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Message-Id: <20220503205503.3054173-6-keescook@chromium.org>
Date: Tue, 3 May 2022 13:55:02 -0700
From: Kees Cook <keescook@...omium.org>
To: Bill Wendling <morbo@...gle.com>
Cc: Kees Cook <keescook@...omium.org>, linux-hardening@...r.kernel.org,
Masahiro Yamada <masahiroy@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
David Howells <dhowells@...hat.com>,
Jeff Layton <jlayton@...nel.org>, linux-kernel@...r.kernel.org,
linux-kbuild@...r.kernel.org, llvm@...ts.linux.dev
Subject: [PATCH 5/6] randstruct: Move seed generation into scripts/basic/
To enable Clang randstruct support, move the structure layout
randomization seed generation out of scripts/gcc-plugins/ into
scripts/basic/ so it happens early enough that it can be used by either
compiler implementation. The gcc-plugin still builds its own header file,
but now does so from the common "randstruct.seed" file.
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
Documentation/dontdiff | 1 +
Documentation/kbuild/reproducible-builds.rst | 5 +++--
include/linux/vermagic.h | 2 +-
scripts/basic/.gitignore | 1 +
scripts/basic/Makefile | 11 +++++++++++
scripts/gcc-plugins/Makefile | 15 ++++++++++-----
scripts/gcc-plugins/gen-random-seed.sh | 9 ---------
scripts/gen-randstruct-seed.sh | 7 +++++++
security/Kconfig.hardening | 9 +++++----
9 files changed, 39 insertions(+), 21 deletions(-)
delete mode 100755 scripts/gcc-plugins/gen-random-seed.sh
create mode 100755 scripts/gen-randstruct-seed.sh
diff --git a/Documentation/dontdiff b/Documentation/dontdiff
index 910b30a2a7d9..352ff53a2306 100644
--- a/Documentation/dontdiff
+++ b/Documentation/dontdiff
@@ -211,6 +211,7 @@ r200_reg_safe.h
r300_reg_safe.h
r420_reg_safe.h
r600_reg_safe.h
+randstruct.seed
randomize_layout_hash.h
randomize_layout_seed.h
recordmcount
diff --git a/Documentation/kbuild/reproducible-builds.rst b/Documentation/kbuild/reproducible-builds.rst
index 81ff30505d35..071f0151a7a4 100644
--- a/Documentation/kbuild/reproducible-builds.rst
+++ b/Documentation/kbuild/reproducible-builds.rst
@@ -100,8 +100,9 @@ Structure randomisation
-----------------------
If you enable ``CONFIG_RANDSTRUCT``, you will need to pre-generate
-the random seed in ``scripts/gcc-plugins/randomize_layout_seed.h``
-so the same value is used in rebuilds.
+the random seed in ``scripts/basic/randstruct.seed`` so the same
+value is used by each build. See ``scripts/gen-randstruct-seed.sh``
+for details.
Debug info conflicts
--------------------
diff --git a/include/linux/vermagic.h b/include/linux/vermagic.h
index efb51a2da599..a54046bf37e5 100644
--- a/include/linux/vermagic.h
+++ b/include/linux/vermagic.h
@@ -33,7 +33,7 @@
#define MODULE_VERMAGIC_MODVERSIONS ""
#endif
#ifdef RANDSTRUCT
-#include <generated/randomize_layout_hash.h>
+#include <generated/randstruct_hash.h>
#define MODULE_RANDSTRUCT "RANDSTRUCT_" RANDSTRUCT_HASHED_SEED
#else
#define MODULE_RANDSTRUCT
diff --git a/scripts/basic/.gitignore b/scripts/basic/.gitignore
index 961c91c8a884..07c195f605a1 100644
--- a/scripts/basic/.gitignore
+++ b/scripts/basic/.gitignore
@@ -1,2 +1,3 @@
# SPDX-License-Identifier: GPL-2.0-only
/fixdep
+/randstruct.seed
diff --git a/scripts/basic/Makefile b/scripts/basic/Makefile
index eeb6a38c5551..dd289a6725ac 100644
--- a/scripts/basic/Makefile
+++ b/scripts/basic/Makefile
@@ -3,3 +3,14 @@
# fixdep: used to generate dependency information during build process
hostprogs-always-y += fixdep
