[PATCH v4 0/3] LoadPin: Enable loading from trusted dm-verity devices

[PATCH v4 0/3] LoadPin: Enable loading from trusted dm-verity devices

[Matthias Kaehlcke]

As of now LoadPin restricts loading of kernel files to a single pinned
filesystem, typically the rootfs. This works for many systems, however it
can result in a bloated rootfs (and OTA updates) on platforms where
multiple boards with different hardware configurations use the same rootfs
image. Especially when 'optional' files are large it may be preferable to
download/install them only when they are actually needed by a given board.
Chrome OS uses Downloadable Content (DLC) [1] to deploy certain 'packages'
at runtime. As an example a DLC package could contain firmware for a
peripheral that is not present on all boards. DLCs use dm-verity [2] to
verify the integrity of the DLC content.

This series extends LoadPin to allow loading of kernel files from trusted
dm-verity devices. LoadPin maintains a list of root digests of verity
devices it considers trusted. Userspace can populate this list through an
ioctl on the new LoadPin securityfs entry 'dm-verity'. The ioctl receives
a file descriptor of a file with verity digests as parameter. Verity reads
the digests from this file after confirming that the file is located on the
pinned root. The digest file must contain one digest per line. The list of
trusted digests can only be set up once, which is typically done at boot
time.

When a kernel file is read LoadPin first checks (as usual) whether the file
is located on the pinned root, if so the file can be loaded. Otherwise, if
the verity extension is enabled, LoadPin determines whether the file is
located on a verity backed device and whether the root digest of that
device is in the list of trusted digests. The file can be loaded if the
verity device has a trusted root digest.

[1] https://chromium.googlesource.com/chromiumos/platform2/+/HEAD/dlcservice/docs/developer.md
[2] https://www.kernel.org/doc/html/latest/admin-guide/device-mapper/verity.html

Changes in v4:
- a trusted verity device must have a single target of
  type 'verity'
- changed struct trusted_root_digest to have an unsized
  u8 array instead of a pointer
- use shared list of verity digests, deleted
  dm_verity_loadpin_set_trusted_root_digests()
- use newline as separator in digest file instead of comma
- after reading an invalid/corrupt digest file deny further attempts
  of setting up the list of digests
- added comment to read_trusted_verity_root_digests() explaining that
  an invalid digests entry invalidates the entire list of digests
- minor refactoring of verity related code in LoadPin

Changes in v3:
- added securityfs for LoadPin (currently only populated when
  CONFIG_SECURITY_LOADPIN_VERITY=y)
- added uapi include for LoadPin
- changed the interface for setting up the list of trusted
  digests from sysctl to ioctl on securityfs entry
- added stub for loadpin_is_fs_trusted() to be used
  CONFIG_SECURITY_LOADPIN_VERITY is not select
- depend on CONFIG_SECURITYFS instead of CONFIG_SYSTCL
- updated Kconfig help
- minor changes in read_trusted_verity_root_digests()
- updated commit message

Changes in v2:
- userspace now passes the path of the file with the verity digests
  via systcl, instead of the digests themselves
- renamed sysctl file to 'trusted_verity_root_digests_path'
- have CONFIG_SECURITY_LOADPIN_VERITY depend on CONFIG_SYSCTL
- updated Kconfig doc
- updated commit message

Matthias Kaehlcke (3):
  dm: Add verity helpers for LoadPin
  LoadPin: Enable loading from trusted dm-verity devices
  dm: verity-loadpin: Use CONFIG_SECURITY_LOADPIN_VERITY for conditional
    compilation

 drivers/md/Makefile               |   1 +
 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 +++++
 include/uapi/linux/loadpin.h      |  22 ++++
 security/loadpin/Kconfig          |  16 +++
 security/loadpin/loadpin.c        | 167 +++++++++++++++++++++++++++++-
 8 files changed, 343 insertions(+), 1 deletion(-)
 create mode 100644 drivers/md/dm-verity-loadpin.c
 create mode 100644 include/linux/dm-verity-loadpin.h
 create mode 100644 include/uapi/linux/loadpin.h

-- 
2.36.0.550.gb090851708-goog

[PATCH v4 1/3] dm: Add verity helpers for LoadPin

[Matthias Kaehlcke]

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@chromium.org>
---

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, 144 insertions(+)
 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..3226fbe4a1fe
--- /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(loadpin_trusted_verity_root_digests);
+
+static bool is_trusted_verity_target(struct dm_target *ti)
+{
+	u8 *root_digest;
+	unsigned int digest_size;
+	struct 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, &loadpin_trusted_verity_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_sb_trusted(struct super_block *sb)
+{
+	struct mapped_device *md;
+	struct dm_table *table;
+	struct dm_target *ti;
+	int srcu_idx;
+	bool trusted = false;
+
+	if (list_empty(&loadpin_trusted_verity_root_digests))
+		return false;
+
+	md = dm_get_md(sb->s_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 80133aae0db3..6f07b849fcb2 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"
 
