[linux-block.git] / security / loadpin / loadpin.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Module and Firmware Pinning Security Module
 *
 * Copyright 2011-2016 Google Inc.
 *
 * Author: Kees Cook <keescook@chromium.org>
 */

#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/blkdev.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 char *exclude_read_files[READING_MAX_ID];
static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
static struct super_block *pinned_root;
static DEFINE_SPINLOCK(pinned_root_spinlock);

#ifdef CONFIG_SYSCTL

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         = SYSCTL_ZERO,
		.extra2         = SYSCTL_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);

	/* If the file id is excluded, ignore the pinning. */
	if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
	    ignore_read_file_id[id]) {
		report_load(origin, file, "pinning-excluded");
		return 0;
	}

	/* 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),
};

static void __init parse_exclude(void)
{
	int i, j;
	char *cur;

	/*
	 * Make sure all the arrays stay within expected sizes. This
	 * is slightly weird because kernel_read_file_str[] includes
	 * READING_MAX_ID, which isn't actually meaningful here.
	 */
	BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
		     ARRAY_SIZE(ignore_read_file_id));
	BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
		     ARRAY_SIZE(ignore_read_file_id));

	for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
		cur = exclude_read_files[i];
		if (!cur)
			break;
		if (*cur == '\0')
			continue;

		for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
			if (strcmp(cur, kernel_read_file_str[j]) == 0) {
				pr_info("excluding: %s\n",
					kernel_read_file_str[j]);
				ignore_read_file_id[j] = 1;
				/*
				 * Can not break, because one read_file_str
				 * may map to more than on read_file_id.
				 */
			}
		}
	}
}

static int __init loadpin_init(void)
{
	pr_info("ready to pin (currently %senforcing)\n",
		enforce ? "" : "not ");
	parse_exclude();
	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
	return 0;
}

DEFINE_LSM(loadpin) = {
	.name = "loadpin",
	.init = loadpin_init,
};

/* 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");
module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");
Commit	Line	Data
9c92ab61	1	// SPDX-License-Identifier: GPL-2.0-only
9b091556 KC	2	/*
	3	* Module and Firmware Pinning Security Module
	4	*
	5	* Copyright 2011-2016 Google Inc.
	6	*
	7	* Author: Kees Cook <keescook@chromium.org>
9b091556 KC	8	*/
	9
	10	#define pr_fmt(fmt) "LoadPin: " fmt
	11
	12	#include <linux/module.h>
	13	#include <linux/fs.h>
9b091556 KC	14	#include <linux/lsm_hooks.h>
9b091556 KC	15	#include <linux/mount.h>
3f1266f1	16	#include <linux/blkdev.h>
9b091556 KC	17	#include <linux/path.h>
	18	#include <linux/sched.h> /* current */
	19	#include <linux/string_helpers.h>
	20
	21	static 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
13523bef	40	static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
0ff98480 KW	41	static char *exclude_read_files[READING_MAX_ID];
0ff98480 KW	42	static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
9b091556 KC	43	static struct super_block *pinned_root;
	44	static DEFINE_SPINLOCK(pinned_root_spinlock);
	45
	46	#ifdef CONFIG_SYSCTL
9b091556 KC	47
	48	static struct ctl_path loadpin_sysctl_path[] = {
	49	{ .procname = "kernel", },
	50	{ .procname = "loadpin", },
	51	{ }
	52	};
	53
	54	static struct ctl_table loadpin_sysctl_table[] = {
	55	{
13523bef KC	56	.procname = "enforce",
13523bef KC	57	.data = &enforce,
9b091556 KC	58	.maxlen = sizeof(int),
	59	.mode = 0644,
	60	.proc_handler = proc_dointvec_minmax,
eec4844f MC	61	.extra1 = SYSCTL_ZERO,
eec4844f MC	62	.extra2 = SYSCTL_ONE,
9b091556 KC	63	},
	64	{ }
	65	};
	66
	67	/*
	68	* This must be called after early kernel init, since then the rootdev
	69	* is available.
	70	*/
	71	static 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) {
f4b626d6 KC	80	char bdev[BDEVNAME_SIZE];
f4b626d6 KC	81
9b091556	82	ro = bdev_read_only(mnt_sb->s_bdev);
f4b626d6 KC	83	bdevname(mnt_sb->s_bdev, bdev);
f4b626d6 KC	84	pr_info("%s (%u:%u): %s\n", bdev,
9b091556 KC	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
13523bef	96	pr_info("enforcement can be disabled.\n");
9b091556 KC	97	} else
	98	pr_info("load pinning engaged.\n");
	99	}
	100	#else
	101	static void check_pinning_enforcement(struct super_block *mnt_sb)
	102	{
	103	pr_info("load pinning engaged.\n");
	104	}
	105	#endif
	106
	107	static 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
	120	static 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
0ff98480 KW	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
9b091556 KC	132	/* This handles the older init_module API that has a NULL file. */
9b091556 KC	133	if (!file) {
13523bef	134	if (!enforce) {
9b091556 KC	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
13523bef	157	* enforcing. This would be purely cosmetic.
9b091556 KC	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) {
13523bef	167	if (unlikely(!enforce)) {
9b091556 KC	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
c77b8cdf MZ	179	static 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
ca97d939	184	static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
9b091556 KC	185	LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
9b091556 KC	186	LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
c77b8cdf	187	LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
9b091556 KC	188	};
9b091556 KC	189
0ff98480 KW	190	static 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
70b62c25	226	static int __init loadpin_init(void)
9b091556	227	{
13523bef KC	228	pr_info("ready to pin (currently %senforcing)\n",
13523bef KC	229	enforce ? "" : "not ");
0ff98480	230	parse_exclude();
d69dece5	231	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
70b62c25	232	return 0;
9b091556 KC	233	}
9b091556 KC	234
70b62c25 KC	235	DEFINE_LSM(loadpin) = {
	236	.name = "loadpin",
	237	.init = loadpin_init,
	238	};
	239
9b091556	240	/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
13523bef KC	241	module_param(enforce, int, 0);
13523bef KC	242	MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
0ff98480 KW	243	module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
0ff98480 KW	244	MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");