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 char bdev[BDEVNAME_SIZE]; 82 83 ro = bdev_read_only(mnt_sb->s_bdev); 84 bdevname(mnt_sb->s_bdev, bdev); 85 pr_info("%s (%u:%u): %s\n", bdev, 86 MAJOR(mnt_sb->s_bdev->bd_dev), 87 MINOR(mnt_sb->s_bdev->bd_dev), 88 ro ? "read-only" : "writable"); 89 } else 90 pr_info("mnt_sb lacks block device, treating as: writable\n"); 91 92 if (!ro) { 93 if (!register_sysctl_paths(loadpin_sysctl_path, 94 loadpin_sysctl_table)) 95 pr_notice("sysctl registration failed!\n"); 96 else 97 pr_info("enforcement can be disabled.\n"); 98 } else 99 pr_info("load pinning engaged.\n"); 100 } 101 #else 102 static void check_pinning_enforcement(struct super_block *mnt_sb) 103 { 104 pr_info("load pinning engaged.\n"); 105 } 106 #endif 107 108 static void loadpin_sb_free_security(struct super_block *mnt_sb) 109 { 110 /* 111 * When unmounting the filesystem we were using for load 112 * pinning, we acknowledge the superblock release, but make sure 113 * no other modules or firmware can be loaded. 114 */ 115 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) { 116 pinned_root = ERR_PTR(-EIO); 117 pr_info("umount pinned fs: refusing further loads\n"); 118 } 119 } 120 121 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id, 122 bool contents) 123 { 124 struct super_block *load_root; 125 const char *origin = kernel_read_file_id_str(id); 126 127 /* 128 * If we will not know that we'll be seeing the full contents 129 * then we cannot trust a load will be complete and unchanged 130 * off disk. Treat all contents=false hooks as if there were 131 * no associated file struct. 132 */ 133 if (!contents) 134 file = NULL; 135 136 /* If the file id is excluded, ignore the pinning. */ 137 if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) && 138 ignore_read_file_id[id]) { 139 report_load(origin, file, "pinning-excluded"); 140 return 0; 141 } 142 143 /* This handles the older init_module API that has a NULL file. */ 144 if (!file) { 145 if (!enforce) { 146 report_load(origin, NULL, "old-api-pinning-ignored"); 147 return 0; 148 } 149 150 report_load(origin, NULL, "old-api-denied"); 151 return -EPERM; 152 } 153 154 load_root = file->f_path.mnt->mnt_sb; 155 156 /* First loaded module/firmware defines the root for all others. */ 157 spin_lock(&pinned_root_spinlock); 158 /* 159 * pinned_root is only NULL at startup. Otherwise, it is either 160 * a valid reference, or an ERR_PTR. 161 */ 162 if (!pinned_root) { 163 pinned_root = load_root; 164 /* 165 * Unlock now since it's only pinned_root we care about. 166 * In the worst case, we will (correctly) report pinning 167 * failures before we have announced that pinning is 168 * enforcing. This would be purely cosmetic. 169 */ 170 spin_unlock(&pinned_root_spinlock); 171 check_pinning_enforcement(pinned_root); 172 report_load(origin, file, "pinned"); 173 } else { 174 spin_unlock(&pinned_root_spinlock); 175 } 176 177 if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) { 178 if (unlikely(!enforce)) { 179 report_load(origin, file, "pinning-ignored"); 180 return 0; 181 } 182 183 report_load(origin, file, "denied"); 184 return -EPERM; 185 } 186 187 return 0; 188 } 189 190 static int loadpin_load_data(enum kernel_load_data_id id, bool contents) 191 { 192 return loadpin_read_file(NULL, (enum kernel_read_file_id) id, contents); 193 } 194 195 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = { 196 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security), 197 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file), 198 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data), 199 }; 200 201 static void __init parse_exclude(void) 202 { 203 int i, j; 204 char *cur; 205 206 /* 207 * Make sure all the arrays stay within expected sizes. This 208 * is slightly weird because kernel_read_file_str[] includes 209 * READING_MAX_ID, which isn't actually meaningful here. 210 */ 211 BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) != 212 ARRAY_SIZE(ignore_read_file_id)); 213 BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) < 214 ARRAY_SIZE(ignore_read_file_id)); 215 216 for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) { 217 cur = exclude_read_files[i]; 218 if (!cur) 219 break; 220 if (*cur == '\0') 221 continue; 222 223 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) { 224 if (strcmp(cur, kernel_read_file_str[j]) == 0) { 225 pr_info("excluding: %s\n", 226 kernel_read_file_str[j]); 227 ignore_read_file_id[j] = 1; 228 /* 229 * Can not break, because one read_file_str 230 * may map to more than on read_file_id. 231 */ 232 } 233 } 234 } 235 } 236 237 static int __init loadpin_init(void) 238 { 239 pr_info("ready to pin (currently %senforcing)\n", 240 enforce ? "" : "not "); 241 parse_exclude(); 242 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin"); 243 return 0; 244 } 245 246 DEFINE_LSM(loadpin) = { 247 .name = "loadpin", 248 .init = loadpin_init, 249 }; 250 251 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */ 252 module_param(enforce, int, 0); 253 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning"); 254 module_param_array_named(exclude, exclude_read_files, charp, NULL, 0); 255 MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types"); 256