Commit 2a61f474 authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

stack-protector: test compiler capability in Kconfig and drop AUTO mode



Move the test for -fstack-protector(-strong) option to Kconfig.

If the compiler does not support the option, the corresponding menu
is automatically hidden.  If STRONG is not supported, it will fall
back to REGULAR.  If REGULAR is not supported, it will be disabled.
This means, AUTO is implicitly handled by the dependency solver of
Kconfig, hence removed.

I also turned the 'choice' into only two boolean symbols.  The use of
'choice' is not a good idea here, because all of all{yes,mod,no}config
would choose the first visible value, while we want allnoconfig to
disable as many features as possible.

X86 has additional shell scripts in case the compiler supports those
options, but generates broken code.  I added CC_HAS_SANE_STACKPROTECTOR
to test this.  I had to add -m32 to gcc-x86_32-has-stack-protector.sh
to make it work correctly.
Signed-off-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: default avatarKees Cook <keescook@chromium.org>
parent 315bab4e
......@@ -686,55 +686,11 @@ ifneq ($(CONFIG_FRAME_WARN),0)
KBUILD_CFLAGS += $(call cc-option,-Wframe-larger-than=${CONFIG_FRAME_WARN})
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
else
ifdef CONFIG_CC_STACKPROTECTOR_STRONG
stackp-flag := -fstack-protector-strong
stackp-name := STRONG
else
# If either there is no stack protector for this architecture or
# CONFIG_CC_STACKPROTECTOR_NONE is selected, we're done, and $(stackp-name)
# is empty, skipping all remaining stack protector tests.
#
# Force off for distro compilers that enable stack protector by default.
KBUILD_CFLAGS += $(call cc-option, -fno-stack-protector)
endif
endif
endif
# Find arch-specific stack protector compiler sanity-checking script.
ifdef stackp-name
ifneq ($(stackp-flag),)
stackp-path := $(srctree)/scripts/gcc-$(SRCARCH)_$(BITS)-has-stack-protector.sh
stackp-check := $(wildcard $(stackp-path))
# If the wildcard test matches a test script, run it to check functionality.
ifdef stackp-check
ifneq ($(shell $(CONFIG_SHELL) $(stackp-check) $(CC) $(KBUILD_CPPFLAGS) $(biarch)),y)
stackp-broken := y
endif
endif
ifndef stackp-broken
# If the stack protector is functional, enable code that depends on it.
KBUILD_CPPFLAGS += -DCONFIG_CC_STACKPROTECTOR
# Either we've already detected the flag (for AUTO) or we'll fail the
# build in the prepare-compiler-check rule (for specific flag).
KBUILD_CFLAGS += $(stackp-flag)
else
# We have to make sure stack protector is unconditionally disabled if
# the compiler is broken (in case we're going to continue the build in
# AUTO mode).
KBUILD_CFLAGS += $(call cc-option, -fno-stack-protector)
endif
endif
endif
stackp-flags-$(CONFIG_CC_HAS_STACKPROTECTOR_NONE) := -fno-stack-protector
stackp-flags-$(CONFIG_CC_STACKPROTECTOR) := -fstack-protector
stackp-flags-$(CONFIG_CC_STACKPROTECTOR_STRONG) := -fstack-protector-strong
KBUILD_CFLAGS += $(stackp-flags-y)
ifeq ($(cc-name),clang)
KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
......@@ -1118,7 +1074,7 @@ endif
# 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
prepare2: prepare3 outputmakefile asm-generic
prepare1: prepare2 $(version_h) $(autoksyms_h) include/generated/utsrelease.h \
include/config/auto.conf
......@@ -1144,43 +1100,6 @@ uapi-asm-generic:
PHONY += prepare-objtool
prepare-objtool: $(objtool_target)
# Check for CONFIG flags that require compiler support. Abort the build
# after .config has been processed, but before the kernel build starts.
#
# For security-sensitive CONFIG options, we don't want to fallback and/or
# silently change which compiler flags will be used, since that leads to
# producing kernels with different security feature characteristics
# depending on the compiler used. (For example, "But I selected
# CC_STACKPROTECTOR_STRONG! Why did it build with _REGULAR?!")
PHONY += prepare-compiler-check
prepare-compiler-check: FORCE
# Make sure compiler supports requested stack protector flag.
ifdef stackp-name
