On May 4, 2022 12:54:17 PM PDT, Matthias Kaehlcke <mka@xxxxxxxxxxxx> wrote: >LoadPin limits loading of kernel modules, firmware and certain >other files to a 'pinned' file system (typically a read-only >rootfs). To provide more flexibility LoadPin is being extended >to also allow loading these files from trusted dm-verity >devices. For that purpose LoadPin can be provided with a list >of verity root digests that it should consider as trusted. > >Add a bunch of helpers to allow LoadPin to check whether a DM >device is a trusted verity device. The new functions broadly >fall in two categories: those that need access to verity >internals (like the root digest), and the 'glue' between >LoadPin and verity. The new file dm-verity-loadpin.c contains >the glue functions. > >Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx> > [...] >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; Does this need to exist in two places? (i.e. why can't dm and loadpin share this instead of needing dm_verity_loadpin_set_trusted_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; >+ } >+ } Pardon my lack of dm vocabulary, but what is "target" vs "table" here? I was only thinking of "whole device", so I must not understand what this is examining. > [...] >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; >+}; To avoid the double-alloc in patch 2 (and save 1 pointer size of memory), this could just be: struct trusted_root_digest { struct list_head node; unsigned int len; u8 data[]; }; Otherwise, looks good to me! -- Kees Cook -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel