[PATCH v4 13/19] liveupdate: Add feature header to struct luo_flb_header_ser

[Tarun Sahu <tarunsahu@google.com>]

Precede struct luo_flb_header_ser with struct kho_ser_hdr via
DECLARE_KHO_SER so future File-Lifecycle-Bound (FLB) header features can
append fields to struct luo_flb_header_ser without breaking compatibility
between adjacent kernels.

Initialize the header in luo_flb_setup_outgoing() and place the outgoing
entry array immediately after kho_ser_size(luo_flb_header_ser). On the
incoming path in luo_flb_setup_incoming(), validate the feature header
with kho_ser_validate() and locate the incoming entry array at
fhdr->size so entries remain properly aligned even if the source kernel
serialized a different header layout.

Signed-off-by: Tarun Sahu <tarunsahu@google.com>
---
 include/linux/kho/abi/luo.h      |  6 ++----
 kernel/liveupdate/luo_core.c     |  4 +---
 kernel/liveupdate/luo_flb.c      | 36 +++++++++++++++++++++-----------
 kernel/liveupdate/luo_internal.h |  2 +-
 4 files changed, 28 insertions(+), 20 deletions(-)

diff --git a/include/linux/kho/abi/luo.h b/include/linux/kho/abi/luo.h
index 38b4658183a2..4913707ba0d3 100644
--- a/include/linux/kho/abi/luo.h
+++ b/include/linux/kho/abi/luo.h
@@ -157,16 +157,14 @@ DECLARE_KHO_SER(luo_session_ser, 72, 0, 0);
  * This structure is located at the physical address specified by the
  * flbs_pa in luo_ser.
  *
- * If this structure is modified, `LUO_ABI_COMPATIBLE` must be updated.
+ * Preceded by &struct kho_ser_hdr.
  */
 struct luo_flb_header_ser {
 	u64 pgcnt;
 	u64 count;
 };
 
-static_assert(sizeof(struct luo_flb_header_ser) == 16);
-static_assert(!IS_ENABLED(CONFIG_64BIT) ||
-	      __alignof__(struct luo_flb_header_ser) == 8);
+DECLARE_KHO_SER(luo_flb_header_ser, 16, 0, 0);
 
 /**
  * struct luo_flb_ser - Represents the serialized state of a single FLB object.
diff --git a/kernel/liveupdate/luo_core.c b/kernel/liveupdate/luo_core.c
index d0f72f27001d..79bb5f64bfac 100644
--- a/kernel/liveupdate/luo_core.c
+++ b/kernel/liveupdate/luo_core.c
@@ -131,9 +131,7 @@ static int __init luo_early_startup(void)
 	if (err)
 		goto out_free_ser;
 
-	luo_flb_setup_incoming(luo_ser->flbs_pa);
-
-	err = 0;
+	err = luo_flb_setup_incoming(luo_ser->flbs_pa);
 
 out_free_ser:
 	kho_restore_free(fhdr);
diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c
index cd715a7c1d99..a8dcdb8456fd 100644
--- a/kernel/liveupdate/luo_flb.c
+++ b/kernel/liveupdate/luo_flb.c
@@ -53,7 +53,7 @@
 
 #define LUO_FLB_PGCNT		1ul
 #define LUO_FLB_MAX		(((LUO_FLB_PGCNT << PAGE_SHIFT) -	\
-		sizeof(struct luo_flb_header_ser)) / sizeof(struct luo_flb_ser))
+		kho_ser_size(luo_flb_header_ser)) / sizeof(struct luo_flb_ser))
 
 struct luo_flb_header {
 	struct luo_flb_header_ser *header_ser;
@@ -559,33 +559,45 @@ int liveupdate_flb_get_outgoing(struct liveupdate_flb *flb, void **objp)
 
 int __init luo_flb_setup_outgoing(u64 *flbs_pa)
 {
+	DECLARE_KHO_SER_HDR(luo_flb_header_ser, *fhdr);
 	struct luo_flb_header_ser *header_ser;
 
-	header_ser = kho_alloc_preserve(LUO_FLB_PGCNT << PAGE_SHIFT);
-	if (IS_ERR(header_ser))
-		return PTR_ERR(header_ser);
+	fhdr = kho_alloc_preserve(LUO_FLB_PGCNT << PAGE_SHIFT);
+	if (IS_ERR(fhdr))
+		return PTR_ERR(fhdr);
 
-	*flbs_pa = virt_to_phys(header_ser);
+	kho_ser_init(fhdr, luo_flb_header_ser);
+	header_ser = kho_ser_payload(fhdr, luo_flb_header_ser);
+
+	*flbs_pa = virt_to_phys(fhdr);
 
 	header_ser->pgcnt = LUO_FLB_PGCNT;
 	luo_flb_global.outgoing.header_ser = header_ser;
-	luo_flb_global.outgoing.ser = (void *)(header_ser + 1);
+	luo_flb_global.outgoing.ser = (void *)fhdr + kho_ser_size(luo_flb_header_ser);
 	luo_flb_global.outgoing.active = true;
 
 	return 0;
 }
 
-void __init luo_flb_setup_incoming(u64 flbs_pa)
+int __init luo_flb_setup_incoming(u64 flbs_pa)
 {
-	struct luo_flb_header_ser *header_ser;
+	DECLARE_KHO_SER_HDR(luo_flb_header_ser, *fhdr);
+	int err;
 
 	if (!flbs_pa)
-		return;
+		return 0;
 
-	header_ser = phys_to_virt(flbs_pa);
-	luo_flb_global.incoming.header_ser = header_ser;
-	luo_flb_global.incoming.ser = (void *)(header_ser + 1);
+	fhdr = phys_to_virt(flbs_pa);
+	err = kho_ser_validate(fhdr, luo_flb_header_ser);
+	if (err)
+		return err;
+
+	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.active = true;
+
+	return 0;
 }
 
 /**
diff --git a/kernel/liveupdate/luo_internal.h b/kernel/liveupdate/luo_internal.h
index e22a8cf39d91..df8306d73768 100644
--- a/kernel/liveupdate/luo_internal.h
+++ b/kernel/liveupdate/luo_internal.h
@@ -121,7 +121,7 @@ void luo_flb_file_unpreserve(struct liveupdate_file_handler *fh);
 void luo_flb_file_finish(struct liveupdate_file_handler *fh);
 void luo_flb_unregister_all(struct liveupdate_file_handler *fh);
 int __init luo_flb_setup_outgoing(u64 *flbs_pa);
-void __init luo_flb_setup_incoming(u64 flbs_pa);
+int __init luo_flb_setup_incoming(u64 flbs_pa);
 void luo_flb_serialize(void);
 
 #ifdef CONFIG_LIVEUPDATE_TEST
-- 
2.56.0.506.g506a7eabc5-goog