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_EFI_TEST] = "/dev/efi_test access",
  24         [LOCKDOWN_KEXEC] = "kexec of unsigned images",
  25         [LOCKDOWN_HIBERNATION] = "hibernation",
  26         [LOCKDOWN_PCI_ACCESS] = "direct PCI access",
  27         [LOCKDOWN_IOPORT] = "raw io port access",
  28         [LOCKDOWN_MSR] = "raw MSR access",
  29         [LOCKDOWN_ACPI_TABLES] = "modifying ACPI tables",
  30         [LOCKDOWN_PCMCIA_CIS] = "direct PCMCIA CIS storage",
  31         [LOCKDOWN_TIOCSSERIAL] = "reconfiguration of serial port IO",
  32         [LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",
  33         [LOCKDOWN_MMIOTRACE] = "unsafe mmio",
  34         [LOCKDOWN_DEBUGFS] = "debugfs access",
  35         [LOCKDOWN_XMON_WR] = "xmon write access",
  36         [LOCKDOWN_DBG_WRITE_KERNEL] = "use of kgdb/kdb to write kernel RAM",
  37         [LOCKDOWN_INTEGRITY_MAX] = "integrity",
  38         [LOCKDOWN_KCORE] = "/proc/kcore access",
  39         [LOCKDOWN_KPROBES] = "use of kprobes",
  40         [LOCKDOWN_BPF_READ] = "use of bpf to read kernel RAM",
  41         [LOCKDOWN_DBG_READ_KERNEL] = "use of kgdb/kdb to read kernel RAM",
  42         [LOCKDOWN_PERF] = "unsafe use of perf",
  43         [LOCKDOWN_TRACEFS] = "use of tracefs",
  44         [LOCKDOWN_XMON_RW] = "xmon read and write access",
  45         [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
  46 };
  47
  48 static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
  49                                                  LOCKDOWN_INTEGRITY_MAX,
  50                                                  LOCKDOWN_CONFIDENTIALITY_MAX};
  51
  52 /*
  53  * Put the kernel into lock-down mode.
  54  */
  55 static int lock_kernel_down(const char *where, enum lockdown_reason level)
  56 {
  57         if (kernel_locked_down >= level)
  58                 return -EPERM;
  59
  60         kernel_locked_down = level;
  61         pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
  62                   where);
  63         return 0;
  64 }
  65
  66 static int __init lockdown_param(char *level)
  67 {
  68         if (!level)
  69                 return -EINVAL;
  70
  71         if (strcmp(level, "integrity") == 0)
  72                 lock_kernel_down("command line", LOCKDOWN_INTEGRITY_MAX);
  73         else if (strcmp(level, "confidentiality") == 0)
  74                 lock_kernel_down("command line", LOCKDOWN_CONFIDENTIALITY_MAX);
  75         else
  76                 return -EINVAL;
  77
  78         return 0;
  79 }
  80
  81 early_param("lockdown", lockdown_param);
  82
  83 /**
  84  * lockdown_is_locked_down - Find out if the kernel is locked down
  85  * @what: Tag to use in notice generated if lockdown is in effect
  86  */
  87 static int lockdown_is_locked_down(enum lockdown_reason what)
  88 {
  89         if (WARN(what >= LOCKDOWN_CONFIDENTIALITY_MAX,
  90                  "Invalid lockdown reason"))
  91                 return -EPERM;
  92
  93         if (kernel_locked_down >= what) {
  94                 if (lockdown_reasons[what])
  95                         pr_notice("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
  96                                   current->comm, lockdown_reasons[what]);
  97                 return -EPERM;
  98         }
  99
 100         return 0;
 101 }
 102
 103 static struct security_hook_list lockdown_hooks[] __lsm_ro_after_init = {
 104         LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
 105 };
 106
 107 static int __init lockdown_lsm_init(void)
 108 {
 109 #if defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY)
 110         lock_kernel_down("Kernel configuration", LOCKDOWN_INTEGRITY_MAX);
 111 #elif defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY)
 112         lock_kernel_down("Kernel configuration", LOCKDOWN_CONFIDENTIALITY_MAX);
 113 #endif
 114         security_add_hooks(lockdown_hooks, ARRAY_SIZE(lockdown_hooks),
 115                            "lockdown");
 116         return 0;
 117 }
 118
 119 static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
 120                              loff_t *ppos)
 121 {
 122         char temp[80];
 123         int i, offset = 0;
 124
 125         for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
 126                 enum lockdown_reason level = lockdown_levels[i];
 127
 128                 if (lockdown_reasons[level]) {
 129                         const char *label = lockdown_reasons[level];
 130
 131                         if (kernel_locked_down == level)
 132                                 offset += sprintf(temp+offset, "[%s] ", label);
 133                         else
 134                                 offset += sprintf(temp+offset, "%s ", label);
 135                 }
 136         }
 137
 138         /* Convert the last space to a newline if needed. */
 139         if (offset > 0)
 140                 temp[offset-1] = '\n';
 141
 142         return simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
 143 }
 144
 145 static ssize_t lockdown_write(struct file *file, const char __user *buf,
 146                               size_t n, loff_t *ppos)
 147 {
 148         char *state;
 149         int i, len, err = -EINVAL;
 150
 151         state = memdup_user_nul(buf, n);
 152         if (IS_ERR(state))
 153                 return PTR_ERR(state);
 154
 155         len = strlen(state);
 156         if (len && state[len-1] == '\n') {
 157                 state[len-1] = '\0';
 158                 len--;
 159         }
 160
 161         for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
 162                 enum lockdown_reason level = lockdown_levels[i];
 163                 const char *label = lockdown_reasons[level];
 164
 165                 if (label && !strcmp(state, label))
 166                         err = lock_kernel_down("securityfs", level);
 167         }
 168
 169         kfree(state);
 170         return err ? err : n;
 171 }
 172
 173 static const struct file_operations lockdown_ops = {
 174         .read  = lockdown_read,
 175         .write = lockdown_write,
 176 };
 177
 178 static int __init lockdown_secfs_init(void)
 179 {
 180         struct dentry *dentry;
 181
 182         dentry = securityfs_create_file("lockdown", 0644, NULL, NULL,
 183                                         &lockdown_ops);
 184         return PTR_ERR_OR_ZERO(dentry);
 185 }
 186
 187 core_initcall(lockdown_secfs_init);
 188
 189 #ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
 190 DEFINE_EARLY_LSM(lockdown) = {
 191 #else
 192 DEFINE_LSM(lockdown) = {
 193 #endif
 194         .name = "lockdown",
 195         .init = lockdown_lsm_init,
 196 };