From mboxrd@z Thu Jan 1 00:00:00 1970 From: keescook@chromium.org (Kees Cook) Date: Thu, 7 Jan 2016 10:40:46 -0800 Subject: [PATCH v3] ARM: fix atags_to_fdt with stack-protector-strong In-Reply-To: <20160107113029.GE19062@n2100.arm.linux.org.uk> References: <20160106233656.GA9316@www.outflux.net> <20160107113029.GE19062@n2100.arm.linux.org.uk> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Jan 7, 2016 at 3:30 AM, Russell King - ARM Linux wrote: > On Wed, Jan 06, 2016 at 03:36:56PM -0800, Kees Cook wrote: >> diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile >> index 3f9a9ebc77c3..d7d2c2981f65 100644 >> --- a/arch/arm/boot/compressed/Makefile >> +++ b/arch/arm/boot/compressed/Makefile >> @@ -106,6 +106,14 @@ ORIG_CFLAGS := $(KBUILD_CFLAGS) >> KBUILD_CFLAGS = $(subst -pg, , $(ORIG_CFLAGS)) >> endif >> >> +# -fstack-protector-strong triggers protection checks in this code, >> +# but it is being used too early to link to meaningful stack_chk logic. >> +CFLAGS_atags_to_fdt.o := $(call cc-option, -fno-stack-protector) >> +CFLAGS_fdt.o := $(call cc-option, -fno-stack-protector) >> +CFLAGS_fdt_ro.o := $(call cc-option, -fno-stack-protector) >> +CFLAGS_fdt_rw.o := $(call cc-option, -fno-stack-protector) >> +CFLAGS_fdt_wip.o := $(call cc-option, -fno-stack-protector) > > This will result in "$(call cc-option, -fno-stack-protector)" being > called five times when this Makefile is parsed, which seems very > wasteful. I'm sure there's better solutions to that - maybe caching > the value in a variable in a higher level makefile (eg, > arch/arm/Makefile) ? Good point; I will adjust this to get a single invocation. > Also, I suspect that all of the decompressor should be built with > -fno-stack-protector as we don't have sufficient environment here. > Maybe it should be placed in the global CFLAGS for the decompressor? I prefer keeping it disabled in as narrow a range as possible. If other code gains a level of complexity that it triggers the stack protector code insertion, I think that's worth examining when it happens. If this ever becomes an actual burden, then yeah, let's do it for the whole decompressor, but I think it'd be best to revisit it if it happens again. -Kees -- Kees Cook Chrome OS & Brillo Security