security/loadpin/loadpin.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Module and Firmware Pinning Security Module
   4  *
   5  * Copyright 2011-2016 Google Inc.
   6  *
   7  * Author: Kees Cook <keescook@chromium.org>
   8  */
   9
  10 #define pr_fmt(fmt) "LoadPin: " fmt
  11
  12 #include <linux/module.h>
  13 #include <linux/fs.h>
  14 #include <linux/lsm_hooks.h>
  15 #include <linux/mount.h>
  16 #include <linux/path.h>
  17 #include <linux/sched.h>        /* current */
  18 #include <linux/string_helpers.h>
  19
  20 static void report_load(const char *origin, struct file *file, char *operation)
  21 {
  22         char *cmdline, *pathname;
  23
  24         pathname = kstrdup_quotable_file(file, GFP_KERNEL);
  25         cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
  26
  27         pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
  28                   origin, operation,
  29                   (pathname && pathname[0] != '<') ? "\"" : "",
  30                   pathname,
  31                   (pathname && pathname[0] != '<') ? "\"" : "",
  32                   task_pid_nr(current),
  33                   cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
  34
  35         kfree(cmdline);
  36         kfree(pathname);
  37 }
  38
  39 static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
  40 static struct super_block *pinned_root;
  41 static DEFINE_SPINLOCK(pinned_root_spinlock);
  42
  43 #ifdef CONFIG_SYSCTL
  44 static int zero;
  45 static int one = 1;
  46
  47 static struct ctl_path loadpin_sysctl_path[] = {
  48         { .procname = "kernel", },
  49         { .procname = "loadpin", },
  50         { }
  51 };
  52
  53 static struct ctl_table loadpin_sysctl_table[] = {
  54         {
  55                 .procname       = "enforce",
  56                 .data           = &enforce,
  57                 .maxlen         = sizeof(int),
  58                 .mode           = 0644,
  59                 .proc_handler   = proc_dointvec_minmax,
  60                 .extra1         = &zero,
  61                 .extra2         = &one,
  62         },
  63         { }
  64 };
  65
  66 /*
  67  * This must be called after early kernel init, since then the rootdev
  68  * is available.
  69  */
  70 static void check_pinning_enforcement(struct super_block *mnt_sb)
  71 {
  72         bool ro = false;
  73
  74         /*
  75          * If load pinning is not enforced via a read-only block
  76          * device, allow sysctl to change modes for testing.
  77          */
  78         if (mnt_sb->s_bdev) {
  79                 char bdev[BDEVNAME_SIZE];
  80
  81                 ro = bdev_read_only(mnt_sb->s_bdev);
  82                 bdevname(mnt_sb->s_bdev, bdev);
  83                 pr_info("%s (%u:%u): %s\n", bdev,
  84                         MAJOR(mnt_sb->s_bdev->bd_dev),
  85                         MINOR(mnt_sb->s_bdev->bd_dev),
  86                         ro ? "read-only" : "writable");
  87         } else
  88                 pr_info("mnt_sb lacks block device, treating as: writable\n");
  89
  90         if (!ro) {
  91                 if (!register_sysctl_paths(loadpin_sysctl_path,
  92                                            loadpin_sysctl_table))
  93                         pr_notice("sysctl registration failed!\n");
  94                 else
  95                         pr_info("enforcement can be disabled.\n");
  96         } else
  97                 pr_info("load pinning engaged.\n");
  98 }
  99 #else
 100 static void check_pinning_enforcement(struct super_block *mnt_sb)
 101 {
 102         pr_info("load pinning engaged.\n");
 103 }
 104 #endif
 105
 106 static void loadpin_sb_free_security(struct super_block *mnt_sb)
 107 {
 108         /*
 109          * When unmounting the filesystem we were using for load
 110          * pinning, we acknowledge the superblock release, but make sure
 111          * no other modules or firmware can be loaded.
 112          */
 113         if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
 114                 pinned_root = ERR_PTR(-EIO);
 115                 pr_info("umount pinned fs: refusing further loads\n");
 116         }
 117 }
 118
 119 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id)
 120 {
 121         struct super_block *load_root;
 122         const char *origin = kernel_read_file_id_str(id);
 123
 124         /* This handles the older init_module API that has a NULL file. */
 125         if (!file) {
 126                 if (!enforce) {
 127                         report_load(origin, NULL, "old-api-pinning-ignored");
 128                         return 0;
 129                 }
 130
 131                 report_load(origin, NULL, "old-api-denied");
 132                 return -EPERM;
 133         }
 134
 135         load_root = file->f_path.mnt->mnt_sb;
 136
 137         /* First loaded module/firmware defines the root for all others. */
 138         spin_lock(&pinned_root_spinlock);
 139         /*
 140          * pinned_root is only NULL at startup. Otherwise, it is either
 141          * a valid reference, or an ERR_PTR.
 142          */
 143         if (!pinned_root) {
 144                 pinned_root = load_root;
 145                 /*
 146                  * Unlock now since it's only pinned_root we care about.
 147                  * In the worst case, we will (correctly) report pinning
 148                  * failures before we have announced that pinning is
 149                  * enforcing. This would be purely cosmetic.
 150                  */
 151                 spin_unlock(&pinned_root_spinlock);
 152                 check_pinning_enforcement(pinned_root);
 153                 report_load(origin, file, "pinned");
 154         } else {
 155                 spin_unlock(&pinned_root_spinlock);
 156         }
 157
 158         if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
 159                 if (unlikely(!enforce)) {
 160                         report_load(origin, file, "pinning-ignored");
 161                         return 0;
 162                 }
 163
 164                 report_load(origin, file, "denied");
 165                 return -EPERM;
 166         }
 167
 168         return 0;
 169 }
 170
 171 static int loadpin_load_data(enum kernel_load_data_id id)
 172 {
 173         return loadpin_read_file(NULL, (enum kernel_read_file_id) id);
 174 }
 175
 176 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
 177         LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
 178         LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
 179         LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
 180 };
 181
 182 static int __init loadpin_init(void)
 183 {
 184         pr_info("ready to pin (currently %senforcing)\n",
 185                 enforce ? "" : "not ");
 186         security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
 187         return 0;
 188 }
 189
 190 DEFINE_LSM(loadpin) = {
 191         .name = "loadpin",
 192         .init = loadpin_init,
 193 };
 194
 195 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
 196 module_param(enforce, int, 0);
 197 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");