336 #else 337 pr_err("FAIL: this test is x86_64-only\n"); 338 #endif 339 } 340