On Thu, May 21, 2020 at 09:56:35AM -0700, Kristen Carlson Accardi wrote: > Allow user to select CONFIG_FG_KASLR if dependencies are met. Change > the make file to build with -ffunction-sections if CONFIG_FG_KASLR > > Signed-off-by: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx> > Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx> > Tested-by: Tony Luck <tony.luck@xxxxxxxxx> > --- > Makefile | 4 ++++ > arch/x86/Kconfig | 13 +++++++++++++ > 2 files changed, 17 insertions(+) > > diff --git a/Makefile b/Makefile > index 04f5662ae61a..28e515baa824 100644 > --- a/Makefile > +++ b/Makefile > @@ -862,6 +862,10 @@ ifdef CONFIG_LIVEPATCH > KBUILD_CFLAGS += $(call cc-option, -flive-patching=inline-clone) > endif > > +ifdef CONFIG_FG_KASLR > +KBUILD_CFLAGS += -ffunction-sections > +endif > + > # arch Makefile may override CC so keep this after arch Makefile is included > NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index 2d3f963fd6f1..50e83ea57d70 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -2183,6 +2183,19 @@ config RANDOMIZE_BASE > > If unsure, say Y. > > +config FG_KASLR > + bool "Function Granular Kernel Address Space Layout Randomization" > + depends on $(cc-option, -ffunction-sections) > + depends on RANDOMIZE_BASE && X86_64 > + help > + This option improves the randomness of the kernel text > + over basic Kernel Address Space Layout Randomization (KASLR) > + by reordering the kernel text at boot time. This feature > + uses information generated at compile time to re-layout the > + kernel text section at boot time at function level granularity. > + > + If unsure, say N. > + > # Relocation on x86 needs some additional build support > config X86_NEED_RELOCS > def_bool y Kconfig bikeshedding: how about putting FG_KASLR in arch/Kconfig, add a "depends on ARCH_HAS_FG_KASLR", and remove the arch-specific depends. Then in arch/x86 have ARCH_HAS_FG_KASLR as a def_bool y with the RANDOMIZE_BASE && X86_64 depends. This will more cleanly split the build elements (compiler flags) from the arch elements (64-bit x86, arch-specific flags, etc). With that split out: Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -- Kees Cook
