lockdown.c

  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#include <uapi/linux/lsm.h>
 17
 18static enum lockdown_reason kernel_locked_down;
 19
 20static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
 21						 LOCKDOWN_INTEGRITY_MAX,
 22						 LOCKDOWN_CONFIDENTIALITY_MAX};
 23
 24/*
 25 * Put the kernel into lock-down mode.
 26 */
 27static int lock_kernel_down(const char *where, enum lockdown_reason level)
 28{
 29	if (kernel_locked_down >= level)
 30		return -EPERM;
 31
 32	kernel_locked_down = level;
 33	pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
 34		  where);
 35	return 0;
 36}
 37
 38static int __init lockdown_param(char *level)
 39{
 40	if (!level)
 41		return -EINVAL;
 42
 43	if (strcmp(level, "integrity") == 0)
 44		lock_kernel_down("command line", LOCKDOWN_INTEGRITY_MAX);
 45	else if (strcmp(level, "confidentiality") == 0)
 46		lock_kernel_down("command line", LOCKDOWN_CONFIDENTIALITY_MAX);
 47	else
 48		return -EINVAL;
 49
 50	return 0;
 51}
 52
 53early_param("lockdown", lockdown_param);
 54
 55/**
 56 * lockdown_is_locked_down - Find out if the kernel is locked down
 57 * @what: Tag to use in notice generated if lockdown is in effect
 58 */
 59static int lockdown_is_locked_down(enum lockdown_reason what)
 60{
 61	if (WARN(what >= LOCKDOWN_CONFIDENTIALITY_MAX,
 62		 "Invalid lockdown reason"))
 63		return -EPERM;
 64
 65	if (kernel_locked_down >= what) {
 66		if (lockdown_reasons[what])
 67			pr_notice_ratelimited("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
 68				  current->comm, lockdown_reasons[what]);
 69		return -EPERM;
 70	}
 71
 72	return 0;
 73}
 74
 75static struct security_hook_list lockdown_hooks[] __ro_after_init = {
 76	LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
 77};
 78
 79static const struct lsm_id lockdown_lsmid = {
 80	.name = "lockdown",
 81	.id = LSM_ID_LOCKDOWN,
 82};
 83
 84static int __init lockdown_lsm_init(void)
 85{
 86#if defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY)
 87	lock_kernel_down("Kernel configuration", LOCKDOWN_INTEGRITY_MAX);
 88#elif defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY)
 89	lock_kernel_down("Kernel configuration", LOCKDOWN_CONFIDENTIALITY_MAX);
 90#endif
 91	security_add_hooks(lockdown_hooks, ARRAY_SIZE(lockdown_hooks),
 92			   &lockdown_lsmid);
 93	return 0;
 94}
 95
 96static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
 97			     loff_t *ppos)
 98{
 99	char temp[80] = "";
100	int i, offset = 0;
101
102	for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
103		enum lockdown_reason level = lockdown_levels[i];
104
105		if (lockdown_reasons[level]) {
106			const char *label = lockdown_reasons[level];
107
108			if (kernel_locked_down == level)
109				offset += sprintf(temp+offset, "[%s] ", label);
110			else
111				offset += sprintf(temp+offset, "%s ", label);
112		}
113	}
114
115	/* Convert the last space to a newline if needed. */
116	if (offset > 0)
117		temp[offset-1] = '\n';
118
119	return simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
120}
121
122static ssize_t lockdown_write(struct file *file, const char __user *buf,
123			      size_t n, loff_t *ppos)
124{
125	char *state;
126	int i, len, err = -EINVAL;
127
128	state = memdup_user_nul(buf, n);
129	if (IS_ERR(state))
130		return PTR_ERR(state);
131
132	len = strlen(state);
133	if (len && state[len-1] == '\n') {
134		state[len-1] = '\0';
135		len--;
136	}
137
138	for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
139		enum lockdown_reason level = lockdown_levels[i];
140		const char *label = lockdown_reasons[level];
141
142		if (label && !strcmp(state, label))
143			err = lock_kernel_down("securityfs", level);
144	}
145
146	kfree(state);
147	return err ? err : n;
148}
149
150static const struct file_operations lockdown_ops = {
151	.read  = lockdown_read,
152	.write = lockdown_write,
153};
154
155static int __init lockdown_secfs_init(void)
156{
157	struct dentry *dentry;
158
159	dentry = securityfs_create_file("lockdown", 0644, NULL, NULL,
160					&lockdown_ops);
161	return PTR_ERR_OR_ZERO(dentry);
162}
163
164#ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
165DEFINE_EARLY_LSM(lockdown) = {
166#else
167DEFINE_LSM(lockdown) = {
168#endif
169	.id = &lockdown_lsmid,
170	.init = lockdown_lsm_init,
171	.initcall_core = lockdown_secfs_init,
172};