@@ -1310,6 +1311,38 @@ 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;
+}
+EXPORT_SYMBOL_GPL(dm_is_verity_target);
+
+/*
+ * 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;
+}
+EXPORT_SYMBOL_GPL(dm_verity_get_root_digest);
+
 static struct target_type verity_target = {
 	.name		= "verity",
 	.version	= {1, 8, 0},
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..c2bfd2b9c651
--- /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 super_block;
+
+extern struct list_head loadpin_trusted_verity_root_digests;
+
+struct 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_sb_trusted(struct super_block *sb);
+#else
+static inline bool dm_verity_loadpin_is_sb_trusted(struct super_block *sb);
+{
+	return false;
+}
+#endif
+
+#endif /* __LINUX_DM_LOADPIN_H */
-- 
2.36.0.550.gb090851708-goog

[PATCH v4 2/3] LoadPin: Enable loading from trusted dm-verity devices

[Matthias Kaehlcke]

Extend LoadPin to allow loading of kernel files from trusted dm-verity [1]
devices.

This change adds the concept of trusted verity devices to LoadPin. LoadPin
maintains a list of root digests of verity devices it considers trusted.
Userspace can populate this list through an ioctl on the new LoadPin
securityfs entry 'dm-verity'. The ioctl receives a file descriptor of
a file with verity digests as parameter. Verity reads the digests from
this file after confirming that the file is located on the pinned root.
The digest file must contain one digest per line. The list of trusted
digests can only be set up once, which is typically done at boot time.

When a kernel file is read LoadPin first checks (as usual) whether the file
is located on the pinned root, if so the file can be loaded. Otherwise, if
the verity extension is enabled, LoadPin determines whether the file is
located on a verity backed device and whether the root digest of that
device is in the list of trusted digests. The file can be loaded if the
verity device has a trusted root digest.

Background:

As of now LoadPin restricts loading of kernel files to a single pinned
filesystem, typically the rootfs. This works for many systems, however it
can result in a bloated rootfs (and OTA updates) on platforms where
multiple boards with different hardware configurations use the same rootfs
image. Especially when 'optional' files are large it may be preferable to
download/install them only when they are actually needed by a given board.
Chrome OS uses Downloadable Content (DLC) [2] to deploy certain 'packages'
at runtime. As an example a DLC package could contain firmware for a
peripheral that is not present on all boards. DLCs use dm-verity to verify
the integrity of the DLC content.

[1] https://www.kernel.org/doc/html/latest/admin-guide/device-mapper/verity.html
[2] https://chromium.googlesource.com/chromiumos/platform2/+/HEAD/dlcservice/docs/developer.md

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---

Changes in v4:
- use newline as separator in digest file instead of comma
- after reading an invalid/corrupt digest file deny further attempts
  of setting up the list of digests
- added comment to read_trusted_verity_root_digests() explaining that
  an invalid digests entry invalidates the entire list of digests
- refactored read_trusted_verity_root_digests() to avoid cast of 'data' at
  assignment
- add the format of the digest file and the path of the securityfs
  attribute to the ioctl comment.
- adapted to struct trusted_root_digest with unsized array 'data'
- call dm_verity_loadpin_is_sb_trusted() instead of
  loadpin_is_fs_trusted()
- deleted loadpin_is_fs_trusted()
- use '%ld' in format string for PTR_ERR()
- added note about digest file format to the commit message

Changes in v3:
- added securityfs for LoadPin (currently only populated when
  CONFIG_SECURITY_LOADPIN_VERITY=y)
- added uapi include for LoadPin
- changed the interface for setting up the list of trusted
  digests from sysctl to ioctl on securityfs entry
- added stub for loadpin_is_fs_trusted() to be used
  CONFIG_SECURITY_LOADPIN_VERITY is not select
- depend on CONFIG_SECURITYFS instead of CONFIG_SYSTCL
- updated Kconfig help
- minor changes in read_trusted_verity_root_digests()
- updated commit message

Changes in v2:
- userspace now passes the path of the file with the verity digests
  via systcl, instead of the digests themselves
- renamed sysctl file to 'trusted_verity_root_digests_path'
- have CONFIG_SECURITY_LOADPIN_VERITY depend on CONFIG_SYSCTL
- updated Kconfig doc
- updated commit message

 include/uapi/linux/loadpin.h |  22 +++++
 security/loadpin/Kconfig     |  16 ++++
 security/loadpin/loadpin.c   | 167 ++++++++++++++++++++++++++++++++++-
 3 files changed, 204 insertions(+), 1 deletion(-)
 create mode 100644 include/uapi/linux/loadpin.h

