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(where: "command line", level: LOCKDOWN_INTEGRITY_MAX);
45 else if (strcmp(level, "confidentiality") == 0)
46 lock_kernel_down(where: "command line", level: 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
79static const 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(hooks: lockdown_hooks, ARRAY_SIZE(lockdown_hooks),
92 lsmid: &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(buf: temp+offset, fmt: "[%s] ", label);
110 else
111 offset += sprintf(buf: temp+offset, fmt: "%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(to: buf, count, ppos, from: 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(ptr: state))
130 return PTR_ERR(ptr: 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(where: "securityfs", level);
144 }
145
146 kfree(objp: 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(name: "lockdown", mode: 0644, NULL, NULL,
160 fops: &lockdown_ops);
161 return PTR_ERR_OR_ZERO(ptr: dentry);
162}
163
164#ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
165DEFINE_EARLY_LSM(lockdown) = {
166#else
167DEFINE_LSM(lockdown) = {
168#endif
169 .id = &lockdown_lsmid,
170 .init = lockdown_lsm_init,
171 .initcall_core = lockdown_secfs_init,
172};
173

source code of linux/security/lockdown/lockdown.c