| // SPDX-License-Identifier: GPL-2.0-only |
| /* |
| * Module and Firmware Pinning Security Module |
| * |
| * Copyright 2011-2016 Google Inc. |
| * |
| * Author: Kees Cook <keescook@chromium.org> |
| */ |
| |
| #define pr_fmt(fmt) "LoadPin: " fmt |
| |
| #include <linux/module.h> |
| #include <linux/fs.h> |
| #include <linux/kernel_read_file.h> |
| #include <linux/lsm_hooks.h> |
| #include <linux/mount.h> |
| #include <linux/blkdev.h> |
| #include <linux/path.h> |
| #include <linux/sched.h> /* current */ |
| #include <linux/string_helpers.h> |
| #include <linux/dm-verity-loadpin.h> |
| #include <uapi/linux/loadpin.h> |
| |
| static void report_load(const char *origin, struct file *file, char *operation) |
| { |
| char *cmdline, *pathname; |
| |
| pathname = kstrdup_quotable_file(file, GFP_KERNEL); |
| cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL); |
| |
| pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n", |
| origin, operation, |
| (pathname && pathname[0] != '<') ? "\"" : "", |
| pathname, |
| (pathname && pathname[0] != '<') ? "\"" : "", |
| task_pid_nr(current), |
| cmdline ? "\"" : "", cmdline, cmdline ? "\"" : ""); |
| |
| kfree(cmdline); |
| kfree(pathname); |
| } |
| |
| static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE); |
| static char *exclude_read_files[READING_MAX_ID]; |
| static int ignore_read_file_id[READING_MAX_ID] __ro_after_init; |
| static struct super_block *pinned_root; |
| static DEFINE_SPINLOCK(pinned_root_spinlock); |
| #ifdef CONFIG_SECURITY_LOADPIN_VERITY |
| static bool deny_reading_verity_digests; |
| #endif |
| |
| #ifdef CONFIG_SYSCTL |
| |
| static struct ctl_path loadpin_sysctl_path[] = { |
| { .procname = "kernel", }, |
| { .procname = "loadpin", }, |
| { } |
| }; |
| |
| static struct ctl_table loadpin_sysctl_table[] = { |
| { |
| .procname = "enforce", |
| .data = &enforce, |
| .maxlen = sizeof(int), |
| .mode = 0644, |
| .proc_handler = proc_dointvec_minmax, |
| .extra1 = SYSCTL_ZERO, |
| .extra2 = SYSCTL_ONE, |
| }, |
| { } |
| }; |
| |
| /* |
| * This must be called after early kernel init, since then the rootdev |
| * is available. |
| */ |
| static void check_pinning_enforcement(struct super_block *mnt_sb) |
| { |
| bool ro = false; |
| |
| /* |
| * If load pinning is not enforced via a read-only block |
| * device, allow sysctl to change modes for testing. |
| */ |
| if (mnt_sb->s_bdev) { |
| ro = bdev_read_only(mnt_sb->s_bdev); |
| pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev, |
| MAJOR(mnt_sb->s_bdev->bd_dev), |
| MINOR(mnt_sb->s_bdev->bd_dev), |
| ro ? "read-only" : "writable"); |
| } else |
| pr_info("mnt_sb lacks block device, treating as: writable\n"); |
| |
| if (!ro) { |
| if (!register_sysctl_paths(loadpin_sysctl_path, |
| loadpin_sysctl_table)) |
| pr_notice("sysctl registration failed!\n"); |
| else |
| pr_info("enforcement can be disabled.\n"); |
| } else |
| pr_info("load pinning engaged.\n"); |
| } |
| #else |
| static void check_pinning_enforcement(struct super_block *mnt_sb) |
| { |
| pr_info("load pinning engaged.\n"); |
| } |
| #endif |
| |
| static void loadpin_sb_free_security(struct super_block *mnt_sb) |
| { |
| /* |
| * When unmounting the filesystem we were using for load |
| * pinning, we acknowledge the superblock release, but make sure |
| * no other modules or firmware can be loaded. |
| */ |
| if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) { |
| pinned_root = ERR_PTR(-EIO); |
| pr_info("umount pinned fs: refusing further loads\n"); |
| } |
| } |
| |
| static int loadpin_read_file(struct file *file, enum kernel_read_file_id id, |
| bool contents) |
| { |
| struct super_block *load_root; |
| const char *origin = kernel_read_file_id_str(id); |
| |
| /* |
| * If we will not know that we'll be seeing the full contents |
