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