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randstruct: Move seed generation into scripts/basic/

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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@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220503205503.3054173-6-keescook@chromium.org
This commit is contained in:
Kees Cook 2022-05-03 13:55:02 -07:00
parent 613f4b3ed7
commit be2b34fa9b
9 changed files with 39 additions and 21 deletions
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1
Documentation/dontdiff
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@ -211,6 +211,7 @@ r200_reg_safe.h
r300_reg_safe.h r300_reg_safe.h
r420_reg_safe.h r420_reg_safe.h
r600_reg_safe.h r600_reg_safe.h
randstruct.seed
randomize_layout_hash.h randomize_layout_hash.h
randomize_layout_seed.h randomize_layout_seed.h
recordmcount recordmcount

5
Documentation/kbuild/reproducible-builds.rst
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@ -100,8 +100,9 @@ Structure randomisation
----------------------- -----------------------
If you enable ``CONFIG_RANDSTRUCT``, you will need to pre-generate If you enable ``CONFIG_RANDSTRUCT``, you will need to pre-generate
the random seed in ``scripts/gcc-plugins/randomize_layout_seed.h`` the random seed in ``scripts/basic/randstruct.seed`` so the same
so the same value is used in rebuilds. value is used by each build. See ``scripts/gen-randstruct-seed.sh``
for details.
Debug info conflicts Debug info conflicts
-------------------- --------------------

2
include/linux/vermagic.h
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@ -33,7 +33,7 @@
#define MODULE_VERMAGIC_MODVERSIONS "" #define MODULE_VERMAGIC_MODVERSIONS ""
#endif #endif
#ifdef RANDSTRUCT #ifdef RANDSTRUCT
#include <generated/randomize_layout_hash.h> #include <generated/randstruct_hash.h>
#define MODULE_RANDSTRUCT "RANDSTRUCT_" RANDSTRUCT_HASHED_SEED #define MODULE_RANDSTRUCT "RANDSTRUCT_" RANDSTRUCT_HASHED_SEED
#else #else
#define MODULE_RANDSTRUCT #define MODULE_RANDSTRUCT

1
scripts/basic/.gitignore vendored
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@ -1,2 +1,3 @@
# SPDX-License-Identifier: GPL-2.0-only # SPDX-License-Identifier: GPL-2.0-only
/fixdep /fixdep
/randstruct.seed

11
scripts/basic/Makefile
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@ -3,3 +3,14 @@
# fixdep: used to generate dependency information during build process # fixdep: used to generate dependency information during build process
hostprogs-always-y += fixdep 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

15
scripts/gcc-plugins/Makefile
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@ -1,12 +1,17 @@
# SPDX-License-Identifier: GPL-2.0 # SPDX-License-Identifier: GPL-2.0
$(obj)/randomize_layout_plugin.so: $(objtree)/$(obj)/randomize_layout_seed.h $(obj)/randomize_layout_plugin.so: $(obj)/randomize_layout_seed.h
quiet_cmd_create_randomize_layout_seed = GENSEED $@ quiet_cmd_create_randomize_layout_seed = SEEDHDR $@
cmd_create_randomize_layout_seed = \ cmd_create_randomize_layout_seed = \
$(CONFIG_SHELL) $(srctree)/$(src)/gen-random-seed.sh $@ $(objtree)/include/generated/randomize_layout_hash.h SEED=$$(cat $(filter-out FORCE,$^) </dev/null); \
$(objtree)/$(obj)/randomize_layout_seed.h: FORCE echo '/*' > $@; \
echo ' * This file is automatically generated. Keep it private.' >> $@; \
echo ' * Exposing this value will expose the layout of randomized structures.' >> $@; \
echo ' */' >> $@; \
echo "const char *randstruct_seed = \"$$SEED\";" >> $@
$(obj)/randomize_layout_seed.h: $(objtree)/scripts/basic/randstruct.seed FORCE
$(call if_changed,create_randomize_layout_seed) $(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 # Build rules for plugins
# #

9
scripts/gcc-plugins/gen-random-seed.sh
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@ -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

7
scripts/gen-randstruct-seed.sh Executable file
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@ -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"

9
security/Kconfig.hardening
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@ -284,10 +284,11 @@ choice
tools like Volatility against the system (unless the kernel tools like Volatility against the system (unless the kernel
source tree isn't cleaned after kernel installation). source tree isn't cleaned after kernel installation).
The seed used for compilation is located at The seed used for compilation is in scripts/basic/randomize.seed.
scripts/randomize_layout_seed.h. It remains after a "make clean" It remains after a "make clean" to allow for external modules to
to allow for external modules to be compiled with the existing be compiled with the existing seed and will be removed by a
seed and will be removed by a "make mrproper" or "make distclean". "make mrproper" or "make distclean". This file should not be made
public, or the structure layout can be determined.
config RANDSTRUCT_NONE config RANDSTRUCT_NONE
bool "Disable structure layout randomization" bool "Disable structure layout randomization"