thermal: int340x: Use struct_group() for memcpy() region

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

Use struct_group() in struct art around members weight, and
ac[0-9]_max, 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 weight.

"pahole" shows no size nor member offset changes to struct art.
"objdump -d" shows no meaningful object code changes (i.e. only
source line number induced differences).

Signed-off-by: Kees Cook <[email protected]>
Reviewed-by: Srinivas Pandruvada <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>

drivers/thermal/intel/int340x_thermal/acpi_thermal_rel.c

@@ -250,8 +250,9 @@ static int fill_art(char __user *ubuf)
 		get_single_name(arts[i].source, art_user[i].source_device);
 		get_single_name(arts[i].target, art_user[i].target_device);
 		/* copy the rest int data in addition to source and target */
-		memcpy(&art_user[i].weight, &arts[i].weight,
-			sizeof(u64) * (ACPI_NR_ART_ELEMENTS - 2));
+		BUILD_BUG_ON(sizeof(art_user[i].data) !=
+			     sizeof(u64) * (ACPI_NR_ART_ELEMENTS - 2));
+		memcpy(&art_user[i].data, &arts[i].data, sizeof(art_user[i].data));
 	}
 
 	if (copy_to_user(ubuf, art_user, art_len))

drivers/thermal/intel/int340x_thermal/acpi_thermal_rel.h

@@ -17,17 +17,19 @@
 struct art {
 	acpi_handle source;
 	acpi_handle target;
-	u64 weight;
-	u64 ac0_max;
-	u64 ac1_max;
-	u64 ac2_max;
-	u64 ac3_max;
-	u64 ac4_max;
-	u64 ac5_max;
-	u64 ac6_max;
-	u64 ac7_max;
-	u64 ac8_max;
-	u64 ac9_max;
+	struct_group(data,
+		u64 weight;
+		u64 ac0_max;
+		u64 ac1_max;
+		u64 ac2_max;
+		u64 ac3_max;
+		u64 ac4_max;
+		u64 ac5_max;
+		u64 ac6_max;
+		u64 ac7_max;
+		u64 ac8_max;
+		u64 ac9_max;
+	);
 } __packed;
 
 struct trt {
@@ -47,17 +49,19 @@ union art_object {
 	struct {
 		char source_device[8]; /* ACPI single name */
 		char target_device[8]; /* ACPI single name */
-		u64 weight;
-		u64 ac0_max_level;
-		u64 ac1_max_level;
-		u64 ac2_max_level;
-		u64 ac3_max_level;
-		u64 ac4_max_level;
-		u64 ac5_max_level;
-		u64 ac6_max_level;
-		u64 ac7_max_level;
-		u64 ac8_max_level;
-		u64 ac9_max_level;
+		struct_group(data,
+			u64 weight;
+			u64 ac0_max_level;
+			u64 ac1_max_level;
+			u64 ac2_max_level;
+			u64 ac3_max_level;
+			u64 ac4_max_level;
+			u64 ac5_max_level;
+			u64 ac6_max_level;
+			u64 ac7_max_level;
+			u64 ac8_max_level;
+			u64 ac9_max_level;
+		);
 	};
 	u64 __data[ACPI_NR_ART_ELEMENTS];
 };