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 char *const lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
20 [LOCKDOWN_NONE] = "none",
21 [LOCKDOWN_MODULE_SIGNATURE] = "unsigned module loading",
22 [LOCKDOWN_DEV_MEM] = "/dev/mem,kmem,port",
23 [LOCKDOWN_EFI_TEST] = "/dev/efi_test access",
24 [LOCKDOWN_KEXEC] = "kexec of unsigned images",
25 [LOCKDOWN_HIBERNATION] = "hibernation",
26 [LOCKDOWN_PCI_ACCESS] = "direct PCI access",
27 [LOCKDOWN_IOPORT] = "raw io port access",
28 [LOCKDOWN_MSR] = "raw MSR access",
29 [LOCKDOWN_ACPI_TABLES] = "modifying ACPI tables",
30 [LOCKDOWN_PCMCIA_CIS] = "direct PCMCIA CIS storage",
31 [LOCKDOWN_TIOCSSERIAL] = "reconfiguration of serial port IO",
32 [LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",
33 [LOCKDOWN_MMIOTRACE] = "unsafe mmio",
34 [LOCKDOWN_DEBUGFS] = "debugfs access",
35 [LOCKDOWN_XMON_WR] = "xmon write access",
36 [LOCKDOWN_DBG_WRITE_KERNEL] = "use of kgdb/kdb to write kernel RAM",
37 [LOCKDOWN_INTEGRITY_MAX] = "integrity",
38 [LOCKDOWN_KCORE] = "/proc/kcore access",
39 [LOCKDOWN_KPROBES] = "use of kprobes",
40 [LOCKDOWN_BPF_READ] = "use of bpf to read kernel RAM",
41 [LOCKDOWN_DBG_READ_KERNEL] = "use of kgdb/kdb to read kernel RAM",
42 [LOCKDOWN_PERF] = "unsafe use of perf",
43 [LOCKDOWN_TRACEFS] = "use of tracefs",
44 [LOCKDOWN_XMON_RW] = "xmon read and write access",
45 [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
46 };
47
48 static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
49 LOCKDOWN_INTEGRITY_MAX,
50 LOCKDOWN_CONFIDENTIALITY_MAX};
51
52 /*
53 * Put the kernel into lock-down mode.
54 */
lock_kernel_down(const char * where,enum lockdown_reason level)55 static int lock_kernel_down(const char *where, enum lockdown_reason level)
56 {
57 if (kernel_locked_down >= level)
58 return -EPERM;
59
60 kernel_locked_down = level;
61 pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
62 where);
63 return 0;
64 }
65
lockdown_param(char * level)66 static int __init lockdown_param(char *level)
67 {
68 if (!level)
69 return -EINVAL;
70
71 if (strcmp(level, "integrity") == 0)
72 lock_kernel_down("command line", LOCKDOWN_INTEGRITY_MAX);
73 else if (strcmp(level, "confidentiality") == 0)
74 lock_kernel_down("command line", LOCKDOWN_CONFIDENTIALITY_MAX);
75 else
76 return -EINVAL;
77
78 return 0;
79 }
80
81 early_param("lockdown", lockdown_param);
82
83 /**
84 * lockdown_is_locked_down - Find out if the kernel is locked down
85 * @what: Tag to use in notice generated if lockdown is in effect
86 */
lockdown_is_locked_down(enum lockdown_reason what)87 static int lockdown_is_locked_down(enum lockdown_reason what)
88 {
89 if (WARN(what >= LOCKDOWN_CONFIDENTIALITY_MAX,
90 "Invalid lockdown reason"))
91 return -EPERM;
92
93 if (kernel_locked_down >= what) {
94 if (lockdown_reasons[what])
95 pr_notice("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
96 current->comm, lockdown_reasons[what]);
97 return -EPERM;
98 }
99
100 return 0;
101 }
102
103 static struct security_hook_list lockdown_hooks[] __lsm_ro_after_init = {
104 LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
105 };
106
lockdown_lsm_init(void)107 static int __init lockdown_lsm_init(void)
108 {
109 #if defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY)
110 lock_kernel_down("Kernel configuration", LOCKDOWN_INTEGRITY_MAX);
111 #elif defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY)
112 lock_kernel_down("Kernel configuration", LOCKDOWN_CONFIDENTIALITY_MAX);
113 #endif
114 security_add_hooks(lockdown_hooks, ARRAY_SIZE(lockdown_hooks),
115 "lockdown");
116 return 0;
117 }
118
lockdown_read(struct file * filp,char __user * buf,size_t count,loff_t * ppos)119 static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
120 loff_t *ppos)
121 {
122 char temp[80];
123 int i, offset = 0;
124
125 for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
126 enum lockdown_reason level = lockdown_levels[i];
127
128 if (lockdown_reasons[level]) {
129 const char *label = lockdown_reasons[level];
130
131 if (kernel_locked_down == level)
132 offset += sprintf(temp+offset, "[%s] ", label);
133 else
134 offset += sprintf(temp+offset, "%s ", label);
135 }
136 }
137
138 /* Convert the last space to a newline if needed. */
139 if (offset > 0)
140 temp[offset-1] = '\n';
141
142 return simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
143 }
144
lockdown_write(struct file * file,const char __user * buf,size_t n,loff_t * ppos)145 static ssize_t lockdown_write(struct file *file, const char __user *buf,
146 size_t n, loff_t *ppos)
147 {
148 char *state;
149 int i, len, err = -EINVAL;
150
151 state = memdup_user_nul(buf, n);
152 if (IS_ERR(state))
153 return PTR_ERR(state);
154
155 len = strlen(state);
156 if (len && state[len-1] == '\n') {
157 state[len-1] = '\0';
158 len--;
159 }
160
161 for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
162 enum lockdown_reason level = lockdown_levels[i];
163 const char *label = lockdown_reasons[level];
164
165 if (label && !strcmp(state, label))
166 err = lock_kernel_down("securityfs", level);
167 }
168
169 kfree(state);
170 return err ? err : n;
171 }
172
173 static const struct file_operations lockdown_ops = {
174 .read = lockdown_read,
175 .write = lockdown_write,
176 };
177
lockdown_secfs_init(void)178 static int __init lockdown_secfs_init(void)
179 {
180 struct dentry *dentry;
181
182 dentry = securityfs_create_file("lockdown", 0644, NULL, NULL,
183 &lockdown_ops);
184 return PTR_ERR_OR_ZERO(dentry);
185 }
186
187 core_initcall(lockdown_secfs_init);
188
189 #ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
190 DEFINE_EARLY_LSM(lockdown) = {
191 #else
192 DEFINE_LSM(lockdown) = {
193 #endif
194 .name = "lockdown",
195 .init = lockdown_lsm_init,
196 };
197