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

[PATCH 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. It adds the concept of
trusted verity devices to LoadPin. Userspace can use the
new systl file 'loadpin/trusted_verity_root_digests' to
provide LoadPin with a list of root digests from dm-verity
devices that LoadPin should consider as trusted. 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.

The list of trusted root digests can only be written once
(typically at boot time), to limit the possiblity of
attackers setting up rogue verity devices and marking them
as trusted.

[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


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    |  80 ++++++++++++++
 drivers/md/dm-verity-target.c     |  34 ++++++
 drivers/md/dm-verity.h            |   4 +
 include/linux/dm-verity-loadpin.h |  27 +++++
 security/loadpin/Kconfig          |  11 ++
 security/loadpin/loadpin.c        | 168 +++++++++++++++++++++++++++++-
 7 files changed, 324 insertions(+), 1 deletion(-)
 create mode 100644 drivers/md/dm-verity-loadpin.c
 create mode 100644 include/linux/dm-verity-loadpin.h

-- 
2.36.0.rc0.470.gd361397f0d-goog

[dm-devel] [PATCH 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. It adds the concept of
trusted verity devices to LoadPin. Userspace can use the
new systl file 'loadpin/trusted_verity_root_digests' to
provide LoadPin with a list of root digests from dm-verity
devices that LoadPin should consider as trusted. 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.

The list of trusted root digests can only be written once
(typically at boot time), to limit the possiblity of
attackers setting up rogue verity devices and marking them
as trusted.

[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


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    |  80 ++++++++++++++
 drivers/md/dm-verity-target.c     |  34 ++++++
 drivers/md/dm-verity.h            |   4 +
 include/linux/dm-verity-loadpin.h |  27 +++++
 security/loadpin/Kconfig          |  11 ++
 security/loadpin/loadpin.c        | 168 +++++++++++++++++++++++++++++-
 7 files changed, 324 insertions(+), 1 deletion(-)
 create mode 100644 drivers/md/dm-verity-loadpin.c
 create mode 100644 include/linux/dm-verity-loadpin.h

-- 
2.36.0.rc0.470.gd361397f0d-goog

--
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https://listman.redhat.com/mailman/listinfo/dm-devel

[PATCH 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>
---

 drivers/md/Makefile               |  6 +++
 drivers/md/dm-verity-loadpin.c    | 80 +++++++++++++++++++++++++++++++
 drivers/md/dm-verity-target.c     | 34 +++++++++++++
 drivers/md/dm-verity.h            |  4 ++
 include/linux/dm-verity-loadpin.h | 27 +++++++++++
 5 files changed, 151 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..e12cd004d375 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -100,6 +100,12 @@ ifeq ($(CONFIG_IMA),y)
 dm-mod-objs			+= dm-ima.o
 endif
 
+ifeq ($(CONFIG_DM_VERITY),y)
+ifeq ($(CONFIG_SECURITY_LOADPIN),y)
+dm-mod-objs			+= dm-verity-loadpin.o
+endif
+endif
+
 ifeq ($(CONFIG_DM_VERITY_FEC),y)
 dm-verity-objs			+= dm-verity-fec.o
 endif
diff --git a/drivers/md/dm-verity-loadpin.c b/drivers/md/dm-verity-loadpin.c
new file mode 100644
index 000000000000..972ca93a2231
--- /dev/null
+++ b/drivers/md/dm-verity-loadpin.c
@@ -0,0 +1,80 @@
+// 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"
+
+static struct list_head *trusted_root_digests;
+
+/*
+ * Sets the root digests of verity devices which LoadPin considers as trusted.
+ *
+ * This function must only be called once.
+ */
+void dm_verity_loadpin_set_trusted_root_digests(struct list_head *digests)
+{
+	if (!trusted_root_digests)
+		trusted_root_digests = digests;
+	else
+		pr_warn("verity root digests trusted by LoadPin are already set!!!\n");
+}
+
+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, 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 a mapped device is a verity device that is trusted
+ * by LoadPin.
+ */
+bool dm_verity_loadpin_is_md_trusted(struct mapped_device *md)
+{
+	int srcu_idx;
+	struct dm_table *table;
+	unsigned int num_targets;
+	bool trusted = false;
+	int i;
+
+	if (!trusted_root_digests || list_empty(trusted_root_digests))
+		return false;
+
+	table = dm_get_live_table(md, &srcu_idx);
+	num_targets = dm_table_get_num_targets(table);
+	for (i = 0; i < num_targets; i++) {
+		struct dm_target *ti = dm_table_get_target(table, i);
+
+		if (is_trusted_verity_target(ti)) {
+			trusted = true;
+			break;
+		}
+	}
+
+	dm_put_live_table(md, srcu_idx);
+
+	return trusted;
+}
diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index 80133aae0db3..6bea9692cd39 100644
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -16,9 +16,11 @@
 #include "dm-verity.h"
 #include "dm-verity-fec.h"
 #include "dm-verity-verify-sig.h"
+#include <crypto/hash.h>
 #include <linux/module.h>
 #include <linux/reboot.h>
 #include <linux/scatterlist.h>
+#include <linux/string.h>
 