diff --git a/include/uapi/linux/loadpin.h b/include/uapi/linux/loadpin.h
new file mode 100644
index 000000000000..daa6dbb8bb02
--- /dev/null
+++ b/include/uapi/linux/loadpin.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Copyright (c) 2022, Google LLC
+ */
+
+#ifndef _UAPI_LINUX_LOOP_LOADPIN_H
+#define _UAPI_LINUX_LOOP_LOADPIN_H
+
+#define LOADPIN_IOC_MAGIC	'L'
+
+/**
+ * LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS - Set up the root digests of verity devices
+ *                                          that loadpin should trust.
+ *
+ * Takes a file descriptor from which to read the root digests of trusted verity devices. The file
+ * is expected to contain a list of digests in ASCII format, with one line per digest. The ioctl
+ * must be issued on the securityfs attribute 'loadpin/dm-verity' (which can be typically found
+ * under /sys/kernel/security/loadpin/dm-verity).
+ */
+#define LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS _IOW(LOADPIN_IOC_MAGIC, 0x00, unsigned int)
+
+#endif /* _UAPI_LINUX_LOOP_LOADPIN_H */
diff --git a/security/loadpin/Kconfig b/security/loadpin/Kconfig
index 91be65dec2ab..e319ca8e3f3d 100644
--- a/security/loadpin/Kconfig
+++ b/security/loadpin/Kconfig
@@ -18,3 +18,19 @@ config SECURITY_LOADPIN_ENFORCE
 	  If selected, LoadPin will enforce pinning at boot. If not
 	  selected, it can be enabled at boot with the kernel parameter
 	  "loadpin.enforce=1".
+
+config SECURITY_LOADPIN_VERITY
+	bool "Allow reading files from certain other filesystems that use dm-verity"
+	depends on DM_VERITY=y && SECURITYFS
+	help
+	  If selected LoadPin can allow reading files from filesystems
+	  that use dm-verity. LoadPin maintains a list of verity root
+	  digests it considers trusted. A verity backed filesystem is
+	  considered trusted if its root digest is found in the list
+	  of trusted digests.
+
+	  The list of trusted verity can be populated through an ioctl
+	  on the LoadPin securityfs entry 'dm-verity'. The ioctl
+	  expects a file descriptor of a file with verity digests as
+	  parameter. The file must be located on the pinned root and
+	  contain a comma separated list of digests.
diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
index b12f7d986b1e..67be496befaa 100644
--- a/security/loadpin/loadpin.c
+++ b/security/loadpin/loadpin.c
@@ -18,6 +18,8 @@
 #include <linux/path.h>
 #include <linux/sched.h>	/* current */
 #include <linux/string_helpers.h>
+#include <linux/dm-verity-loadpin.h>
+#include <uapi/linux/loadpin.h>
 
 static void report_load(const char *origin, struct file *file, char *operation)
 {
@@ -43,6 +45,9 @@ 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_SECURITY_LOADPIN_VERITY
+static bool deny_reading_verity_digests;
+#endif
 
 #ifdef CONFIG_SYSCTL
 
@@ -174,7 +179,8 @@ static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
 		spin_unlock(&pinned_root_spinlock);
 	}
 
-	if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
+	if (IS_ERR_OR_NULL(pinned_root) ||
+	    ((load_root != pinned_root) && !dm_verity_loadpin_is_sb_trusted(load_root))) {
 		if (unlikely(!enforce)) {
 			report_load(origin, file, "pinning-ignored");
 			return 0;
@@ -240,6 +246,7 @@ static int __init loadpin_init(void)
 		enforce ? "" : "not ");
 	parse_exclude();
 	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
+
 	return 0;
 }
 
@@ -248,6 +255,164 @@ DEFINE_LSM(loadpin) = {
 	.init = loadpin_init,
 };
 
