Commit b6c1c574 authored by Matthias Kaehlcke's avatar Matthias Kaehlcke Committed by Kees Cook
Browse files

dm: Add verity helpers for LoadPin 



LoadPin limits loading of kernel modules, firmware and certain
other files to a 'pinned' file system (typically a read-only
rootfs). To provide more flexibility LoadPin is being extended
to also allow loading these files from trusted dm-verity
devices. For that purpose LoadPin can be provided with a list
of verity root digests that it should consider as trusted.

Add a bunch of helpers to allow LoadPin to check whether a DM
device is a trusted verity device. The new functions broadly
fall in two categories: those that need access to verity
internals (like the root digest), and the 'glue' between
LoadPin and verity. The new file dm-verity-loadpin.c contains
the glue functions.

Signed-off-by: default avatarMatthias Kaehlcke <mka@chromium.org>
Acked-by: default avatarMike Snitzer <snitzer@kernel.org>
Link: https://lore.kernel.org/lkml/20220627083512.v7.1.I3e928575a23481121e73286874c4c2bdb403355d@changeid


Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent 375561bd

drivers/md/Makefile

+6 −0
Original line number Diff line number Diff line
@@ -108,6 +108,12 @@ ifeq ($(CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG),y) 
dm-verity-objs			+= dm-verity-verify-sig.o

endif



ifeq ($(CONFIG_DM_VERITY),y)

ifeq ($(CONFIG_SECURITY_LOADPIN),y)

dm-verity-objs			+= dm-verity-loadpin.o

endif

endif



ifeq ($(CONFIG_DM_AUDIT),y)

dm-mod-objs			+= dm-audit.o

endif

drivers/md/dm-verity-loadpin.c

0 → 100644
+74 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0-only



#include <linux/list.h>

#include <linux/kernel.h>

#include <linux/dm-verity-loadpin.h>



#include "dm.h"

#include "dm-verity.h"



#define DM_MSG_PREFIX	"verity-loadpin"



LIST_HEAD(dm_verity_loadpin_trusted_root_digests);



static bool is_trusted_verity_target(struct dm_target *ti)

{

	u8 *root_digest;

	unsigned int digest_size;

	struct dm_verity_loadpin_trusted_root_digest *trd;

	bool trusted = false;



	if (!dm_is_verity_target(ti))

		return false;



	if (dm_verity_get_root_digest(ti, &root_digest, &digest_size))

		return false;



	list_for_each_entry(trd, &dm_verity_loadpin_trusted_root_digests, node) {

		if ((trd->len == digest_size) &&

		    !memcmp(trd->data, root_digest, digest_size)) {

			trusted = true;

			break;

		}

	}



	kfree(root_digest);



	return trusted;

}



/*

 * Determines whether the file system of a superblock is located on

 * a verity device that is trusted by LoadPin.

 */

bool dm_verity_loadpin_is_bdev_trusted(struct block_device *bdev)

{

	struct mapped_device *md;

	struct dm_table *table;

	struct dm_target *ti;

	int srcu_idx;

	bool trusted = false;



	if (list_empty(&dm_verity_loadpin_trusted_root_digests))

		return false;



	md = dm_get_md(bdev->bd_dev);

	if (!md)

		return false;



	table = dm_get_live_table(md, &srcu_idx);



	if (dm_table_get_num_targets(table) != 1)

		goto out;



	ti = dm_table_get_target(table, 0);



	if (is_trusted_verity_target(ti))

		trusted = true;



out:

	dm_put_live_table(md, srcu_idx);

	dm_put(md);



	return trusted;

}

drivers/md/dm-verity-target.c

+32 −1
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ 
#include <linux/module.h>

#include <linux/reboot.h>

#include <linux/scatterlist.h>

#include <linux/string.h>



#define DM_MSG_PREFIX			"verity"
@@ -1310,10 +1311,40 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv) 
	return r;

}



/*

 * Check whether a DM target is a verity target.

 */

bool dm_is_verity_target(struct dm_target *ti)

{

	return ti->type->module == THIS_MODULE;

}



/*

 * Get the root digest of a verity target.

 *

 * Returns a copy of the root digest, the caller is responsible for

 * freeing the memory of the digest.

 */

int dm_verity_get_root_digest(struct dm_target *ti, u8 **root_digest, unsigned int *digest_size)

{

	struct dm_verity *v = ti->private;



	if (!dm_is_verity_target(ti))

		return -EINVAL;



	*root_digest = kmemdup(v->root_digest, v->digest_size, GFP_KERNEL);

	if (*root_digest == NULL)

		return -ENOMEM;



	*digest_size = v->digest_size;



	return 0;

}



static struct target_type verity_target = {

	.name		= "verity",

	.features	= DM_TARGET_IMMUTABLE,

	.version	= {1, 8, 0},

	.version	= {1, 8, 1},

	.module		= THIS_MODULE,

	.ctr		= verity_ctr,

	.dtr		= verity_dtr,

drivers/md/dm-verity.h

+4 −0
Original line number Diff line number Diff line
@@ -129,4 +129,8 @@ extern int verity_hash(struct dm_verity *v, struct ahash_request *req, 
extern int verity_hash_for_block(struct dm_verity *v, struct dm_verity_io *io,

				 sector_t block, u8 *digest, bool *is_zero);



extern bool dm_is_verity_target(struct dm_target *ti);

extern int dm_verity_get_root_digest(struct dm_target *ti, u8 **root_digest,

				     unsigned int *digest_size);



#endif /* DM_VERITY_H */

include/linux/dm-verity-loadpin.h

0 → 100644
+27 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */



#ifndef __LINUX_DM_VERITY_LOADPIN_H

#define __LINUX_DM_VERITY_LOADPIN_H



#include <linux/list.h>



struct block_device;



extern struct list_head dm_verity_loadpin_trusted_root_digests;



struct dm_verity_loadpin_trusted_root_digest {

	struct list_head node;

	unsigned int len;

	u8 data[];

};



#if IS_ENABLED(CONFIG_SECURITY_LOADPIN) && IS_BUILTIN(CONFIG_DM_VERITY)

bool dm_verity_loadpin_is_bdev_trusted(struct block_device *bdev);

#else

static inline bool dm_verity_loadpin_is_bdev_trusted(struct block_device *bdev)

{

	return false;

}

#endif



#endif /* __LINUX_DM_VERITY_LOADPIN_H */