@@ -676,6 +676,10 @@ endif
# This selects the stack protector compiler flag. Testing it is delayed
# until after .config has been reprocessed, in the prepare-compiler-check
# target.
+ifdef CONFIG_CC_STACKPROTECTOR_AUTO
+ stackp-flag := $(call cc-option,-fstack-protector-strong,$(call cc-option,-fstack-protector))
+ stackp-name := AUTO
+else
ifdef CONFIG_CC_STACKPROTECTOR_REGULAR
stackp-flag := -fstack-protector
stackp-name := REGULAR
@@ -688,6 +692,7 @@ else
stackp-flag := $(call cc-option, -fno-stack-protector)
endif
endif
+endif
ifdef stackp-name
# If the stack protector has been selected, inform the rest of the build.
KBUILD_CFLAGS += -DCONFIG_CC_STACKPROTECTOR
@@ -1084,6 +1089,12 @@ PHONY += prepare-compiler-check
prepare-compiler-check: FORCE
# Make sure compiler supports requested stack protector flag.
ifdef stackp-name
+ # Warn about CONFIG_CC_STACKPROTECTOR_AUTO having found no option.
+ ifeq ($(stackp-flag),)
+ @echo CONFIG_CC_STACKPROTECTOR_$(stackp-name): \
+ Compiler does not support any known stack-protector >&2
+ endif
+ # Fail if specifically requested stack protector is missing.
ifeq ($(call cc-option, $(stackp-flag)),)
@echo Cannot use CONFIG_CC_STACKPROTECTOR_$(stackp-name): \
$(stackp-flag) not supported by compiler >&2 && exit 1
@@ -526,7 +526,7 @@ config HAVE_CC_STACKPROTECTOR
choice
prompt "Stack Protector buffer overflow detection"
depends on HAVE_CC_STACKPROTECTOR
- default CC_STACKPROTECTOR_NONE
+ default CC_STACKPROTECTOR_AUTO
help
This option turns on the "stack-protector" GCC feature. This
feature puts, at the beginning of functions, a canary value on
@@ -573,6 +573,12 @@ config CC_STACKPROTECTOR_STRONG
about 20% of all kernel functions, which increases the kernel code
size by about 2%.
+config CC_STACKPROTECTOR_AUTO
+ bool "Automatic"
+ help
+ If the compiler supports it, the best available stack-protector
+ option will be chosen.
+
endchoice
config THIN_ARCHIVES
Nearly all modern compilers support a stack-protector option, and nearly all modern distributions enable the kernel stack-protector, so enabling this by default in kernel builds would make sense. However, Kconfig does not have knowledge of available compiler features, so it isn't safe to force on, as this would unconditionally break builds for the compilers or architectures that don't have support. Instead, this introduces a new option, CONFIG_CC_STACKPROTECTOR_AUTO, which attempts to discover the best possible stack-protector available, and will allow builds to proceed even if the compiler doesn't support any stack-protector. This option is made the default so that kernels built with modern compilers will be protected-by-default against stack buffer overflows, avoiding things like the recent BlueBorne attack. Selection of a specific stack-protector option remains available, including disabling it. Cc: Masahiro Yamada <yamada.masahiro@socionext.com> Cc: Michal Marek <mmarek@suse.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Laura Abbott <labbott@redhat.com> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: linux-kbuild@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> --- Makefile | 11 +++++++++++ arch/Kconfig | 8 +++++++- 2 files changed, 18 insertions(+), 1 deletion(-)