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
 17static enum lockdown_reason kernel_locked_down;
 18
 19static 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_INTEGRITY_MAX] = "integrity",
 36	[LOCKDOWN_KCORE] = "/proc/kcore access",
 37	[LOCKDOWN_KPROBES] = "use of kprobes",
 38	[LOCKDOWN_BPF_READ] = "use of bpf to read kernel RAM",
 39	[LOCKDOWN_PERF] = "unsafe use of perf",
 40	[LOCKDOWN_TRACEFS] = "use of tracefs",
 41	[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 42};
 43
 44static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
 45						 LOCKDOWN_INTEGRITY_MAX,
 46						 LOCKDOWN_CONFIDENTIALITY_MAX};
 47
 48/*
 49 * Put the kernel into lock-down mode.
 50 */
 51static int lock_kernel_down(const char *where, enum lockdown_reason level)
 52{
 53	if (kernel_locked_down >= level)
 54		return -EPERM;
 55
 56	kernel_locked_down = level;
 57	pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
 58		  where);
 59	return 0;
 60}
 61
 62static int __init lockdown_param(char *level)
 63{
 64	if (!level)
 65		return -EINVAL;
 66
 67	if (strcmp(level, "integrity") == 0)
 68		lock_kernel_down("command line", LOCKDOWN_INTEGRITY_MAX);
 69	else if (strcmp(level, "confidentiality") == 0)
 70		lock_kernel_down("command line", LOCKDOWN_CONFIDENTIALITY_MAX);
 71	else
 72		return -EINVAL;
 73
 74	return 0;
 75}
 76
 77early_param("lockdown", lockdown_param);
 78
 79/**
 80 * lockdown_is_locked_down - Find out if the kernel is locked down
 81 * @what: Tag to use in notice generated if lockdown is in effect
 82 */
 83static int lockdown_is_locked_down(enum lockdown_reason what)
 84{
 85	if (WARN(what >= LOCKDOWN_CONFIDENTIALITY_MAX,
 86		 "Invalid lockdown reason"))
 87		return -EPERM;
 88
 89	if (kernel_locked_down >= what) {
 90		if (lockdown_reasons[what])
 91			pr_notice("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
 92				  current->comm, lockdown_reasons[what]);
 93		return -EPERM;
 94	}
 95
 96	return 0;
 97}
 98
 99static struct security_hook_list lockdown_hooks[] __lsm_ro_after_init = {
100	LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
101};
102
103static int __init lockdown_lsm_init(void)
104{
105#if defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY)
106	lock_kernel_down("Kernel configuration", LOCKDOWN_INTEGRITY_MAX);
107#elif defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY)
108	lock_kernel_down("Kernel configuration", LOCKDOWN_CONFIDENTIALITY_MAX);
109#endif
110	security_add_hooks(lockdown_hooks, ARRAY_SIZE(lockdown_hooks),
111			   "lockdown");
112	return 0;
113}
114
115static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
116			     loff_t *ppos)
117{
118	char temp[80];
119	int i, offset = 0;
120
121	for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
122		enum lockdown_reason level = lockdown_levels[i];
123
124		if (lockdown_reasons[level]) {
125			const char *label = lockdown_reasons[level];
126
127			if (kernel_locked_down == level)
128				offset += sprintf(temp+offset, "[%s] ", label);
129			else
130				offset += sprintf(temp+offset, "%s ", label);
131		}
132	}
133
134	/* Convert the last space to a newline if needed. */
135	if (offset > 0)
136		temp[offset-1] = '\n';
137
138	return simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
139}
140
141static ssize_t lockdown_write(struct file *file, const char __user *buf,
142			      size_t n, loff_t *ppos)
143{
144	char *state;
145	int i, len, err = -EINVAL;
146
147	state = memdup_user_nul(buf, n);
148	if (IS_ERR(state))
149		return PTR_ERR(state);
150
151	len = strlen(state);
152	if (len && state[len-1] == '\n') {
153		state[len-1] = '\0';
154		len--;
155	}
156
157	for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
158		enum lockdown_reason level = lockdown_levels[i];
159		const char *label = lockdown_reasons[level];
160
161		if (label && !strcmp(state, label))
162			err = lock_kernel_down("securityfs", level);
163	}
164
165	kfree(state);
166	return err ? err : n;
167}
168
169static const struct file_operations lockdown_ops = {
170	.read  = lockdown_read,
171	.write = lockdown_write,
172};
173
174static int __init lockdown_secfs_init(void)
175{
176	struct dentry *dentry;
177
178	dentry = securityfs_create_file("lockdown", 0600, NULL, NULL,
179					&lockdown_ops);
180	return PTR_ERR_OR_ZERO(dentry);
181}
182
183core_initcall(lockdown_secfs_init);
184
185#ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
186DEFINE_EARLY_LSM(lockdown) = {
187#else
188DEFINE_LSM(lockdown) = {
189#endif
190	.name = "lockdown",
191	.init = lockdown_lsm_init,
192};