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_BPF_WRITE_USER] = "use of bpf to write user 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_PERF] = "unsafe use of perf",
42 [LOCKDOWN_TRACEFS] = "use of tracefs",
43 [LOCKDOWN_XMON_RW] = "xmon read and write access",
44 [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
45 };
46
47 static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
48 LOCKDOWN_INTEGRITY_MAX,
49 LOCKDOWN_CONFIDENTIALITY_MAX};
50
51 /*
52 * Put the kernel into lock-down mode.
53 */
lock_kernel_down(const char * where,enum lockdown_reason level)54 static int lock_kernel_down(const char *where, enum lockdown_reason level)
55 {
56 if (kernel_locked_down >= level)
57 return -EPERM;
58
59 kernel_locked_down = level;
60 pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
61 where);
62 return 0;
63 }
64
lockdown_param(char * level)65 static int __init lockdown_param(char *level)
66 {
67 if (!level)
68 return -EINVAL;
69
70 if (strcmp(level, "integrity") == 0)
71 lock_kernel_down("command line", LOCKDOWN_INTEGRITY_MAX);
72 else if (strcmp(level, "confidentiality") == 0)
73 lock_kernel_down("command line", LOCKDOWN_CONFIDENTIALITY_MAX);
74 else
75 return -EINVAL;
76
77 return 0;
78 }
79
80 early_param("lockdown", lockdown_param);
81
82 /**
83 * lockdown_is_locked_down - Find out if the kernel is locked down
84 * @what: Tag to use in notice generated if lockdown is in effect
85 */
lockdown_is_locked_down(enum lockdown_reason what)86 static int lockdown_is_locked_down(enum lockdown_reason what)
87 {
88 if (WARN(what >= LOCKDOWN_CONFIDENTIALITY_MAX,
89 "Invalid lockdown reason"))
90 return -EPERM;
91
92 if (kernel_locked_down >= what) {
93 if (lockdown_reasons[what])
94 pr_notice("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
95 current->comm, lockdown_reasons[what]);
96 return -EPERM;
97 }
98
99 return 0;
100 }
101
102 static struct security_hook_list lockdown_hooks[] __lsm_ro_after_init = {
103 LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
104 };
105
lockdown_lsm_init(void)106 static int __init lockdown_lsm_init(void)
107 {
108 #if defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY)
109 lock_kernel_down("Kernel configuration", LOCKDOWN_INTEGRITY_MAX);
110 #elif defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY)
111 lock_kernel_down("Kernel configuration", LOCKDOWN_CONFIDENTIALITY_MAX);
112 #endif
113 security_add_hooks(lockdown_hooks, ARRAY_SIZE(lockdown_hooks),
114 "lockdown");
115 return 0;
116 }
117
lockdown_read(struct file * filp,char __user * buf,size_t count,loff_t * ppos)118 static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
119 loff_t *ppos)
120 {
121 char temp[80];
122 int i, offset = 0;
123
124 for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
125 enum lockdown_reason level = lockdown_levels[i];
126
127 if (lockdown_reasons[level]) {
128 const char *label = lockdown_reasons[level];
129
130 if (kernel_locked_down == level)
131 offset += sprintf(temp+offset, "[%s] ", label);
132 else
133 offset += sprintf(temp+offset, "%s ", label);
134 }
135 }
136
137 /* Convert the last space to a newline if needed. */
138 if (offset > 0)
139 temp[offset-1] = '\n';
140
141 return simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
142 }
143
lockdown_write(struct file * file,const char __user * buf,size_t n,loff_t * ppos)144 static ssize_t lockdown_write(struct file *file, const char __user *buf,
145 size_t n, loff_t *ppos)
146 {
147 char *state;
148 int i, len, err = -EINVAL;
149
150 state = memdup_user_nul(buf, n);
151 if (IS_ERR(state))
152 return PTR_ERR(state);
153
154 len = strlen(state);
155 if (len && state[len-1] == '\n') {
156 state[len-1] = '\0';
157 len--;
158 }
159
160 for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
161 enum lockdown_reason level = lockdown_levels[i];
162 const char *label = lockdown_reasons[level];
163
164 if (label && !strcmp(state, label))
165 err = lock_kernel_down("securityfs", level);
166 }
167
168 kfree(state);
169 return err ? err : n;
170 }
171
172 static const struct file_operations lockdown_ops = {
173 .read = lockdown_read,
174 .write = lockdown_write,
175 };
176
lockdown_secfs_init(void)177 static int __init lockdown_secfs_init(void)
178 {
179 struct dentry *dentry;
180
181 dentry = securityfs_create_file("lockdown", 0644, NULL, NULL,
182 &lockdown_ops);
183 return PTR_ERR_OR_ZERO(dentry);
184 }
185
186 core_initcall(lockdown_secfs_init);
187
188 #ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
189 DEFINE_EARLY_LSM(lockdown) = {
190 #else
191 DEFINE_LSM(lockdown) = {
192 #endif
193 .name = "lockdown",
194 .init = lockdown_lsm_init,
195 };
196