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Date: Sun, 12 Jun 2016 15:25:39 -0700
From: Kees Cook <keescook@...omium.org>
To: Emese Revfy <re.emese@...il.com>
Cc: Paul Gortmaker <paul.gortmaker@...driver.com>, Michal Marek <mmarek@...e.com>,
Stephen Rothwell <sfr@...b.auug.org.au>, Sudip Mukherjee <sudipm.mukherjee@...il.com>,
Linux-Next <linux-next@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH] gcc-plugins: disable under COMPILE_TEST
On Sun, Jun 12, 2016 at 3:12 PM, Emese Revfy <re.emese@...il.com> wrote:
> On Sat, 11 Jun 2016 12:29:26 -0400
> Paul Gortmaker <paul.gortmaker@...driver.com> wrote:
>
>> [[PATCH] gcc-plugins: disable under COMPILE_TEST] On 11/06/2016 (Sat 09:12) Kees Cook wrote:
>>
>> > Since adding the gcc plugin development headers is required for the
>> > gcc plugin support, we should ease into this new kernel build dependency
>> > more slowly. For now, disable the gcc plugins under COMPILE_TEST so that
>> > all*config builds will skip it.
>>
>> Wouldn't it be better to test compile a one line program that tries to
>> source the header(s) and then react accordingly?
>
> The scripts/gcc-plugin.sh script does exactly that.
>
>> Then at least you would get the test coverage from people who have the
>> headers installed who are doing all[yes|mod]config. This "for now"
>> solution doesn't really have a path forward other than assuming all
>> distros install the plugin headers sometime in the future.
>>
>> Either way, this is an improvement over the current situation, so thanks
>> for that.
>
> If it is not too late I think this patch would be better:
I don't like this because it means if someone specifically selects
some plugins in their .config, and the headers are missing, the kernel
will successfully compile. For many plugins, this results in a kernel
that lacks the requested security features, and that I really do not
want to have happening. I'm okay leaving these disabled for compile
tests for now. We can revisit this once more distros have plugins
enabled by default.
-Kees
>
>
> When there is no gcc plugin support then don't compile the plugins
> (but still print a warning). This allows building allyes/allmod configs
> until the gcc plugin headers get installed.
>
> Signed-off-by: Emese Revfy <re.emese@...il.com>
> ---
> Makefile | 6 +++---
> scripts/Makefile.gcc-plugins | 8 ++++----
> 2 files changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index a49c075..715210c 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -623,15 +623,15 @@ endif
> # Tell gcc to never replace conditional load with a non-conditional one
> KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0)
>
> +include scripts/Makefile.gcc-plugins
> +
> PHONY += gcc-plugins
> gcc-plugins: scripts_basic
> -ifdef CONFIG_GCC_PLUGINS
> +ifneq ($(GCC_PLUGINS_CFLAGS),)
> $(Q)$(MAKE) $(build)=scripts/gcc-plugins
> endif
> @:
>
> -include scripts/Makefile.gcc-plugins
> -
> ifdef CONFIG_READABLE_ASM
> # Disable optimizations that make assembler listings hard to read.
> # reorder blocks reorders the control in the function
> diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
> index c7372cb..2f101ea 100644
> --- a/scripts/Makefile.gcc-plugins
> +++ b/scripts/Makefile.gcc-plugins
> @@ -21,6 +21,7 @@ ifdef CONFIG_GCC_PLUGINS
> CFLAGS_KCOV := $(SANCOV_PLUGIN)
> else
> $(warning warning: cannot use CONFIG_KCOV: -fsanitize-coverage=trace-pc is not supported by compiler)
> + CFLAGS_KCOV =
> endif
> endif
> endif
> @@ -37,13 +38,12 @@ ifdef CONFIG_GCC_PLUGINS
> else
> $(warning warning: your gcc version does not support plugins, you should upgrade it to gcc 4.5 at least)
> endif
> + GCC_PLUGINS_CFLAGS =
> endif
> - else
> - # SANCOV_PLUGIN can be only in CFLAGS_KCOV because avoid duplication.
> - GCC_PLUGINS_CFLAGS := $(filter-out $(SANCOV_PLUGIN), $(GCC_PLUGINS_CFLAGS))
> endif
>
> - KBUILD_CFLAGS += $(GCC_PLUGINS_CFLAGS)
> + # SANCOV_PLUGIN can be only in CFLAGS_KCOV because avoid duplication.
> + KBUILD_CFLAGS += $(filter-out $(SANCOV_PLUGIN), $(GCC_PLUGINS_CFLAGS))
> GCC_PLUGIN := $(gcc-plugin-y)
>
> endif
>
> --
> 2.8.1
--
Kees Cook
Chrome OS & Brillo Security
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