 #define DM_MSG_PREFIX			"verity"
 
@@ -1310,6 +1312,38 @@ 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 digests, 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..12a86911d05a
--- /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 mapped_device;
+
+struct trusted_root_digest {
+	u8 *data;
+	unsigned int len;
+	struct list_head node;
+};
+
+#if IS_ENABLED(CONFIG_SECURITY_LOADPIN) && IS_BUILTIN(CONFIG_DM_VERITY)
+void dm_verity_loadpin_set_trusted_root_digests(struct list_head *digests);
+bool dm_verity_loadpin_is_md_trusted(struct mapped_device *md);
+#else
+static inline void dm_verity_loadpin_set_trusted_root_digests(struct list_head *digests) {}
+static inline bool dm_verity_loadpin_is_md_trusted(struct mapped_device *md)
+{
+	return false;
+}
+#endif
+
+#endif /* __LINUX_DM_LOADPIN_H */
-- 
2.36.0.rc0.470.gd361397f0d-goog

[dm-devel] [PATCH 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>
---

 drivers/md/Makefile               |  6 +++
 drivers/md/dm-verity-loadpin.c    | 80 +++++++++++++++++++++++++++++++
 drivers/md/dm-verity-target.c     | 34 +++++++++++++
 drivers/md/dm-verity.h            |  4 ++
 include/linux/dm-verity-loadpin.h | 27 +++++++++++
 5 files changed, 151 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..e12cd004d375 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -100,6 +100,12 @@ ifeq ($(CONFIG_IMA),y)
 dm-mod-objs			+= dm-ima.o
 endif
 
+ifeq ($(CONFIG_DM_VERITY),y)
+ifeq ($(CONFIG_SECURITY_LOADPIN),y)
+dm-mod-objs			+= dm-verity-loadpin.o
+endif
+endif
+
 ifeq ($(CONFIG_DM_VERITY_FEC),y)
 dm-verity-objs			+= dm-verity-fec.o
 endif
diff --git a/drivers/md/dm-verity-loadpin.c b/drivers/md/dm-verity-loadpin.c
new file mode 100644
index 000000000000..972ca93a2231
--- /dev/null
+++ b/drivers/md/dm-verity-loadpin.c
@@ -0,0 +1,80 @@
+// 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"
+
+static struct list_head *trusted_root_digests;
+
+/*
+ * Sets the root digests of verity devices which LoadPin considers as trusted.
+ *
+ * This function must only be called once.
+ */
+void dm_verity_loadpin_set_trusted_root_digests(struct list_head *digests)
+{
+	if (!trusted_root_digests)
+		trusted_root_digests = digests;
+	else
+		pr_warn("verity root digests trusted by LoadPin are already set!!!\n");
+}
+
+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, 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 a mapped device is a verity device that is trusted
+ * by LoadPin.
+ */
+bool dm_verity_loadpin_is_md_trusted(struct mapped_device *md)
+{
+	int srcu_idx;
+	struct dm_table *table;
+	unsigned int num_targets;
+	bool trusted = false;
+	int i;
+
+	if (!trusted_root_digests || list_empty(trusted_root_digests))
+		return false;
+
+	table = dm_get_live_table(md, &srcu_idx);
+	num_targets = dm_table_get_num_targets(table);
+	for (i = 0; i < num_targets; i++) {
+		struct dm_target *ti = dm_table_get_target(table, i);
+
+		if (is_trusted_verity_target(ti)) {
+			trusted = true;
+			break;
+		}
+	}
+
+	dm_put_live_table(md, srcu_idx);
+
+	return trusted;
+}
diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index 80133aae0db3..6bea9692cd39 100644
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -16,9 +16,11 @@
 #include "dm-verity.h"
 #include "dm-verity-fec.h"
 #include "dm-verity-verify-sig.h"
+#include <crypto/hash.h>
 #include <linux/module.h>
 #include <linux/reboot.h>
 #include <linux/scatterlist.h>
+#include <linux/string.h>
 
 #define DM_MSG_PREFIX			"verity"
 
@@ -1310,6 +1312,38 @@ 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 digests, 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..12a86911d05a
--- /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 mapped_device;
+
+struct trusted_root_digest {
+	u8 *data;
+	unsigned int len;
+	struct list_head node;
+};
+
+#if IS_ENABLED(CONFIG_SECURITY_LOADPIN) && IS_BUILTIN(CONFIG_DM_VERITY)
+void dm_verity_loadpin_set_trusted_root_digests(struct list_head *digests);
+bool dm_verity_loadpin_is_md_trusted(struct mapped_device *md);
+#else
+static inline void dm_verity_loadpin_set_trusted_root_digests(struct list_head *digests) {}
+static inline bool dm_verity_loadpin_is_md_trusted(struct mapped_device *md)
+{
+	return false;
+}
+#endif
+
+#endif /* __LINUX_DM_LOADPIN_H */
-- 
2.36.0.rc0.470.gd361397f0d-goog

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[PATCH 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. Userspace can use the new systl file
'loadpin/trusted_verity_root_digests' to provide LoadPin
with a list of root digests from dm-verity devices that
LoadPin should consider as trusted. 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.

