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
report_load(const char * origin,struct file * file,char * operation)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 char *exclude_read_files[READING_MAX_ID];
41 static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
42 static struct super_block *pinned_root;
43 static DEFINE_SPINLOCK(pinned_root_spinlock);
44
45 #ifdef CONFIG_SYSCTL
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 = SYSCTL_ZERO,
61 .extra2 = SYSCTL_ONE,
62 },
63 { }
64 };
65
66 /*
67 * This must be called after early kernel init, since then the rootdev
68 * is available.
69 */
check_pinning_enforcement(struct super_block * mnt_sb)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
check_pinning_enforcement(struct super_block * mnt_sb)100 static void check_pinning_enforcement(struct super_block *mnt_sb)
101 {
102 pr_info("load pinning engaged.\n");
103 }
104 #endif
105
loadpin_sb_free_security(struct super_block * mnt_sb)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
loadpin_read_file(struct file * file,enum kernel_read_file_id id)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 /* If the file id is excluded, ignore the pinning. */
125 if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
126 ignore_read_file_id[id]) {
127 report_load(origin, file, "pinning-excluded");
128 return 0;
129 }
130
131 /* This handles the older init_module API that has a NULL file. */
132 if (!file) {
133 if (!enforce) {
134 report_load(origin, NULL, "old-api-pinning-ignored");
135 return 0;
136 }
137
138 report_load(origin, NULL, "old-api-denied");
139 return -EPERM;
140 }
141
142 load_root = file->f_path.mnt->mnt_sb;
143
144 /* First loaded module/firmware defines the root for all others. */
145 spin_lock(&pinned_root_spinlock);
146 /*
147 * pinned_root is only NULL at startup. Otherwise, it is either
148 * a valid reference, or an ERR_PTR.
149 */
150 if (!pinned_root) {
151 pinned_root = load_root;
152 /*
153 * Unlock now since it's only pinned_root we care about.
154 * In the worst case, we will (correctly) report pinning
155 * failures before we have announced that pinning is
156 * enforcing. This would be purely cosmetic.
157 */
158 spin_unlock(&pinned_root_spinlock);
159 check_pinning_enforcement(pinned_root);
160 report_load(origin, file, "pinned");
161 } else {
162 spin_unlock(&pinned_root_spinlock);
163 }
164
165 if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
166 if (unlikely(!enforce)) {
167 report_load(origin, file, "pinning-ignored");
168 return 0;
169 }
170
171 report_load(origin, file, "denied");
172 return -EPERM;
173 }
174
175 return 0;
176 }
177
loadpin_load_data(enum kernel_load_data_id id)178 static int loadpin_load_data(enum kernel_load_data_id id)
179 {
180 return loadpin_read_file(NULL, (enum kernel_read_file_id) id);
181 }
182
183 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
184 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
185 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
186 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
187 };
188
parse_exclude(void)189 static void __init parse_exclude(void)
190 {
191 int i, j;
192 char *cur;
193
194 /*
195 * Make sure all the arrays stay within expected sizes. This
196 * is slightly weird because kernel_read_file_str[] includes
197 * READING_MAX_ID, which isn't actually meaningful here.
198 */
199 BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
200 ARRAY_SIZE(ignore_read_file_id));
201 BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
202 ARRAY_SIZE(ignore_read_file_id));
203
204 for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
205 cur = exclude_read_files[i];
206 if (!cur)
207 break;
208 if (*cur == '\0')
209 continue;
210
211 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
212 if (strcmp(cur, kernel_read_file_str[j]) == 0) {
213 pr_info("excluding: %s\n",
214 kernel_read_file_str[j]);
215 ignore_read_file_id[j] = 1;
216 /*
217 * Can not break, because one read_file_str
218 * may map to more than on read_file_id.
219 */
220 }
221 }
222 }
223 }
224
loadpin_init(void)225 static int __init loadpin_init(void)
226 {
227 pr_info("ready to pin (currently %senforcing)\n",
228 enforce ? "" : "not ");
229 parse_exclude();
230 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
231 return 0;
232 }
233
234 DEFINE_LSM(loadpin) = {
235 .name = "loadpin",
236 .init = loadpin_init,
237 };
238
239 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
240 module_param(enforce, int, 0);
241 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
242 module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
243 MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");
244