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 struct super_block *pinned_root; 41 static DEFINE_SPINLOCK(pinned_root_spinlock); 42 43 #ifdef CONFIG_SYSCTL 44 static int zero; 45 static int one = 1; 46 47 static struct ctl_path loadpin_sysctl_path[] = { 48 { .procname = "kernel", }, 49 { .procname = "loadpin", }, 50 { } 51 }; 52 53 static struct ctl_table loadpin_sysctl_table[] = { 54 { 55 .procname = "enforce", 56 .data = &enforce, 57 .maxlen = sizeof(int), 58 .mode = 0644, 59 .proc_handler = proc_dointvec_minmax, 60 .extra1 = &zero, 61 .extra2 = &one, 62 }, 63 { } 64 }; 65 66 /* 67 * This must be called after early kernel init, since then the rootdev 68 * is available. 69 */ 70 static void check_pinning_enforcement(struct super_block *mnt_sb) 71 { 72 bool ro = false; 73 74 /* 75 * If load pinning is not enforced via a read-only block 76 * device, allow sysctl to change modes for testing. 77 */ 78 if (mnt_sb->s_bdev) { 79 char bdev[BDEVNAME_SIZE]; 80 81 ro = bdev_read_only(mnt_sb->s_bdev); 82 bdevname(mnt_sb->s_bdev, bdev); 83 pr_info("%s (%u:%u): %s\n", bdev, 84 MAJOR(mnt_sb->s_bdev->bd_dev), 85 MINOR(mnt_sb->s_bdev->bd_dev), 86 ro ? "read-only" : "writable"); 87 } else 88 pr_info("mnt_sb lacks block device, treating as: writable\n"); 89 90 if (!ro) { 91 if (!register_sysctl_paths(loadpin_sysctl_path, 92 loadpin_sysctl_table)) 93 pr_notice("sysctl registration failed!\n"); 94 else 95 pr_info("enforcement can be disabled.\n"); 96 } else 97 pr_info("load pinning engaged.\n"); 98 } 99 #else 100 static void check_pinning_enforcement(struct super_block *mnt_sb) 101 { 102 pr_info("load pinning engaged.\n"); 103 } 104 #endif 105 106 static void loadpin_sb_free_security(struct super_block *mnt_sb) 107 { 108 /* 109 * When unmounting the filesystem we were using for load 110 * pinning, we acknowledge the superblock release, but make sure 111 * no other modules or firmware can be loaded. 112 */ 113 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) { 114 pinned_root = ERR_PTR(-EIO); 115 pr_info("umount pinned fs: refusing further loads\n"); 116 } 117 } 118 119 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id) 120 { 121 struct super_block *load_root; 122 const char *origin = kernel_read_file_id_str(id); 123 124 /* This handles the older init_module API that has a NULL file. */ 125 if (!file) { 126 if (!enforce) { 127 report_load(origin, NULL, "old-api-pinning-ignored"); 128 return 0; 129 } 130 131 report_load(origin, NULL, "old-api-denied"); 132 return -EPERM; 133 } 134 135 load_root = file->f_path.mnt->mnt_sb; 136 137 /* First loaded module/firmware defines the root for all others. */ 138 spin_lock(&pinned_root_spinlock); 139 /* 140 * pinned_root is only NULL at startup. Otherwise, it is either 141 * a valid reference, or an ERR_PTR. 142 */ 143 if (!pinned_root) { 144 pinned_root = load_root; 145 /* 146 * Unlock now since it's only pinned_root we care about. 147 * In the worst case, we will (correctly) report pinning 148 * failures before we have announced that pinning is 149 * enforcing. This would be purely cosmetic. 150 */ 151 spin_unlock(&pinned_root_spinlock); 152 check_pinning_enforcement(pinned_root); 153 report_load(origin, file, "pinned"); 154 } else { 155 spin_unlock(&pinned_root_spinlock); 156 } 157 158 if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) { 159 if (unlikely(!enforce)) { 160 report_load(origin, file, "pinning-ignored"); 161 return 0; 162 } 163 164 report_load(origin, file, "denied"); 165 return -EPERM; 166 } 167 168 return 0; 169 } 170 171 static int loadpin_load_data(enum kernel_load_data_id id) 172 { 173 return loadpin_read_file(NULL, (enum kernel_read_file_id) id); 174 } 175 176 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = { 177 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security), 178 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file), 179 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data), 180 }; 181 182 static int __init loadpin_init(void) 183 { 184 pr_info("ready to pin (currently %senforcing)\n", 185 enforce ? "" : "not "); 186 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin"); 187 return 0; 188 } 189 190 DEFINE_LSM(loadpin) = { 191 .name = "loadpin", 192 .init = loadpin_init, 193 }; 194 195 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */ 196 module_param(enforce, int, 0); 197 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning"); 198