The list of trusted root digests can only be written once
(typically at boot time), to limit the possiblity of
attackers setting up rogue verity devices and marking them
as trusted.

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>
---

 security/loadpin/Kconfig   |  11 +++
 security/loadpin/loadpin.c | 168 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 178 insertions(+), 1 deletion(-)

diff --git a/security/loadpin/Kconfig b/security/loadpin/Kconfig
index 91be65dec2ab..cf3e6431e02d 100644
--- a/security/loadpin/Kconfig
+++ b/security/loadpin/Kconfig
@@ -18,3 +18,14 @@ 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
+	help
+	  If selected LoadPin can allow reading files from filesystems
+	  that use dm-verity. A verity filesystem can be configured as
+	  being trusted by LoadPin by writing its root digest to the
+	  sysctl file 'trusted_verity_root_digests'. The sysctl file
+	  can only be written once (typically at boot) and accepts a
+	  list of comma separated digests.
diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
index b12f7d986b1e..b9c174f8687d 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/device-mapper.h>
+#include <linux/dm-verity-loadpin.h>
 
 static void report_load(const char *origin, struct file *file, char *operation)
 {
@@ -43,6 +45,10 @@ 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 verity_digests_set;
+static LIST_HEAD(trusted_verity_root_digests);
+#endif
 
 #ifdef CONFIG_SYSCTL
 
@@ -65,6 +71,144 @@ static struct ctl_table loadpin_sysctl_table[] = {
 	{ }
 };
 
+#ifdef CONFIG_SECURITY_LOADPIN_VERITY
+
+static int proc_verity_root_digests(struct ctl_table *table, int write,
+				    void *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct trusted_root_digest *trd;
+	char *buf;
+	int rc;
+
+	if (write) {
+		struct ctl_table tbl = *table;
+		char *p, *d;
+
+		if (*ppos)
+			return -EINVAL;
+
+		if (verity_digests_set)
+			return -EPERM;
+
+		buf = kzalloc(tbl.maxlen, GFP_KERNEL);
+		if (!buf)
+			return -ENOMEM;
+
+		tbl.data = buf;
+
+		rc = proc_dostring(&tbl, write, buffer, lenp, ppos);
+		if (rc) {
+			kfree(buf);
+			return rc;
+		}
+
+		if (strlen(buf) == 0) {
+			verity_digests_set = true;
+			return false;
+		}
+
+		p = buf;
+		while ((d = strsep(&p, ",")) != NULL) {
+			int len = strlen(d);
+
+			if (len % 2) {
+				rc = -EINVAL;
+				goto err;
+			}
+
+			len /= 2;
+
+			trd = kzalloc(sizeof(*trd), GFP_KERNEL);
+			if (!trd) {
+				rc = -ENOMEM;
+				goto err;
+			}
+
+			list_add_tail(&trd->node, &trusted_verity_root_digests);
+
+			trd->data = kzalloc(len, GFP_KERNEL);
+			if (!trd->data) {
+				rc = -ENOMEM;
+				goto err;
+			}
+
+			if (hex2bin(trd->data, d, len)) {
+				rc = -EINVAL;
+				goto err;
+			}
+
+			trd->len = len;
+		}
+
+		kfree(buf);
+
+		if (!list_empty(&trusted_verity_root_digests)) {
+			dm_verity_loadpin_set_trusted_root_digests(&trusted_verity_root_digests);
+			verity_digests_set = true;
+		}
+	} else {
+		struct ctl_table tbl = { .maxlen = 0 };
+		size_t off = 0;
+
+		list_for_each_entry(trd, &trusted_verity_root_digests, node) {
+			/* two ASCII characters per byte and a comma / '\0' */
+			tbl.maxlen += (trd->len * 2) + 1;
+		}
+
+		tbl.data = kzalloc(tbl.maxlen, GFP_KERNEL);
+
+		list_for_each_entry(trd, &trusted_verity_root_digests, node) {
+			int i;
+
+			if (off > 0) {
+				snprintf(tbl.data + off, tbl.maxlen - off, ",");
+				off++;
+			}
+
+			for (i = 0; i < trd->len; i++) {
+				snprintf(tbl.data + off, tbl.maxlen - off, "%02x", trd->data[i]);
+				off += 2;
+			}
+		}
+
+		proc_dostring(&tbl, write, buffer, lenp, ppos);
+		kfree(tbl.data);
+	}
+
+	return 0;
+
+err:
+	kfree(buf);
+
+	{
+		struct trusted_root_digest *tmp;
+
+		list_for_each_entry_safe(trd, tmp, &trusted_verity_root_digests, node) {
+			kfree(trd->data);
+			list_del(&trd->node);
+			kfree(trd);
+		}
+	}
+
+	return rc;
+}
+
+static struct ctl_table loadpin_sysctl_table_verity[] = {
+	{
+		.procname       = "trusted_verity_root_digests",
+		.maxlen         = SZ_4K,
+		.mode           = 0644,
+		.proc_handler   = proc_verity_root_digests,
+	},
+
+	{ }
+};
+#else
+
+static struct ctl_table loadpin_sysctl_table_verity[] = {};
+
+#endif /* CONFIG_SECURITY_LOADPIN_VERITY */
+
 /*
  * This must be called after early kernel init, since then the rootdev
  * is available.
@@ -118,6 +262,20 @@ static void loadpin_sb_free_security(struct super_block *mnt_sb)
 	}
 }
 
