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 v7:
- rebased on v5.19-rc4
Changes in v6:
- added missing dependency on CONFIG_SECURITY_LOADPIN to
CONFIG_SECURITY_LOADPIN_VERITY
- s/loadpin_trusted_verity_root_digests/dm_verity_loadpin_trusted_root_digests/
- s/trusted_root_digest/dm_verity_loadpin_trusted_root_digest/
- removed unnecessary symbol exports
Changes in v5:
- changed dm_verity_loadpin_is_sb_trusted() to
dm_verity_loadpin_is_bdev_trusted()
- deleted bad semicolon in declaration of stub for
dm_verity_loadpin_is_bdev_trusted()
- bumped verity version number to 1.8.1
- added 'Acked-by' tags from Kees
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, 342 insertions(+), 2 deletions(-)
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
--
2.37.0.rc0.161.g10f37bed90-goog
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 <[email protected]>
Acked-by: Kees Cook <[email protected]>
---
Changes in v7:
- rebased on v5.19-rc4
Changes in v6:
- s/loadpin_trusted_verity_root_digests/dm_verity_loadpin_trusted_root_digests/
- s/trusted_root_digest/dm_verity_loadpin_trusted_root_digest/
- removed unnecessary symbol exports
Changes in v5:
- changed dm_verity_loadpin_is_sb_trusted() to
dm_verity_loadpin_is_bdev_trusted()
- bumped version number to 1.8.1
- deleted bad semicolon in declaration of stub for
dm_verity_loadpin_is_bdev_trusted()
- added 'Acked-by' tag from Kees
Changes in v4:
- a trusted verity device must have a single target of
type 'verity'
- share list of verity digests with loadpin, deleted
dm_verity_loadpin_set_trusted_root_digests()
- dm_verity_loadpin_is_md_trusted() is now dm_verity_loadpin_is_sb_trusted(),
it receives a super_block instead of mapped_device. Updated kernel doc.
- changed struct trusted_root_digest to have an unsized
u8 array instead of a pointer
- extend 'dm-verity-objs' instead of 'dm-mod-objs'
Changes in v3:
- none
Changes in v2:
- none
drivers/md/Makefile | 6 +++
drivers/md/dm-verity-loadpin.c | 74 +++++++++++++++++++++++++++++++
drivers/md/dm-verity-target.c | 33 +++++++++++++-
drivers/md/dm-verity.h | 4 ++
include/linux/dm-verity-loadpin.h | 27 +++++++++++
5 files changed, 143 insertions(+), 1 deletion(-)
create mode 100644 drivers/md/dm-verity-loadpin.c
create mode 100644 include/linux/dm-verity-loadpin.h
diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index 0454b0885b01..71771901c823 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -108,6 +108,12 @@ ifeq ($(CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG),y)
dm-verity-objs += dm-verity-verify-sig.o
endif
+ifeq ($(CONFIG_DM_VERITY),y)
+ifeq ($(CONFIG_SECURITY_LOADPIN),y)
+dm-verity-objs += dm-verity-loadpin.o
+endif
+endif
+
ifeq ($(CONFIG_DM_AUDIT),y)
dm-mod-objs += dm-audit.o
endif
diff --git a/drivers/md/dm-verity-loadpin.c b/drivers/md/dm-verity-loadpin.c
new file mode 100644
index 000000000000..10c18bc1652c
--- /dev/null
+++ b/drivers/md/dm-verity-loadpin.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/list.h>
+#include <linux/kernel.h>
+#include <linux/dm-verity-loadpin.h>
+
+#include "dm.h"
+#include "dm-verity.h"
+
+#define DM_MSG_PREFIX "verity-loadpin"
+
+LIST_HEAD(dm_verity_loadpin_trusted_root_digests);
+
+static bool is_trusted_verity_target(struct dm_target *ti)
+{
+ u8 *root_digest;
+ unsigned int digest_size;
+ struct dm_verity_loadpin_trusted_root_digest *trd;
+ bool trusted = false;
+
+ if (!dm_is_verity_target(ti))
+ return false;
+
+ if (dm_verity_get_root_digest(ti, &root_digest, &digest_size))
+ return false;
+
+ list_for_each_entry(trd, &dm_verity_loadpin_trusted_root_digests, node) {
+ if ((trd->len == digest_size) &&
+ !memcmp(trd->data, root_digest, digest_size)) {
+ trusted = true;
+ break;
+ }
+ }
+
+ kfree(root_digest);
+
+ return trusted;
+}
+
+/*
+ * Determines whether the file system of a superblock is located on
+ * a verity device that is trusted by LoadPin.
