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("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