+static bool loadpin_is_fs_trusted(struct super_block *sb)
+{
+	struct mapped_device *md = dm_get_md(sb->s_bdev->bd_dev);
+	bool trusted;
+
+	if (!md)
+		return false;
+
+	trusted = dm_verity_loadpin_is_md_trusted(md);
+	dm_put(md);
+
+	return trusted;
+}
+
 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
 			     bool contents)
 {
@@ -174,7 +332,8 @@ 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) && !loadpin_is_fs_trusted(load_root))) {
 		if (unlikely(!enforce)) {
 			report_load(origin, file, "pinning-ignored");
 			return 0;
@@ -240,6 +399,13 @@ static int __init loadpin_init(void)
 		enforce ? "" : "not ");
 	parse_exclude();
 	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
+
+	if (IS_ENABLED(CONFIG_SECURITY_LOADPIN_VERITY)) {
+		if (!register_sysctl_paths(loadpin_sysctl_path,
+					   loadpin_sysctl_table_verity))
+			pr_notice("sysctl registration failed!\n");
+	}
+
 	return 0;
 }
 
-- 
2.36.0.rc0.470.gd361397f0d-goog

[dm-devel] [PATCH 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. Userspace can use the new systl file
'loadpin/trusted_verity_root_digests' to provide LoadPin
with a list of root digests from dm-verity devices that
LoadPin should consider as trusted. 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.

The list of trusted root digests can only be written once
(typically at boot time), to limit the possiblity of
attackers setting up rogue verity devices and marking them
as trusted.

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>
---

 security/loadpin/Kconfig   |  11 +++
 security/loadpin/loadpin.c | 168 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 178 insertions(+), 1 deletion(-)

diff --git a/security/loadpin/Kconfig b/security/loadpin/Kconfig
index 91be65dec2ab..cf3e6431e02d 100644
--- a/security/loadpin/Kconfig
+++ b/security/loadpin/Kconfig
@@ -18,3 +18,14 @@ 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
+	help
+	  If selected LoadPin can allow reading files from filesystems
+	  that use dm-verity. A verity filesystem can be configured as
+	  being trusted by LoadPin by writing its root digest to the
+	  sysctl file 'trusted_verity_root_digests'. The sysctl file
+	  can only be written once (typically at boot) and accepts a
+	  list of comma separated digests.
diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
index b12f7d986b1e..b9c174f8687d 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/device-mapper.h>
+#include <linux/dm-verity-loadpin.h>
 
 static void report_load(const char *origin, struct file *file, char *operation)
 {
@@ -43,6 +45,10 @@ 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 verity_digests_set;
+static LIST_HEAD(trusted_verity_root_digests);
+#endif
 
 #ifdef CONFIG_SYSCTL
 
@@ -65,6 +71,144 @@ static struct ctl_table loadpin_sysctl_table[] = {
 	{ }
 };
 
