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/lsm_hooks.h> 15 #include <linux/mount.h> 16 #include <linux/path.h> 17 #include <linux/sched.h> /* current */ 18 #include <linux/string_helpers.h> 19 20 static void report_load(const char *origin, struct file *file, char *operation) 21 { 22 char *cmdline, *pathname; 23 24 pathname = kstrdup_quotable_file(file, GFP_KERNEL); 25 cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL); 26 27 pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n", 28 origin, operation, 29 (pathname && pathname[0] != '<') ? "\"" : "", 30 pathname, 31 (pathname && pathname[0] != '<') ? "\"" : "", 32 task_pid_nr(current), 33 cmdline ? "\"" : "", cmdline, cmdline ? "\"" : ""); 34 35 kfree(cmdline); 36 kfree(pathname); 37 } 38 39 static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE); 40 static char *exclude_read_files[READING_MAX_ID]; 41 static int ignore_read_file_id[READING_MAX_ID] __ro_after_init; 42 static struct super_block *pinned_root; 43 static DEFINE_SPINLOCK(pinned_root_spinlock); 44 45 #ifdef CONFIG_SYSCTL 46 static int zero; 47 static int one = 1; 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 = &zero, 63 .extra2 = &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 { 123 struct super_block *load_root; 124 const char *origin = kernel_read_file_id_str(id); 125 126 /* If the file id is excluded, ignore the pinning. */ 127 if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) && 128 ignore_read_file_id[id]) { 129 report_load(origin, file, "pinning-excluded"); 130 return 0; 131 } 132 133 /* This handles the older init_module API that has a NULL file. */ 134 if (!file) { 135 if (!enforce) { 136 report_load(origin, NULL, "old-api-pinning-ignored"); 137 return 0; 138 } 139 140 report_load(origin, NULL, "old-api-denied"); 141 return -EPERM; 142 } 143 144 load_root = file->f_path.mnt->mnt_sb; 145 146 /* First loaded module/firmware defines the root for all others. */ 147 spin_lock(&pinned_root_spinlock); 148 /* 149 * pinned_root is only NULL at startup. Otherwise, it is either 150 * a valid reference, or an ERR_PTR. 151 */ 152 if (!pinned_root) { 153 pinned_root = load_root; 154 /* 155 * Unlock now since it's only pinned_root we care about. 156 * In the worst case, we will (correctly) report pinning 157 * failures before we have announced that pinning is 158 * enforcing. This would be purely cosmetic. 159 */ 160 spin_unlock(&pinned_root_spinlock); 161 check_pinning_enforcement(pinned_root); 162 report_load(origin, file, "pinned"); 163 } else { 164 spin_unlock(&pinned_root_spinlock); 165 } 166 167 if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) { 168 if (unlikely(!enforce)) { 169 report_load(origin, file, "pinning-ignored"); 170 return 0; 171 } 172 173 report_load(origin, file, "denied"); 174 return -EPERM; 175 } 176 177 return 0; 178 } 179 180 static int loadpin_load_data(enum kernel_load_data_id id) 181 { 182 return loadpin_read_file(NULL, (enum kernel_read_file_id) id); 183 } 184 185 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = { 186 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security), 187 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file), 188 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data), 189 }; 190 191 static void __init parse_exclude(void) 192 { 193 int i, j; 194 char *cur; 195 196 /* 197 * Make sure all the arrays stay within expected sizes. This 198 * is slightly weird because kernel_read_file_str[] includes 199 * READING_MAX_ID, which isn't actually meaningful here. 200 */ 201 BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) != 202 ARRAY_SIZE(ignore_read_file_id)); 203 BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) < 204 ARRAY_SIZE(ignore_read_file_id)); 205 206 for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) { 207 cur = exclude_read_files[i]; 208 if (!cur) 209 break; 210 if (*cur == '\0') 211 continue; 212 213 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) { 214 if (strcmp(cur, kernel_read_file_str[j]) == 0) { 215 pr_info("excluding: %s\n", 216 kernel_read_file_str[j]); 217 ignore_read_file_id[j] = 1; 218 /* 219 * Can not break, because one read_file_str 220 * may map to more than on read_file_id. 221 */ 222 } 223 } 224 } 225 } 226 227 static int __init loadpin_init(void) 228 { 229 pr_info("ready to pin (currently %senforcing)\n", 230 enforce ? "" : "not "); 231 parse_exclude(); 232 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin"); 233 return 0; 234 } 235 236 DEFINE_LSM(loadpin) = { 237 .name = "loadpin", 238 .init = loadpin_init, 239 }; 240 241 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */ 242 module_param(enforce, int, 0); 243 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning"); 244 module_param_array_named(exclude, exclude_read_files, charp, NULL, 0); 245 MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types"); 246