blob: 44521582dcba2464de36fa4119293df724dd1c51 [file] [log] [blame]
// 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;
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");