From a4691deabf284a601149a067525759939cc563b2 Mon Sep 17 00:00:00 2001 From: Vegard Nossum Date: Tue, 2 Aug 2016 14:07:30 -0700 Subject: [PATCH] kcov: allow more fine-grained coverage instrumentation For more targeted fuzzing, it's better to disable kernel-wide instrumentation and instead enable it on a per-subsystem basis. This follows the pattern of UBSAN and allows you to compile in the kcov driver without instrumenting the whole kernel. To instrument a part of the kernel, you can use either # for a single file in the current directory KCOV_INSTRUMENT_filename.o := y or # for all the files in the current directory (excluding subdirectories) KCOV_INSTRUMENT := y or # (same as above) ccflags-y += $(CFLAGS_KCOV) or # for all the files in the current directory (including subdirectories) subdir-ccflags-y += $(CFLAGS_KCOV) Link: http://lkml.kernel.org/r/1464008380-11405-1-git-send-email-vegard.nossum@oracle.com Signed-off-by: Vegard Nossum Cc: Dmitry Vyukov Cc: Quentin Casasnovas Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/Kconfig.debug | 11 +++++++++++ scripts/Makefile.lib | 2 +- 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index f07842e2d69f..cc02f282d05b 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -719,6 +719,17 @@ config KCOV For more details, see Documentation/kcov.txt. +config KCOV_INSTRUMENT_ALL + bool "Instrument all code by default" + depends on KCOV + default y if KCOV + help + If you are doing generic system call fuzzing (like e.g. syzkaller), + then you will want to instrument the whole kernel and you should + say y here. If you are doing more targeted fuzzing (like e.g. + filesystem fuzzing with AFL) then you will want to enable coverage + for more specific subsets of files, and should say n here. + config DEBUG_SHIRQ bool "Debug shared IRQ handlers" depends on DEBUG_KERNEL diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib index e7df0f5db7ec..76494e15417b 100644 --- a/scripts/Makefile.lib +++ b/scripts/Makefile.lib @@ -138,7 +138,7 @@ endif ifeq ($(CONFIG_KCOV),y) _c_flags += $(if $(patsubst n%,, \ - $(KCOV_INSTRUMENT_$(basetarget).o)$(KCOV_INSTRUMENT)y), \ + $(KCOV_INSTRUMENT_$(basetarget).o)$(KCOV_INSTRUMENT)$(CONFIG_KCOV_INSTRUMENT_ALL)), \ $(CFLAGS_KCOV)) endif -- 2.20.1