Clang 15 will support randstruct via the -frandomize-layout-seed-file=... option. Update the Kconfig and Makefile to recognize this feature. Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx> Cc: linux-kbuild@xxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- scripts/Makefile.randstruct | 3 +++ security/Kconfig.hardening | 14 ++++++++++++-- 2 files changed, 15 insertions(+), 2 deletions(-) diff --git a/scripts/Makefile.randstruct b/scripts/Makefile.randstruct index 4d741e6db554..24e283e89893 100644 --- a/scripts/Makefile.randstruct +++ b/scripts/Makefile.randstruct @@ -7,6 +7,9 @@ randstruct-cflags-y \ += -fplugin=$(objtree)/scripts/gcc-plugins/randomize_layout_plugin.so randstruct-cflags-$(CONFIG_RANDSTRUCT_PERFORMANCE) \ += -fplugin-arg-randomize_layout_plugin-performance-mode +else +randstruct-cflags-y \ + += -frandomize-layout-seed-file=$(objtree)/scripts/basic/randstruct.seed endif export RANDSTRUCT_CFLAGS := $(randstruct-cflags-y) diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening index 0277ba578779..bd2aabb2c60f 100644 --- a/security/Kconfig.hardening +++ b/security/Kconfig.hardening @@ -266,9 +266,12 @@ config ZERO_CALL_USED_REGS endmenu +config CC_HAS_RANDSTRUCT + def_bool $(cc-option,-frandomize-layout-seed-file=/dev/null) + choice prompt "Randomize layout of sensitive kernel structures" - default RANDSTRUCT_FULL if COMPILE_TEST && GCC_PLUGINS + default RANDSTRUCT_FULL if COMPILE_TEST && (GCC_PLUGINS || CC_HAS_RANDSTRUCT) default RANDSTRUCT_NONE help If you enable this, the layouts of structures that are entirely @@ -297,13 +300,20 @@ choice config RANDSTRUCT_FULL bool "Fully randomize structure layout" - depends on GCC_PLUGINS + depends on CC_HAS_RANDSTRUCT || GCC_PLUGINS select MODVERSIONS if MODULES help Fully randomize the member layout of sensitive structures as much as possible, which may have both a memory size and performance impact. + One difference between the Clang and GCC plugin + implementations is the handling of bitfields. The GCC + plugin treats them as fully separate variables, + introducing sometimes significant padding. Clang tries + to keep adjacent bitfields together, but with their bit + ordering randomized. + config RANDSTRUCT_PERFORMANCE bool "Limit randomization of structure layout to cache-lines" depends on GCC_PLUGINS -- 2.32.0