+#ifdef CONFIG_SECURITY_LOADPIN_VERITY
+
+static int proc_verity_root_digests(struct ctl_table *table, int write,
+				    void *buffer, size_t *lenp, loff_t *ppos)
+{
+	struct trusted_root_digest *trd;
+	char *buf;
+	int rc;
+
+	if (write) {
+		struct ctl_table tbl = *table;
+		char *p, *d;
+
+		if (*ppos)
+			return -EINVAL;
+
+		if (verity_digests_set)
+			return -EPERM;
+
+		buf = kzalloc(tbl.maxlen, GFP_KERNEL);
+		if (!buf)
+			return -ENOMEM;
+
+		tbl.data = buf;
+
+		rc = proc_dostring(&tbl, write, buffer, lenp, ppos);
+		if (rc) {
+			kfree(buf);
+			return rc;
+		}
+
+		if (strlen(buf) == 0) {
+			verity_digests_set = true;
+			return false;
+		}
+
+		p = buf;
+		while ((d = strsep(&p, ",")) != NULL) {
+			int len = strlen(d);
+
+			if (len % 2) {
+				rc = -EINVAL;
+				goto err;
+			}
+
+			len /= 2;
+
+			trd = kzalloc(sizeof(*trd), GFP_KERNEL);
+			if (!trd) {
+				rc = -ENOMEM;
+				goto err;
+			}
+
+			list_add_tail(&trd->node, &trusted_verity_root_digests);
+
+			trd->data = kzalloc(len, GFP_KERNEL);
+			if (!trd->data) {
+				rc = -ENOMEM;
+				goto err;
+			}
+
+			if (hex2bin(trd->data, d, len)) {
+				rc = -EINVAL;
+				goto err;
+			}
+
+			trd->len = len;
+		}
+
+		kfree(buf);
+
+		if (!list_empty(&trusted_verity_root_digests)) {
+			dm_verity_loadpin_set_trusted_root_digests(&trusted_verity_root_digests);
+			verity_digests_set = true;
+		}
+	} else {
+		struct ctl_table tbl = { .maxlen = 0 };
+		size_t off = 0;
+
+		list_for_each_entry(trd, &trusted_verity_root_digests, node) {
+			/* two ASCII characters per byte and a comma / '\0' */
+			tbl.maxlen += (trd->len * 2) + 1;
+		}
+
+		tbl.data = kzalloc(tbl.maxlen, GFP_KERNEL);
+
+		list_for_each_entry(trd, &trusted_verity_root_digests, node) {
+			int i;
+
+			if (off > 0) {
+				snprintf(tbl.data + off, tbl.maxlen - off, ",");
+				off++;
+			}
+
+			for (i = 0; i < trd->len; i++) {
+				snprintf(tbl.data + off, tbl.maxlen - off, "%02x", trd->data[i]);
+				off += 2;
+			}
+		}
+
+		proc_dostring(&tbl, write, buffer, lenp, ppos);
+		kfree(tbl.data);
+	}
+
+	return 0;
+
+err:
+	kfree(buf);
+
+	{
+		struct trusted_root_digest *tmp;
+
+		list_for_each_entry_safe(trd, tmp, &trusted_verity_root_digests, node) {
+			kfree(trd->data);
+			list_del(&trd->node);
+			kfree(trd);
+		}
+	}
+
+	return rc;
+}
+
+static struct ctl_table loadpin_sysctl_table_verity[] = {
+	{
+		.procname       = "trusted_verity_root_digests",
+		.maxlen         = SZ_4K,
+		.mode           = 0644,
+		.proc_handler   = proc_verity_root_digests,
+	},
+
+	{ }
+};
+#else
+
+static struct ctl_table loadpin_sysctl_table_verity[] = {};
+
+#endif /* CONFIG_SECURITY_LOADPIN_VERITY */
+
 /*
  * This must be called after early kernel init, since then the rootdev
  * is available.
@@ -118,6 +262,20 @@ static void loadpin_sb_free_security(struct super_block *mnt_sb)
 	}
 }
 
+static bool loadpin_is_fs_trusted(struct super_block *sb)
+{
+	struct mapped_device *md = dm_get_md(sb->s_bdev->bd_dev);
+	bool trusted;
+
+	if (!md)
+		return false;
+
+	trusted = dm_verity_loadpin_is_md_trusted(md);
+	dm_put(md);
+
+	return trusted;
+}
+
 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
 			     bool contents)
 {
@@ -174,7 +332,8 @@ 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) && !loadpin_is_fs_trusted(load_root))) {
 		if (unlikely(!enforce)) {
 			report_load(origin, file, "pinning-ignored");
 			return 0;
@@ -240,6 +399,13 @@ static int __init loadpin_init(void)
 		enforce ? "" : "not ");
 	parse_exclude();
 	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
+
+	if (IS_ENABLED(CONFIG_SECURITY_LOADPIN_VERITY)) {
+		if (!register_sysctl_paths(loadpin_sysctl_path,
+					   loadpin_sysctl_table_verity))
+			pr_notice("sysctl registration failed!\n");
+	}
+
 	return 0;
 }
 
-- 
2.36.0.rc0.470.gd361397f0d-goog

--
dm-devel mailing list
dm-devel@redhat.com
https://listman.redhat.com/mailman/listinfo/dm-devel

Re: [PATCH 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 v5.18-rc3 next-20220414]
[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/20220419-051810
base:   https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git for-next
config: powerpc-buildonly-randconfig-r002-20220417 (https://download.01.org/0day-ci/archive/20220419/202204191222.n0HWtNe0-lkp@intel.com/config)
compiler: powerpc-linux-gcc (GCC) 11.2.0
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/5af892969b227a2602732e4be44a0c4a41967400
        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/20220419-051810
        git checkout 5af892969b227a2602732e4be44a0c4a41967400
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=powerpc 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 errors (new ones prefixed by >>):

