Precede each serialized File-Lifecycle-Bound (FLB) entry in the preserved
FLB array with struct kho_ser_hdr via DECLARE_KHO_SER so future FLB
metadata features can append fields to struct luo_flb_ser without breaking
compatibility between adjacent kernels.

Compute LUO_FLB_MAX and outgoing entry offsets using
kho_ser_size(luo_flb_ser), and initialize each entry feature header in
luo_flb_serialize(). On the incoming path in luo_flb_retrieve_one(),
validate each entry feature header with kho_ser_validate() and advance
between entries using fhdr->size so entries written with a different
feature layout are traversed accurately.

Signed-off-by: Tarun Sahu <tarunsahu@google.com>
---
 include/linux/kho/abi/luo.h |  6 ++----
 kernel/liveupdate/luo_flb.c | 39 +++++++++++++++++++++++++------------
 2 files changed, 29 insertions(+), 16 deletions(-)

diff --git a/include/linux/kho/abi/luo.h b/include/linux/kho/abi/luo.h
index 4913707ba0d3..1b660d41bb90 100644
--- a/include/linux/kho/abi/luo.h
+++ b/include/linux/kho/abi/luo.h
@@ -181,7 +181,7 @@ DECLARE_KHO_SER(luo_flb_header_ser, 16, 0, 0);
  * passed to the new kernel. Each entry allows the LUO core to restore one
  * global, shared object.
  *
- * If this structure is modified, `LUO_ABI_COMPATIBLE` must be updated.
+ * Preceded by &struct kho_ser_hdr.
  */
 struct luo_flb_ser {
 	char name[LIVEUPDATE_FLB_COMPAT_LENGTH];
@@ -189,9 +189,7 @@ struct luo_flb_ser {
 	u64 count;
 };
 
-static_assert(sizeof(struct luo_flb_ser) == 64);
-static_assert(!IS_ENABLED(CONFIG_64BIT) ||
-	      __alignof__(struct luo_flb_ser) == 8);
+DECLARE_KHO_SER(luo_flb_ser, 64, 0, 0);
 
 /* Kernel Live Update Test ABI */
 #ifdef CONFIG_LIVEUPDATE_TEST
diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c
index a8dcdb8456fd..d38c223741ff 100644
--- a/kernel/liveupdate/luo_flb.c
+++ b/kernel/liveupdate/luo_flb.c
@@ -53,11 +53,11 @@
 
 #define LUO_FLB_PGCNT		1ul
 #define LUO_FLB_MAX		(((LUO_FLB_PGCNT << PAGE_SHIFT) -	\
-		kho_ser_size(luo_flb_header_ser)) / sizeof(struct luo_flb_ser))
+		kho_ser_size(luo_flb_header_ser)) / kho_ser_size(luo_flb_ser))
 
 struct luo_flb_header {
 	struct luo_flb_header_ser *header_ser;
-	struct luo_flb_ser *ser;
+	DECLARE_KHO_SER_HDR(luo_flb_ser, *fhdr);
 	bool active;
 };
 
@@ -159,6 +159,7 @@ static int luo_flb_retrieve_one(struct liveupdate_flb *flb)
 {
 	struct luo_flb_private *private = luo_flb_get_private(flb);
 	struct luo_flb_header *fh = &luo_flb_global.incoming;
+	DECLARE_KHO_SER_HDR(luo_flb_ser, *fhdr) = fh->fhdr;
 	struct liveupdate_flb_op_args args = {0};
 	bool found = false;
 	int err;
@@ -177,10 +178,18 @@ static int luo_flb_retrieve_one(struct liveupdate_flb *flb)
 	if (!fh->active)
 		return -ENODATA;
 
-	for (int i = 0; i < fh->header_ser->count; i++) {
-		if (!strcmp(fh->ser[i].name, flb->compatible)) {
-			private->incoming.data = fh->ser[i].data;
-			refcount_set(&private->incoming.count, fh->ser[i].count);
+	for (u64 i = 0; i < fh->header_ser->count;
+	     i++, fhdr = (void *)fhdr + fhdr->size) {
+		struct luo_flb_ser *ser;
+
+		err = kho_ser_validate(fhdr, luo_flb_ser);
+		if (err)
+			return err;
+
+		ser = kho_ser_payload(fhdr, luo_flb_ser);
+		if (!strcmp(ser->name, flb->compatible)) {
+			private->incoming.data = ser->data;
+			refcount_set(&private->incoming.count, ser->count);
 			found = true;
 			break;
 		}
@@ -573,7 +582,7 @@ int __init luo_flb_setup_outgoing(u64 *flbs_pa)
 
 	header_ser->pgcnt = LUO_FLB_PGCNT;
 	luo_flb_global.outgoing.header_ser = header_ser;
-	luo_flb_global.outgoing.ser = (void *)fhdr + kho_ser_size(luo_flb_header_ser);
+	luo_flb_global.outgoing.fhdr = (void *)fhdr + kho_ser_size(luo_flb_header_ser);
 	luo_flb_global.outgoing.active = true;
 
 	return 0;
@@ -594,7 +603,7 @@ int __init luo_flb_setup_incoming(u64 flbs_pa)
 
 	luo_flb_global.incoming.header_ser =
 		kho_ser_payload(fhdr, luo_flb_header_ser);
-	luo_flb_global.incoming.ser = (void *)fhdr + fhdr->size;
+	luo_flb_global.incoming.fhdr = (void *)fhdr + fhdr->size;
 	luo_flb_global.incoming.active = true;
 
 	return 0;
@@ -626,10 +635,16 @@ void luo_flb_serialize(void)
 		long count = refcount_read(&private->outgoing.count);
 
 		if (count > 0) {
-			strscpy(fh->ser[i].name, gflb->compatible,
-				sizeof(fh->ser[i].name));
-			fh->ser[i].data = private->outgoing.data;
-			fh->ser[i].count = count;
+			DECLARE_KHO_SER_HDR(luo_flb_ser, *fhdr) =
+				(void *)fh->fhdr + i * kho_ser_size(luo_flb_ser);
+			struct luo_flb_ser *ser;
+
+			kho_ser_init(fhdr, luo_flb_ser);
+			ser = kho_ser_payload(fhdr, luo_flb_ser);
+			strscpy(ser->name, gflb->compatible,
+				sizeof(ser->name));
+			ser->data = private->outgoing.data;
+			ser->count = count;
 			i++;
 		}
 	}
-- 
2.56.0.506.g506a7eabc5-goog