| * then we cannot trust a load will be complete and unchanged |
| * off disk. Treat all contents=false hooks as if there were |
| * no associated file struct. |
| */ |
| if (!contents) |
| file = NULL; |
| |
| /* If the file id is excluded, ignore the pinning. */ |
| if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) && |
| ignore_read_file_id[id]) { |
| report_load(origin, file, "pinning-excluded"); |
| return 0; |
| } |
| |
| /* This handles the older init_module API that has a NULL file. */ |
| if (!file) { |
| if (!enforce) { |
| report_load(origin, NULL, "old-api-pinning-ignored"); |
| return 0; |
| } |
| |
| report_load(origin, NULL, "old-api-denied"); |
| return -EPERM; |
| } |
| |
| load_root = file->f_path.mnt->mnt_sb; |
| |
| /* First loaded module/firmware defines the root for all others. */ |
| spin_lock(&pinned_root_spinlock); |
| /* |
| * pinned_root is only NULL at startup. Otherwise, it is either |
| * a valid reference, or an ERR_PTR. |
| */ |
| if (!pinned_root) { |
| pinned_root = load_root; |
| /* |
| * Unlock now since it's only pinned_root we care about. |
| * In the worst case, we will (correctly) report pinning |
| * failures before we have announced that pinning is |
| * enforcing. This would be purely cosmetic. |
| */ |
| spin_unlock(&pinned_root_spinlock); |
| check_pinning_enforcement(pinned_root); |
| report_load(origin, file, "pinned"); |
| } else { |
| spin_unlock(&pinned_root_spinlock); |
| } |
| |
| if (IS_ERR_OR_NULL(pinned_root) || |
| ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(load_root->s_bdev))) { |
| if (unlikely(!enforce)) { |
| report_load(origin, file, "pinning-ignored"); |
| return 0; |
| } |
| |
| report_load(origin, file, "denied"); |
| return -EPERM; |
| } |
| |
| return 0; |
| } |
| |
| static int loadpin_load_data(enum kernel_load_data_id id, bool contents) |
| { |
| return loadpin_read_file(NULL, (enum kernel_read_file_id) id, contents); |
| } |
| |
| static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = { |
| LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security), |
| LSM_HOOK_INIT(kernel_read_file, loadpin_read_file), |
| LSM_HOOK_INIT(kernel_load_data, loadpin_load_data), |
| }; |
| |
| static void __init parse_exclude(void) |
| { |
| int i, j; |
| char *cur; |
| |
| /* |
| * Make sure all the arrays stay within expected sizes. This |
| * is slightly weird because kernel_read_file_str[] includes |
| * READING_MAX_ID, which isn't actually meaningful here. |
| */ |
| BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) != |
| ARRAY_SIZE(ignore_read_file_id)); |
| BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) < |
| ARRAY_SIZE(ignore_read_file_id)); |
| |
| for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) { |
| cur = exclude_read_files[i]; |
| if (!cur) |
| break; |
| if (*cur == '\0') |
| continue; |
| |
| for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) { |
| if (strcmp(cur, kernel_read_file_str[j]) == 0) { |
| pr_info("excluding: %s\n", |
| kernel_read_file_str[j]); |
| ignore_read_file_id[j] = 1; |
| /* |
| * Can not break, because one read_file_str |
| * may map to more than on read_file_id. |
| */ |
| } |
| } |
| } |
| } |
| |
| static int __init loadpin_init(void) |
| { |
| pr_info("ready to pin (currently %senforcing)\n", |
| enforce ? "" : "not "); |
| parse_exclude(); |
| security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin"); |
| |
| return 0; |
| } |
| |
| DEFINE_LSM(loadpin) = { |
| .name = "loadpin", |
| .init = loadpin_init, |
| }; |
| |
| #ifdef CONFIG_SECURITY_LOADPIN_VERITY |
| |
| enum loadpin_securityfs_interface_index { |
| LOADPIN_DM_VERITY, |
| }; |
| |
| static int read_trusted_verity_root_digests(unsigned int fd) |
| { |