+#ifdef CONFIG_SECURITY_LOADPIN_VERITY
+
+enum loadpin_securityfs_interface_index {
+	LOADPIN_DM_VERITY,
+};
+
+static int read_trusted_verity_root_digests(unsigned int fd)
+{
+	struct fd f;
+	void *data;
+	int rc;
+	char *p, *d;
+
+	if (deny_reading_verity_digests)
+		return -EPERM;
+
+	/* The list of trusted root digests can only be set up once */
+	if (!list_empty(&loadpin_trusted_verity_root_digests))
+		return -EPERM;
+
+	f = fdget(fd);
+	if (!f.file)
+		return -EINVAL;
+
+	data = kzalloc(SZ_4K, GFP_KERNEL);
+	if (!data) {
+		rc = -ENOMEM;
+		goto err;
+	}
+
+	rc = kernel_read_file(f.file, 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY);
+	if (rc < 0)
+		goto err;
+
+	p = data;
+	p[rc] = '\0';
+	p = strim(p);
+
+	p = strim(data);
+	while ((d = strsep(&p, "\n")) != NULL) {
+		int len = strlen(d);
+		struct trusted_root_digest *trd;
+
+		if (len % 2) {
+			rc = -EPROTO;
+			goto err;
+		}
+
+		len /= 2;
+
+		trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL);
+		if (!trd) {
+			rc = -ENOMEM;
+			goto err;
+		}
+
+		if (hex2bin(trd->data, d, len)) {
+			kfree(trd);
+			rc = -EPROTO;
+			goto err;
+		}
+
+		trd->len = len;
+
+		list_add_tail(&trd->node, &loadpin_trusted_verity_root_digests);
+	}
+
+	if (list_empty(&loadpin_trusted_verity_root_digests)) {
+		rc = -EPROTO;
+		goto err;
+	}
+
+	kfree(data);
+	fdput(f);
+
+	return 0;
+
+err:
+	kfree(data);
+
+	/* any failure in loading/parsing invalidates the entire list */
+	{
+		struct trusted_root_digest *trd, *tmp;
+
+		list_for_each_entry_safe(trd, tmp, &loadpin_trusted_verity_root_digests, node) {
+			list_del(&trd->node);
+			kfree(trd);
+		}
+	}
+
+	/* disallow further attempts after reading a corrupt/invalid file */
+	deny_reading_verity_digests = true;
+
+	fdput(f);
+
+	return rc;
+}
+
+/******************************** securityfs ********************************/
+
+static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
+{
+	void __user *uarg = (void __user *)arg;
+	unsigned int fd;
+	int rc;
+
+	switch (cmd) {
+	case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
+		rc = copy_from_user(&fd, uarg, sizeof(fd));
+		if (rc)
+			return rc;
+
+		return read_trusted_verity_root_digests(fd);
+
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct file_operations loadpin_dm_verity_ops = {
+	.unlocked_ioctl = dm_verity_ioctl,
+	.compat_ioctl = compat_ptr_ioctl,
+};
+
+/**
+ * init_loadpin_securityfs - create the securityfs directory for LoadPin
+ *
+ * We can not put this method normally under the loadpin_init() code path since
+ * the security subsystem gets initialized before the vfs caches.
+ *
+ * Returns 0 if the securityfs directory creation was successful.
+ */
+static int __init init_loadpin_securityfs(void)
+{
+	struct dentry *loadpin_dir, *dentry;
+
+	loadpin_dir = securityfs_create_dir("loadpin", NULL);
+	if (IS_ERR(loadpin_dir)) {
+		pr_err("LoadPin: could not create securityfs dir: %ld\n",
+		       PTR_ERR(loadpin_dir));
+		return PTR_ERR(loadpin_dir);
+	}
+
+	dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir,
+					(void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops);
+	if (IS_ERR(dentry)) {
+		pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
+		       PTR_ERR(dentry));
+		return PTR_ERR(dentry);
+	}
+
+	return 0;
+}
+
+fs_initcall(init_loadpin_securityfs);
+
+#endif /* CONFIG_SECURITY_LOADPIN_VERITY */
+
 /* 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");
-- 
2.36.0.550.gb090851708-goog

[PATCH v4 3/3] dm: verity-loadpin: Use CONFIG_SECURITY_LOADPIN_VERITY for conditional compilation

[Matthias Kaehlcke]

The verity glue for LoadPin is only needed when CONFIG_SECURITY_LOADPIN_VERITY
is set, use this option for conditional compilation instead of the combo of
CONFIG_DM_VERITY and CONFIG_SECURITY_LOADPIN.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---

Changes in v4:
- none

Changes in v3:
- none

Changes in v2:
- none

 drivers/md/Makefile               | 7 +------
 include/linux/dm-verity-loadpin.h | 2 +-
 2 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index 71771901c823..a96441752ec7 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -83,6 +83,7 @@ obj-$(CONFIG_DM_LOG_WRITES)	+= dm-log-writes.o
 obj-$(CONFIG_DM_INTEGRITY)	+= dm-integrity.o
 obj-$(CONFIG_DM_ZONED)		+= dm-zoned.o
 obj-$(CONFIG_DM_WRITECACHE)	+= dm-writecache.o
+obj-$(CONFIG_SECURITY_LOADPIN_VERITY)	+= dm-verity-loadpin.o
 
 ifeq ($(CONFIG_DM_INIT),y)
 dm-mod-objs			+= dm-init.o
@@ -108,12 +109,6 @@ ifeq ($(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/include/linux/dm-verity-loadpin.h b/include/linux/dm-verity-loadpin.h
index c2bfd2b9c651..dd66ece9a751 100644
--- a/include/linux/dm-verity-loadpin.h
+++ b/include/linux/dm-verity-loadpin.h
@@ -15,7 +15,7 @@ struct trusted_root_digest {
 	u8 data[];
 };
 
-#if IS_ENABLED(CONFIG_SECURITY_LOADPIN) && IS_BUILTIN(CONFIG_DM_VERITY)
+#if IS_ENABLED(CONFIG_SECURITY_LOADPIN_VERITY)
 bool dm_verity_loadpin_is_sb_trusted(struct super_block *sb);
 #else
 static inline bool dm_verity_loadpin_is_sb_trusted(struct super_block *sb);
-- 
2.36.0.550.gb090851708-goog

Re: [dm-devel] [PATCH v4 1/3] dm: Add verity helpers for LoadPin

[Milan Broz]

On 18/05/2022 01:34, Matthias Kaehlcke wrote:
> 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@chromium.org>

...

> +
> +	if (dm_verity_get_root_digest(ti, &root_digest, &digest_size))
> +		return false;

Almost unrelated note, but as there are more and more situations
that checks verity root digest, shouldn't we export this as read-only
sysfs attribute for DM verity devices?

Attacker can always calculate (but not change) Merkle tree, so this
is not something that need to be hidden.

It would allow userspace to easily enumerate trusted DM devices without
calling kernel ioctls...

