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_INTEGRITY_MAX] = "integrity",
  36         [LOCKDOWN_KCORE] = "/proc/kcore access",
  37         [LOCKDOWN_KPROBES] = "use of kprobes",
  38         [LOCKDOWN_BPF_READ] = "use of bpf to read kernel RAM",
  39         [LOCKDOWN_PERF] = "unsafe use of perf",
  40         [LOCKDOWN_TRACEFS] = "use of tracefs",
  41         [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
  42 };
  43
  44 static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
  45                                                  LOCKDOWN_INTEGRITY_MAX,
  46                                                  LOCKDOWN_CONFIDENTIALITY_MAX};
  47
  48 /*
  49  * Put the kernel into lock-down mode.
  50  */
  51 static int lock_kernel_down(const char *where, enum lockdown_reason level)
  52 {
  53         if (kernel_locked_down >= level)
  54                 return -EPERM;
  55
  56         kernel_locked_down = level;
  57         pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
  58                   where);
  59         return 0;
  60 }
  61
  62 static int __init lockdown_param(char *level)
  63 {
  64         if (!level)
  65                 return -EINVAL;
  66
  67         if (strcmp(level, "integrity") == 0)
  68                 lock_kernel_down("command line", LOCKDOWN_INTEGRITY_MAX);
  69         else if (strcmp(level, "confidentiality") == 0)
  70                 lock_kernel_down("command line", LOCKDOWN_CONFIDENTIALITY_MAX);
  71         else
  72                 return -EINVAL;
  73
  74         return 0;
  75 }
  76
  77 early_param("lockdown", lockdown_param);
  78
  79 /**
  80  * lockdown_is_locked_down - Find out if the kernel is locked down
  81  * @what: Tag to use in notice generated if lockdown is in effect
  82  */
  83 static int lockdown_is_locked_down(enum lockdown_reason what)
  84 {
  85         if (WARN(what >= LOCKDOWN_CONFIDENTIALITY_MAX,
  86                  "Invalid lockdown reason"))
  87                 return -EPERM;
  88
  89         if (kernel_locked_down >= what) {
  90                 if (lockdown_reasons[what])
  91                         pr_notice("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
  92                                   current->comm, lockdown_reasons[what]);
  93                 return -EPERM;
  94         }
  95
  96         return 0;
  97 }
  98
  99 static struct security_hook_list lockdown_hooks[] __lsm_ro_after_init = {
 100         LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
 101 };
 102
 103 static int __init lockdown_lsm_init(void)
 104 {
 105 #if defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY)
 106         lock_kernel_down("Kernel configuration", LOCKDOWN_INTEGRITY_MAX);
 107 #elif defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY)
 108         lock_kernel_down("Kernel configuration", LOCKDOWN_CONFIDENTIALITY_MAX);
 109 #endif
 110         security_add_hooks(lockdown_hooks, ARRAY_SIZE(lockdown_hooks),
 111                            "lockdown");
 112         return 0;
 113 }
 114
 115 static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
 116                              loff_t *ppos)
 117 {
 118         char temp[80];
 119         int i, offset = 0;
 120
 121         for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
 122                 enum lockdown_reason level = lockdown_levels[i];
 123
 124                 if (lockdown_reasons[level]) {
 125                         const char *label = lockdown_reasons[level];
 126
 127                         if (kernel_locked_down == level)
 128                                 offset += sprintf(temp+offset, "[%s] ", label);
 129                         else
 130                                 offset += sprintf(temp+offset, "%s ", label);
 131                 }
 132         }
 133
 134         /* Convert the last space to a newline if needed. */
 135         if (offset > 0)
 136                 temp[offset-1] = '\n';
 137
 138         return simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
 139 }
 140
 141 static ssize_t lockdown_write(struct file *file, const char __user *buf,
 142                               size_t n, loff_t *ppos)
 143 {
 144         char *state;
 145         int i, len, err = -EINVAL;
 146
 147         state = memdup_user_nul(buf, n);
 148         if (IS_ERR(state))
 149                 return PTR_ERR(state);
 150
 151         len = strlen(state);
 152         if (len && state[len-1] == '\n') {
 153                 state[len-1] = '\0';
 154                 len--;
 155         }
 156
 157         for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
 158                 enum lockdown_reason level = lockdown_levels[i];
 159                 const char *label = lockdown_reasons[level];
 160
 161                 if (label && !strcmp(state, label))
 162                         err = lock_kernel_down("securityfs", level);
 163         }
 164
 165         kfree(state);
 166         return err ? err : n;
 167 }
 168
 169 static const struct file_operations lockdown_ops = {
 170         .read  = lockdown_read,
 171         .write = lockdown_write,
 172 };
 173
 174 static int __init lockdown_secfs_init(void)
 175 {
 176         struct dentry *dentry;
 177
 178         dentry = securityfs_create_file("lockdown", 0600, NULL, NULL,
 179                                         &lockdown_ops);
 180         return PTR_ERR_OR_ZERO(dentry);
 181 }
 182
 183 core_initcall(lockdown_secfs_init);
 184
 185 #ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
 186 DEFINE_EARLY_LSM(lockdown) = {
 187 #else
 188 DEFINE_LSM(lockdown) = {
 189 #endif
 190         .name = "lockdown",
 191         .init = lockdown_lsm_init,
 192 };