diff options
Diffstat (limited to 'security/loadpin')
| -rw-r--r-- | security/loadpin/Kconfig | 20 | ||||
| -rw-r--r-- | security/loadpin/Makefile | 2 | ||||
| -rw-r--r-- | security/loadpin/loadpin.c | 261 |
3 files changed, 283 insertions, 0 deletions
diff --git a/security/loadpin/Kconfig b/security/loadpin/Kconfig new file mode 100644 index 000000000..91be65dec --- /dev/null +++ b/security/loadpin/Kconfig @@ -0,0 +1,20 @@ +# SPDX-License-Identifier: GPL-2.0-only +config SECURITY_LOADPIN + bool "Pin load of kernel files (modules, fw, etc) to one filesystem" + depends on SECURITY && BLOCK + help + Any files read through the kernel file reading interface + (kernel modules, firmware, kexec images, security policy) + can be pinned to the first filesystem used for loading. When + enabled, any files that come from other filesystems will be + rejected. This is best used on systems without an initrd that + have a root filesystem backed by a read-only device such as + dm-verity or a CDROM. + +config SECURITY_LOADPIN_ENFORCE + bool "Enforce LoadPin at boot" + depends on SECURITY_LOADPIN + help + If selected, LoadPin will enforce pinning at boot. If not + selected, it can be enabled at boot with the kernel parameter + "loadpin.enforce=1". diff --git a/security/loadpin/Makefile b/security/loadpin/Makefile new file mode 100644 index 000000000..0ead1c310 --- /dev/null +++ b/security/loadpin/Makefile @@ -0,0 +1,2 @@ +# SPDX-License-Identifier: GPL-2.0-only +obj-$(CONFIG_SECURITY_LOADPIN) += loadpin.o diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c new file mode 100644 index 000000000..5fce105a3 --- /dev/null +++ b/security/loadpin/loadpin.c @@ -0,0 +1,261 @@ +// 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"); |