From 5aadfdeb8de001ca04d500586e3b033404c28617 Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Mon, 28 May 2018 18:22:04 +0900 Subject: [PATCH] kcov: test compiler capability in Kconfig and correct dependency 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 Reviewed-by: Kees Cook --- Makefile | 2 +- lib/Kconfig.debug | 11 +++++++---- scripts/Makefile.gcc-plugins | 8 ++------ scripts/Makefile.kcov | 10 ++++++---- scripts/gcc-plugins/Makefile | 4 ---- 5 files changed, 16 insertions(+), 19 deletions(-) diff --git a/Makefile b/Makefile index ca9d98b4a71b..73f0bb2c7a98 100644 --- a/Makefile +++ b/Makefile @@ -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 diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index eb885942eb0f..d543c65ce0eb 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -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 $(cc-option,-fsanitize-coverage=trace-cmp) help KCOV also exposes operands of every comparison in the instrumented code along with operand sizes and PCs of the comparison instructions. @@ -765,7 +768,7 @@ config KCOV_ENABLE_COMPARISONS config KCOV_INSTRUMENT_ALL bool "Instrument all code by default" depends on KCOV - default y if KCOV + default y help If you are doing generic system call fuzzing (like e.g. syzkaller), then you will want to instrument the whole kernel and you should diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins index 7f5c86246138..708c8f6a5717 100644 --- a/scripts/Makefile.gcc-plugins +++ b/scripts/Makefile.gcc-plugins @@ -14,16 +14,12 @@ ifdef CONFIG_GCC_PLUGINS endif ifdef CONFIG_GCC_PLUGIN_SANCOV - ifeq ($(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. diff --git a/scripts/Makefile.kcov b/scripts/Makefile.kcov index 5cc72037e423..3d61c4bfcbee 100644 --- a/scripts/Makefile.kcov +++ b/scripts/Makefile.kcov @@ -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 := $(kcov-flags-y) endif diff --git a/scripts/gcc-plugins/Makefile b/scripts/gcc-plugins/Makefile index e2ff425f4c7e..ea465799ced5 100644 --- a/scripts/gcc-plugins/Makefile +++ b/scripts/gcc-plugins/Makefile @@ -13,10 +13,6 @@ else export HOST_EXTRACXXFLAGS endif -ifneq ($(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