Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
1/*
2 * Module and Firmware Pinning Security Module
3 *
4 * Copyright 2011-2016 Google Inc.
5 *
6 * Author: Kees Cook <keescook@chromium.org>
7 *
8 * This software is licensed under the terms of the GNU General Public
9 * License version 2, as published by the Free Software Foundation, and
10 * may be copied, distributed, and modified under those terms.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
16 */
17
18#define pr_fmt(fmt) "LoadPin: " fmt
19
20#include <linux/module.h>
21#include <linux/fs.h>
22#include <linux/lsm_hooks.h>
23#include <linux/mount.h>
24#include <linux/path.h>
25#include <linux/sched.h> /* current */
26#include <linux/string_helpers.h>
27
28static void report_load(const char *origin, struct file *file, char *operation)
29{
30 char *cmdline, *pathname;
31
32 pathname = kstrdup_quotable_file(file, GFP_KERNEL);
33 cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
34
35 pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
36 origin, operation,
37 (pathname && pathname[0] != '<') ? "\"" : "",
38 pathname,
39 (pathname && pathname[0] != '<') ? "\"" : "",
40 task_pid_nr(current),
41 cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
42
43 kfree(cmdline);
44 kfree(pathname);
45}
46
47static int enabled = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENABLED);
48static struct super_block *pinned_root;
49static DEFINE_SPINLOCK(pinned_root_spinlock);
50
51#ifdef CONFIG_SYSCTL
52static int zero;
53static int one = 1;
54
55static struct ctl_path loadpin_sysctl_path[] = {
56 { .procname = "kernel", },
57 { .procname = "loadpin", },
58 { }
59};
60
61static struct ctl_table loadpin_sysctl_table[] = {
62 {
63 .procname = "enabled",
64 .data = &enabled,
65 .maxlen = sizeof(int),
66 .mode = 0644,
67 .proc_handler = proc_dointvec_minmax,
68 .extra1 = &zero,
69 .extra2 = &one,
70 },
71 { }
72};
73
74/*
75 * This must be called after early kernel init, since then the rootdev
76 * is available.
77 */
78static void check_pinning_enforcement(struct super_block *mnt_sb)
79{
80 bool ro = false;
81
82 /*
83 * If load pinning is not enforced via a read-only block
84 * device, allow sysctl to change modes for testing.
85 */
86 if (mnt_sb->s_bdev) {
87 ro = bdev_read_only(mnt_sb->s_bdev);
88 pr_info("dev(%u,%u): %s\n",
89 MAJOR(mnt_sb->s_bdev->bd_dev),
90 MINOR(mnt_sb->s_bdev->bd_dev),
91 ro ? "read-only" : "writable");
92 } else
93 pr_info("mnt_sb lacks block device, treating as: writable\n");
94
95 if (!ro) {
96 if (!register_sysctl_paths(loadpin_sysctl_path,
97 loadpin_sysctl_table))
98 pr_notice("sysctl registration failed!\n");
99 else
100 pr_info("load pinning can be disabled.\n");
101 } else
102 pr_info("load pinning engaged.\n");
103}
104#else
105static void check_pinning_enforcement(struct super_block *mnt_sb)
106{
107 pr_info("load pinning engaged.\n");
108}
109#endif
110
111static void loadpin_sb_free_security(struct super_block *mnt_sb)
112{
113 /*
114 * When unmounting the filesystem we were using for load
115 * pinning, we acknowledge the superblock release, but make sure
116 * no other modules or firmware can be loaded.
117 */
118 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
119 pinned_root = ERR_PTR(-EIO);
120 pr_info("umount pinned fs: refusing further loads\n");
121 }
122}
123
124static int loadpin_read_file(struct file *file, enum kernel_read_file_id id)
125{
126 struct super_block *load_root;
127 const char *origin = kernel_read_file_id_str(id);
128
129 /* This handles the older init_module API that has a NULL file. */
130 if (!file) {
131 if (!enabled) {
132 report_load(origin, NULL, "old-api-pinning-ignored");
133 return 0;
134 }
135
136 report_load(origin, NULL, "old-api-denied");
137 return -EPERM;
138 }
139
140 load_root = file->f_path.mnt->mnt_sb;
141
142 /* First loaded module/firmware defines the root for all others. */
143 spin_lock(&pinned_root_spinlock);
144 /*
145 * pinned_root is only NULL at startup. Otherwise, it is either
146 * a valid reference, or an ERR_PTR.
147 */
148 if (!pinned_root) {
149 pinned_root = load_root;
150 /*
151 * Unlock now since it's only pinned_root we care about.
152 * In the worst case, we will (correctly) report pinning
153 * failures before we have announced that pinning is
154 * enabled. This would be purely cosmetic.
155 */
156 spin_unlock(&pinned_root_spinlock);
157 check_pinning_enforcement(pinned_root);
158 report_load(origin, file, "pinned");
159 } else {
160 spin_unlock(&pinned_root_spinlock);
161 }
162
163 if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
164 if (unlikely(!enabled)) {
165 report_load(origin, file, "pinning-ignored");
166 return 0;
167 }
168
169 report_load(origin, file, "denied");
170 return -EPERM;
171 }
172
173 return 0;
174}
175
176static 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};
180
181void __init loadpin_add_hooks(void)
182{
183 pr_info("ready to pin (currently %sabled)", enabled ? "en" : "dis");
184 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
185}
186
187/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
188module_param(enabled, int, 0);
189MODULE_PARM_DESC(enabled, "Pin module/firmware loading (default: true)");