...

> +
> +	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;

What happens is someone reloads verity table later with
a different content (or even different target type)?
Does LoadPin even care here?

...

>   static struct target_type verity_target = {
>   	.name		= "verity",
>   	.version	= {1, 8, 0},

Please increase the minor version, it is very useful to detect (in logs)
that the target driver has compatible extensions.


I guess this change does not affect userspace veristysetup
(as it is used handled by different tooling), right?

Thanks,
Milan

Re: [PATCH v4 2/3] LoadPin: Enable loading from trusted dm-verity devices

[kernel test robot]

Hi Matthias,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on device-mapper-dm/for-next]
[also build test WARNING on song-md/md-next kees/for-next/pstore linus/master v5.18-rc7 next-20220517]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/intel-lab-lkp/linux/commits/Matthias-Kaehlcke/LoadPin-Enable-loading-from-trusted-dm-verity-devices/20220518-073635
base:   https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git for-next
config: m68k-allmodconfig (https://download.01.org/0day-ci/archive/20220518/202205181616.3eTP2DaC-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 11.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/755e5d82e4d054b2b58a54c94681080cc8cb4582
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Matthias-Kaehlcke/LoadPin-Enable-loading-from-trusted-dm-verity-devices/20220518-073635
        git checkout 755e5d82e4d054b2b58a54c94681080cc8cb4582
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.3.0 make.cross W=1 O=build_dir ARCH=m68k SHELL=/bin/bash security/loadpin/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   In file included from security/loadpin/loadpin.c:21:
   include/linux/dm-verity-loadpin.h:22:1: error: expected identifier or '(' before '{' token
      22 | {
         | ^
>> include/linux/dm-verity-loadpin.h:21:20: warning: 'dm_verity_loadpin_is_sb_trusted' used but never defined
      21 | static inline bool dm_verity_loadpin_is_sb_trusted(struct super_block *sb);
         |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


vim +/dm_verity_loadpin_is_sb_trusted +21 include/linux/dm-verity-loadpin.h

afd03270f57b8c Matthias Kaehlcke 2022-05-17  17  
afd03270f57b8c Matthias Kaehlcke 2022-05-17  18  #if IS_ENABLED(CONFIG_SECURITY_LOADPIN) && IS_BUILTIN(CONFIG_DM_VERITY)
afd03270f57b8c Matthias Kaehlcke 2022-05-17  19  bool dm_verity_loadpin_is_sb_trusted(struct super_block *sb);
afd03270f57b8c Matthias Kaehlcke 2022-05-17  20  #else
afd03270f57b8c Matthias Kaehlcke 2022-05-17 @21  static inline bool dm_verity_loadpin_is_sb_trusted(struct super_block *sb);
afd03270f57b8c Matthias Kaehlcke 2022-05-17 @22  {
afd03270f57b8c Matthias Kaehlcke 2022-05-17  23  	return false;
afd03270f57b8c Matthias Kaehlcke 2022-05-17  24  }
afd03270f57b8c Matthias Kaehlcke 2022-05-17  25  #endif
afd03270f57b8c Matthias Kaehlcke 2022-05-17  26  

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

Re: [PATCH v4 2/3] LoadPin: Enable loading from trusted dm-verity devices

[kernel test robot]

Hi Matthias,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on device-mapper-dm/for-next]
[also build test ERROR on song-md/md-next kees/for-next/pstore linus/master v5.18-rc7 next-20220517]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/intel-lab-lkp/linux/commits/Matthias-Kaehlcke/LoadPin-Enable-loading-from-trusted-dm-verity-devices/20220518-073635
base:   https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git for-next
config: m68k-allmodconfig (https://download.01.org/0day-ci/archive/20220518/202205182059.6QY3zspw-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 11.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/755e5d82e4d054b2b58a54c94681080cc8cb4582
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Matthias-Kaehlcke/LoadPin-Enable-loading-from-trusted-dm-verity-devices/20220518-073635
        git checkout 755e5d82e4d054b2b58a54c94681080cc8cb4582
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.3.0 make.cross W=1 O=build_dir ARCH=m68k SHELL=/bin/bash security/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   In file included from security/loadpin/loadpin.c:21:
>> include/linux/dm-verity-loadpin.h:22:1: error: expected identifier or '(' before '{' token
      22 | {
         | ^
   include/linux/dm-verity-loadpin.h:21:20: warning: 'dm_verity_loadpin_is_sb_trusted' used but never defined
      21 | static inline bool dm_verity_loadpin_is_sb_trusted(struct super_block *sb);
         |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


vim +22 include/linux/dm-verity-loadpin.h

afd03270f57b8c Matthias Kaehlcke 2022-05-17  17  
afd03270f57b8c Matthias Kaehlcke 2022-05-17  18  #if IS_ENABLED(CONFIG_SECURITY_LOADPIN) && IS_BUILTIN(CONFIG_DM_VERITY)
afd03270f57b8c Matthias Kaehlcke 2022-05-17  19  bool dm_verity_loadpin_is_sb_trusted(struct super_block *sb);
afd03270f57b8c Matthias Kaehlcke 2022-05-17  20  #else
afd03270f57b8c Matthias Kaehlcke 2022-05-17  21  static inline bool dm_verity_loadpin_is_sb_trusted(struct super_block *sb);
afd03270f57b8c Matthias Kaehlcke 2022-05-17 @22  {
afd03270f57b8c Matthias Kaehlcke 2022-05-17  23  	return false;
afd03270f57b8c Matthias Kaehlcke 2022-05-17  24  }
afd03270f57b8c Matthias Kaehlcke 2022-05-17  25  #endif
afd03270f57b8c Matthias Kaehlcke 2022-05-17  26  

