Precede each serialized file entry in a LUO file set KHO block set with
struct kho_ser_hdr via DECLARE_KHO_SER so future per-file metadata
features can append fields to struct luo_file_ser without breaking
compatibility between adjacent kernels.

Initialize file set block sets with kho_ser_size(luo_file_ser), initialize
each entry feature header in luo_file_freeze(), and validate the incoming
feature header in luo_file_deserialize_one() before accessing the struct
luo_file_ser payload.

Signed-off-by: Tarun Sahu <tarunsahu@google.com>
---
 include/linux/kho/abi/luo.h  |  6 +++---
 kernel/liveupdate/luo_file.c | 26 +++++++++++++++++++-------
 2 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/include/linux/kho/abi/luo.h b/include/linux/kho/abi/luo.h
index bd19211c64e1..38b4658183a2 100644
--- a/include/linux/kho/abi/luo.h
+++ b/include/linux/kho/abi/luo.h
@@ -92,6 +92,8 @@ DECLARE_KHO_SER(luo_ser, 24, 0, 0);
  * @compatible:  File handler compatible string.
  * @data:        Private data
  * @token:       User provided token for this file
+ *
+ * Preceded by &struct kho_ser_hdr.
  */
 struct luo_file_ser {
 	char compatible[LIVEUPDATE_HNDL_COMPAT_LENGTH];
@@ -99,9 +101,7 @@ struct luo_file_ser {
 	u64 token;
 };
 
-static_assert(sizeof(struct luo_file_ser) == 64);
-static_assert(!IS_ENABLED(CONFIG_64BIT) ||
-	      __alignof__(struct luo_file_ser) == 8);
+DECLARE_KHO_SER(luo_file_ser, 64, 0, 0);
 
 /**
  * struct luo_file_set_ser - Represents the serialized metadata for file set
diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index 02d09a80d785..2da327f8bdae 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -486,10 +486,12 @@ int luo_file_freeze(struct luo_file_set *file_set,
 	kho_block_set_it_init(&it, &file_set->block_set);
 
 	list_for_each_entry(luo_file, &file_set->files_list, list) {
-		struct luo_file_ser *file_ser = kho_block_set_it_reserve_entry(&it);
+		DECLARE_KHO_SER_HDR(luo_file_ser, *fhdr) =
+			kho_block_set_it_reserve_entry(&it);
+		struct luo_file_ser *file_ser;
 
 		/* This should not fail normally as blocks were pre-allocated */
-		if (WARN_ON_ONCE(!file_ser)) {
+		if (WARN_ON_ONCE(!fhdr)) {
 			err = -ENOSPC;
 			goto err_unfreeze;
 		}
@@ -502,6 +504,8 @@ int luo_file_freeze(struct luo_file_set *file_set,
 			goto err_unfreeze;
 		}
 
+		kho_ser_init(fhdr, luo_file_ser);
+		file_ser = kho_ser_payload(fhdr, luo_file_ser);
 		strscpy(file_ser->compatible, luo_file->fh->compatible,
 			sizeof(file_ser->compatible));
 		file_ser->data = luo_file->serialized_data;
@@ -742,11 +746,19 @@ int luo_file_finish(struct luo_file_set *file_set)
 }
 
 static int luo_file_deserialize_one(struct luo_file_set *file_set,
-				    struct luo_file_ser *ser)
+				    DECLARE_KHO_SER_HDR(luo_file_ser, *fhdr))
 {
 	struct liveupdate_file_handler *fh;
 	bool handler_found = false;
+	struct luo_file_ser *ser;
 	struct luo_file *luo_file;
+	int err;
+
+	err = kho_ser_validate(fhdr, luo_file_ser);
+	if (err)
+		return err;
+
+	ser = kho_ser_payload(fhdr, luo_file_ser);
 
 	down_read(&luo_register_rwlock);
 	list_private_for_each_entry(fh, &luo_file_handler_list, list) {
@@ -810,7 +822,7 @@ int luo_file_deserialize(struct luo_file_set *file_set,
 			 DECLARE_KHO_SER_HDR(luo_file_set_ser, *file_set_fhdr))
 {
 	struct luo_file_set_ser *file_set_ser;
-	struct luo_file_ser *file_ser;
+	DECLARE_KHO_SER_HDR(luo_file_ser, *fhdr);
 	struct kho_block_set_it it;
 	int err;
 
@@ -848,8 +860,8 @@ int luo_file_deserialize(struct luo_file_set *file_set,
 	 * reliably reset devices and reclaim memory.
 	 */
 	kho_block_set_it_init(&it, &file_set->block_set);
-	while ((file_ser = kho_block_set_it_read_entry(&it))) {
-		err = luo_file_deserialize_one(file_set, file_ser);
+	while ((fhdr = kho_block_set_it_read_entry(&it))) {
+		err = luo_file_deserialize_one(file_set, fhdr);
 		if (err)
 			goto err_destroy_blocks;
 		file_set->count++;
@@ -883,7 +895,7 @@ int luo_file_deserialize(struct luo_file_set *file_set,
 void luo_file_set_init(struct luo_file_set *file_set)
 {
 	INIT_LIST_HEAD(&file_set->files_list);
-	kho_block_set_init(&file_set->block_set, sizeof(struct luo_file_ser));
+	kho_block_set_init(&file_set->block_set, kho_ser_size(luo_file_ser));
 }
 
 void luo_file_set_destroy(struct luo_file_set *file_set)
-- 
2.56.0.506.g506a7eabc5-goog