Commit c965b105 authored by Kees Cook's avatar Kees Cook Committed by Linus Torvalds

kbuild: abort build on bad stack protector flag

Before, the stack protector flag was sanity checked before .config had
been reprocessed.  This meant the build couldn't be aborted early, and
only a warning could be emitted followed later by the compiler blowing
up with an unknown flag.  This has caused a lot of confusion over time,
so this splits the flag selection from sanity checking and performs the
sanity checking after the make has been restarted from a reprocessed
.config, so builds can be aborted as early as possible now.

Additionally moves the x86-specific sanity check to the same location,
since it suffered from the same warn-then-wait-for-compiler-failure
problem.

Link: http://lkml.kernel.org/r/20160712223043.GA11664@www.outflux.netSigned-off-by: default avatarKees Cook <keescook@chromium.org>
Cc: Michal Marek <mmarek@suse.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3bd96463
......@@ -647,41 +647,28 @@ ifneq ($(CONFIG_FRAME_WARN),0)
KBUILD_CFLAGS += $(call cc-option,-Wframe-larger-than=${CONFIG_FRAME_WARN})
endif
# Handle stack protector mode.
#
# Since kbuild can potentially perform two passes (first with the old
# .config values and then with updated .config values), we cannot error out
# if a desired compiler option is unsupported. If we were to error, kbuild
# could never get to the second pass and actually notice that we changed
# the option to something that was supported.
#
# Additionally, we don't want to fallback and/or silently change which compiler
# flags will be used, since that leads to producing kernels with different
# security feature characteristics depending on the compiler used. ("But I
# selected CC_STACKPROTECTOR_STRONG! Why did it build with _REGULAR?!")
#
# The middle ground is to warn here so that the failed option is obvious, but
# to let the build fail with bad compiler flags so that we can't produce a
# kernel when there is a CONFIG and compiler mismatch.
#
# 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_REGULAR
stackp-flag := -fstack-protector
ifeq ($(call cc-option, $(stackp-flag)),)
$(warning Cannot use CONFIG_CC_STACKPROTECTOR_REGULAR: \
-fstack-protector not supported by compiler)
endif
stackp-name := REGULAR
else
ifdef CONFIG_CC_STACKPROTECTOR_STRONG
stackp-flag := -fstack-protector-strong
ifeq ($(call cc-option, $(stackp-flag)),)
$(warning Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: \
-fstack-protector-strong not supported by compiler)
endif
stackp-name := STRONG
else
# Force off for distro compilers that enable stack protector by default.
stackp-flag := $(call cc-option, -fno-stack-protector)
endif
endif
# Find arch-specific stack protector compiler sanity-checking script.
ifdef CONFIG_CC_STACKPROTECTOR
stackp-path := $(srctree)/scripts/gcc-$(ARCH)_$(BITS)-has-stack-protector.sh
ifneq ($(wildcard $(stackp-path)),)
stackp-check := $(stackp-path)
endif
endif
KBUILD_CFLAGS += $(stackp-flag)
ifdef CONFIG_KCOV
......@@ -1017,8 +1004,10 @@ ifneq ($(KBUILD_SRC),)
fi;
endif
# prepare2 creates a makefile if using a separate output directory
prepare2: prepare3 outputmakefile asm-generic
# prepare2 creates a makefile if using a separate output directory.
# From this point forward, .config has been reprocessed, so any rules
# that need to depend on updated CONFIG_* values can be checked here.
prepare2: prepare3 prepare-compiler-check outputmakefile asm-generic
prepare1: prepare2 $(version_h) include/generated/utsrelease.h \
include/config/auto.conf
......@@ -1049,6 +1038,32 @@ endif
PHONY += prepare-objtool
prepare-objtool: $(objtool_target)
# Check for CONFIG flags that require compiler support. Abort the build
# after .config has been processed, but before the kernel build starts.
#
# For security-sensitive CONFIG options, we don't want to fallback and/or
# silently change which compiler flags will be used, since that leads to
# producing kernels with different security feature characteristics
# depending on the compiler used. (For example, "But I selected
# CC_STACKPROTECTOR_STRONG! Why did it build with _REGULAR?!")
PHONY += prepare-compiler-check
prepare-compiler-check: FORCE
# Make sure compiler supports requested stack protector flag.
ifdef stackp-name
ifeq ($(call cc-option, $(stackp-flag)),)
@echo Cannot use CONFIG_CC_STACKPROTECTOR_$(stackp-name): \
$(stackp-flag) not supported by compiler >&2 && exit 1
endif
endif
# Make sure compiler does not have buggy stack-protector support.
ifdef stackp-check
ifneq ($(shell $(CONFIG_SHELL) $(stackp-check) $(CC) $(KBUILD_CPPFLAGS) $(biarch)),y)
@echo Cannot use CONFIG_CC_STACKPROTECTOR_$(stackp-name): \
$(stackp-flag) available but compiler is broken >&2 && exit 1
endif
endif
@:
# Generate some files
# ---------------------------------------------------------------------------
......
......@@ -126,14 +126,6 @@ else
KBUILD_CFLAGS += $(call cc-option,-maccumulate-outgoing-args)
endif
# Make sure compiler does not have buggy stack-protector support.
ifdef CONFIG_CC_STACKPROTECTOR
cc_has_sp := $(srctree)/scripts/gcc-x86_$(BITS)-has-stack-protector.sh
ifneq ($(shell $(CONFIG_SHELL) $(cc_has_sp) $(CC) $(KBUILD_CPPFLAGS) $(biarch)),y)
$(warning stack-protector enabled but compiler support broken)
endif
endif
ifdef CONFIG_X86_X32
x32_ld_ok := $(call try-run,\
/bin/echo -e '1: .quad 1b' | \
......
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