1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * This is for all the tests related to validating kernel memory 4 * permissions: non-executable regions, non-writable regions, and 5 * even non-readable regions. 6 */ 7 #include "lkdtm.h" 8 #include <linux/slab.h> 9 #include <linux/vmalloc.h> 10 #include <linux/mman.h> 11 #include <linux/uaccess.h> 12 #include <asm/cacheflush.h> 13 #include <asm/sections.h> 14 15 /* Whether or not to fill the target memory area with do_nothing(). */ 16 #define CODE_WRITE true 17 #define CODE_AS_IS false 18 19 /* How many bytes to copy to be sure we've copied enough of do_nothing(). */ 20 #define EXEC_SIZE 64 21 22 /* This is non-const, so it will end up in the .data section. */ 23 static u8 data_area[EXEC_SIZE]; 24 25 /* This is const, so it will end up in the .rodata section. */ 26 static const unsigned long rodata = 0xAA55AA55; 27 28 /* This is marked __ro_after_init, so it should ultimately be .rodata. */ 29 static unsigned long ro_after_init __ro_after_init = 0x55AA5500; 30 31 /* 32 * This just returns to the caller. It is designed to be copied into 33 * non-executable memory regions. 34 */ 35 static noinline void do_nothing(void) 36 { 37 return; 38 } 39 40 /* Must immediately follow do_nothing for size calculuations to work out. */ 41 static noinline void do_overwritten(void) 42 { 43 pr_info("do_overwritten wasn't overwritten!\n"); 44 return; 45 } 46 47 static noinline void do_almost_nothing(void) 48 { 49 pr_info("do_nothing was hijacked!\n"); 50 } 51 52 static void *setup_function_descriptor(func_desc_t *fdesc, void *dst) 53 { 54 if (!have_function_descriptors()) 55 return dst; 56 57 memcpy(fdesc, do_nothing, sizeof(*fdesc)); 58 fdesc->addr = (unsigned long)dst; 59 barrier(); 60 61 return fdesc; 62 } 63 64 static noinline void execute_location(void *dst, bool write) 65 { 66 void (*func)(void); 67 func_desc_t fdesc; 68 void *do_nothing_text = dereference_function_descriptor(do_nothing); 69 70 pr_info("attempting ok execution at %px\n", do_nothing_text); 71 do_nothing(); 72 73 if (write == CODE_WRITE) { 74 memcpy(dst, do_nothing_text, EXEC_SIZE); 75 flush_icache_range((unsigned long)dst, 76 (unsigned long)dst + EXEC_SIZE); 77 } 78 pr_info("attempting bad execution at %px\n", dst); 79 func = setup_function_descriptor(&fdesc, dst); 80 func(); 81 pr_err("FAIL: func returned\n"); 82 } 83 84 static void execute_user_location(void *dst) 85 { 86 int copied; 87 88 /* Intentionally crossing kernel/user memory boundary. */ 89 void (*func)(void); 90 func_desc_t fdesc; 91 void *do_nothing_text = dereference_function_descriptor(do_nothing); 92 93 pr_info("attempting ok execution at %px\n", do_nothing_text); 94 do_nothing(); 95 96 copied = access_process_vm(current, (unsigned long)dst, do_nothing_text, 97 EXEC_SIZE, FOLL_WRITE); 98 if (copied < EXEC_SIZE) 99 return; 100 pr_info("attempting bad execution at %px\n", dst); 101 func = setup_function_descriptor(&fdesc, dst); 102 func(); 103 pr_err("FAIL: func returned\n"); 104 } 105 106 void lkdtm_WRITE_RO(void) 107 { 108 /* Explicitly cast away "const" for the test and make volatile. */ 109 volatile unsigned long *ptr = (unsigned long *)&rodata; 110 111 pr_info("attempting bad rodata write at %px\n", ptr); 112 *ptr ^= 0xabcd1234; 113 pr_err("FAIL: survived bad write\n"); 114 } 115 116 void lkdtm_WRITE_RO_AFTER_INIT(void) 117 { 118 volatile unsigned long *ptr = &ro_after_init; 119 120 /* 121 * Verify we were written to during init. Since an Oops 122 * is considered a "success", a failure is to just skip the 123 * real test. 124 */ 125 if ((*ptr & 0xAA) != 0xAA) { 126 pr_info("%p was NOT written during init!?