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 <m...@chromium.org> --- Changes in v2: - none drivers/md/Makefile | 6 +++ drivers/md/dm-verity-loadpin.c | 80 +++++++++++++++++++++++++++++++ drivers/md/dm-verity-target.c | 33 +++++++++++++ drivers/md/dm-verity.h | 4 ++ include/linux/dm-verity-loadpin.h | 27 +++++++++++ 5 files changed, 150 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..0638e61dba51 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 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.rc2.479.g8af0fa9b8e-goog -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel