Commit a4691dea authored Aug 02, 2016 by Vegard Nossum Committed by Linus Torvalds Aug 02, 2016

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 <vegard.nossum@oracle.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent f1cb637e

lib/Kconfig.debug

+11 −0

Original line number	Diff line number	Diff line
		@@ -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

scripts/Makefile.lib

+1 −1

Original line number	Diff line number	Diff line
		@@ -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

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