[RFC PATCH v3 1/4] liveupdate: Remove __packed from LUO and memfd ABI structures

[Tarun Sahu]

All structures in include/linux/kho/abi/luo.h (struct luo_ser, struct
luo_file_ser, struct luo_file_set_ser, struct luo_session_ser, struct
luo_flb_header_ser, struct luo_flb_ser) and include/linux/kho/abi/memfd.h
(struct memfd_luo_folio_ser, struct memfd_luo_ser) have naturally aligned
fields on 64-bit architectures, with no padding holes between fields or
tail padding. Any future unaligned field addition should come with
reserved field to keep the structure aligned.

Signed-off-by: Tarun Sahu <tarunsahu at google.com>
---
 include/linux/kho/abi/luo.h   | 25 +++++++++++++++++++------
 include/linux/kho/abi/memfd.h | 11 ++++++++---
 2 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/include/linux/kho/abi/luo.h b/include/linux/kho/abi/luo.h
index 288076de6d4a..899943877e41 100644
--- a/include/linux/kho/abi/luo.h
+++ b/include/linux/kho/abi/luo.h
@@ -58,6 +58,7 @@
 #define _LINUX_KHO_ABI_LUO_H
 
 #include <linux/align.h>
+#include <linux/build_bug.h>
 #include <linux/kho/abi/block.h>
 #include <uapi/linux/liveupdate.h>
 
@@ -82,7 +83,9 @@ struct luo_ser {
 	u64 liveupdate_num;
 	u64 sessions_pa;
 	u64 flbs_pa;
-} __packed;
+};
+
+static_assert(sizeof(struct luo_ser) == 32);
 
 #define LIVEUPDATE_HNDL_COMPAT_LENGTH	48
 
@@ -98,7 +101,9 @@ struct luo_file_ser {
 	char compatible[LIVEUPDATE_HNDL_COMPAT_LENGTH];
 	u64 data;
 	u64 token;
-} __packed;
+};
+
+static_assert(sizeof(struct luo_file_ser) == 64);
 
 /**
  * struct luo_file_set_ser - Represents the serialized metadata for file set
@@ -113,7 +118,9 @@ struct luo_file_ser {
 struct luo_file_set_ser {
 	u64 files;
 	u64 count;
-} __packed;
+};
+
+static_assert(sizeof(struct luo_file_set_ser) == 16);
 
 /**
  * struct luo_session_ser - Represents the serialized metadata for a LUO session.
@@ -131,7 +138,9 @@ struct luo_file_set_ser {
 struct luo_session_ser {
 	char name[LIVEUPDATE_SESSION_NAME_LENGTH];
 	struct luo_file_set_ser file_set_ser;
-} __packed;
+};
+
+static_assert(sizeof(struct luo_session_ser) == 80);
 
 /* The max size is set so it can be reliably used during in serialization */
 #define LIVEUPDATE_FLB_COMPAT_LENGTH	48
@@ -152,7 +161,9 @@ struct luo_session_ser {
 struct luo_flb_header_ser {
 	u64 pgcnt;
 	u64 count;
-} __packed;
+};
+
+static_assert(sizeof(struct luo_flb_header_ser) == 16);
 
 /**
  * struct luo_flb_ser - Represents the serialized state of a single FLB object.
@@ -175,7 +186,9 @@ struct luo_flb_ser {
 	char name[LIVEUPDATE_FLB_COMPAT_LENGTH];
 	u64 data;
 	u64 count;
-} __packed;
+};
+
+static_assert(sizeof(struct luo_flb_ser) == 64);
 
 /* Kernel Live Update Test ABI */
 #ifdef CONFIG_LIVEUPDATE_TEST
diff --git a/include/linux/kho/abi/memfd.h b/include/linux/kho/abi/memfd.h
index 08b10fea2afc..7115a8a77cfd 100644
--- a/include/linux/kho/abi/memfd.h
+++ b/include/linux/kho/abi/memfd.h
@@ -11,6 +11,7 @@
 #ifndef _LINUX_KHO_ABI_MEMFD_H
 #define _LINUX_KHO_ABI_MEMFD_H
 
+#include <linux/build_bug.h>
 #include <linux/types.h>
 #include <linux/kho/abi/kexec_handover.h>
 
@@ -20,7 +21,7 @@
  * memfd uses the ABI defined below for preserving its state across a kexec
  * reboot using the LUO.
  *
- * The state is serialized into a packed structure `struct memfd_luo_ser`
+ * The state is serialized into `struct memfd_luo_ser`
  * which is handed over to the next kernel via the KHO mechanism.
  *
  * This interface is a contract. Any modification to the structure layout
@@ -54,7 +55,9 @@ struct memfd_luo_folio_ser {
 	u64 pfn:52;
 	u64 flags:12;
 	u64 index;
-} __packed;
+};
+
+static_assert(sizeof(struct memfd_luo_folio_ser) == 16);
 
 /*
  * The set of seals this version supports preserving. If support for any new
@@ -85,7 +88,9 @@ struct memfd_luo_ser {
 	u32 flags;
 	u64 nr_folios;
 	struct kho_vmalloc folios;
-} __packed;
+};
+
+static_assert(sizeof(struct memfd_luo_ser) == 48);
 
 /* The compatibility string for memfd file handler */
 #define MEMFD_LUO_FH_COMPATIBLE	"memfd-v2"
-- 
2.56.0.307.g5fe7bd680c-goog