# Warn about CONFIG_CC_STACKPROTECTOR_AUTO having found no option.
ifeq ($(stackp-flag),)
@echo CONFIG_CC_STACKPROTECTOR_$(stackp-name): \
Compiler does not support any known stack-protector >&2
else
# Fail if specifically requested stack protector is missing.
ifeq ($(call cc-option, $(stackp-flag)),)
@echo Cannot use CONFIG_CC_STACKPROTECTOR_$(stackp-name): \
$(stackp-flag) not supported by compiler >&2 && exit 1
endif
endif
endif
# Make sure compiler does not have buggy stack-protector support. If a
# specific stack-protector was requested, fail the build, otherwise warn.
ifdef stackp-broken
ifeq ($(stackp-name),AUTO)
@echo CONFIG_CC_STACKPROTECTOR_$(stackp-name): \
$(stackp-flag) available but compiler is broken: disabling >&2
else
@echo Cannot use CONFIG_CC_STACKPROTECTOR_$(stackp-name): \
$(stackp-flag) available but compiler is broken >&2 && exit 1
endif
endif
@:
# Generate some files
# ---------------------------------------------------------------------------
......
......@@ -536,13 +536,16 @@ config HAVE_CC_STACKPROTECTOR
bool
help
An arch should select this symbol if:
- its compiler supports the -fstack-protector option
- it has implemented a stack canary (e.g. __stack_chk_guard)
choice
prompt "Stack Protector buffer overflow detection"
config CC_HAS_STACKPROTECTOR_NONE
def_bool $(cc-option,-fno-stack-protector)
config CC_STACKPROTECTOR
bool "Stack Protector buffer overflow detection"
depends on HAVE_CC_STACKPROTECTOR
default CC_STACKPROTECTOR_AUTO
depends on $(cc-option,-fstack-protector)
default y
help
This option turns on the "stack-protector" GCC feature. This
feature puts, at the beginning of functions, a canary value on
......@@ -552,14 +555,6 @@ choice
overwrite the canary, which gets detected and the attack is then
neutralized via a kernel panic.
config CC_STACKPROTECTOR_NONE
bool "None"
help
Disable "stack-protector" GCC feature.
config CC_STACKPROTECTOR_REGULAR
bool "Regular"
help
Functions will have the stack-protector canary logic added if they
have an 8-byte or larger character array on the stack.
......@@ -571,7 +566,10 @@ config CC_STACKPROTECTOR_REGULAR
by about 0.3%.
config CC_STACKPROTECTOR_STRONG
bool "Strong"
bool "Strong Stack Protector"
depends on CC_STACKPROTECTOR
depends on $(cc-option,-fstack-protector-strong)
default y
help
Functions will have the stack-protector canary logic added in any
of the following conditions:
......@@ -589,14 +587,6 @@ 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 HAVE_ARCH_WITHIN_STACK_FRAMES
bool
help
......
......@@ -129,7 +129,7 @@ config X86
select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64
select HAVE_ARCH_VMAP_STACK if X86_64
select HAVE_ARCH_WITHIN_STACK_FRAMES
select HAVE_CC_STACKPROTECTOR
select HAVE_CC_STACKPROTECTOR if CC_HAS_SANE_STACKPROTECTOR
select HAVE_CMPXCHG_DOUBLE
select HAVE_CMPXCHG_LOCAL
select HAVE_CONTEXT_TRACKING if X86_64
......@@ -341,6 +341,15 @@ config PGTABLE_LEVELS
default 2
source "init/Kconfig"
config CC_HAS_SANE_STACKPROTECTOR
bool
default $(success,$(srctree)/scripts/gcc-x86_64-has-stack-protector.sh $(CC)) if 64BIT
default $(success,$(srctree)/scripts/gcc-x86_32-has-stack-protector.sh $(CC))
help
We have to make sure stack protector is unconditionally disabled if
the compiler produces broken code.
source "kernel/Kconfig.freezer"
menu "Processor type and features"
......
#!/bin/sh
# SPDX-License-Identifier: GPL-2.0
echo "int foo(void) { char X[200]; return 3; }" | $* -S -x c -c -O0 -fstack-protector - -o - 2> /dev/null | grep -q "%gs"
if [ "$?" -eq "0" ] ; then
echo y
else
echo n
fi
echo "int foo(void) { char X[200]; return 3; }" | $* -S -x c -c -m32 -O0 -fstack-protector - -o - 2> /dev/null | grep -q "%gs"
......@@ -2,8 +2,3 @@
# SPDX-License-Identifier: GPL-2.0
echo "int foo(void) { char X[200]; return 3; }" | $* -S -x c -c -O0 -mcmodel=kernel -fno-PIE -fstack-protector - -o - 2> /dev/null | grep -q "%gs"
if [ "$?" -eq "0" ] ; then
echo y
else
echo n
fi
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