\n", ptr); 127 return; 128 } 129 130 pr_info("attempting bad ro_after_init write at %px\n", ptr); 131 *ptr ^= 0xabcd1234; 132 pr_err("FAIL: survived bad write\n"); 133 } 134 135 void lkdtm_WRITE_KERN(void) 136 { 137 size_t size; 138 volatile unsigned char *ptr; 139 140 size = (unsigned long)dereference_function_descriptor(do_overwritten) - 141 (unsigned long)dereference_function_descriptor(do_nothing); 142 ptr = dereference_function_descriptor(do_overwritten); 143 144 pr_info("attempting bad %zu byte write at %px\n", size, ptr); 145 memcpy((void *)ptr, (unsigned char *)do_nothing, size); 146 flush_icache_range((unsigned long)ptr, (unsigned long)(ptr + size)); 147 pr_err("FAIL: survived bad write\n"); 148 149 do_overwritten(); 150 } 151 152 void lkdtm_WRITE_OPD(void) 153 { 154 size_t size = sizeof(func_desc_t); 155 void (*func)(void) = do_nothing; 156 157 if (!have_function_descriptors()) { 158 pr_info("XFAIL: Platform doesn't use function descriptors.\n"); 159 return; 160 } 161 pr_info("attempting bad %zu bytes write at %px\n", size, do_nothing); 162 memcpy(do_nothing, do_almost_nothing, size); 163 pr_err("FAIL: survived bad write\n"); 164 165 asm("" : "=m"(func)); 166 func(); 167 } 168 169 void lkdtm_EXEC_DATA(void) 170 { 171 execute_location(data_area, CODE_WRITE); 172 } 173 174 void lkdtm_EXEC_STACK(void) 175 { 176 u8 stack_area[EXEC_SIZE]; 177 execute_location(stack_area, CODE_WRITE); 178 } 179 180 void lkdtm_EXEC_KMALLOC(void) 181 { 182 u32 *kmalloc_area = kmalloc(EXEC_SIZE, GFP_KERNEL); 183 execute_location(kmalloc_area, CODE_WRITE); 184 kfree(kmalloc_area); 185 } 186 187 void lkdtm_EXEC_VMALLOC(void) 188 { 189 u32 *vmalloc_area = vmalloc(EXEC_SIZE); 190 execute_location(vmalloc_area, CODE_WRITE); 191 vfree(vmalloc_area); 192 } 193 194 void lkdtm_EXEC_RODATA(void) 195 { 196 execute_location(dereference_function_descriptor(lkdtm_rodata_do_nothing), 197 CODE_AS_IS); 198 } 199 200 void lkdtm_EXEC_USERSPACE(void) 201 { 202 unsigned long user_addr; 203 204 user_addr = vm_mmap(NULL, 0, PAGE_SIZE, 205 PROT_READ | PROT_WRITE | PROT_EXEC, 206 MAP_ANONYMOUS | MAP_PRIVATE, 0); 207 if (user_addr >= TASK_SIZE) { 208 pr_warn("Failed to allocate user memory\n"); 209 return; 210 } 211 execute_user_location((void *)user_addr); 212 vm_munmap(user_addr, PAGE_SIZE); 213 } 214 215 void lkdtm_EXEC_NULL(void) 216 { 217 execute_location(NULL, CODE_AS_IS); 218 } 219 220 void lkdtm_ACCESS_USERSPACE(void) 221 { 222 unsigned long user_addr, tmp = 0; 223 unsigned long *ptr; 224 225 user_addr = vm_mmap(NULL, 0, PAGE_SIZE, 226 PROT_READ | PROT_WRITE | PROT_EXEC, 227 MAP_ANONYMOUS | MAP_PRIVATE, 0); 228 if (user_addr >= TASK_SIZE) { 229 pr_warn("Failed to allocate user memory\n"); 230 return; 231 } 232 233 if (copy_to_user((void __user *)user_addr, &tmp, sizeof(tmp))) { 234 pr_warn("copy_to_user failed\n"); 235 vm_munmap(user_addr, PAGE_SIZE); 236 return; 237 } 238 239 ptr = (unsigned long *)user_addr; 240 241 pr_info("attempting bad read at %px\n", ptr); 242 tmp = *ptr; 243 tmp += 0xc0dec0de; 244 pr_err("FAIL: survived bad read\n"); 245 246 pr_info("attempting bad write at %px\n", ptr); 247 *ptr = tmp; 248 pr_err("FAIL: survived bad write\n"); 249 250 vm_munmap(user_addr, PAGE_SIZE); 251 } 252 253 void lkdtm_ACCESS_NULL(void) 254 { 255 unsigned long tmp; 256 volatile unsigned long *ptr = (unsigned long *)NULL; 257 258 pr_info("attempting bad read at %px\n", ptr); 259 tmp = *ptr; 260 tmp += 0xc0dec0de; 261 pr_err("FAIL: survived bad read\n"); 262 263 pr_info("attempting bad write at %px\n", ptr); 264 *ptr = tmp; 265 pr_err("FAIL: survived bad write\n"); 266 } 267 268 void __init lkdtm_perms_init(void) 269 { 270 /* Make sure we can write to __ro_after_init values during __init */ 271 ro_after_init |= 0xAA; 272 } 273