| struct fd f; |
| void *data; |
| int rc; |
| char *p, *d; |
| |
| if (deny_reading_verity_digests) |
| return -EPERM; |
| |
| /* The list of trusted root digests can only be set up once */ |
| if (!list_empty(&dm_verity_loadpin_trusted_root_digests)) |
| return -EPERM; |
| |
| f = fdget(fd); |
| if (!f.file) |
| return -EINVAL; |
| |
| data = kzalloc(SZ_4K, GFP_KERNEL); |
| if (!data) { |
| rc = -ENOMEM; |
| goto err; |
| } |
| |
| rc = kernel_read_file(f.file, 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY); |
| if (rc < 0) |
| goto err; |
| |
| p = data; |
| p[rc] = '\0'; |
| p = strim(p); |
| |
| p = strim(data); |
| while ((d = strsep(&p, "\n")) != NULL) { |
| int len = strlen(d); |
| struct dm_verity_loadpin_trusted_root_digest *trd; |
| |
| if (len % 2) { |
| rc = -EPROTO; |
| goto err; |
| } |
| |
| len /= 2; |
| |
| trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL); |
| if (!trd) { |
| rc = -ENOMEM; |
| goto err; |
| } |
| |
| if (hex2bin(trd->data, d, len)) { |
| kfree(trd); |
| rc = -EPROTO; |
| goto err; |
| } |
| |
| trd->len = len; |
| |
| list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests); |
| } |
| |
| if (list_empty(&dm_verity_loadpin_trusted_root_digests)) { |
| rc = -EPROTO; |
| goto err; |
| } |
| |
| kfree(data); |
| fdput(f); |
| |
| return 0; |
| |
| err: |
| kfree(data); |
| |
| /* any failure in loading/parsing invalidates the entire list */ |
| { |
| struct dm_verity_loadpin_trusted_root_digest *trd, *tmp; |
| |
| list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) { |
| list_del(&trd->node); |
| kfree(trd); |
| } |
| } |
| |
| /* disallow further attempts after reading a corrupt/invalid file */ |
| deny_reading_verity_digests = true; |
| |
| fdput(f); |
| |
| return rc; |
| } |
| |
| /******************************** securityfs ********************************/ |
| |
| static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) |
| { |
| void __user *uarg = (void __user *)arg; |
| unsigned int fd; |
| int rc; |
| |
| switch (cmd) { |
| case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS: |
| rc = copy_from_user(&fd, uarg, sizeof(fd)); |
| if (rc) |
| return rc; |
| |
| return read_trusted_verity_root_digests(fd); |
| |
| default: |
| return -EINVAL; |
| } |
| } |
| |
| static const struct file_operations loadpin_dm_verity_ops = { |
| .unlocked_ioctl = dm_verity_ioctl, |
| .compat_ioctl = compat_ptr_ioctl, |
| }; |
| |
| /** |
| * init_loadpin_securityfs - create the securityfs directory for LoadPin |
| * |
| * We can not put this method normally under the loadpin_init() code path since |
| * the security subsystem gets initialized before the vfs caches. |
| * |
| * Returns 0 if the securityfs directory creation was successful. |
| */ |
| static int __init init_loadpin_securityfs(void) |
| { |
| struct dentry *loadpin_dir, *dentry; |
| |
| loadpin_dir = securityfs_create_dir("loadpin", NULL); |
| if (IS_ERR(loadpin_dir)) { |
| pr_err("LoadPin: could not create securityfs dir: %ld\n", |
| PTR_ERR(loadpin_dir)); |
| return PTR_ERR(loadpin_dir); |
| } |
| |
| dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir, |
| (void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops); |
| if (IS_ERR(dentry)) { |
| pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n", |
| PTR_ERR(dentry)); |
| return PTR_ERR(dentry); |
| } |
| |
| return 0; |
| } |
| |
| fs_initcall(init_loadpin_securityfs); |
| |
| #endif /* CONFIG_SECURITY_LOADPIN_VERITY */ |
| |
| /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */ |
| module_param(enforce, int, 0); |
| MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning"); |
| module_param_array_named(exclude, exclude_read_files, charp, NULL, 0); |
| MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types"); |