In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally writing across neighboring fields.

Use struct_group() in struct ivhd_entry around members ext and hidh, so
they can be referenced together. This will allow memcpy() and sizeof()
to more easily reason about sizes, improve readability, and avoid future
warnings about writing beyond the end of ext.

"pahole" shows no size nor member offset changes to struct ivhd_entry.
"objdump -d" shows no object code changes.

Signed-off-by: Kees Cook <redacted>
---
 drivers/iommu/amd/init.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 46280e6e1535..2df84737417b 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c

@@ -121,8 +121,10 @@ struct ivhd_entry {
 	u8 type;
 	u16 devid;
 	u8 flags;
-	u32 ext;
-	u32 hidh;
+	struct_group(ext_hid,
+		u32 ext;
+		u32 hidh;
+	);
 	u64 cid;
 	u8 uidf;
 	u8 uidl;

@@ -1378,7 +1380,8 @@ static int __init init_iommu_from_acpi(struct amd_iommu *iommu,
 				break;
 			}
 
-			memcpy(hid, (u8 *)(&e->ext), ACPIHID_HID_LEN - 1);
+			BUILD_BUG_ON(sizeof(e->ext_hid) != ACPIHID_HID_LEN - 1);
+			memcpy(hid, &e->ext_hid, ACPIHID_HID_LEN - 1);
 			hid[ACPIHID_HID_LEN - 1] = '\0';
 
 			if (!(*hid)) {

-- 
2.30.2