summaryrefslogtreecommitdiff
path: root/security/loadpin/loadpin.c
blob: 48f39631b370a45677f166f8f746b8918c5dfe83 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
/*
 * Module and Firmware Pinning Security Module
 *
 * Copyright 2011-2016 Google Inc.
 *
 * Author: Kees Cook <keescook@chromium.org>
 *
 * This software is licensed under the terms of the GNU General Public
 * License version 2, as published by the Free Software Foundation, and
 * may be copied, distributed, and modified under those terms.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#define pr_fmt(fmt) "LoadPin: " fmt

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/lsm_hooks.h>
#include <linux/mount.h>
#include <linux/path.h>
#include <linux/sched.h>	/* current */
#include <linux/string_helpers.h>

static void report_load(const char *origin, struct file *file, char *operation)
{
	char *cmdline, *pathname;

	pathname = kstrdup_quotable_file(file, GFP_KERNEL);
	cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);

	pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
		  origin, operation,
		  (pathname && pathname[0] != '<') ? "\"" : "",
		  pathname,
		  (pathname && pathname[0] != '<') ? "\"" : "",
		  task_pid_nr(current),
		  cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");

	kfree(cmdline);
	kfree(pathname);
}

static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
static struct super_block *pinned_root;
static DEFINE_SPINLOCK(pinned_root_spinlock);

#ifdef CONFIG_SYSCTL
static int zero;
static int one = 1;

static struct ctl_path loadpin_sysctl_path[] = {
	{ .procname = "kernel", },
	{ .procname = "loadpin", },
	{ }
};

static struct ctl_table loadpin_sysctl_table[] = {
	{
		.procname       = "enforce",
		.data           = &enforce,
		.maxlen         = sizeof(int),
		.mode           = 0644,
		.proc_handler   = proc_dointvec_minmax,
		.extra1         = &zero,
		.extra2         = &one,
	},
	{ }
};

/*
 * This must be called after early kernel init, since then the rootdev
 * is available.
 */
static void check_pinning_enforcement(struct super_block *mnt_sb)
{
	bool ro = false;

	/*
	 * If load pinning is not enforced via a read-only block
	 * device, allow sysctl to change modes for testing.
	 */
	if (mnt_sb->s_bdev) {
		char bdev[BDEVNAME_SIZE];

		ro = bdev_read_only(mnt_sb->s_bdev);
		bdevname(mnt_sb->s_bdev, bdev);
		pr_info("%s (%u:%u): %s\n", bdev,
			MAJOR(mnt_sb->s_bdev->bd_dev),
			MINOR(mnt_sb->s_bdev->bd_dev),
			ro ? "read-only" : "writable");
	} else
		pr_info("mnt_sb lacks block device, treating as: writable\n");

	if (!ro) {
		if (!register_sysctl_paths(loadpin_sysctl_path,
					   loadpin_sysctl_table))
			pr_notice("sysctl registration failed!\n");
		else
			pr_info("enforcement can be disabled.\n");
	} else
		pr_info("load pinning engaged.\n");
}
#else
static void check_pinning_enforcement(struct super_block *mnt_sb)
{
	pr_info("load pinning engaged.\n");
}
#endif

static void loadpin_sb_free_security(struct super_block *mnt_sb)
{
	/*
	 * When unmounting the filesystem we were using for load
	 * pinning, we acknowledge the superblock release, but make sure
	 * no other modules or firmware can be loaded.
	 */
	if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
		pinned_root = ERR_PTR(-EIO);
		pr_info("umount pinned fs: refusing further loads\n");
	}
}

static int loadpin_read_file(struct file *file, enum kernel_read_file_id id)
{
	struct super_block *load_root;
	const char *origin = kernel_read_file_id_str(id);

	/* This handles the older init_module API that has a NULL file. */
	if (!file) {
		if (!enforce) {
			report_load(origin, NULL, "old-api-pinning-ignored");
			return 0;
		}

		report_load(origin, NULL, "old-api-denied");
		return -EPERM;
	}

	load_root = file->f_path.mnt->mnt_sb;

	/* First loaded module/firmware defines the root for all others. */
	spin_lock(&pinned_root_spinlock);
	/*
	 * pinned_root is only NULL at startup. Otherwise, it is either
	 * a valid reference, or an ERR_PTR.
	 */
	if (!pinned_root) {
		pinned_root = load_root;
		/*
		 * Unlock now since it's only pinned_root we care about.
		 * In the worst case, we will (correctly) report pinning
		 * failures before we have announced that pinning is
		 * enforcing. This would be purely cosmetic.
		 */
		spin_unlock(&pinned_root_spinlock);
		check_pinning_enforcement(pinned_root);
		report_load(origin, file, "pinned");
	} else {
		spin_unlock(&pinned_root_spinlock);
	}

	if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
		if (unlikely(!enforce)) {
			report_load(origin, file, "pinning-ignored");
			return 0;
		}

		report_load(origin, file, "denied");
		return -EPERM;
	}

	return 0;
}

static int loadpin_load_data(enum kernel_load_data_id id)
{
	return loadpin_read_file(NULL, (enum kernel_read_file_id) id);
}

static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
	LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
	LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
	LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
};

void __init loadpin_add_hooks(void)
{
	pr_info("ready to pin (currently %senforcing)\n",
		enforce ? "" : "not ");
	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
}

/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
module_param(enforce, int, 0);
MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");