1 /* 2 * Module and Firmware Pinning Security Module 3 * 4 * Copyright 2011-2016 Google Inc. 5 * 6 * Author: Kees Cook <keescook@chromium.org> 7 * 8 * This software is licensed under the terms of the GNU General Public 9 * License version 2, as published by the Free Software Foundation, and 10 * may be copied, distributed, and modified under those terms. 11 * 12 * This program is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15 * GNU General Public License for more details. 16 */ 17 18 #define pr_fmt(fmt) "LoadPin: " fmt 19 20 #include <linux/module.h> 21 #include <linux/fs.h> 22 #include <linux/lsm_hooks.h> 23 #include <linux/mount.h> 24 #include <linux/path.h> 25 #include <linux/sched.h> /* current */ 26 #include <linux/string_helpers.h> 27 28 static void report_load(const char *origin, struct file *file, char *operation) 29 { 30 char *cmdline, *pathname; 31 32 pathname = kstrdup_quotable_file(file, GFP_KERNEL); 33 cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL); 34 35 pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n", 36 origin, operation, 37 (pathname && pathname[0] != '<') ? "\"" : "", 38 pathname, 39 (pathname && pathname[0] != '<') ? "\"" : "", 40 task_pid_nr(current), 41 cmdline ? "\"" : "", cmdline, cmdline ? "\"" : ""); 42 43 kfree(cmdline); 44 kfree(pathname); 45 } 46 47 static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE); 48 static struct super_block *pinned_root; 49 static DEFINE_SPINLOCK(pinned_root_spinlock); 50 51 #ifdef CONFIG_SYSCTL 52 static int zero; 53 static int one = 1; 54 55 static struct ctl_path loadpin_sysctl_path[] = { 56 { .procname = "kernel", }, 57 { .procname = "loadpin", }, 58 { } 59 }; 60 61 static struct ctl_table loadpin_sysctl_table[] = { 62 { 63 .procname = "enforce", 64 .data = &enforce, 65 .maxlen = sizeof(int), 66 .mode = 0644, 67 .proc_handler = proc_dointvec_minmax, 68 .extra1 = &zero, 69 .extra2 = &one, 70 }, 71 { } 72 }; 73 74 /* 75 * This must be called after early kernel init, since then the rootdev 76 * is available. 77 */ 78 static void check_pinning_enforcement(struct super_block *mnt_sb) 79 { 80 bool ro = false; 81 82 /* 83 * If load pinning is not enforced via a read-only block 84 * device, allow sysctl to change modes for testing. 85 */ 86 if (mnt_sb->s_bdev) { 87 char bdev[BDEVNAME_SIZE]; 88 89 ro = bdev_read_only(mnt_sb->s_bdev); 90 bdevname(mnt_sb->s_bdev, bdev); 91 pr_info("%s (%u:%u): %s\n", bdev, 92 MAJOR(mnt_sb->s_bdev->bd_dev), 93 MINOR(mnt_sb->s_bdev->bd_dev), 94 ro ? "read-only" : "writable"); 95 } else 96 pr_info("mnt_sb lacks block device, treating as: writable\n"); 97 98 if (!ro) { 99 if (!register_sysctl_paths(loadpin_sysctl_path, 100 loadpin_sysctl_table)) 101 pr_notice("sysctl registration failed!\n"); 102 else 103 pr_info("enforcement can be disabled.\n"); 104 } else 105 pr_info("load pinning engaged.\n"); 106 } 107 #else 108 static void check_pinning_enforcement(struct super_block *mnt_sb) 109 { 110 pr_info("load pinning engaged.\n"); 111 } 112 #endif 113 114 static void loadpin_sb_free_security(struct super_block *mnt_sb) 115 { 116 /* 117 * When unmounting the filesystem we were using for load 118 * pinning, we acknowledge the superblock release, but make sure 119 * no other modules or firmware can be loaded. 120 */ 121 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) { 122 pinned_root = ERR_PTR(-EIO); 123 pr_info("umount pinned fs: refusing further loads\n"); 124 } 125 } 126 127 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id) 128 { 129 struct super_block *load_root; 130 const char *origin = kernel_read_file_id_str(id); 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 int __init loadpin_init(void) 191 { 192 pr_info("ready to pin (currently %senforcing)\n", 193 enforce ? "" : "not "); 194 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin"); 195 return 0; 196 } 197 198 DEFINE_LSM(loadpin) = { 199 .name = "loadpin", 200 .init = loadpin_init, 201 }; 202 203 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */ 204 module_param(enforce, int, 0); 205 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning"); 206