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

Re: [PATCH v4 2/3] LoadPin: Enable loading from trusted dm-verity devices

[Matthias Kaehlcke]

On Wed, May 18, 2022 at 04:58:06PM +0800, kernel test robot wrote:
> Hi Matthias,
> 
> Thank you for the patch! Perhaps something to improve:
> 
> [auto build test WARNING on device-mapper-dm/for-next]
> [also build test WARNING on song-md/md-next kees/for-next/pstore linus/master v5.18-rc7 next-20220517]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Matthias-Kaehlcke/LoadPin-Enable-loading-from-trusted-dm-verity-devices/20220518-073635
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git for-next
> config: m68k-allmodconfig (https://download.01.org/0day-ci/archive/20220518/202205181616.3eTP2DaC-lkp@intel.com/config)
> compiler: m68k-linux-gcc (GCC) 11.3.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://github.com/intel-lab-lkp/linux/commit/755e5d82e4d054b2b58a54c94681080cc8cb4582
>         git remote add linux-review https://github.com/intel-lab-lkp/linux
>         git fetch --no-tags linux-review Matthias-Kaehlcke/LoadPin-Enable-loading-from-trusted-dm-verity-devices/20220518-073635
>         git checkout 755e5d82e4d054b2b58a54c94681080cc8cb4582
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.3.0 make.cross W=1 O=build_dir ARCH=m68k SHELL=/bin/bash security/loadpin/
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
> 
> All warnings (new ones prefixed by >>):
> 
>    In file included from security/loadpin/loadpin.c:21:
>    include/linux/dm-verity-loadpin.h:22:1: error: expected identifier or '(' before '{' token
>       22 | {
>          | ^
> >> include/linux/dm-verity-loadpin.h:21:20: warning: 'dm_verity_loadpin_is_sb_trusted' used but never defined
>       21 | static inline bool dm_verity_loadpin_is_sb_trusted(struct super_block *sb);
>          |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> 
> vim +/dm_verity_loadpin_is_sb_trusted +21 include/linux/dm-verity-loadpin.h
> 
> afd03270f57b8c Matthias Kaehlcke 2022-05-17  17  
> afd03270f57b8c Matthias Kaehlcke 2022-05-17  18  #if IS_ENABLED(CONFIG_SECURITY_LOADPIN) && IS_BUILTIN(CONFIG_DM_VERITY)
> afd03270f57b8c Matthias Kaehlcke 2022-05-17  19  bool dm_verity_loadpin_is_sb_trusted(struct super_block *sb);
> afd03270f57b8c Matthias Kaehlcke 2022-05-17  20  #else
> afd03270f57b8c Matthias Kaehlcke 2022-05-17 @21  static inline bool dm_verity_loadpin_is_sb_trusted(struct super_block *sb);
> afd03270f57b8c Matthias Kaehlcke 2022-05-17 @22  {
> afd03270f57b8c Matthias Kaehlcke 2022-05-17  23  	return false;
> afd03270f57b8c Matthias Kaehlcke 2022-05-17  24  }
> afd03270f57b8c Matthias Kaehlcke 2022-05-17  25  #endif
> afd03270f57b8c Matthias Kaehlcke 2022-05-17  26  

Oops, will fix

Re: [dm-devel] [PATCH v4 1/3] dm: Add verity helpers for LoadPin

[Matthias Kaehlcke]

Hi Milan,

On Wed, May 18, 2022 at 09:57:43AM +0200, Milan Broz wrote:
> On 18/05/2022 01:34, Matthias Kaehlcke wrote:
> > 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@chromium.org>
> 
> ...
> 
> > +
> > +	if (dm_verity_get_root_digest(ti, &root_digest, &digest_size))
> > +		return false;
> 
> Almost unrelated note, but as there are more and more situations
> that checks verity root digest, shouldn't we export this as read-only
> sysfs attribute for DM verity devices?
> 
> Attacker can always calculate (but not change) Merkle tree, so this
> is not something that need to be hidden.
> 
> It would allow userspace to easily enumerate trusted DM devices without
> calling kernel ioctls...

I guess that's an option if there are scenarios where it is useful. It
should probably be a separate patch, since it isn't directly related with
extending LoadPin support to trusted verity devices.

> > +
> > +	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;
> 
> What happens is someone reloads verity table later with
> a different content (or even different target type)?
> Does LoadPin even care here?

LoadPin cares, but only when new kernel files are loaded. It will then check
against the new verity table, and only allow loading of the file if it comes
from a verity target with a trusted digest.

