security/lockdown/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
  18 static enum lockdown_reason kernel_locked_down;
  19
  20 static 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  */
  27 static 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
  38 static 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
  53 early_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  */
  59 static 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
  75 static struct security_hook_list lockdown_hooks[] __ro_after_init = {
  76         LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
  77 };
  78
  79 const struct lsm_id lockdown_lsmid = {
  80         .name = "lockdown",
  81         .id = LSM_ID_LOCKDOWN,
  82 };
  83
  84 static 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
  96 static 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
 122 static 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
 150 static const struct file_operations lockdown_ops = {
 151         .read  = lockdown_read,
 152         .write = lockdown_write,
 153 };
 154
 155 static 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 core_initcall(lockdown_secfs_init);
 165
 166 #ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
 167 DEFINE_EARLY_LSM(lockdown) = {
 168 #else
 169 DEFINE_LSM(lockdown) = {
 170 #endif
 171         .name = "lockdown",
 172         .init = lockdown_lsm_init,
 173 };