1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Module and Firmware Pinning Security Module 4 * 5 * Copyright 2011-2016 Google Inc. 6 * 7 * Author: Kees Cook <keescook@chromium.org> 8 */ 9 10 #define pr_fmt(fmt) "LoadPin: " fmt 11 12 #include <linux/module.h> 13 #include <linux/fs.h> 14 #include <linux/kernel_read_file.h> 15 #include <linux/lsm_hooks.h> 16 #include <linux/mount.h> 17 #include <linux/blkdev.h> 18 #include <linux/path.h> 19 #include <linux/sched.h> /* current */ 20 #include <linux/string_helpers.h> 21 22 static void report_load(const char *origin, struct file *file, char *operation) 23 { 24 char *cmdline, *pathname; 25 26 pathname = kstrdup_quotable_file(file, GFP_KERNEL); 27 cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL); 28 29 pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n", 30 origin, operation, 31 (pathname && pathname[0] != '<') ? "\"" : "", 32 pathname, 33 (pathname && pathname[0] != '<') ? "\"" : "", 34 task_pid_nr(current), 35 cmdline ? "\"" : "", cmdline, cmdline ? "\"" : ""); 36 37 kfree(cmdline); 38 kfree(pathname); 39 } 40 41 static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE); 42 static char *exclude_read_files[READING_MAX_ID]; 43 static int ignore_read_file_id[READING_MAX_ID] __ro_after_init; 44 static struct super_block *pinned_root; 45 static DEFINE_SPINLOCK(pinned_root_spinlock); 46 47 #ifdef CONFIG_SYSCTL 48 49 static struct ctl_path loadpin_sysctl_path[] = { 50 { .procname = "kernel", }, 51 { .procname = "loadpin", }, 52 { } 53 }; 54 55 static struct ctl_table loadpin_sysctl_table[] = { 56 { 57 .procname = "enforce", 58 .data = &enforce, 59 .maxlen = sizeof(int), 60 .mode = 0644, 61 .proc_handler = proc_dointvec_minmax, 62 .extra1 = SYSCTL_ZERO, 63 .extra2 = SYSCTL_ONE, 64 }, 65 { } 66 }; 67 68 /* 69 * This must be called after early kernel init, since then the rootdev 70 * is available. 71 */ 72 static void check_pinning_enforcement(struct super_block *mnt_sb) 73 { 74 bool ro = false; 75 76 /* 77 * If load pinning is not enforced via a read-only block 78 * device, allow sysctl to change modes for testing. 79 */ 80 if (mnt_sb->s_bdev) { 81 ro = bdev_read_only(mnt_sb->s_bdev); 82 pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev, 83 MAJOR(mnt_sb->s_bdev->bd_dev), 84 MINOR(mnt_sb->s_bdev->bd_dev), 85 ro ? "read-only" : "writable"); 86 } else 87 pr_info("mnt_sb lacks block device, treating as: writable\n"); 88 89 if (!ro) { 90 if (!register_sysctl_paths(loadpin_sysctl_path, 91 loadpin_sysctl_table)) 92 pr_notice("sysctl registration failed!\n"); 93 else 94 pr_info("enforcement can be disabled.\n"); 95 } else 96 pr_info("load pinning engaged.\n"); 97 } 98 #else 99 static void check_pinning_enforcement(struct super_block *mnt_sb) 100 { 101 pr_info("load pinning engaged.\n"); 102 } 103 #endif 104 105 static void loadpin_sb_free_security(struct super_block *mnt_sb) 106 { 107 /* 108 * When unmounting the filesystem we were using for load 109 * pinning, we acknowledge the superblock release, but make sure 110 * no other modules or firmware can be loaded. 111 */ 112 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) { 113 pinned_root = ERR_PTR(-EIO); 114 pr_info("umount pinned fs: refusing further loads\n"); 115 } 116 } 117 118 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id, 119 bool contents) 120 { 121 struct super_block *load_root; 122 const char *origin = kernel_read_file_id_str(id); 123 124 /* 125 * If we will not know that we'll be seeing the full contents 126 * then we cannot trust a load will be complete and unchanged 127 * off disk. Treat all contents=false hooks as if there were 128 * no associated file struct. 129 */ 130 if (!contents) 131 file = NULL; 132 133 /* If the file id is excluded, ignore the pinning. */ 134 if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) && 135 ignore_read_file_id[id]) { 136 report_load(origin, file, "pinning-excluded"); 137 return 0; 138 } 139 140 /* This handles the older init_module API that has a NULL file. */ 141 if (!file) { 142 if (!enforce) { 143 report_load(origin, NULL, "old-api-pinning-ignored"); 144 return 0; 145 } 146 147 report_load(origin, NULL, "old-api-denied"); 148 return -EPERM; 149 } 150 151 load_root = file->f_path.mnt->mnt_sb; 152 153 /* First loaded module/firmware defines the root for all others. */ 154 spin_lock(&pinned_root_spinlock); 155 /* 156 * pinned_root is only NULL at startup. Otherwise, it is either 157 * a valid reference, or an ERR_PTR. 158 */ 159 if (!pinned_root) { 160 pinned_root = load_root; 161 /* 162 * Unlock now since it's only pinned_root we care about. 163 * In the worst case, we will (correctly) report pinning 164 * failures before we have announced that pinning is 165 * enforcing. This would be purely cosmetic. 166 */ 167 spin_unlock(&pinned_root_spinlock); 168 check_pinning_enforcement(pinned_root); 169 report_load(origin, file, "pinned"); 170 } else { 171 spin_unlock(&pinned_root_spinlock); 172 } 173 174 if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) { 175 if (unlikely(!enforce)) { 176 report_load(origin, file, "pinning-ignored"); 177 return 0; 178 } 179 180 report_load(origin, file, "denied"); 181 return -EPERM; 182 } 183 184 return 0; 185 } 186 187 static int loadpin_load_data(enum kernel_load_data_id id, bool contents) 188 { 189 return loadpin_read_file(NULL, (enum kernel_read_file_id) id, contents); 190 } 191 192 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = { 193 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security), 194 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file), 195 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data), 196 }; 197 198 static void __init parse_exclude(void) 199 { 200 int i, j; 201 char *cur; 202 203 /* 204 * Make sure all the arrays stay within expected sizes. This 205 * is slightly weird because kernel_read_file_str[] includes 206 * READING_MAX_ID, which isn't actually meaningful here. 207 */ 208 BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) != 209 ARRAY_SIZE(ignore_read_file_id)); 210 BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) < 211 ARRAY_SIZE(ignore_read_file_id)); 212 213 for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) { 214 cur = exclude_read_files[i]; 215 if (!cur) 216 break; 217 if (*cur == '\0') 218 continue; 219 220 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) { 221 if (strcmp(cur, kernel_read_file_str[j]) == 0) { 222 pr_info("excluding: %s\n", 223 kernel_read_file_str[j]); 224 ignore_read_file_id[j] = 1; 225 /* 226 * Can not break, because one read_file_str 227 * may map to more than on read_file_id. 228 */ 229 } 230 } 231 } 232 } 233 234 static int __init loadpin_init(void) 235 { 236 pr_info("ready to pin (currently %senforcing)\n", 237 enforce ? "" : "not "); 238 parse_exclude(); 239 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin"); 240 return 0; 241 } 242 243 DEFINE_LSM(loadpin) = { 244 .name = "loadpin", 245 .init = loadpin_init, 246 }; 247 248 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */ 249 module_param(enforce, int, 0); 250 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning"); 251 module_param_array_named(exclude, exclude_read_files, charp, NULL, 0); 252 MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types"); 253