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/fs_struct.h> 23 #include <linux/lsm_hooks.h> 24 #include <linux/mount.h> 25 #include <linux/path.h> 26 #include <linux/sched.h> /* current */ 27 #include <linux/string_helpers.h> 28 29 static void report_load(const char *origin, struct file *file, char *operation) 30 { 31 char *cmdline, *pathname; 32 33 pathname = kstrdup_quotable_file(file, GFP_KERNEL); 34 cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL); 35 36 pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n", 37 origin, operation, 38 (pathname && pathname[0] != '<') ? "\"" : "", 39 pathname, 40 (pathname && pathname[0] != '<') ? "\"" : "", 41 task_pid_nr(current), 42 cmdline ? "\"" : "", cmdline, cmdline ? "\"" : ""); 43 44 kfree(cmdline); 45 kfree(pathname); 46 } 47 48 static int enabled = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENABLED); 49 static struct super_block *pinned_root; 50 static DEFINE_SPINLOCK(pinned_root_spinlock); 51 52 #ifdef CONFIG_SYSCTL 53 static int zero; 54 static int one = 1; 55 56 static struct ctl_path loadpin_sysctl_path[] = { 57 { .procname = "kernel", }, 58 { .procname = "loadpin", }, 59 { } 60 }; 61 62 static struct ctl_table loadpin_sysctl_table[] = { 63 { 64 .procname = "enabled", 65 .data = &enabled, 66 .maxlen = sizeof(int), 67 .mode = 0644, 68 .proc_handler = proc_dointvec_minmax, 69 .extra1 = &zero, 70 .extra2 = &one, 71 }, 72 { } 73 }; 74 75 /* 76 * This must be called after early kernel init, since then the rootdev 77 * is available. 78 */ 79 static void check_pinning_enforcement(struct super_block *mnt_sb) 80 { 81 bool ro = false; 82 83 /* 84 * If load pinning is not enforced via a read-only block 85 * device, allow sysctl to change modes for testing. 86 */ 87 if (mnt_sb->s_bdev) { 88 ro = bdev_read_only(mnt_sb->s_bdev); 89 pr_info("dev(%u,%u): %s\n", 90 MAJOR(mnt_sb->s_bdev->bd_dev), 91 MINOR(mnt_sb->s_bdev->bd_dev), 92 ro ? "read-only" : "writable"); 93 } else 94 pr_info("mnt_sb lacks block device, treating as: writable\n"); 95 96 if (!ro) { 97 if (!register_sysctl_paths(loadpin_sysctl_path, 98 loadpin_sysctl_table)) 99 pr_notice("sysctl registration failed!\n"); 100 else 101 pr_info("load pinning can be disabled.\n"); 102 } else 103 pr_info("load pinning engaged.\n"); 104 } 105 #else 106 static void check_pinning_enforcement(struct super_block *mnt_sb) 107 { 108 pr_info("load pinning engaged.\n"); 109 } 110 #endif 111 112 static void loadpin_sb_free_security(struct super_block *mnt_sb) 113 { 114 /* 115 * When unmounting the filesystem we were using for load 116 * pinning, we acknowledge the superblock release, but make sure 117 * no other modules or firmware can be loaded. 118 */ 119 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) { 120 pinned_root = ERR_PTR(-EIO); 121 pr_info("umount pinned fs: refusing further loads\n"); 122 } 123 } 124 125 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id) 126 { 127 struct super_block *load_root; 128 const char *origin = kernel_read_file_id_str(id); 129 130 /* This handles the older init_module API that has a NULL file. */ 131 if (!file) { 132 if (!enabled) { 133 report_load(origin, NULL, "old-api-pinning-ignored"); 134 return 0; 135 } 136 137 report_load(origin, NULL, "old-api-denied"); 138 return -EPERM; 139 } 140 141 load_root = file->f_path.mnt->mnt_sb; 142 143 /* First loaded module/firmware defines the root for all others. */ 144 spin_lock(&pinned_root_spinlock); 145 /* 146 * pinned_root is only NULL at startup. Otherwise, it is either 147 * a valid reference, or an ERR_PTR. 148 */ 149 if (!pinned_root) { 150 pinned_root = load_root; 151 /* 152 * Unlock now since it's only pinned_root we care about. 153 * In the worst case, we will (correctly) report pinning 154 * failures before we have announced that pinning is 155 * enabled. This would be purely cosmetic. 156 */ 157 spin_unlock(&pinned_root_spinlock); 158 check_pinning_enforcement(pinned_root); 159 report_load(origin, file, "pinned"); 160 } else { 161 spin_unlock(&pinned_root_spinlock); 162 } 163 164 if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) { 165 if (unlikely(!enabled)) { 166 report_load(origin, file, "pinning-ignored"); 167 return 0; 168 } 169 170 report_load(origin, file, "denied"); 171 return -EPERM; 172 } 173 174 return 0; 175 } 176 177 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = { 178 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security), 179 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file), 180 }; 181 182 void __init loadpin_add_hooks(void) 183 { 184 pr_info("ready to pin (currently %sabled)", enabled ? "en" : "dis"); 185 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin"); 186 } 187 188 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */ 189 module_param(enabled, int, 0); 190 MODULE_PARM_DESC(enabled, "Pin module/firmware loading (default: true)"); 191