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 enabled = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENABLED); 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 = "enabled", 64 .data = &enabled, 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 ro = bdev_read_only(mnt_sb->s_bdev); 88 pr_info("dev(%u,%u): %s\n", 89 MAJOR(mnt_sb->s_bdev->bd_dev), 90 MINOR(mnt_sb->s_bdev->bd_dev), 91 ro ? "read-only" : "writable"); 92 } else 93 pr_info("mnt_sb lacks block device, treating as: writable\n"); 94 95 if (!ro) { 96 if (!register_sysctl_paths(loadpin_sysctl_path, 97 loadpin_sysctl_table)) 98 pr_notice("sysctl registration failed!\n"); 99 else 100 pr_info("load pinning can be disabled.\n"); 101 } else 102 pr_info("load pinning engaged.\n"); 103 } 104 #else 105 static void check_pinning_enforcement(struct super_block *mnt_sb) 106 { 107 pr_info("load pinning engaged.\n"); 108 } 109 #endif 110 111 static void loadpin_sb_free_security(struct super_block *mnt_sb) 112 { 113 /* 114 * When unmounting the filesystem we were using for load 115 * pinning, we acknowledge the superblock release, but make sure 116 * no other modules or firmware can be loaded. 117 */ 118 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) { 119 pinned_root = ERR_PTR(-EIO); 120 pr_info("umount pinned fs: refusing further loads\n"); 121 } 122 } 123 124 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id) 125 { 126 struct super_block *load_root; 127 const char *origin = kernel_read_file_id_str(id); 128 129 /* This handles the older init_module API that has a NULL file. */ 130 if (!file) { 131 if (!enabled) { 132 report_load(origin, NULL, "old-api-pinning-ignored"); 133 return 0; 134 } 135 136 report_load(origin, NULL, "old-api-denied"); 137 return -EPERM; 138 } 139 140 load_root = file->f_path.mnt->mnt_sb; 141 142 /* First loaded module/firmware defines the root for all others. */ 143 spin_lock(&pinned_root_spinlock); 144 /* 145 * pinned_root is only NULL at startup. Otherwise, it is either 146 * a valid reference, or an ERR_PTR. 147 */ 148 if (!pinned_root) { 149 pinned_root = load_root; 150 /* 151 * Unlock now since it's only pinned_root we care about. 152 * In the worst case, we will (correctly) report pinning 153 * failures before we have announced that pinning is 154 * enabled. This would be purely cosmetic. 155 */ 156 spin_unlock(&pinned_root_spinlock); 157 check_pinning_enforcement(pinned_root); 158 report_load(origin, file, "pinned"); 159 } else { 160 spin_unlock(&pinned_root_spinlock); 161 } 162 163 if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) { 164 if (unlikely(!enabled)) { 165 report_load(origin, file, "pinning-ignored"); 166 return 0; 167 } 168 169 report_load(origin, file, "denied"); 170 return -EPERM; 171 } 172 173 return 0; 174 } 175 176 static int loadpin_load_data(enum kernel_load_data_id id) 177 { 178 return loadpin_read_file(NULL, (enum kernel_read_file_id) id); 179 } 180 181 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = { 182 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security), 183 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file), 184 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data), 185 }; 186 187 void __init loadpin_add_hooks(void) 188 { 189 pr_info("ready to pin (currently %sabled)", enabled ? "en" : "dis"); 190 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin"); 191 } 192 193 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */ 194 module_param(enabled, int, 0); 195 MODULE_PARM_DESC(enabled, "Pin module/firmware loading (default: true)"); 196