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Subject[RFC PATCH 7/7] Test stackprotector options in Kconfig to kill CC_STACKPROTECTOR_AUTO
Date
Add CC_HAS_STACKPROTECTOR(_STRONG) and proper dependency.

I re-arranged the choice values, _STRONG, _REGULAR, _NONE in this order
because the default of choice is the first visible symbol.

TODO:
Broken stackprotector is not tested.
scripts/gcc-$(SRCARCH)_$(BITS)-has-stack-protector.sh should be
evaluated in Kconfig.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Test stackprotector options in Kconfig to kill CC_STACKPROTECTOR_AUTO

Add CC_HAS_STACKPROTECTOR(_STRONG) and proper dependency.

I re-arranged the choice values, _STRONG, _REGULAR, _NONE in this order
because the default of choice is the first visible symbol.

TODO:
Broken stackprotector is not tested.
scripts/gcc-$(SRCARCH)_$(BITS)-has-stack-protector.sh should be
evaluated in Kconfig.

---

Makefile | 58 +++++++++++-----------------------------------------------
arch/Kconfig | 54 +++++++++++++++++++++++++++++++-----------------------
2 files changed, 42 insertions(+), 70 deletions(-)

diff --git a/Makefile b/Makefile
index 9afd617..8123ccf 100644
--- a/Makefile
+++ b/Makefile
@@ -679,56 +679,20 @@ 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 += $(call cc-option, -fno-stack-protector)
- endif
+ifeq ($(CONFIG_CC_STACKPROTECTOR_STRONG),y)
+KBUILD_CFLAGS += -fstack-protector-strong
endif
+ifeq ($(CONFIG_CC_STACKPROTECTOR_REGULAR),y)
+KBUILD_CFLAGS += -fstack-protector
endif

+# is this necessary?
+#ifeq ($(CONFIG_CC_STACKPROTECTOR_NONE),y)
+#KBUILD_CFLAGS += -fno-stack-protector
+#endif
+
+# TODO: run scripts/gcc-$(SRCARCH)_$(BITS)-has-stack-protector.sh from Kconfig
+
ifeq ($(cc-name),clang)
KBUILD_CPPFLAGS += $(call cc-option,-Qunused-arguments,)
KBUILD_CFLAGS += $(call cc-disable-warning, unused-variable)
diff --git a/arch/Kconfig b/arch/Kconfig
index 76c0b54..50723d8 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -538,10 +538,20 @@ config HAVE_CC_STACKPROTECTOR
- its compiler supports the -fstack-protector option
- it has implemented a stack canary (e.g. __stack_chk_guard)

+config CC_HAS_STACKPROTECTOR
+ bool
+ option shell="$CC -Werror -fstack-protector -c -x c /dev/null"
+
+config CC_HAS_STACKPROTECTOR_STRONG
+ bool
+ option shell="$CC -Werror -fstack-protector-strong -c -x c /dev/null"
+
+config CC_STACKPROTECTOR
+ bool
+
choice
prompt "Stack Protector buffer overflow detection"
depends on HAVE_CC_STACKPROTECTOR
- 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
@@ -551,26 +561,10 @@ 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.
-
- This feature requires gcc version 4.2 or above, or a distribution
- gcc with the feature backported ("-fstack-protector").
-
- On an x86 "defconfig" build, this feature adds canary checks to
- about 3% of all kernel functions, which increases kernel code size
- by about 0.3%.
-
config CC_STACKPROTECTOR_STRONG
bool "Strong"
+ depends on CC_HAS_STACKPROTECTOR_STRONG
+ select CC_STACKPROTECTOR
help
Functions will have the stack-protector canary logic added in any
of the following conditions:
@@ -588,11 +582,25 @@ 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"
+config CC_STACKPROTECTOR_REGULAR
+ bool "Regular"
+ depends on CC_HAS_STACKPROTECTOR
+ select CC_STACKPROTECTOR
+ help
+ Functions will have the stack-protector canary logic added if they
+ have an 8-byte or larger character array on the stack.
+
+ This feature requires gcc version 4.2 or above, or a distribution
+ gcc with the feature backported ("-fstack-protector").
+
+ On an x86 "defconfig" build, this feature adds canary checks to
+ about 3% of all kernel functions, which increases kernel code size
+ by about 0.3%.
+
+config CC_STACKPROTECTOR_NONE
+ bool "None"
help
- If the compiler supports it, the best available stack-protector
- option will be chosen.
+ Disable "stack-protector" GCC feature.

endchoice

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2.7.4
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