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// 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_read_file(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_load_data(enum kernel_load_data_id id, bool contents)
{
return loadpin_read_file(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");
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