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
17 static enum lockdown_reason kernel_locked_down;
18
19 static 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 */
lock_kernel_down(const char * where,enum lockdown_reason level)26 static 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
lockdown_param(char * level)37 static 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
52 early_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 */
lockdown_is_locked_down(enum lockdown_reason what)58 static 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_ratelimited("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
74 static struct security_hook_list lockdown_hooks[] __lsm_ro_after_init = {
75 LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
76 };
77
lockdown_lsm_init(void)78 static 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
lockdown_read(struct file * filp,char __user * buf,size_t count,loff_t * ppos)90 static 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
lockdown_write(struct file * file,const char __user * buf,size_t n,loff_t * ppos)116 static 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
144 static const struct file_operations lockdown_ops = {
145 .read = lockdown_read,
146 .write = lockdown_write,
147 };
148
lockdown_secfs_init(void)149 static 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
158 core_initcall(lockdown_secfs_init);
159
160 #ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
161 DEFINE_EARLY_LSM(lockdown) = {
162 #else
163 DEFINE_LSM(lockdown) = {
164 #endif
165 .name = "lockdown",
166 .init = lockdown_lsm_init,
167 };
168
