linux-kernel - Re: [patch core/stackprotector] stackprotector: Fix build when compiler lacks support

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Date:	Mon, 30 Dec 2013 16:45:44 -0800
From:	Kees Cook <keescook@...omium.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	ralf@...ux-mips.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	James Hogan <james.hogan@...tec.com>,
	Michal Marek <mmarek@...e.cz>,
	Paul Mundt <lethal@...ux-sh.org>,
	Shawn Guo <shawn.guo@...aro.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-kbuild <linux-kbuild@...r.kernel.org>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [patch core/stackprotector] stackprotector: Fix build when
 compiler lacks support

On Mon, Dec 30, 2013 at 1:37 PM, David Rientjes <rientjes@...gle.com> wrote:
> 8779657d29c0 ("stackprotector: Introduce CONFIG_CC_STACKPROTECTOR_STRONG")
> causes the build to break when the compiler doesn't support
> -fstack-protector-strong:
>
>         cc1: error: unrecognized command line option ‘-fstack-protector-strong’
>         cc1: error: unrecognized command line option ‘-fstack-protector-strong’
>
> with at least gcc 4.6.3.
>
> Instead of breaking the build, just warn of the failure and disable the
> feature.

NAK. If you have selected CONFIG_CC_STACKPROTECTOR_STRONG, the build
the fail hard. Without this, it means you'll end up with kernels that
build and show a stackprotector option in their config, which is
false.

-Kees

>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
>  Makefile | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/Makefile b/Makefile
> --- a/Makefile
> +++ b/Makefile
> @@ -603,10 +603,11 @@ ifdef CONFIG_CC_STACKPROTECTOR_REGULAR
>               -fstack-protector not supported by compiler))
>    endif
>  else ifdef CONFIG_CC_STACKPROTECTOR_STRONG
> -  stackp-flag := -fstack-protector-strong
> -  ifeq ($(call cc-option, $(stackp-flag)),)
> +  ifeq ($(call cc-option, -fstack-protector-strong),)
>      $(warning Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: \
>               -fstack-protector-strong not supported by compiler)
> +  else
> +    stackp-flag := -fstack-protector-strong
>    endif
>  else
>    # Force off for distro compilers that enable stack protector by default.



-- 
Kees Cook
Chrome OS Security
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