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
  17 static enum lockdown_reason kernel_locked_down;
  18
  19 static char *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_KEXEC] = "kexec of unsigned images",
  24         [LOCKDOWN_HIBERNATION] = "hibernation",
  25         [LOCKDOWN_PCI_ACCESS] = "direct PCI access",
  26         [LOCKDOWN_IOPORT] = "raw io port access",
  27         [LOCKDOWN_MSR] = "raw MSR access",
  28         [LOCKDOWN_ACPI_TABLES] = "modifying ACPI tables",
  29         [LOCKDOWN_PCMCIA_CIS] = "direct PCMCIA CIS storage",
  30         [LOCKDOWN_TIOCSSERIAL] = "reconfiguration of serial port IO",
  31         [LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",
  32         [LOCKDOWN_INTEGRITY_MAX] = "integrity",
  33         [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
  34 };
  35
  36 static enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
  37                                                  LOCKDOWN_INTEGRITY_MAX,
  38                                                  LOCKDOWN_CONFIDENTIALITY_MAX};
  39
  40 /*
  41  * Put the kernel into lock-down mode.
  42  */
  43 static int lock_kernel_down(const char *where, enum lockdown_reason level)
  44 {
  45         if (kernel_locked_down >= level)
  46                 return -EPERM;
  47
  48         kernel_locked_down = level;
  49         pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
  50                   where);
  51         return 0;
  52 }
  53
  54 static int __init lockdown_param(char *level)
  55 {
  56         if (!level)
  57                 return -EINVAL;
  58
  59         if (strcmp(level, "integrity") == 0)
  60                 lock_kernel_down("command line", LOCKDOWN_INTEGRITY_MAX);
  61         else if (strcmp(level, "confidentiality") == 0)
  62                 lock_kernel_down("command line", LOCKDOWN_CONFIDENTIALITY_MAX);
  63         else
  64                 return -EINVAL;
  65
  66         return 0;
  67 }
  68
  69 early_param("lockdown", lockdown_param);
  70
  71 /**
  72  * lockdown_is_locked_down - Find out if the kernel is locked down
  73  * @what: Tag to use in notice generated if lockdown is in effect
  74  */
  75 static int lockdown_is_locked_down(enum lockdown_reason what)
  76 {
  77         if (kernel_locked_down >= what) {
  78                 if (lockdown_reasons[what])
  79                         pr_notice("Lockdown: %s is restricted; see man kernel_lockdown.7\n",
  80                                   lockdown_reasons[what]);
  81                 return -EPERM;
  82         }
  83
  84         return 0;
  85 }
  86
  87 static struct security_hook_list lockdown_hooks[] __lsm_ro_after_init = {
  88         LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
  89 };
  90
  91 static int __init lockdown_lsm_init(void)
  92 {
  93 #if defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY)
  94         lock_kernel_down("Kernel configuration", LOCKDOWN_INTEGRITY_MAX);
  95 #elif defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY)
  96         lock_kernel_down("Kernel configuration", LOCKDOWN_CONFIDENTIALITY_MAX);
  97 #endif
  98         security_add_hooks(lockdown_hooks, ARRAY_SIZE(lockdown_hooks),
  99                            "lockdown");
 100         return 0;
 101 }
 102
 103 static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
 104                              loff_t *ppos)
 105 {
 106         char temp[80];
 107         int i, offset = 0;
 108
 109         for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
 110                 enum lockdown_reason level = lockdown_levels[i];
 111
 112                 if (lockdown_reasons[level]) {
 113                         const char *label = lockdown_reasons[level];
 114
 115                         if (kernel_locked_down == level)
 116                                 offset += sprintf(temp+offset, "[%s] ", label);
 117                         else
 118                                 offset += sprintf(temp+offset, "%s ", label);
 119                 }
 120         }
 121
 122         /* Convert the last space to a newline if needed. */
 123         if (offset > 0)
 124                 temp[offset-1] = '\n';
 125
 126         return simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
 127 }
 128
 129 static ssize_t lockdown_write(struct file *file, const char __user *buf,
 130                               size_t n, loff_t *ppos)
 131 {
 132         char *state;
 133         int i, len, err = -EINVAL;
 134
 135         state = memdup_user_nul(buf, n);
 136         if (IS_ERR(state))
 137                 return PTR_ERR(state);
 138
 139         len = strlen(state);
 140         if (len && state[len-1] == '\n') {
 141                 state[len-1] = '\0';
 142                 len--;
 143         }
 144
 145         for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
 146                 enum lockdown_reason level = lockdown_levels[i];
 147                 const char *label = lockdown_reasons[level];
 148
 149                 if (label && !strcmp(state, label))
 150                         err = lock_kernel_down("securityfs", level);
 151         }
 152
 153         kfree(state);
 154         return err ? err : n;
 155 }
 156
 157 static const struct file_operations lockdown_ops = {
 158         .read  = lockdown_read,
 159         .write = lockdown_write,
 160 };
 161
 162 static int __init lockdown_secfs_init(void)
 163 {
 164         struct dentry *dentry;
 165
 166         dentry = securityfs_create_file("lockdown", 0600, NULL, NULL,
 167                                         &lockdown_ops);
 168         return PTR_ERR_OR_ZERO(dentry);
 169 }
 170
 171 core_initcall(lockdown_secfs_init);
 172
 173 #ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
 174 DEFINE_EARLY_LSM(lockdown) = {
 175 #else
 176 DEFINE_LSM(lockdown) = {
 177 #endif
 178         .name = "lockdown",
 179         .init = lockdown_lsm_init,
 180 };