> >   static struct target_type verity_target = {
> >   	.name		= "verity",
> >   	.version	= {1, 8, 0},
> 
> Please increase the minor version, it is very useful to detect (in logs)
> that the target driver has compatible extensions.

I can do that, but would like to confirm that this is really needed/desired.
This patch adds kernel-internal APIs which aren't accessible to userspace,
that don't impact verity directly, so I'm not sure an increased minor version
would be useful.

> I guess this change does not affect userspace veristysetup
> (as it is used handled by different tooling), right?

Correct, from the verity side this is effectively a NOP, the new
kernel-internal APIs only provide information to LoadPin, but don't
change any verity specific behavior.

Re: [PATCH v4 0/3] LoadPin: Enable loading from trusted dm-verity devices

[Kees Cook]

On Tue, May 17, 2022 at 04:34:54PM -0700, Matthias Kaehlcke wrote:
> As of now LoadPin restricts loading of kernel files to a single pinned
> filesystem, typically the rootfs. This works for many systems, however it
> can result in a bloated rootfs (and OTA updates) on platforms where
> multiple boards with different hardware configurations use the same rootfs
> image. Especially when 'optional' files are large it may be preferable to
> download/install them only when they are actually needed by a given board.
> Chrome OS uses Downloadable Content (DLC) [1] to deploy certain 'packages'
> at runtime. As an example a DLC package could contain firmware for a
> peripheral that is not present on all boards. DLCs use dm-verity [2] to
> verify the integrity of the DLC content.

For the coming v5 (which will fix the 0-day reports), if I can get some
Acks from the dm folks, I can carry this with other loadpin changes in
my tree. Though I'm fine with this going via the dm tree, too:

Acked-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

Re: [PATCH v4 0/3] LoadPin: Enable loading from trusted dm-verity devices

[Mike Snitzer]

On Wed, May 18 2022 at  3:23P -0400,
Kees Cook <keescook@chromium.org> wrote:

> On Tue, May 17, 2022 at 04:34:54PM -0700, Matthias Kaehlcke wrote:
> > As of now LoadPin restricts loading of kernel files to a single pinned
> > filesystem, typically the rootfs. This works for many systems, however it
> > can result in a bloated rootfs (and OTA updates) on platforms where
> > multiple boards with different hardware configurations use the same rootfs
> > image. Especially when 'optional' files are large it may be preferable to
> > download/install them only when they are actually needed by a given board.
> > Chrome OS uses Downloadable Content (DLC) [1] to deploy certain 'packages'
> > at runtime. As an example a DLC package could contain firmware for a
> > peripheral that is not present on all boards. DLCs use dm-verity [2] to
> > verify the integrity of the DLC content.
> 
> For the coming v5 (which will fix the 0-day reports), if I can get some
> Acks from the dm folks, I can carry this with other loadpin changes in
> my tree. Though I'm fine with this going via the dm tree, too:
> 
> Acked-by: Kees Cook <keescook@chromium.org>

I'll review it once it's posted.

But I'm going to reply to v4's 1/3 now.

Re: [PATCH v4 1/3] dm: Add verity helpers for LoadPin

[Mike Snitzer]

On Tue, May 17 2022 at  7:34P -0400,
Matthias Kaehlcke <mka@chromium.org> wrote:

> 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@chromium.org>
> ---
> 
> 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, 144 insertions(+)
>  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..3226fbe4a1fe
> --- /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(loadpin_trusted_verity_root_digests);
> +
> +static bool is_trusted_verity_target(struct dm_target *ti)
> +{
> +	u8 *root_digest;
> +	unsigned int digest_size;
> +	struct 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, &loadpin_trusted_verity_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_sb_trusted(struct super_block *sb)
> +{
> +	struct mapped_device *md;
> +	struct dm_table *table;
> +	struct dm_target *ti;
> +	int srcu_idx;
> +	bool trusted = false;
> +
> +	if (list_empty(&loadpin_trusted_verity_root_digests))
> +		return false;
> +
> +	md = dm_get_md(sb->s_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;
> +}

Not seeing why passing a super_block a block layer interface was
chosen.

Please pass the super_block's block_device and rename to
dm_verity_loadpin_is_bdev_trusted()

Thanks,
Mike

Re: [PATCH v4 1/3] dm: Add verity helpers for LoadPin

[Mike Snitzer]

On Wed, May 18 2022 at 11:13P -0400,
Matthias Kaehlcke <mka@chromium.org> wrote:

