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_MMIOTRACE] = "unsafe mmio",
  33         [LOCKDOWN_INTEGRITY_MAX] = "integrity",
  34         [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
  35 };
  36
  37 static enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
  38                                                  LOCKDOWN_INTEGRITY_MAX,
  39                                                  LOCKDOWN_CONFIDENTIALITY_MAX};
  40
  41 /*
  42  * Put the kernel into lock-down mode.
  43  */
  44 static int lock_kernel_down(const char *where, enum lockdown_reason level)
  45 {
  46         if (kernel_locked_down >= level)
  47                 return -EPERM;
  48
  49         kernel_locked_down = level;
  50         pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
  51                   where);
  52         return 0;
  53 }
  54
  55 static int __init lockdown_param(char *level)
  56 {
  57         if (!level)
  58                 return -EINVAL;
  59
  60         if (strcmp(level, "integrity") == 0)
  61                 lock_kernel_down("command line", LOCKDOWN_INTEGRITY_MAX);
  62         else if (strcmp(level, "confidentiality") == 0)
  63                 lock_kernel_down("command line", LOCKDOWN_CONFIDENTIALITY_MAX);
  64         else
  65                 return -EINVAL;
  66
  67         return 0;
  68 }
  69
  70 early_param("lockdown", lockdown_param);
  71
  72 /**
  73  * lockdown_is_locked_down - Find out if the kernel is locked down
  74  * @what: Tag to use in notice generated if lockdown is in effect
  75  */
  76 static int lockdown_is_locked_down(enum lockdown_reason what)
  77 {
  78         if (kernel_locked_down >= what) {
  79                 if (lockdown_reasons[what])
  80                         pr_notice("Lockdown: %s is restricted; see man kernel_lockdown.7\n",
  81                                   lockdown_reasons[what]);
  82                 return -EPERM;
  83         }
  84
  85         return 0;
  86 }
  87
  88 static struct security_hook_list lockdown_hooks[] __lsm_ro_after_init = {
  89         LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
  90 };
  91
  92 static int __init lockdown_lsm_init(void)
  93 {
  94 #if defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY)
  95         lock_kernel_down("Kernel configuration", LOCKDOWN_INTEGRITY_MAX);
  96 #elif defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY)
  97         lock_kernel_down("Kernel configuration", LOCKDOWN_CONFIDENTIALITY_MAX);
  98 #endif
  99         security_add_hooks(lockdown_hooks, ARRAY_SIZE(lockdown_hooks),
 100                            "lockdown");
 101         return 0;
 102 }
 103
 104 static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
 105                              loff_t *ppos)
 106 {
 107         char temp[80];
 108         int i, offset = 0;
 109
 110         for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
 111                 enum lockdown_reason level = lockdown_levels[i];
 112
 113                 if (lockdown_reasons[level]) {
 114                         const char *label = lockdown_reasons[level];
 115
 116                         if (kernel_locked_down == level)
 117                                 offset += sprintf(temp+offset, "[%s] ", label);
 118                         else
 119                                 offset += sprintf(temp+offset, "%s ", label);
 120                 }
 121         }
 122
 123         /* Convert the last space to a newline if needed. */
 124         if (offset > 0)
 125                 temp[offset-1] = '\n';
 126
 127         return simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
 128 }
 129
 130 static ssize_t lockdown_write(struct file *file, const char __user *buf,
 131                               size_t n, loff_t *ppos)
 132 {
 133         char *state;
 134         int i, len, err = -EINVAL;
 135
 136         state = memdup_user_nul(buf, n);
 137         if (IS_ERR(state))
 138                 return PTR_ERR(state);
 139
 140         len = strlen(state);
 141         if (len && state[len-1] == '\n') {
 142                 state[len-1] = '\0';
 143                 len--;
 144         }
 145
 146         for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
 147                 enum lockdown_reason level = lockdown_levels[i];
 148                 const char *label = lockdown_reasons[level];
 149
 150                 if (label && !strcmp(state, label))
 151                         err = lock_kernel_down("securityfs", level);
 152         }
 153
 154         kfree(state);
 155         return err ? err : n;
 156 }
 157
 158 static const struct file_operations lockdown_ops = {
 159         .read  = lockdown_read,
 160         .write = lockdown_write,
 161 };
 162
 163 static int __init lockdown_secfs_init(void)
 164 {
 165         struct dentry *dentry;
 166
 167         dentry = securityfs_create_file("lockdown", 0600, NULL, NULL,
 168                                         &lockdown_ops);
 169         return PTR_ERR_OR_ZERO(dentry);
 170 }
 171
 172 core_initcall(lockdown_secfs_init);
 173
 174 #ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
 175 DEFINE_EARLY_LSM(lockdown) = {
 176 #else
 177 DEFINE_LSM(lockdown) = {
 178 #endif
 179         .name = "lockdown",
 180         .init = lockdown_lsm_init,
 181 };