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