[PATCH v7 1/3] dm: Add verity helpers for LoadPin
Matthias Kaehlcke
mka at chromium.org
Mon Jun 27 15:35:24 UTC 2022
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: Matthias Kaehlcke <mka at chromium.org>
Acked-by: Kees Cook <keescook at chromium.org>
---
Changes in v7:
- rebased on v5.19-rc4
Changes in v6:
- s/loadpin_trusted_verity_root_digests/dm_verity_loadpin_trusted_root_digests/
- s/trusted_root_digest/dm_verity_loadpin_trusted_root_digest/
- removed unnecessary symbol exports
Changes in v5:
- changed dm_verity_loadpin_is_sb_trusted() to
dm_verity_loadpin_is_bdev_trusted()
- bumped version number to 1.8.1
- deleted bad semicolon in declaration of stub for
dm_verity_loadpin_is_bdev_trusted()
- added 'Acked-by' tag from Kees
Changes in v4:
- a trusted verity device must have a single target of
type 'verity'
- share list of verity digests with loadpin, deleted
dm_verity_loadpin_set_trusted_root_digests()
- dm_verity_loadpin_is_md_trusted() is now dm_verity_loadpin_is_sb_trusted(),
it receives a super_block instead of mapped_device. Updated kernel doc.
- changed struct trusted_root_digest to have an unsized
u8 array instead of a pointer
- extend 'dm-verity-objs' instead of 'dm-mod-objs'
Changes in v3:
- none
Changes in v2:
- none
drivers/md/Makefile | 6 +++
drivers/md/dm-verity-loadpin.c | 74 +++++++++++++++++++++++++++++++
drivers/md/dm-verity-target.c | 33 +++++++++++++-
drivers/md/dm-verity.h | 4 ++
include/linux/dm-verity-loadpin.h | 27 +++++++++++
5 files changed, 143 insertions(+), 1 deletion(-)
create mode 100644 drivers/md/dm-verity-loadpin.c
create mode 100644 include/linux/dm-verity-loadpin.h
diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index 0454b0885b01..71771901c823 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -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
diff --git a/drivers/md/dm-verity-loadpin.c b/drivers/md/dm-verity-loadpin.c
new file mode 100644
index 000000000000..10c18bc1652c
--- /dev/null
+++ b/drivers/md/dm-verity-loadpin.c
@@ -0,0 +1,74 @@
+// 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;
+}
diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index d6dbd47492a8..e5a01e2f96e9 100644
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -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,
diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h
index 4e769d13473a..c832cc3e3d24 100644
--- a/drivers/md/dm-verity.h
+++ b/drivers/md/dm-verity.h
@@ -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 */
diff --git a/include/linux/dm-verity-loadpin.h b/include/linux/dm-verity-loadpin.h
new file mode 100644
index 000000000000..fb695ecaa5d5
--- /dev/null
+++ b/include/linux/dm-verity-loadpin.h
@@ -0,0 +1,27 @@
+/* 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 */
--
2.37.0.rc0.161.g10f37bed90-goog
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