[v2,16/21] kcov: imply GCC_PLUGINS and GCC_PLUGIN_SANCOV instead of select'ing them

Message ID 1522128575-5326-17-git-send-email-yamada.masahiro@socionext.com
State New
Headers show
Series
  • kconfig: move compiler capability tests to Kconfig
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Commit Message

Masahiro Yamada March 27, 2018, 5:29 a.m.
As Documentation/kbuild/kconfig-language.txt notes, 'select' should be
used with care - it forces a lower limit of another symbol, ignoring
the dependency.  In this case, KCOV can select GCC_PLUGINS even if
'depends on HAVE_GCC_PLUGINS' is unmet.

'imply' is modest enough to observe the dependency, and this makes
sense.  If you enable KCOV, you will probably want to enable
GCC_PLUGIN_SANCOV, but it should not break the dependency.

I also remove unneeded code, I just happened to notice.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

  - Drop depends on GCC_VERSION

---

Changes in v2: None

 lib/Kconfig.debug | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

-- 
2.7.4

Comments

Kees Cook March 28, 2018, 11:25 a.m. | #1
On Mon, Mar 26, 2018 at 10:29 PM, Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
> As Documentation/kbuild/kconfig-language.txt notes, 'select' should be

> used with care - it forces a lower limit of another symbol, ignoring

> the dependency.  In this case, KCOV can select GCC_PLUGINS even if

> 'depends on HAVE_GCC_PLUGINS' is unmet.

>

> 'imply' is modest enough to observe the dependency, and this makes

> sense.  If you enable KCOV, you will probably want to enable

> GCC_PLUGIN_SANCOV, but it should not break the dependency.

>

> I also remove unneeded code, I just happened to notice.

>

> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>


Reviewed-by: Kees Cook <keescook@chromium.org>


-Kees

-- 
Kees Cook
Pixel Security
Kees Cook March 28, 2018, 11:53 a.m. | #2
On Mon, Mar 26, 2018 at 10:29 PM, Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
> As Documentation/kbuild/kconfig-language.txt notes, 'select' should be

> used with care - it forces a lower limit of another symbol, ignoring

> the dependency.  In this case, KCOV can select GCC_PLUGINS even if

> 'depends on HAVE_GCC_PLUGINS' is unmet.

>

> 'imply' is modest enough to observe the dependency, and this makes

> sense.  If you enable KCOV, you will probably want to enable

> GCC_PLUGIN_SANCOV, but it should not break the dependency.

>

> I also remove unneeded code, I just happened to notice.

>

> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

>   - Drop depends on GCC_VERSION

>

> ---

>

> Changes in v2: None

>

>  lib/Kconfig.debug | 7 +++----

>  1 file changed, 3 insertions(+), 4 deletions(-)

>

> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug

> index 5be22e4..8243c9d 100644

> --- a/lib/Kconfig.debug

> +++ b/lib/Kconfig.debug

> @@ -743,8 +743,8 @@ config KCOV

>         bool "Code coverage for fuzzing"

>         depends on ARCH_HAS_KCOV

>         select DEBUG_FS

> -       select GCC_PLUGINS if !COMPILE_TEST

> -       select GCC_PLUGIN_SANCOV if !COMPILE_TEST

> +       imply GCC_PLUGINS

> +       imply GCC_PLUGIN_SANCOV

>         help

>           KCOV exposes kernel code coverage information in a form suitable

>           for coverage-guided fuzzing (randomized testing).


Actually, I think this can be improved, as KCOV should depend on either:

-fsanitize-coverage=trace-pc support (in gcc 6+, see scripts/Makefile.kcov)

or

GCC_PLUGIN_SANCOV (which provides the trace-pc support via the plugin
for gcc before 6)

> @@ -758,7 +758,6 @@ config KCOV

>  config KCOV_ENABLE_COMPARISONS

>         bool "Enable comparison operands collection by KCOV"

>         depends on KCOV

> -       default n

>         help

>           KCOV also exposes operands of every comparison in the instrumented

>           code along with operand sizes and PCs of the comparison instructions.


Similarly, this depends on -fsanitize-coverage=trace-cmp

> @@ -768,7 +767,7 @@ 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

> --

> 2.7.4

>


-Kees

-- 
Kees Cook
Pixel Security

Patch

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 5be22e4..8243c9d 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -743,8 +743,8 @@  config KCOV
 	bool "Code coverage for fuzzing"
 	depends on ARCH_HAS_KCOV
 	select DEBUG_FS
-	select GCC_PLUGINS if !COMPILE_TEST
-	select GCC_PLUGIN_SANCOV if !COMPILE_TEST
+	imply GCC_PLUGINS
+	imply GCC_PLUGIN_SANCOV
 	help
 	  KCOV exposes kernel code coverage information in a form suitable
 	  for coverage-guided fuzzing (randomized testing).
@@ -758,7 +758,6 @@  config KCOV
 config KCOV_ENABLE_COMPARISONS
 	bool "Enable comparison operands collection by KCOV"
 	depends on KCOV
-	default n
 	help
 	  KCOV also exposes operands of every comparison in the instrumented
 	  code along with operand sizes and PCs of the comparison instructions.
@@ -768,7 +767,7 @@  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