On Sat, Jun 27, 2020 at 5:13 AM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > On Fri, Jun 26, 2020 at 12:00 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > > > Some Makefiles already pass -fno-stack-protector unconditionally. > > For example, arch/arm64/kernel/vdso/Makefile, arch/x86/xen/Makefile. > > No problem report so far about hard-coding this option. So, we can > > assume all supported compilers know -fno-stack-protector. > > > > GCC 4.8 and Clang support this option (https://godbolt.org/z/_HDGzN) > > > > Get rid of cc-option from -fno-stack-protector. > > > > Remove CONFIG_CC_HAS_STACKPROTECTOR_NONE, which should always be 'y'. > > > > Note: > > arch/mips/vdso/Makefile adds -fno-stack-protector twice, first > > unconditionally, and second conditionally. I removed the second one. > > > > Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> > > Generally looks pretty good, just a few more questions before adding > my tag explicitly. > > > --- > > > > Documentation/kbuild/kconfig-language.rst | 4 ++-- > > Makefile | 2 +- > > arch/Kconfig | 3 --- > > arch/arm/boot/compressed/Makefile | 3 +-- > > arch/mips/vdso/Makefile | 3 +-- > > arch/powerpc/kernel/Makefile | 2 +- > > arch/powerpc/platforms/powermac/Makefile | 2 +- > > arch/sparc/vdso/Makefile | 4 ++-- > > arch/um/Makefile | 3 +-- > > arch/x86/Makefile | 2 +- > > arch/x86/boot/compressed/Makefile | 2 +- > > arch/x86/entry/vdso/Makefile | 4 ++-- > > arch/x86/kernel/cpu/Makefile | 3 +-- > > arch/x86/lib/Makefile | 2 +- > > arch/x86/mm/Makefile | 7 +++---- > > arch/x86/power/Makefile | 3 +-- > > arch/x86/purgatory/Makefile | 2 +- > > arch/x86/um/vdso/Makefile | 2 +- > > arch/x86/xen/Makefile | 5 ++--- > > drivers/firmware/efi/libstub/Makefile | 2 +- > > drivers/xen/Makefile | 3 +-- > > kernel/kcsan/Makefile | 3 +-- > > lib/Makefile | 4 ++-- > > mm/kasan/Makefile | 2 +- > > 24 files changed, 30 insertions(+), 42 deletions(-) > > > > diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst > > index a1601ec3317b..2538e7cb08e6 100644 > > --- a/Documentation/kbuild/kconfig-language.rst > > +++ b/Documentation/kbuild/kconfig-language.rst > > @@ -540,8 +540,8 @@ followed by a test macro:: > > If you need to expose a compiler capability to makefiles and/or C source files, > > `CC_HAS_` is the recommended prefix for the config option:: > > > > - config CC_HAS_STACKPROTECTOR_NONE > > - def_bool $(cc-option,-fno-stack-protector) > > + config CC_HAS_ASM_GOTO > > + def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC)) > > > > Build as module only > > ~~~~~~~~~~~~~~~~~~~~ > > diff --git a/Makefile b/Makefile > > index 5496a32dffa6..73948798ce3f 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -762,7 +762,7 @@ ifneq ($(CONFIG_FRAME_WARN),0) > > KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN) > > endif > > > > -stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector > > +stackp-flags-y := -fno-stack-protector > > stackp-flags-$(CONFIG_STACKPROTECTOR) := -fstack-protector > > stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG) := -fstack-protector-strong > > So it looks like the previous behavior always added > `-fno-stack-protector` (since CONFIG_CC_HAS_STACKPROTECTOR_NONE was > always true), but then we append either `-fstack-protector` or > `-fstack-protector-strong` based on configs. While that's ok, and you > patch doesn't change that behavior, and it's good to be explicit to > set the stack protector or not...it seems weird to have > `-fno-stack-protector -fstack-protector` in the command line flags. I > would prefer if we checked for not having CONFIG_STACKPROTECTOR or > CONFIG_STACKPROTECTOR_STRONG before adding `-fno-stack-protector`. > That doesn't have to be done in this patch, per se. > > > > > diff --git a/arch/Kconfig b/arch/Kconfig > > index 8cc35dc556c7..1ea61290900a 100644 > > --- a/arch/Kconfig > > +++ b/arch/Kconfig > > @@ -478,9 +478,6 @@ config HAVE_STACKPROTECTOR > > An arch should select this symbol if: > > - it has implemented a stack canary (e.g. __stack_chk_guard) > > > > -config CC_HAS_STACKPROTECTOR_NONE > > - def_bool $(cc-option,-fno-stack-protector) > > - > > config STACKPROTECTOR > > bool "Stack Protector buffer overflow detection" > > depends on HAVE_STACKPROTECTOR > > diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile > > index 00602a6fba04..cb7a56c6723c 100644 > > --- a/arch/arm/boot/compressed/Makefile > > +++ b/arch/arm/boot/compressed/Makefile > > @@ -84,9 +84,8 @@ endif > > > > # -fstack-protector-strong