1// SPDX-License-Identifier: GPL-2.0
2/* Lock down the kernel
3 *
4 * Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public Licence
9 * as published by the Free Software Foundation; either version
10 * 2 of the Licence, or (at your option) any later version.
11 */
12
13#include <linux/security.h>
14#include <linux/export.h>
15#include <linux/lsm_hooks.h>
16
17static enum lockdown_reason kernel_locked_down;
18
19static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
20						 LOCKDOWN_INTEGRITY_MAX,
21						 LOCKDOWN_CONFIDENTIALITY_MAX};
22
23/*
24 * Put the kernel into lock-down mode.
25 */
26static int lock_kernel_down(const char *where, enum lockdown_reason level)
27{
28	if (kernel_locked_down >= level)
29		return -EPERM;
30
31	kernel_locked_down = level;
32	pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
33		  where);
34	return 0;
35}
36
37static int __init lockdown_param(char *level)
38{
39	if (!level)
40		return -EINVAL;
41
42	if (strcmp(level, "integrity") == 0)
43		lock_kernel_down("command line", LOCKDOWN_INTEGRITY_MAX);
44	else if (strcmp(level, "confidentiality") == 0)
45		lock_kernel_down("command line", LOCKDOWN_CONFIDENTIALITY_MAX);
46	else
47		return -EINVAL;
48
49	return 0;
50}
51
52early_param("lockdown", lockdown_param);
53
54/**
55 * lockdown_is_locked_down - Find out if the kernel is locked down
56 * @what: Tag to use in notice generated if lockdown is in effect
57 */
58static int lockdown_is_locked_down(enum lockdown_reason what)
59{
60	if (WARN(what >= LOCKDOWN_CONFIDENTIALITY_MAX,
61		 "Invalid lockdown reason"))
62		return -EPERM;
63
64	if (kernel_locked_down >= what) {
65		if (lockdown_reasons[what])
66			pr_notice("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
67				  current->comm, lockdown_reasons[what]);
68		return -EPERM;
69	}
70
71	return 0;
72}
73
74static struct security_hook_list lockdown_hooks[] __lsm_ro_after_init = {
75	LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
76};
77
78static int __init lockdown_lsm_init(void)
79{
80#if defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY)
81	lock_kernel_down("Kernel configuration", LOCKDOWN_INTEGRITY_MAX);
82#elif defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY)
83	lock_kernel_down("Kernel configuration", LOCKDOWN_CONFIDENTIALITY_MAX);
84#endif
85	security_add_hooks(lockdown_hooks, ARRAY_SIZE(lockdown_hooks),
86			   "lockdown");
87	return 0;
88}
89
90static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
91			     loff_t *ppos)
92{
93	char temp[80];
94	int i, offset = 0;
95
96	for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
97		enum lockdown_reason level = lockdown_levels[i];
98
99		if (lockdown_reasons[level]) {
100			const char *label = lockdown_reasons[level];
101
102			if (kernel_locked_down == level)
103				offset += sprintf(temp+offset, "[%s] ", label);
104			else
105				offset += sprintf(temp+offset, "%s ", label);
106		}
107	}
108
109	/* Convert the last space to a newline if needed. */
110	if (offset > 0)
111		temp[offset-1] = '\n';
112
113	return simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
114}
115
116static ssize_t lockdown_write(struct file *file, const char __user *buf,
117			      size_t n, loff_t *ppos)
118{
119	char *state;
120	int i, len, err = -EINVAL;
121
122	state = memdup_user_nul(buf, n);
123	if (IS_ERR(state))
124		return PTR_ERR(state);
125
126	len = strlen(state);
127	if (len && state[len-1] == '\n') {
128		state[len-1] = '\0';
129		len--;
130	}
131
132	for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
133		enum lockdown_reason level = lockdown_levels[i];
134		const char *label = lockdown_reasons[level];
135
136		if (label && !strcmp(state, label))
137			err = lock_kernel_down("securityfs", level);
138	}
139
140	kfree(state);
141	return err ? err : n;
142}
143
144static const struct file_operations lockdown_ops = {
145	.read  = lockdown_read,
146	.write = lockdown_write,
147};
148
149static int __init lockdown_secfs_init(void)
150{
151	struct dentry *dentry;
152
153	dentry = securityfs_create_file("lockdown", 0644, NULL, NULL,
154					&lockdown_ops);
155	return PTR_ERR_OR_ZERO(dentry);
156}
157
158core_initcall(lockdown_secfs_init);
159
160#ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
161DEFINE_EARLY_LSM(lockdown) = {
162#else
163DEFINE_LSM(lockdown) = {
164#endif
165	.name = "lockdown",
166	.init = lockdown_lsm_init,
167};
168