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 14 /* Whether or not to fill the target memory area with do_nothing(). */ 15 #define CODE_WRITE true 16 #define CODE_AS_IS false 17 18 /* How many bytes to copy to be sure we've copied enough of do_nothing(). */ 19 #define EXEC_SIZE 64 20 21 /* This is non-const, so it will end up in the .data section. */ 22 static u8 data_area[EXEC_SIZE]; 23 24 /* This is cost, so it will end up in the .rodata section. */ 25 static const unsigned long rodata = 0xAA55AA55; 26 27 /* This is marked __ro_after_init, so it should ultimately be .rodata. */ 28 static unsigned long ro_after_init __ro_after_init = 0x55AA5500; 29 30 /* 31 * This just returns to the caller. It is designed to be copied into 32 * non-executable memory regions. 33 */ 34 static void do_nothing(void) 35 { 36 return; 37 } 38 39 /* Must immediately follow do_nothing for size calculuations to work out. */ 40 static void do_overwritten(void) 41 { 42 pr_info("do_overwritten wasn't overwritten!\n"); 43 return; 44 } 45 46 static noinline void execute_location(void *dst, bool write) 47 { 48 void (*func)(void) = dst; 49 50 pr_info("attempting ok execution at %p\n", do_nothing); 51 do_nothing(); 52 53 if (write == CODE_WRITE) { 54 memcpy(dst, do_nothing, EXEC_SIZE); 55 flush_icache_range((unsigned long)dst, 56 (unsigned long)dst + EXEC_SIZE); 57 } 58 pr_info("attempting bad execution at %p\n", func); 59 func(); 60 } 61 62 static void execute_user_location(void *dst) 63 { 64 int copied; 65 66 /* Intentionally crossing kernel/user memory boundary. */ 67 void (*func)(void) = dst; 68 69 pr_info("attempting ok execution at %p\n", do_nothing); 70 do_nothing(); 71 72 copied = access_process_vm(current, (unsigned long)dst, do_nothing, 73 EXEC_SIZE, FOLL_WRITE); 74 if (copied < EXEC_SIZE) 75 return; 76 pr_info("attempting bad execution at %p\n", func); 77 func(); 78 } 79 80 void lkdtm_WRITE_RO(void) 81 { 82 /* Explicitly cast away "const" for the test. */ 83 unsigned long *ptr = (unsigned long *)&rodata; 84 85 pr_info("attempting bad rodata write at %p\n", ptr); 86 *ptr ^= 0xabcd1234; 87 } 88 89 void lkdtm_WRITE_RO_AFTER_INIT(void) 90 { 91 unsigned long *ptr = &ro_after_init; 92 93 /* 94 * Verify we were written to during init. Since an Oops 95 * is considered a "success", a failure is to just skip the 96 * real test. 97 */ 98 if ((*ptr & 0xAA) != 0xAA) { 99 pr_info("%p was NOT written during init!?\n", ptr); 100 return; 101 } 102 103 pr_info("attempting bad ro_after_init write at %p\n", ptr); 104 *ptr ^= 0xabcd1234; 105 } 106 107 void lkdtm_WRITE_KERN(void) 108 { 109 size_t size; 110 unsigned char *ptr; 111 112 size = (unsigned long)do_overwritten - (unsigned long)do_nothing; 113 ptr = (unsigned char *)do_overwritten; 114 115 pr_info("attempting bad %zu byte write at %p\n", size, ptr); 116 memcpy(ptr, (unsigned char *)do_nothing, size); 117 flush_icache_range((unsigned long)ptr, (unsigned long)(ptr + size)); 118 119 do_overwritten(); 120 } 121 122 void lkdtm_EXEC_DATA(void) 123 { 124 execute_location(data_area, CODE_WRITE); 125 } 126 127 void lkdtm_EXEC_STACK(void) 128 { 129 u8 stack_area[EXEC_SIZE]; 130 execute_location(stack_area, CODE_WRITE); 131 } 132 133 void lkdtm_EXEC_KMALLOC(void) 134 { 135 u32 *kmalloc_area = kmalloc(EXEC_SIZE, GFP_KERNEL); 136 execute_location(kmalloc_area, CODE_WRITE); 137 kfree(kmalloc_area); 138 } 139 140 void lkdtm_EXEC_VMALLOC(void) 141 { 142 u32 *vmalloc_area = vmalloc(EXEC_SIZE); 143 execute_location(vmalloc_area, CODE_WRITE); 144 vfree(vmalloc_area); 145 } 146 147 void lkdtm_EXEC_RODATA(void) 148 { 149 execute_location(lkdtm_rodata_do_nothing, CODE_AS_IS); 150 } 151 152 void lkdtm_EXEC_USERSPACE(void) 153 { 154 unsigned long user_addr; 155 156 user_addr = vm_mmap(NULL, 0, PAGE_SIZE, 157 PROT_READ | PROT_WRITE | PROT_EXEC, 158 MAP_ANONYMOUS | MAP_PRIVATE, 0); 159 if (user_addr >= TASK_SIZE) { 160 pr_warn("Failed to allocate user memory\n"); 161 return; 162 } 163 execute_user_location((void *)user_addr); 164 vm_munmap(user_addr, PAGE_SIZE); 165 } 166 167 void lkdtm_ACCESS_USERSPACE(void) 168 { 169 unsigned long user_addr, tmp = 0; 170 unsigned long *ptr; 171 172 user_addr = vm_mmap(NULL, 0, PAGE_SIZE, 173 PROT_READ | PROT_WRITE | PROT_EXEC, 174 MAP_ANONYMOUS | MAP_PRIVATE, 0); 175 if (user_addr >= TASK_SIZE) { 176 pr_warn("Failed to allocate user memory\n"); 177 return; 178 } 179 180 if (copy_to_user((void __user *)user_addr, &tmp, sizeof(tmp))) { 181 pr_warn("copy_to_user failed\n"); 182 vm_munmap(user_addr, PAGE_SIZE); 183 return; 184 } 185 186 ptr = (unsigned long *)user_addr; 187 188 pr_info("attempting bad read at %p\n", ptr); 189 tmp = *ptr; 190 tmp += 0xc0dec0de; 191 192 pr_info("attempting bad write at %p\n", ptr); 193 *ptr = tmp; 194 195 vm_munmap(user_addr, PAGE_SIZE); 196 } 197 198 void __init lkdtm_perms_init(void) 199 { 200 /* Make sure we can write to __ro_after_init values during __init */ 201 ro_after_init |= 0xAA; 202 203 } 204