+ */
+bool dm_verity_loadpin_is_bdev_trusted(struct block_device *bdev)
+{
+ struct mapped_device *md;
+ struct dm_table *table;
+ struct dm_target *ti;
+ int srcu_idx;
+ bool trusted = false;
+
+ if (list_empty(&dm_verity_loadpin_trusted_root_digests))
+ return false;
+
+ md = dm_get_md(bdev->bd_dev);
+ if (!md)
+ return false;
+
+ table = dm_get_live_table(md, &srcu_idx);
+
+ if (dm_table_get_num_targets(table) != 1)
+ goto out;
+
+ ti = dm_table_get_target(table, 0);
+
+ if (is_trusted_verity_target(ti))
+ trusted = true;
+
+out:
+ dm_put_live_table(md, srcu_idx);
+ dm_put(md);
+
+ return trusted;
+}
diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index d6dbd47492a8..e5a01e2f96e9 100644
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -19,6 +19,7 @@
#include <linux/module.h>
#include <linux/reboot.h>
#include <linux/scatterlist.h>
+#include <linux/string.h>
#define DM_MSG_PREFIX "verity"
@@ -1310,10 +1311,40 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
return r;
}
+/*
+ * Check whether a DM target is a verity target.
+ */
+bool dm_is_verity_target(struct dm_target *ti)
+{
+ return ti->type->module == THIS_MODULE;
+}
+
+/*
+ * Get the root digest of a verity target.
+ *
+ * Returns a copy of the root digest, the caller is responsible for
+ * freeing the memory of the digest.
+ */
+int dm_verity_get_root_digest(struct dm_target *ti, u8 **root_digest, unsigned int *digest_size)
+{
+ struct dm_verity *v = ti->private;
+
+ if (!dm_is_verity_target(ti))
+ return -EINVAL;
+
+ *root_digest = kmemdup(v->root_digest, v->digest_size, GFP_KERNEL);
+ if (*root_digest == NULL)
+ return -ENOMEM;
+
+ *digest_size = v->digest_size;
+
+ return 0;
+}
+
static struct target_type verity_target = {
.name = "verity",
.features = DM_TARGET_IMMUTABLE,
- .version = {1, 8, 0},
+ .version = {1, 8, 1},
.module = THIS_MODULE,
.ctr = verity_ctr,
.dtr = verity_dtr,
diff --git a/drivers/md/dm-verity.h b/drivers/md/dm-verity.h
index 4e769d13473a..c832cc3e3d24 100644
--- a/drivers/md/dm-verity.h
+++ b/drivers/md/dm-verity.h
@@ -129,4 +129,8 @@ extern int verity_hash(struct dm_verity *v, struct ahash_request *req,
extern int verity_hash_for_block(struct dm_verity *v, struct dm_verity_io *io,
sector_t block, u8 *digest, bool *is_zero);
+extern bool dm_is_verity_target(struct dm_target *ti);
+extern int dm_verity_get_root_digest(struct dm_target *ti, u8 **root_digest,
+ unsigned int *digest_size);
+
#endif /* DM_VERITY_H */
diff --git a/include/linux/dm-verity-loadpin.h b/include/linux/dm-verity-loadpin.h
new file mode 100644
index 000000000000..fb695ecaa5d5
--- /dev/null
+++ b/include/linux/dm-verity-loadpin.h
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __LINUX_DM_VERITY_LOADPIN_H
+#define __LINUX_DM_VERITY_LOADPIN_H
+
+#include <linux/list.h>
+
+struct block_device;
+
+extern struct list_head dm_verity_loadpin_trusted_root_digests;
+
+struct dm_verity_loadpin_trusted_root_digest {
+ struct list_head node;
+ unsigned int len;
+ u8 data[];
+};
+
+#if IS_ENABLED(CONFIG_SECURITY_LOADPIN) && IS_BUILTIN(CONFIG_DM_VERITY)
+bool dm_verity_loadpin_is_bdev_trusted(struct block_device *bdev);
+#else
+static inline bool dm_verity_loadpin_is_bdev_trusted(struct block_device *bdev)
+{
+ return false;
+}
+#endif
+
+#endif /* __LINUX_DM_VERITY_LOADPIN_H */
--
2.37.0.rc0.161.g10f37bed90-goog
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 <[email protected]>
Acked-by: Kees Cook <[email protected]>
---
Changes in v7:
- none
Changes in v6:
- added missing dependency on CONFIG_SECURITY_LOADPIN
- s/loadpin_trusted_verity_root_digests/dm_verity_loadpin_trusted_root_digests/
Changes in v5:
- call dm_verity_loadpin_is_sb_trusted() instead of
dm_verity_loadpin_is_bdev_trusted()
