| // 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> |
| |
| 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_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) { |
| char bdev[BDEVNAME_SIZE]; |
| |
| ro = bdev_read_only(mnt_sb->s_bdev); |
| bdevname(mnt_sb->s_bdev, bdev); |
| pr_info("%s (%u:%u): %s\n", 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_check(struct file *file, enum kernel_read_file_id id) |
| { |
| struct super_block *load_root; |
| const char *origin = kernel_read_file_id_str(id); |
| |
| /* 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) { |
| if (unlikely(!enforce)) { |
| report_load(origin, file, "pinning-ignored"); |
| return 0; |
| } |
| |
| report_load(origin, file, "denied"); |
| return -EPERM; |
| } |
| |
| return 0; |
| } |
| |
| static int loadpin_read_file(struct file *file, enum kernel_read_file_id id, |
| bool contents) |
| { |
| /* |
| * LoadPin only cares about the _origin_ of a file, not its |
| * contents, so we can ignore the "are full contents available" |
| * argument here. |
| */ |
| return loadpin_check(file, id); |
| } |
| |
| static int loadpin_load_data(enum kernel_load_data_id id, bool contents) |
| { |
| /* |
| * LoadPin only cares about the _origin_ of a file, not its |
| * contents, so a NULL file is passed, and we can ignore the |
| * state of "contents". |
| */ |
| return loadpin_check(NULL, (enum kernel_read_file_id) id); |
| } |
| |
| 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, |
| }; |
| |
| /* 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"); |