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#include <uapi/linux/lsm.h>
17
18static enum lockdown_reason kernel_locked_down;
19
20static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
21						 LOCKDOWN_INTEGRITY_MAX,
22						 LOCKDOWN_CONFIDENTIALITY_MAX};
23
24/*
25 * Put the kernel into lock-down mode.
26 */
27static int lock_kernel_down(const char *where, enum lockdown_reason level)
28{
29	if (kernel_locked_down >= level)
30		return -EPERM;
31
32	kernel_locked_down = level;
33	pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
34		  where);
35	return 0;
36}
37
38static int __init lockdown_param(char *level)
39{
40	if (!level)
41		return -EINVAL;
42
43	if (strcmp(level, "integrity") == 0)
44		lock_kernel_down("command line", LOCKDOWN_INTEGRITY_MAX);
45	else if (strcmp(level, "confidentiality") == 0)
46		lock_kernel_down("command line", LOCKDOWN_CONFIDENTIALITY_MAX);
47	else
48		return -EINVAL;
49
50	return 0;
51}
52
53early_param("lockdown", lockdown_param);
54
55/**
56 * lockdown_is_locked_down - Find out if the kernel is locked down
57 * @what: Tag to use in notice generated if lockdown is in effect
58 */
59static int lockdown_is_locked_down(enum lockdown_reason what)
60{
61	if (WARN(what >= LOCKDOWN_CONFIDENTIALITY_MAX,
62		 "Invalid lockdown reason"))
63		return -EPERM;
64
65	if (kernel_locked_down >= what) {
66		if (lockdown_reasons[what])
67			pr_notice_ratelimited("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
68				  current->comm, lockdown_reasons[what]);
69		return -EPERM;
70	}
71
72	return 0;
73}
74
75static struct security_hook_list lockdown_hooks[] __ro_after_init = {
76	LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
77};
78
79const struct lsm_id lockdown_lsmid = {
80	.name = "lockdown",
81	.id = LSM_ID_LOCKDOWN,
82};
83
84static int __init lockdown_lsm_init(void)
85{
86#if defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY)
87	lock_kernel_down("Kernel configuration", LOCKDOWN_INTEGRITY_MAX);
88#elif defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY)
89	lock_kernel_down("Kernel configuration", LOCKDOWN_CONFIDENTIALITY_MAX);
90#endif
91	security_add_hooks(lockdown_hooks, ARRAY_SIZE(lockdown_hooks),
92			   &lockdown_lsmid);
93	return 0;
94}
95
96static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
97			     loff_t *ppos)
98{
99	char temp[80];
100	int i, offset = 0;
101
102	for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
103		enum lockdown_reason level = lockdown_levels[i];
104
105		if (lockdown_reasons[level]) {
106			const char *label = lockdown_reasons[level];
107
108			if (kernel_locked_down == level)
109				offset += sprintf(temp+offset, "[%s] ", label);
110			else
111				offset += sprintf(temp+offset, "%s ", label);
112		}
113	}
114
115	/* Convert the last space to a newline if needed. */
116	if (offset > 0)
117		temp[offset-1] = '\n';
118
119	return simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
120}
121
122static ssize_t lockdown_write(struct file *file, const char __user *buf,
123			      size_t n, loff_t *ppos)
124{
125	char *state;
126	int i, len, err = -EINVAL;
127
128	state = memdup_user_nul(buf, n);
129	if (IS_ERR(state))
130		return PTR_ERR(state);
131
132	len = strlen(state);
133	if (len && state[len-1] == '\n') {
134		state[len-1] = '\0';
135		len--;
136	}
137
138	for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
139		enum lockdown_reason level = lockdown_levels[i];
140		const char *label = lockdown_reasons[level];
141
142		if (label && !strcmp(state, label))
143			err = lock_kernel_down("securityfs", level);
144	}
145
146	kfree(state);
147	return err ? err : n;
148}
149
150static const struct file_operations lockdown_ops = {
151	.read  = lockdown_read,
152	.write = lockdown_write,
153};
154
155static int __init lockdown_secfs_init(void)
156{
157	struct dentry *dentry;
158
159	dentry = securityfs_create_file("lockdown", 0644, NULL, NULL,
160					&lockdown_ops);
161	return PTR_ERR_OR_ZERO(dentry);
162}
163
164core_initcall(lockdown_secfs_init);
165
166#ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
167DEFINE_EARLY_LSM(lockdown) = {
168#else
169DEFINE_LSM(lockdown) = {
170#endif
171	.name = "lockdown",
172	.init = lockdown_lsm_init,
173};
174