triggers protection checks in this code, > > # but it is being used too early to link to meaningful stack_chk logic. > > -nossp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector > > $(foreach o, $(libfdt_objs) atags_to_fdt.o, \ > > - $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt $(nossp-flags-y))) > > + $(eval CFLAGS_$(o) := -I $(srctree)/scripts/dtc/libfdt -fno-stack-protector)) > > > > # These were previously generated C files. When you are building the kernel > > # with O=, make sure to remove the stale files in the output tree. Otherwise, > > diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile > > index 2e64c7600eea..57fe83235281 100644 > > --- a/arch/mips/vdso/Makefile > > +++ b/arch/mips/vdso/Makefile > > @@ -35,8 +35,7 @@ cflags-vdso := $(ccflags-vdso) \ > > -O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \ > > -mrelax-pic-calls $(call cc-option, -mexplicit-relocs) \ > > -fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \ > > - $(call cc-option, -fno-asynchronous-unwind-tables) \ > > - $(call cc-option, -fno-stack-protector) > > + $(call cc-option, -fno-asynchronous-unwind-tables) > > aflags-vdso := $(ccflags-vdso) \ > > -D__ASSEMBLY__ -Wa,-gdwarf-2 > > > > diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile > > index 244542ae2a91..3a83f2b876a5 100644 > > --- a/arch/powerpc/kernel/Makefile > > +++ b/arch/powerpc/kernel/Makefile > > @@ -16,7 +16,7 @@ CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) > > CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) > > CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN) > > > > -CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector) > > +CFLAGS_prom_init.o += -fno-stack-protector > > CFLAGS_prom_init.o += -DDISABLE_BRANCH_PROFILING > > CFLAGS_prom_init.o += -ffreestanding > > > > diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile > > index f4247ade71ca..cf85f0662d0d 100644 > > --- a/arch/powerpc/platforms/powermac/Makefile > > +++ b/arch/powerpc/platforms/powermac/Makefile > > @@ -1,6 +1,6 @@ > > # SPDX-License-Identifier: GPL-2.0 > > CFLAGS_bootx_init.o += -fPIC > > -CFLAGS_bootx_init.o += $(call cc-option, -fno-stack-protector) > > +CFLAGS_bootx_init.o += -fno-stack-protector > > > > KASAN_SANITIZE_bootx_init.o := n > > > > diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile > > index 708cb6304c2d..f44355e46f31 100644 > > --- a/arch/sparc/vdso/Makefile > > +++ b/arch/sparc/vdso/Makefile > > @@ -54,7 +54,7 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE > > # optimize sibling calls. > > # > > CFL := $(PROFILING) -mcmodel=medlow -fPIC -O2 -fasynchronous-unwind-tables -m64 \ > > - $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \ > > + $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \ > > -fno-omit-frame-pointer -foptimize-sibling-calls \ > > -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO > > > > @@ -93,7 +93,7 @@ KBUILD_CFLAGS_32 := $(filter-out -fno-pic,$(KBUILD_CFLAGS_32)) > > KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32)) > > KBUILD_CFLAGS_32 := $(filter-out $(SPARC_REG_CFLAGS),$(KBUILD_CFLAGS_32)) > > KBUILD_CFLAGS_32 += -m32 -msoft-float -fpic > > -KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector) > > +KBUILD_CFLAGS_32 += -fno-stack-protector > > KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls) > > KBUILD_CFLAGS_32 += -fno-omit-frame-pointer > > KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING > > diff --git a/arch/um/Makefile b/arch/um/Makefile > > index 3f27aa3ec0a6..1cea46ff9bb7 100644 > > --- a/arch/um/Makefile > > +++ b/arch/um/Makefile > > @@ -121,8 +121,7 @@ LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static > > LINK-$(CONFIG_LD_SCRIPT_DYN) += -Wl,-rpath,/lib $(call cc-option, -no-pie) > > > > CFLAGS_NO_HARDENING := $(call cc-option, -fno-PIC,) $(call cc-option, -fno-pic,) \ > > - $(call cc-option, -fno-stack-protector,) \ > > - $(call cc-option, -fno-stack-protector-all,) > > + -fno-stack-protector $(call cc-option, -fno-stack-protector-all) > > > > # Options used by linker script > > export LDS_START := $(START) > > diff --git a/arch/x86/Makefile b/arch/x86/Makefile > > index 00e378de8bc0..89c3cdfba753 100644 > > --- a/arch/x86/Makefile > > +++ b/arch/x86/Makefile > > @@ -37,7 +37,7 @@ REALMODE_CFLAGS := $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \ > > -mno-mmx -mno-sse > > > > REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -ffreestanding) > > -REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector) > > +REALMODE_CFLAGS += -fno-stack-protector > > REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -Wno-address-of-packed-member) > > REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4)) > > export REALMODE_CFLAGS > > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile > > index 7619742f91c9..c88a31569a5e 100644 > > --- a/arch/x86/boot/compressed/Makefile > > +++ b/arch/x86/boot/compressed/Makefile > > @@ -36,7 +36,7 @@ cflags-$(CONFIG_X86_64) := -mcmodel=small > > KBUILD_CFLAGS += $(cflags-y) > > KBUILD_CFLAGS += -mno-mmx -mno-sse > > KBUILD_CFLAGS += $(call cc-option,-ffreestanding) > > -KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector) > > +KBUILD_CFLAGS += -fno-stack-protector > > KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) > > KBUILD_CFLAGS += $(call cc-disable-warning, gnu) > > KBUILD_CFLAGS += -Wno-pointer-sign > > diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile > > index 04e65f0698f6..215376d975a2 100644 > > --- a/arch/x86/entry/vdso/Makefile > > +++ b/arch/x86/entry/vdso/Makefile > > @@ -82,7 +82,7 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE > > # optimize sibling calls. > > # > > CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \ > > - $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \ > > + $(filter -g%,$(KBUILD_CFLAGS)) -fno-stack-protector \ > > -fno-omit-frame-pointer -foptimize-sibling-calls \ > > -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO > > > > @@ -151,7 +151,7 @@ KBUILD_CFLAGS_32 := $(filter-out -mfentry,$(KBUILD_CFLAGS_32)) > > KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32)) > > KBUILD_CFLAGS_32 := $(filter-out $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS_32)) > > KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic > > -KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector) > > +KBUILD_CFLAGS_32 += -fno-stack-protector > > KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls) > > KBUILD_CFLAGS_32 += -fno-omit-frame-pointer > > KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING > > diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile > > index dba6a83bc349..93792b457b81 100644 > > --- a/arch/x86/kernel/cpu/Makefile > > +++ b/arch/x86/kernel/cpu/Makefile > > @@ -17,8 +17,7 @@ KCOV_INSTRUMENT_perf_event.o := n > > KCSAN_SANITIZE_common.o := n > > > > # Make sure load_percpu_segment has no stackprotector > > -nostackp := $(call cc-option, -fno-stack-protector) > > -CFLAGS_common.o := $(nostackp) > > +CFLAGS_common.o := -fno-stack-protector > > Any time I see `:=` assignment to a CFLAGS variable, it's a red flag > for overwriting existing CFLAGS, which is a common source of bugs. I > recognize the kernel is current a mix and match for: > > CFLAGS_<file>.o > > rules to either use `+=` or `:=`, but I wish we were consistent, and > consistent in our use of `+=`. For those rules, is there a difference > between the use of `+=` and `:=` like there is for the more general > case of appending to KBUILD_CFLAGS? If not, it's ok to match the > existing style, but it's curious to me in this patch to see a mixed > use of `+=` and `:=`. I think Kees mostly answered your question. Let me add some comments. '+=' is the most used in kernel Makefiles, but ':=' and '=' are also used. So, you are right, we are inconsistent. This applies to not only CFLAGS_<file>.o, but also obj-y, etc. For example, https://github.com/torvalds/linux/blob/v5.7/arch/arm64/kernel/Makefile#L15 'obj-y :=' works since it is the first assignment to obj-y in that file. 'obj-y +=' also works, of course. We can consistently use '+=' everywhere, but I do not send patches for churn. You can use any assignment operator to CFLAGS_<file>.o if it is the first assignment in the Makefile. Using '+=' is robust for future code insertion/removal, though. If the right-hand side contains variable references, there is important difference in the behavior. You may know two flavors in variables (https://www.gnu.org/software/make/manual/make.html#Flavors) CFLAGS_foo.o := $(call cc-option,-fno-stack-protector) The cc-option is expanded immediately when this line is parsed. (So, the compiler is invoked for 'make clean' too) CFLAGS_foo.o += $(call cc-option,-fno-stack-protector) If this is the first assignment in the file, '+=' act as '=', so the evaluation of cc-option is delayed until $(CFLAGS_foo.o) is expanded. (So, the compiler is NOT invoked for 'make clean') -- Best Regards Masahiro Yamada