   security/loadpin/loadpin.c: In function 'loadpin_init':
>> security/loadpin/loadpin.c:404:44: error: 'loadpin_sysctl_path' undeclared (first use in this function)
     404 |                 if (!register_sysctl_paths(loadpin_sysctl_path,
         |                                            ^~~~~~~~~~~~~~~~~~~
   security/loadpin/loadpin.c:404:44: note: each undeclared identifier is reported only once for each function it appears in
>> security/loadpin/loadpin.c:405:44: error: 'loadpin_sysctl_table_verity' undeclared (first use in this function)
     405 |                                            loadpin_sysctl_table_verity))
         |                                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~


vim +/loadpin_sysctl_path +404 security/loadpin/loadpin.c

   395	
   396	static int __init loadpin_init(void)
   397	{
   398		pr_info("ready to pin (currently %senforcing)\n",
   399			enforce ? "" : "not ");
   400		parse_exclude();
   401		security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
   402	
   403		if (IS_ENABLED(CONFIG_SECURITY_LOADPIN_VERITY)) {
 > 404			if (!register_sysctl_paths(loadpin_sysctl_path,
 > 405						   loadpin_sysctl_table_verity))
   406				pr_notice("sysctl registration failed!\n");
   407		}
   408	
   409		return 0;
   410	}
   411	

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

Re: [dm-devel] [PATCH 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 v5.18-rc3 next-20220414]
[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/20220419-051810
base:   https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git for-next
config: powerpc-buildonly-randconfig-r002-20220417 (https://download.01.org/0day-ci/archive/20220419/202204191222.n0HWtNe0-lkp@intel.com/config)
compiler: powerpc-linux-gcc (GCC) 11.2.0
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/5af892969b227a2602732e4be44a0c4a41967400
        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/20220419-051810
        git checkout 5af892969b227a2602732e4be44a0c4a41967400
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=powerpc 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 errors (new ones prefixed by >>):

   security/loadpin/loadpin.c: In function 'loadpin_init':
>> security/loadpin/loadpin.c:404:44: error: 'loadpin_sysctl_path' undeclared (first use in this function)
     404 |                 if (!register_sysctl_paths(loadpin_sysctl_path,
         |                                            ^~~~~~~~~~~~~~~~~~~
   security/loadpin/loadpin.c:404:44: note: each undeclared identifier is reported only once for each function it appears in
>> security/loadpin/loadpin.c:405:44: error: 'loadpin_sysctl_table_verity' undeclared (first use in this function)
     405 |                                            loadpin_sysctl_table_verity))
         |                                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~


vim +/loadpin_sysctl_path +404 security/loadpin/loadpin.c

   395	
   396	static int __init loadpin_init(void)
   397	{
   398		pr_info("ready to pin (currently %senforcing)\n",
   399			enforce ? "" : "not ");
   400		parse_exclude();
   401		security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
   402	
   403		if (IS_ENABLED(CONFIG_SECURITY_LOADPIN_VERITY)) {
 > 404			if (!register_sysctl_paths(loadpin_sysctl_path,
 > 405						   loadpin_sysctl_table_verity))
   406				pr_notice("sysctl registration failed!\n");
   407		}
   408	
   409		return 0;
   410	}
   411	

-- 
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[PATCH 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>
---

 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 e12cd004d375..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 ($(CONFIG_DM_INIT),y)
 dm-mod-objs			+= dm-init.o
@@ -100,12 +101,6 @@ ifeq ($(CONFIG_IMA),y)
 dm-mod-objs			+= dm-ima.o
 endif
 
-ifeq ($(CONFIG_DM_VERITY),y)
-ifeq ($(CONFIG_SECURITY_LOADPIN),y)
-dm-mod-objs			+= dm-verity-loadpin.o
-endif
-endif
-
 ifeq ($(CONFIG_DM_VERITY_FEC),y)
 dm-verity-objs			+= dm-verity-fec.o
 endif
diff --git a/include/linux/dm-verity-loadpin.h b/include/linux/dm-verity-loadpin.h
index 12a86911d05a..be63ac76f98d 100644
--- a/include/linux/dm-verity-loadpin.h
+++ b/include/linux/dm-verity-loadpin.h
@@ -13,7 +13,7 @@ struct trusted_root_digest {
 	struct list_head node;
 };
 
-#if IS_ENABLED(CONFIG_SECURITY_LOADPIN) && IS_BUILTIN(CONFIG_DM_VERITY)
+#if IS_ENABLED(CONFIG_SECURITY_LOADPIN_VERITY)
 void dm_verity_loadpin_set_trusted_root_digests(struct list_head *digests);
 bool dm_verity_loadpin_is_md_trusted(struct mapped_device *md);
 #else
-- 
2.36.0.rc0.470.gd361397f0d-goog

[dm-devel] [PATCH 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>
---

 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 e12cd004d375..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 ($(CONFIG_DM_INIT),y)
 dm-mod-objs			+= dm-init.o
@@ -100,12 +101,6 @@ ifeq ($(CONFIG_IMA),y)
 dm-mod-objs			+= dm-ima.o
 endif
 
