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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
r420_reg_safe.h
r600_reg_safe.h
randstruct.seed
randomize_layout_hash.h
randomize_layout_seed.h
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
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
--------------------

2
include/linux/vermagic.h
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@ -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

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

11
scripts/basic/Makefile
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@ -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

15
scripts/gcc-plugins/Makefile
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@ -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
#

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
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"