linux-hardening - [PATCH 2/3] randstruct: Force full rebuild when seed changes

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Message-Id: <20250501194826.2947101-2-kees@kernel.org>
Date: Thu,  1 May 2025 12:48:17 -0700
From: Kees Cook <kees@...nel.org>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: Kees Cook <kees@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Nicolas Schier <nicolas.schier@...ux.dev>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-kbuild@...r.kernel.org,
	Justin Stitt <justinstitt@...gle.com>,
	Marco Elver <elver@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org,
	kasan-dev@...glegroups.com
Subject: [PATCH 2/3] randstruct: Force full rebuild when seed changes

While the randstruct GCC plugin was being rebuilt if the randstruct
seed changed, Clangs build did not notice the change. Include the hash
header directly so that it becomes a universal build dependency and full
rebuilds will happen if it changes.

Signed-off-by: Kees Cook <kees@...nel.org>
---
Cc: Masahiro Yamada <masahiroy@...nel.org>
Cc: Nathan Chancellor <nathan@...nel.org>
Cc: Nicolas Schier <nicolas.schier@...ux.dev>
Cc: Petr Pavlu <petr.pavlu@...e.com>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: <linux-kbuild@...r.kernel.org>
---
 include/linux/vermagic.h    |  1 -
 scripts/Makefile.randstruct |  3 ++-
 scripts/basic/Makefile      | 11 ++++++-----
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/include/linux/vermagic.h b/include/linux/vermagic.h
index 939ceabcaf06..335c360d4f9b 100644
--- a/include/linux/vermagic.h
+++ b/include/linux/vermagic.h
@@ -33,7 +33,6 @@
 #define MODULE_VERMAGIC_MODVERSIONS ""
 #endif
 #ifdef RANDSTRUCT
-#include <generated/randstruct_hash.h>
 #define MODULE_RANDSTRUCT "RANDSTRUCT_" RANDSTRUCT_HASHED_SEED
 #else
 #define MODULE_RANDSTRUCT
diff --git a/scripts/Makefile.randstruct b/scripts/Makefile.randstruct
index 24e283e89893..ab87219c6149 100644
--- a/scripts/Makefile.randstruct
+++ b/scripts/Makefile.randstruct
@@ -12,6 +12,7 @@ randstruct-cflags-y	\
 	+= -frandomize-layout-seed-file=$(objtree)/scripts/basic/randstruct.seed
 endif
 
-export RANDSTRUCT_CFLAGS := $(randstruct-cflags-y)
+export RANDSTRUCT_CFLAGS := $(randstruct-cflags-y) \
+			    -include $(objtree)/scripts/basic/randstruct_hash.h
 
 KBUILD_CFLAGS	+= $(RANDSTRUCT_CFLAGS)
diff --git a/scripts/basic/Makefile b/scripts/basic/Makefile
index dd289a6725ac..31637ce4dc5c 100644
--- a/scripts/basic/Makefile
+++ b/scripts/basic/Makefile
@@ -8,9 +8,10 @@ hostprogs-always-y	+= fixdep
 # before running a Clang kernel build.
 gen-randstruct-seed	:= $(srctree)/scripts/gen-randstruct-seed.sh
 quiet_cmd_create_randstruct_seed = GENSEED $@
-cmd_create_randstruct_seed = \
-	$(CONFIG_SHELL) $(gen-randstruct-seed) \
-		$@ $(objtree)/include/generated/randstruct_hash.h
-$(obj)/randstruct.seed: $(gen-randstruct-seed) FORCE
+      cmd_create_randstruct_seed = $(CONFIG_SHELL) $(gen-randstruct-seed) \
+		$(obj)/randstruct.seed $(obj)/randstruct_hash.h
+
+$(obj)/randstruct_hash.h $(obj)/randstruct.seed: $(gen-randstruct-seed) FORCE
 	$(call if_changed,create_randstruct_seed)
-always-$(CONFIG_RANDSTRUCT) += randstruct.seed
+
+always-$(CONFIG_RANDSTRUCT) += randstruct.seed randstruct_hash.h
-- 
2.34.1