-ifeq ($(CONFIG_DM_VERITY),y)
-ifeq ($(CONFIG_SECURITY_LOADPIN),y)
-dm-mod-objs			+= dm-verity-loadpin.o
-endif
-endif
-
 ifeq ($(CONFIG_DM_VERITY_FEC),y)
 dm-verity-objs			+= dm-verity-fec.o
 endif
diff --git a/include/linux/dm-verity-loadpin.h b/include/linux/dm-verity-loadpin.h
index 12a86911d05a..be63ac76f98d 100644
--- a/include/linux/dm-verity-loadpin.h
+++ b/include/linux/dm-verity-loadpin.h
@@ -13,7 +13,7 @@ struct trusted_root_digest {
 	struct list_head node;
 };
 
-#if IS_ENABLED(CONFIG_SECURITY_LOADPIN) && IS_BUILTIN(CONFIG_DM_VERITY)
+#if IS_ENABLED(CONFIG_SECURITY_LOADPIN_VERITY)
 void dm_verity_loadpin_set_trusted_root_digests(struct list_head *digests);
 bool dm_verity_loadpin_is_md_trusted(struct mapped_device *md);
 #else
-- 
2.36.0.rc0.470.gd361397f0d-goog

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

[Kees Cook]

[oops, resending to actual CC list]

On Mon, Apr 18, 2022 at 02:15:56PM -0700, Matthias Kaehlcke wrote:
> This series extends LoadPin to allow loading of kernel files
> from trusted dm-verity devices. It adds the concept of
> trusted verity devices to LoadPin. Userspace can use the
> new systl file 'loadpin/trusted_verity_root_digests' to
> provide LoadPin with a list of root digests from dm-verity
> devices that LoadPin should consider as trusted. 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.
> 
> The list of trusted root digests can only be written once
> (typically at boot time), to limit the possiblity of
> attackers setting up rogue verity devices and marking them
> as trusted.

Hi,

Thanks for working all this out! Where does the list of trusted
roothashes come from? I assume some chain of trust exists. Is the list
maybe already stored on the rootfs?

It'd be nice if there was some way to pass the trust chain to LoadPin
more directly.

-Kees

-- 
Kees Cook

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

[Kees Cook]

[oops, resending to actual CC list]

On Mon, Apr 18, 2022 at 02:15:56PM -0700, Matthias Kaehlcke wrote:
> This series extends LoadPin to allow loading of kernel files
> from trusted dm-verity devices. It adds the concept of
> trusted verity devices to LoadPin. Userspace can use the
> new systl file 'loadpin/trusted_verity_root_digests' to
> provide LoadPin with a list of root digests from dm-verity
> devices that LoadPin should consider as trusted. 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.
> 
> The list of trusted root digests can only be written once
> (typically at boot time), to limit the possiblity of
> attackers setting up rogue verity devices and marking them
> as trusted.

Hi,

Thanks for working all this out! Where does the list of trusted
roothashes come from? I assume some chain of trust exists. Is the list
maybe already stored on the rootfs?

It'd be nice if there was some way to pass the trust chain to LoadPin
more directly.

-Kees

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

[Matthias Kaehlcke]

Hi Kees,

On Mon, Apr 18, 2022 at 03:14:14PM -0700, Kees Cook wrote:
> [oops, resending to actual CC list]
> 
> On Mon, Apr 18, 2022 at 02:15:56PM -0700, Matthias Kaehlcke wrote:
> > This series extends LoadPin to allow loading of kernel files
> > from trusted dm-verity devices. It adds the concept of
> > trusted verity devices to LoadPin. Userspace can use the
> > new systl file 'loadpin/trusted_verity_root_digests' to
> > provide LoadPin with a list of root digests from dm-verity
> > devices that LoadPin should consider as trusted. 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.
> > 
> > The list of trusted root digests can only be written once
> > (typically at boot time), to limit the possiblity of
> > attackers setting up rogue verity devices and marking them
> > as trusted.


> Thanks for working all this out! Where does the list of trusted
> roothashes come from? I assume some chain of trust exists. Is the list
> maybe already stored on the rootfs?

Yes, at least the content of the list comes from the rootfs. The
userspace part is still TBD (also pending on the evolution of this
patchset), having the list pre-formatted in a single file on the
rootfs should be fine.

> It'd be nice if there was some way to pass the trust chain to LoadPin
> more directly.

I imagine you envision LoadPin reading the file itself, instead of
just processing the content. That should be doable. One option would
be to pass the path of the file with the hashes through the sysctl
file and use kernel_read_file_from_path() to read it if the path is
in the pinned root (or maybe even in any trusted file system ;-)

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

[Matthias Kaehlcke]

Hi Kees,

On Mon, Apr 18, 2022 at 03:14:14PM -0700, Kees Cook wrote:
> [oops, resending to actual CC list]
> 
> On Mon, Apr 18, 2022 at 02:15:56PM -0700, Matthias Kaehlcke wrote:
> > This series extends LoadPin to allow loading of kernel files
> > from trusted dm-verity devices. It adds the concept of
> > trusted verity devices to LoadPin. Userspace can use the
> > new systl file 'loadpin/trusted_verity_root_digests' to
> > provide LoadPin with a list of root digests from dm-verity
> > devices that LoadPin should consider as trusted. 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.
> > 
> > The list of trusted root digests can only be written once
> > (typically at boot time), to limit the possiblity of
> > attackers setting up rogue verity devices and marking them
> > as trusted.