+
+# randstruct: the seed is needed before building the gcc-plugin or
+# 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
+ $(call if_changed,create_randstruct_seed)
+always-$(CONFIG_RANDSTRUCT) += randstruct.seed
diff --git a/scripts/gcc-plugins/Makefile b/scripts/gcc-plugins/Makefile
index 1952d3bb80c6..148f4639cf09 100644
--- a/scripts/gcc-plugins/Makefile
+++ b/scripts/gcc-plugins/Makefile
@@ -1,12 +1,17 @@
# SPDX-License-Identifier: GPL-2.0
-$(obj)/randomize_layout_plugin.so: $(objtree)/$(obj)/randomize_layout_seed.h
-quiet_cmd_create_randomize_layout_seed = GENSEED $@
+$(obj)/randomize_layout_plugin.so: $(obj)/randomize_layout_seed.h
+quiet_cmd_create_randomize_layout_seed = SEEDHDR $@
cmd_create_randomize_layout_seed = \
- $(CONFIG_SHELL) $(srctree)/$(src)/gen-random-seed.sh $@ $(objtree)/include/generated/randomize_layout_hash.h
-$(objtree)/$(obj)/randomize_layout_seed.h: FORCE
+ SEED=$$(cat $(filter-out FORCE,$^) </dev/null); \
+ echo '/*' > $@; \
+ echo ' * This file is automatically generated. Keep it private.' >> $@; \
+ echo ' * Exposing this value will expose the layout of randomized structures.' >> $@; \
+ echo ' */' >> $@; \
+ echo "const char *randstruct_seed = \"$$SEED\";" >> $@
+$(obj)/randomize_layout_seed.h: $(objtree)/scripts/basic/randstruct.seed FORCE
$(call if_changed,create_randomize_layout_seed)
-targets += randomize_layout_seed.h randomize_layout_hash.h
+targets += randomize_layout_seed.h
# Build rules for plugins
#
diff --git a/scripts/gcc-plugins/gen-random-seed.sh b/scripts/gcc-plugins/gen-random-seed.sh
deleted file mode 100755
index 68af5cc20a64..000000000000
--- a/scripts/gcc-plugins/gen-random-seed.sh
+++ /dev/null
@@ -1,9 +0,0 @@
-#!/bin/sh
-# SPDX-License-Identifier: GPL-2.0
-
-if [ ! -f "$1" ]; then
- SEED=`od -A n -t x8 -N 32 /dev/urandom | tr -d ' \n'`
- echo "const char *randstruct_seed = \"$SEED\";" > "$1"
- HASH=`echo -n "$SEED" | sha256sum | cut -d" " -f1 | tr -d ' \n'`
- echo "#define RANDSTRUCT_HASHED_SEED \"$HASH\"" > "$2"
-fi
diff --git a/scripts/gen-randstruct-seed.sh b/scripts/gen-randstruct-seed.sh
new file mode 100755
index 000000000000..61017b36c464
--- /dev/null
+++ b/scripts/gen-randstruct-seed.sh
@@ -0,0 +1,7 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+SEED=$(od -A n -t x8 -N 32 /dev/urandom | tr -d ' \n')
+echo "$SEED" > "$1"
+HASH=$(echo -n "$SEED" | sha256sum | cut -d" " -f1)
+echo "#define RANDSTRUCT_HASHED_SEED \"$HASH\"" > "$2"
diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
index 364e3f8c6eea..0277ba578779 100644
--- a/security/Kconfig.hardening
+++ b/security/Kconfig.hardening
@@ -284,10 +284,11 @@ choice
tools like Volatility against the system (unless the kernel
source tree isn't cleaned after kernel installation).
- The seed used for compilation is located at
- scripts/randomize_layout_seed.h. It remains after a "make clean"
- to allow for external modules to be compiled with the existing
- seed and will be removed by a "make mrproper" or "make distclean".
+ The seed used for compilation is in scripts/basic/randomize.seed.
+ It remains after a "make clean" to allow for external modules to
+ be compiled with the existing seed and will be removed by a
+ "make mrproper" or "make distclean". This file should not be made
+ public, or the structure layout can be determined.
config RANDSTRUCT_NONE
bool "Disable structure layout randomization"
--
2.32.0
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