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kcov: test compiler capability in Kconfig and correct dependency

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As Documentation/kbuild/kconfig-language.txt notes, 'select' should be
be used with care - it forces a lower limit of another symbol, ignoring
the dependency.  Currently, KCOV can select GCC_PLUGINS even if arch
does not select HAVE_GCC_PLUGINS.  This could cause the unmet direct
dependency.

Now that Kconfig can test compiler capability, let's handle this in a
more sophisticated way.

There are two ways to enable KCOV; use the compiler that natively
supports -fsanitize-coverage=trace-pc, or build the SANCOV plugin if
the compiler has ability to build GCC plugins.  Hence, the correct
dependency for KCOV is:

  depends on CC_HAS_SANCOV_TRACE_PC || GCC_PLUGINS

You do not need to build the SANCOV plugin if the compiler already
supports -fsanitize-coverage=trace-pc.  Hence, the select should be:

  select GCC_PLUGIN_SANCOV if !CC_HAS_SANCOV_TRACE_PC

With this, GCC_PLUGIN_SANCOV is selected only when necessary, so
scripts/Makefile.gcc-plugins can be cleaner.

I also cleaned up Kconfig and scripts/Makefile.kcov as well.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Masahiro Yamada 2018-05-28 18:22:04 +09:00
parent 6a61b70b43
commit 5aadfdeb8d
5 changed files with 16 additions and 19 deletions
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2
Makefile
View file

@ -601,7 +601,7 @@ all: vmlinux
CFLAGS_GCOV := -fprofile-arcs -ftest-coverage \
$(call cc-option,-fno-tree-loop-im) \
$(call cc-disable-warning,maybe-uninitialized,)
export CFLAGS_GCOV CFLAGS_KCOV
export CFLAGS_GCOV
# The arch Makefile can set ARCH_{CPP,A,C}FLAGS to override the default
# values of the respective KBUILD_* variables

11
lib/Kconfig.debug
View file

@ -736,12 +736,15 @@ config ARCH_HAS_KCOV
only for x86_64. KCOV requires testing on other archs, and most likely
disabling of instrumentation for some early boot code.
config CC_HAS_SANCOV_TRACE_PC
def_bool $(cc-option,-fsanitize-coverage=trace-pc)
config KCOV
bool "Code coverage for fuzzing"
depends on ARCH_HAS_KCOV
depends on CC_HAS_SANCOV_TRACE_PC || GCC_PLUGINS
select DEBUG_FS
select GCC_PLUGINS if !COMPILE_TEST
select GCC_PLUGIN_SANCOV if !COMPILE_TEST
select GCC_PLUGIN_SANCOV if !CC_HAS_SANCOV_TRACE_PC
help
KCOV exposes kernel code coverage information in a form suitable
for coverage-guided fuzzing (randomized testing).
@ -755,7 +758,7 @@ config KCOV
config KCOV_ENABLE_COMPARISONS
bool "Enable comparison operands collection by KCOV"
depends on KCOV
default n
depends on $(cc-option,-fsanitize-coverage=trace-cmp)
help
KCOV also exposes operands of every comparison in the instrumented
code along with operand sizes and PCs of the comparison instructions.
@ -765,7 +768,7 @@ config KCOV_ENABLE_COMPARISONS
config KCOV_INSTRUMENT_ALL
bool "Instrument all code by default"
depends on KCOV
default y if KCOV
default y
help
If you are doing generic system call fuzzing (like e.g. syzkaller),
then you will want to instrument the whole kernel and you should

8
scripts/Makefile.gcc-plugins
View file

@ -14,16 +14,12 @@ ifdef CONFIG_GCC_PLUGINS
endif
ifdef CONFIG_GCC_PLUGIN_SANCOV
ifeq ($(strip $(CFLAGS_KCOV)),)
# It is needed because of the gcc-plugin.sh and gcc version checks.
gcc-plugin-$(CONFIG_GCC_PLUGIN_SANCOV) += sancov_plugin.so
ifneq ($(PLUGINCC),)
CFLAGS_KCOV := $(SANCOV_PLUGIN)
else
ifeq ($(PLUGINCC),)
$(warning warning: cannot use CONFIG_KCOV: -fsanitize-coverage=trace-pc is not supported by compiler)
endif
endif
endif
gcc-plugin-$(CONFIG_GCC_PLUGIN_STRUCTLEAK) += structleak_plugin.so
@ -38,7 +34,7 @@ ifdef CONFIG_GCC_PLUGINS
GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y))
export PLUGINCC GCC_PLUGINS_CFLAGS GCC_PLUGIN GCC_PLUGIN_SUBDIR
export SANCOV_PLUGIN DISABLE_LATENT_ENTROPY_PLUGIN
export DISABLE_LATENT_ENTROPY_PLUGIN
ifneq ($(PLUGINCC),)
# SANCOV_PLUGIN can be only in CFLAGS_KCOV because avoid duplication.

10
scripts/Makefile.kcov
View file

@ -1,7 +1,9 @@
ifdef CONFIG_KCOV
CFLAGS_KCOV := $(call cc-option,-fsanitize-coverage=trace-pc,)
ifeq ($(CONFIG_KCOV_ENABLE_COMPARISONS),y)
CFLAGS_KCOV += $(call cc-option,-fsanitize-coverage=trace-cmp,)
endif
kcov-flags-$(CONFIG_CC_HAS_SANCOV_TRACE_PC) += -fsanitize-coverage=trace-pc
kcov-flags-$(CONFIG_KCOV_ENABLE_COMPARISONS) += -fsanitize-coverage=trace-cmp
kcov-flags-$(CONFIG_GCC_PLUGIN_SANCOV) += -fplugin=$(objtree)/scripts/gcc-plugins/sancov_plugin.so
export CFLAGS_KCOV := $(kcov-flags-y)
endif

4
scripts/gcc-plugins/Makefile
View file

@ -13,10 +13,6 @@ else
export HOST_EXTRACXXFLAGS
endif
ifneq ($(CFLAGS_KCOV), $(SANCOV_PLUGIN))
GCC_PLUGIN := $(filter-out $(SANCOV_PLUGIN), $(GCC_PLUGIN))
endif
export HOSTLIBS
$(obj)/randomize_layout_plugin.o: $(objtree)/$(obj)/randomize_layout_seed.h