> Thanks for working all this out! Where does the list of trusted
> roothashes come from? I assume some chain of trust exists. Is the list
> maybe already stored on the rootfs?

Yes, at least the content of the list comes from the rootfs. The
userspace part is still TBD (also pending on the evolution of this
patchset), having the list pre-formatted in a single file on the
rootfs should be fine.

> It'd be nice if there was some way to pass the trust chain to LoadPin
> more directly.

I imagine you envision LoadPin reading the file itself, instead of
just processing the content. That should be doable. One option would
be to pass the path of the file with the hashes through the sysctl
file and use kernel_read_file_from_path() to read it if the path is
in the pinned root (or maybe even in any trusted file system ;-)

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

[Kees Cook]

On Mon, Apr 18, 2022 at 03:43:27PM -0700, Matthias Kaehlcke wrote:
> Hi Kees,
> 
> On Mon, Apr 18, 2022 at 03:14:14PM -0700, Kees Cook wrote:
> > [oops, resending to actual CC list]
> > 
> > On Mon, Apr 18, 2022 at 02:15:56PM -0700, Matthias Kaehlcke wrote:
> > > This series extends LoadPin to allow loading of kernel files
> > > from trusted dm-verity devices. It adds the concept of
> > > trusted verity devices to LoadPin. Userspace can use the
> > > new systl file 'loadpin/trusted_verity_root_digests' to
> > > provide LoadPin with a list of root digests from dm-verity
> > > devices that LoadPin should consider as trusted. 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.
> > > 
> > > The list of trusted root digests can only be written once
> > > (typically at boot time), to limit the possiblity of
> > > attackers setting up rogue verity devices and marking them
> > > as trusted.
> 
> 
> > Thanks for working all this out! Where does the list of trusted
> > roothashes come from? I assume some chain of trust exists. Is the list
> > maybe already stored on the rootfs?
> 
> Yes, at least the content of the list comes from the rootfs. The
> userspace part is still TBD (also pending on the evolution of this
> patchset), having the list pre-formatted in a single file on the
> rootfs should be fine.

Ah-ha, that's perfect.

> > It'd be nice if there was some way to pass the trust chain to LoadPin
> > more directly.
> 
> I imagine you envision LoadPin reading the file itself, instead of
> just processing the content. That should be doable. One option would
> be to pass the path of the file with the hashes through the sysctl
> file and use kernel_read_file_from_path() to read it if the path is
> in the pinned root (or maybe even in any trusted file system ;-)

It could be a boot param or a Kconfig too. But yeah, having LoadPin able
to use itself to validate the file path would be much nicer.

-- 
Kees Cook

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

[Kees Cook]

On Mon, Apr 18, 2022 at 03:43:27PM -0700, Matthias Kaehlcke wrote:
> Hi Kees,
> 
> On Mon, Apr 18, 2022 at 03:14:14PM -0700, Kees Cook wrote:
> > [oops, resending to actual CC list]
> > 
> > On Mon, Apr 18, 2022 at 02:15:56PM -0700, Matthias Kaehlcke wrote:
> > > This series extends LoadPin to allow loading of kernel files
> > > from trusted dm-verity devices. It adds the concept of
> > > trusted verity devices to LoadPin. Userspace can use the
> > > new systl file 'loadpin/trusted_verity_root_digests' to
> > > provide LoadPin with a list of root digests from dm-verity
> > > devices that LoadPin should consider as trusted. 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.
> > > 
> > > The list of trusted root digests can only be written once
> > > (typically at boot time), to limit the possiblity of
> > > attackers setting up rogue verity devices and marking them
> > > as trusted.
> 
> 
> > Thanks for working all this out! Where does the list of trusted
> > roothashes come from? I assume some chain of trust exists. Is the list
> > maybe already stored on the rootfs?
> 
> Yes, at least the content of the list comes from the rootfs. The
> userspace part is still TBD (also pending on the evolution of this
> patchset), having the list pre-formatted in a single file on the
> rootfs should be fine.

Ah-ha, that's perfect.

> > It'd be nice if there was some way to pass the trust chain to LoadPin
> > more directly.
> 
> I imagine you envision LoadPin reading the file itself, instead of
> just processing the content. That should be doable. One option would
> be to pass the path of the file with the hashes through the sysctl
> file and use kernel_read_file_from_path() to read it if the path is
> in the pinned root (or maybe even in any trusted file system ;-)

It could be a boot param or a Kconfig too. But yeah, having LoadPin able
to use itself to validate the file path would be much nicer.

-- 
Kees Cook

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