From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Rutland Date: Tue, 03 Oct 2017 10:04:33 +0000 Subject: Re: [kernel-hardening] [PATCH 0/3] Makefile: Introduce CONFIG_CC_STACKPROTECTOR_AUTO Message-Id: <20171003100433.GA4931@leverpostej> List-Id: References: <1506972007-80614-1-git-send-email-keescook@chromium.org> In-Reply-To: <1506972007-80614-1-git-send-email-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Kees Cook Cc: Andrew Morton , Masahiro Yamada , Michal Marek , Yoshinori Sato , Rich Felker , Ingo Molnar , "David S. Miller" , Nicholas Piggin , Al Viro , Laura Abbott , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-sh@vger.kernel.org, kernel-hardening@lists.openwall.com Hi Kees, On Mon, Oct 02, 2017 at 12:20:04PM -0700, Kees Cook wrote: > As described in the final patch: > > Nearly all modern compilers support a stack-protector option, and nearly > all modern distributions enable the kernel stack-protector, so enabling > this by default in kernel builds would make sense. However, Kconfig does > not have knowledge of available compiler features, so it isn't safe to > force on, as this would unconditionally break builds for the compilers > or architectures that don't have support. Instead, this introduces a new > option, CONFIG_CC_STACKPROTECTOR_AUTO, which attempts to discover the best > possible stack-protector available, and will allow builds to proceed even > if the compiler doesn't support any stack-protector. > > This option is made the default so that kernels built with modern > compilers will be protected-by-default against stack buffer overflows, > avoiding things like the recent BlueBorne attack. Selection of a specific > stack-protector option remains available, including disabling it. I gave this a spin atop of v4.14-rc3 with a few arm64 toolchains I had installed: * Linaro 17.08 GCC 7.1 // strong * Linaro 17.05 GCC 6.1 // strong * Linaro 15.08 GCC 5.1 // strong * Linaro 14.09 GCC 4.9 // strong * Linaro 13.06 GCC 4.8 // none * Linaro 13.01 GCC 4.7 // none AFAICT, the detection is correct, and arm64 toolchains only gained stack protector support in GCC 4.9. I manually tested GCC 4.8 and 4.7, and got: warning: -fstack-protector not supported for this target [enabled by default] ... so that looks good to me. One thing I noticed was taht even when the build system detects no support for stack-protector, it still passes -DCONFIG_CC_STACKPROTECTOR to the toolchain. Is that expected? Thanks, Mark. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751638AbdJCKGK (ORCPT ); Tue, 3 Oct 2017 06:06:10 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:46350 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751450AbdJCKGI (ORCPT ); Tue, 3 Oct 2017 06:06:08 -0400 Date: Tue, 3 Oct 2017 11:04:33 +0100 From: Mark Rutland To: Kees Cook Cc: Andrew Morton , Masahiro Yamada , Michal Marek , Yoshinori Sato , Rich Felker , Ingo Molnar , "David S. Miller" , Nicholas Piggin , Al Viro , Laura Abbott , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-sh@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: Re: [kernel-hardening] [PATCH 0/3] Makefile: Introduce CONFIG_CC_STACKPROTECTOR_AUTO Message-ID: <20171003100433.GA4931@leverpostej> References: <1506972007-80614-1-git-send-email-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1506972007-80614-1-git-send-email-keescook@chromium.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Kees, On Mon, Oct 02, 2017 at 12:20:04PM -0700, Kees Cook wrote: > As described in the final patch: > > Nearly all modern compilers support a stack-protector option, and nearly > all modern distributions enable the kernel stack-protector, so enabling > this by default in kernel builds would make sense. However, Kconfig does > not have knowledge of available compiler features, so it isn't safe to > force on, as this would unconditionally break builds for the compilers > or architectures that don't have support. Instead, this introduces a new > option, CONFIG_CC_STACKPROTECTOR_AUTO, which attempts to discover the best > possible stack-protector available, and will allow builds to proceed even > if the compiler doesn't support any stack-protector. > > This option is made the default so that kernels built with modern > compilers will be protected-by-default against stack buffer overflows, > avoiding things like the recent BlueBorne attack. Selection of a specific > stack-protector option remains available, including disabling it. I gave this a spin atop of v4.14-rc3 with a few arm64 toolchains I had installed: * Linaro 17.08 GCC 7.1 // strong * Linaro 17.05 GCC 6.1 // strong * Linaro 15.08 GCC 5.1 // strong * Linaro 14.09 GCC 4.9 // strong * Linaro 13.06 GCC 4.8 // none * Linaro 13.01 GCC 4.7 // none AFAICT, the detection is correct, and arm64 toolchains only gained stack protector support in GCC 4.9. I manually tested GCC 4.8 and 4.7, and got: warning: -fstack-protector not supported for this target [enabled by default] ... so that looks good to me. One thing I noticed was taht even when the build system detects no support for stack-protector, it still passes -DCONFIG_CC_STACKPROTECTOR to the toolchain. Is that expected? Thanks, Mark.