Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
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linux
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/blkdev.h>
17#include <linux/path.h>
18#include <linux/sched.h> /* current */
19#include <linux/string_helpers.h>
20
21static void report_load(const char *origin, struct file *file, char *operation)
22{
23 char *cmdline, *pathname;
24
25 pathname = kstrdup_quotable_file(file, GFP_KERNEL);
26 cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
27
28 pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
29 origin, operation,
30 (pathname && pathname[0] != '<') ? "\"" : "",
31 pathname,
32 (pathname && pathname[0] != '<') ? "\"" : "",
33 task_pid_nr(current),
34 cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
35
36 kfree(cmdline);
37 kfree(pathname);
38}
39
40static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
41static char *exclude_read_files[READING_MAX_ID];
42static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
43static struct super_block *pinned_root;
44static DEFINE_SPINLOCK(pinned_root_spinlock);
45
46#ifdef CONFIG_SYSCTL
47
48static struct ctl_path loadpin_sysctl_path[] = {
49 { .procname = "kernel", },
50 { .procname = "loadpin", },
51 { }
52};
53
54static struct ctl_table loadpin_sysctl_table[] = {
55 {
56 .procname = "enforce",
57 .data = &enforce,
58 .maxlen = sizeof(int),
59 .mode = 0644,
60 .proc_handler = proc_dointvec_minmax,
61 .extra1 = SYSCTL_ZERO,
62 .extra2 = SYSCTL_ONE,
63 },
64 { }
65};
66
67/*
68 * This must be called after early kernel init, since then the rootdev
69 * is available.
70 */
71static void check_pinning_enforcement(struct super_block *mnt_sb)
72{
73 bool ro = false;
74
75 /*
76 * If load pinning is not enforced via a read-only block
77 * device, allow sysctl to change modes for testing.
78 */
79 if (mnt_sb->s_bdev) {
80 char bdev[BDEVNAME_SIZE];
81
82 ro = bdev_read_only(mnt_sb->s_bdev);
83 bdevname(mnt_sb->s_bdev, bdev);
84 pr_info("%s (%u:%u): %s\n", bdev,
85 MAJOR(mnt_sb->s_bdev->bd_dev),
86 MINOR(mnt_sb->s_bdev->bd_dev),
87 ro ? "read-only" : "writable");
88 } else
89 pr_info("mnt_sb lacks block device, treating as: writable\n");
90
91 if (!ro) {
92 if (!register_sysctl_paths(loadpin_sysctl_path,
93 loadpin_sysctl_table))
94 pr_notice("sysctl registration failed!\n");
95 else
96 pr_info("enforcement can be disabled.\n");
97 } else
98 pr_info("load pinning engaged.\n");
99}
100#else
101static void check_pinning_enforcement(struct super_block *mnt_sb)
102{
103 pr_info("load pinning engaged.\n");
104}
105#endif
106
107static void loadpin_sb_free_security(struct super_block *mnt_sb)
108{
109 /*
110 * When unmounting the filesystem we were using for load
111 * pinning, we acknowledge the superblock release, but make sure
112 * no other modules or firmware can be loaded.
113 */
114 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
115 pinned_root = ERR_PTR(-EIO);
116 pr_info("umount pinned fs: refusing further loads\n");
117 }
118}
119
120static int loadpin_read_file(struct file *file, enum kernel_read_file_id id)
121{
122 struct super_block *load_root;
123 const char *origin = kernel_read_file_id_str(id);
124
125 /* If the file id is excluded, ignore the pinning. */
126 if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
127 ignore_read_file_id[id]) {
128 report_load(origin, file, "pinning-excluded");
129 return 0;
130 }
131
132 /* This handles the older init_module API that has a NULL file. */
133 if (!file) {
134 if (!enforce) {
135 report_load(origin, NULL, "old-api-pinning-ignored");
136 return 0;
137 }
138
139 report_load(origin, NULL, "old-api-denied");
140 return -EPERM;
141 }
142
143 load_root = file->f_path.mnt->mnt_sb;
144
145 /* First loaded module/firmware defines the root for all others. */
146 spin_lock(&pinned_root_spinlock);
147 /*
148 * pinned_root is only NULL at startup. Otherwise, it is either
149 * a valid reference, or an ERR_PTR.
150 */
151 if (!pinned_root) {
152 pinned_root = load_root;
153 /*
154 * Unlock now since it's only pinned_root we care about.
155 * In the worst case, we will (correctly) report pinning
156 * failures before we have announced that pinning is
157 * enforcing. This would be purely cosmetic.
158 */
159 spin_unlock(&pinned_root_spinlock);
160 check_pinning_enforcement(pinned_root);
161 report_load(origin, file, "pinned");
162 } else {
163 spin_unlock(&pinned_root_spinlock);
164 }
165
166 if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
167 if (unlikely(!enforce)) {
168 report_load(origin, file, "pinning-ignored");
169 return 0;
170 }
171
172 report_load(origin, file, "denied");
173 return -EPERM;
174 }
175
176 return 0;
177}
178
179static int loadpin_load_data(enum kernel_load_data_id id)
180{
181 return loadpin_read_file(NULL, (enum kernel_read_file_id) id);
182}
183
184static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
185 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
186 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
187 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
188};
189
190static void __init parse_exclude(void)
191{
192 int i, j;
193 char *cur;
194
195 /*
196 * Make sure all the arrays stay within expected sizes. This
197 * is slightly weird because kernel_read_file_str[] includes
198 * READING_MAX_ID, which isn't actually meaningful here.
199 */
200 BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
201 ARRAY_SIZE(ignore_read_file_id));
202 BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
203 ARRAY_SIZE(ignore_read_file_id));
204
205 for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
206 cur = exclude_read_files[i];
207 if (!cur)
208 break;
209 if (*cur == '\0')
210 continue;
211
212 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
213 if (strcmp(cur, kernel_read_file_str[j]) == 0) {
214 pr_info("excluding: %s\n",
215 kernel_read_file_str[j]);
216 ignore_read_file_id[j] = 1;
217 /*
218 * Can not break, because one read_file_str
219 * may map to more than on read_file_id.
220 */
221 }
222 }
223 }
224}
225
226static int __init loadpin_init(void)
227{
228 pr_info("ready to pin (currently %senforcing)\n",
229 enforce ? "" : "not ");
230 parse_exclude();
231 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
232 return 0;
233}
234
235DEFINE_LSM(loadpin) = {
236 .name = "loadpin",
237 .init = loadpin_init,
238};
239
240/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
241module_param(enforce, int, 0);
242MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
243module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
244MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");