- added 'Acked-by' tag from Kees
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..70e7985b2561 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 SECURITY_LOADPIN && 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 ad4e6756c038..6ab5f2bbf41f 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
@@ -171,7 +176,8 @@ 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_bdev_trusted(load_root->s_bdev))) {
if (unlikely(!enforce)) {
report_load(origin, file, "pinning-ignored");
return 0;
@@ -237,6 +243,7 @@ static int __init loadpin_init(void)
enforce ? "" : "not ");
parse_exclude();
security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
+
return 0;
}
@@ -245,6 +252,164 @@ 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(&dm_verity_loadpin_trusted_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 dm_verity_loadpin_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, &dm_verity_loadpin_trusted_root_digests);
+ }
+
+ if (list_empty(&dm_verity_loadpin_trusted_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 dm_verity_loadpin_trusted_root_digest *trd, *tmp;
+
+ list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_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");
--
2.37.0.rc0.161.g10f37bed90-goog
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 <[email protected]>
Acked-by: Kees Cook <[email protected]>
---
Changes in v7:
- none
Changes in v6:
- none
Changes in v5:
- added 'Acked-by' tag from Kees
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 fb695ecaa5d5..552b817ab102 100644
--- a/include/linux/dm-verity-loadpin.h
+++ b/include/linux/dm-verity-loadpin.h
@@ -15,7 +15,7 @@ struct dm_verity_loadpin_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_bdev_trusted(struct block_device *bdev);
#else
static inline bool dm_verity_loadpin_is_bdev_trusted(struct block_device *bdev)
--
2.37.0.rc0.161.g10f37bed90-goog
On Mon, Jun 27 2022 at 11:35P -0400,
Matthias Kaehlcke <[email protected]> wrote:
> 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 <[email protected]>
> Acked-by: Kees Cook <[email protected]>
Acked-by: Mike Snitzer <[email protected]>
On Mon, Jun 27 2022 at 11:35P -0400,
Matthias Kaehlcke <[email protected]> wrote:
> 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 <[email protected]>
> Acked-by: Kees Cook <[email protected]>
Acked-by: Mike Snitzer <[email protected]>
On Mon, Jun 27 2022 at 11:35P -0400,
Matthias Kaehlcke <[email protected]> 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.
>
> 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
Hi Kees,
Please pick this series up, thanks.
Mike
On Mon, Jun 27 2022 at 11:35P -0400,
Matthias Kaehlcke <[email protected]> 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 <[email protected]>
> Acked-by: Kees Cook <[email protected]>
Acked-by: Mike Snitzer <[email protected]>
On Wed, Jul 06, 2022 at 11:11:58AM -0400, Mike Snitzer wrote:
> On Mon, Jun 27 2022 at 11:35P -0400,
> Matthias Kaehlcke <[email protected]> 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.
> >
> > 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
>
> Hi Kees,
>
> Please pick this series up, thanks.
Thanks for the Acks! I'll get this into -next shortly.
--
Kees Cook
On Mon, 27 Jun 2022 08:35:23 -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.
>
> [...]
Applied to for-next/hardening, thanks!
[1/3] dm: Add verity helpers for LoadPin
https://git.kernel.org/kees/c/b6c1c5745ccc
[2/3] LoadPin: Enable loading from trusted dm-verity devices
https://git.kernel.org/kees/c/3f805f8cc23b
[3/3] dm: verity-loadpin: Use CONFIG_SECURITY_LOADPIN_VERITY for conditional compilation
https://git.kernel.org/kees/c/231af4709018
--
Kees Cook