diff options
Diffstat (limited to 'security/loadpin')
| -rw-r--r-- | security/loadpin/Kconfig | 41 | ||||
| -rw-r--r-- | security/loadpin/Makefile | 2 | ||||
| -rw-r--r-- | security/loadpin/loadpin.c | 435 |
3 files changed, 478 insertions, 0 deletions
diff --git a/security/loadpin/Kconfig b/security/loadpin/Kconfig new file mode 100644 index 000000000..6724eaba3 --- /dev/null +++ b/security/loadpin/Kconfig @@ -0,0 +1,41 @@ +# 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". + +config SECURITY_LOADPIN_VERITY + bool "Allow reading files from certain other filesystems that use dm-verity" + depends on SECURITY_LOADPIN && DM_VERITY=y && SECURITYFS + help + If selected LoadPin can allow reading files from filesystems + that use dm-verity. LoadPin maintains a list of verity root + digests it considers trusted. A verity backed filesystem is + considered trusted if its root digest is found in the list + of trusted digests. + + The list of trusted verity can be populated through an ioctl + on the LoadPin securityfs entry 'dm-verity'. The ioctl + expects a file descriptor of a file with verity digests as + parameter. The file must be located on the pinned root and + start with the line: + + # LOADPIN_TRUSTED_VERITY_ROOT_DIGESTS + + This is followed by the verity digests, with one digest per + line. 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..110a5ab2b --- /dev/null +++ b/security/loadpin/loadpin.c @@ -0,0 +1,435 @@ +// 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> + +#define VERITY_DIGEST_FILE_HEADER "# LOADPIN_TRUSTED_VERITY_ROOT_DIGESTS" + +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_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) && !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_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, +}; + +#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; + struct dm_verity_loadpin_trusted_root_digest *trd; + + if (d == data) { + /* first line, validate header */ + if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) { + rc = -EPROTO; + goto err; + } + + continue; + } + + len = strlen(d); + + 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; + + switch (cmd) { + case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS: + if (copy_from_user(&fd, uarg, sizeof(fd))) + return -EFAULT; + + 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"); |