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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

Makefile

+6 −87
Original line number Diff line number Diff line
@@ -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

# ---------------------------------------------------------------------------

arch/Kconfig

+11 −21
Original line number Diff line number Diff line
@@ -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

arch/x86/Kconfig

+10 −1
Original line number Diff line number Diff line
@@ -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"

scripts/gcc-x86_32-has-stack-protector.sh

+1 −6
Original line number Diff line number Diff line 
#!/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"

scripts/gcc-x86_64-has-stack-protector.sh

+0 −5
Original line number Diff line number Diff line
@@ -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