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