| 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"); |