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