> Hi Milan,
> 
> On Wed, May 18, 2022 at 09:57:43AM +0200, Milan Broz wrote:
> > On 18/05/2022 01:34, Matthias Kaehlcke wrote:
> > > 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@chromium.org>
> > 
> > ...
> > 
> > > +
> > > +	if (dm_verity_get_root_digest(ti, &root_digest, &digest_size))
> > > +		return false;
> > 
> > Almost unrelated note, but as there are more and more situations
> > that checks verity root digest, shouldn't we export this as read-only
> > sysfs attribute for DM verity devices?
> > 
> > Attacker can always calculate (but not change) Merkle tree, so this
> > is not something that need to be hidden.
> > 
> > It would allow userspace to easily enumerate trusted DM devices without
> > calling kernel ioctls...
> 
> I guess that's an option if there are scenarios where it is useful. It
> should probably be a separate patch, since it isn't directly related with
> extending LoadPin support to trusted verity devices.
> 
> > > +
> > > +	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;
> > 
> > What happens is someone reloads verity table later with
> > a different content (or even different target type)?
> > Does LoadPin even care here?
> 
> LoadPin cares, but only when new kernel files are loaded. It will then check
> against the new verity table, and only allow loading of the file if it comes
> from a verity target with a trusted digest.
> 
> > >   static struct target_type verity_target = {
> > >   	.name		= "verity",
> > >   	.version	= {1, 8, 0},
> > 
> > Please increase the minor version, it is very useful to detect (in logs)
> > that the target driver has compatible extensions.
> 
> I can do that, but would like to confirm that this is really needed/desired.
> This patch adds kernel-internal APIs which aren't accessible to userspace,
> that don't impact verity directly, so I'm not sure an increased minor version
> would be useful.

Bumping to 1.8.1 is useful to indicate new changes that offer expanded
use of the verity target (even if by LoadPin).

Re: [PATCH v4 1/3] dm: Add verity helpers for LoadPin

[Matthias Kaehlcke]

On Wed, May 18, 2022 at 04:03:44PM -0400, Mike Snitzer wrote:
> On Wed, May 18 2022 at 11:13P -0400,
> Matthias Kaehlcke <mka@chromium.org> wrote:
> 
> > Hi Milan,
> > 
> > On Wed, May 18, 2022 at 09:57:43AM +0200, Milan Broz wrote:
> > > On 18/05/2022 01:34, Matthias Kaehlcke wrote:
> > > > 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@chromium.org>
> > > 
> > > ...
> > > 
> > > > +
> > > > +	if (dm_verity_get_root_digest(ti, &root_digest, &digest_size))
> > > > +		return false;
> > > 
> > > Almost unrelated note, but as there are more and more situations
> > > that checks verity root digest, shouldn't we export this as read-only
> > > sysfs attribute for DM verity devices?
> > > 
> > > Attacker can always calculate (but not change) Merkle tree, so this
> > > is not something that need to be hidden.
> > > 
> > > It would allow userspace to easily enumerate trusted DM devices without
> > > calling kernel ioctls...
> > 
> > I guess that's an option if there are scenarios where it is useful. It
> > should probably be a separate patch, since it isn't directly related with
> > extending LoadPin support to trusted verity devices.
> > 
> > > > +
> > > > +	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;
> > > 
> > > What happens is someone reloads verity table later with
> > > a different content (or even different target type)?
> > > Does LoadPin even care here?
> > 
> > LoadPin cares, but only when new kernel files are loaded. It will then check
> > against the new verity table, and only allow loading of the file if it comes
> > from a verity target with a trusted digest.
> > 
> > > >   static struct target_type verity_target = {
> > > >   	.name		= "verity",
> > > >   	.version	= {1, 8, 0},
> > > 
> > > Please increase the minor version, it is very useful to detect (in logs)
> > > that the target driver has compatible extensions.
> > 
> > I can do that, but would like to confirm that this is really needed/desired.
> > This patch adds kernel-internal APIs which aren't accessible to userspace,
> > that don't impact verity directly, so I'm not sure an increased minor version
> > would be useful.
> 
> Bumping to 1.8.1 is useful to indicate new changes that offer expanded
> use of the verity target (even if by LoadPin).

Ok, I'll bump the version, thanks for the confirmation.

Re: [PATCH v4 1/3] dm: Add verity helpers for LoadPin

[Matthias Kaehlcke]

On Wed, May 18, 2022 at 03:52:21PM -0400, Mike Snitzer wrote:
> On Tue, May 17 2022 at  7:34P -0400,
> Matthias Kaehlcke <mka@chromium.org> wrote:
> 
> > 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@chromium.org>
> > ---
> > 
> > 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, 144 insertions(+)
> >  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..3226fbe4a1fe
> > --- /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(loadpin_trusted_verity_root_digests);
> > +
> > +static bool is_trusted_verity_target(struct dm_target *ti)
> > +{
> > +	u8 *root_digest;
> > +	unsigned int digest_size;
> > +	struct 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, &loadpin_trusted_verity_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_sb_trusted(struct super_block *sb)
> > +{
> > +	struct mapped_device *md;
> > +	struct dm_table *table;
> > +	struct dm_target *ti;
> > +	int srcu_idx;
> > +	bool trusted = false;
> > +
> > +	if (list_empty(&loadpin_trusted_verity_root_digests))
> > +		return false;
> > +
> > +	md = dm_get_md(sb->s_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;
> > +}
> 
> Not seeing why passing a super_block a block layer interface was
> chosen.
> 
> Please pass the super_block's block_device and rename to
> dm_verity_loadpin_is_bdev_trusted()

Agreed, passing a block_device is a better choice here, I'll
change it as suggested.