Date: Fri, 1 Feb 2019 15:56:07 -0800 From: Thomas Garnier <thgarnie@...omium.org> To: Andy Lutomirski <luto@...capital.net> Cc: Andy Lutomirski <luto@...nel.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, Kristen Carlson Accardi <kristen@...ux.intel.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>, Masahiro Yamada <yamada.masahiro@...ionext.com>, Juergen Gross <jgross@...e.com>, Joerg Roedel <jroedel@...e.de>, Jia Zhang <qianyue.zj@...baba-inc.com>, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, Tim Chen <tim.c.chen@...ux.intel.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v6 20/27] x86: Support global stack cookie On Fri, Feb 1, 2019 at 2:36 PM Andy Lutomirski <luto@...capital.net> wrote: > > > > On Feb 1, 2019, at 12:21 PM, Thomas Garnier <thgarnie@...omium.org> wrote: > > > >> On Fri, Feb 1, 2019 at 11:27 AM Andy Lutomirski <luto@...nel.org> wrote: > >> > >>> On Thu, Jan 31, 2019 at 11:29 AM Thomas Garnier <thgarnie@...omium.org> wrote: > >>> > >>> Add an off-by-default configuration option to use a global stack cookie > >>> instead of the default TLS. This configuration option will only be used > >>> with PIE binaries. > >>> > >>> For kernel stack cookie, the compiler uses the mcmodel=kernel to switch > >>> between the fs segment to gs segment. A PIE binary does not use > >>> mcmodel=kernel because it can be relocated anywhere, therefore the > >>> compiler will default to the fs segment register. This is fixed on the > >>> latest version of gcc. > >> > >> I hate all these gcc-sucks-so-we-hack-it-and-change-nasty-semantics > >> options. How about just preventing use of both stack protector and > >> PIE unless the version of gcc in use is new enough. > > > > So fail the build in this scenario? > > Fail the build or use some Kconfig magic to prevent this from being configured in the first place. Ok, I can do that in next iteration. > > > > >> > >> Also, does -mstack-protector-guard-reg not solve this? See > >> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81708. Or is there > >> another bug? Or are you worried about gcc versions that don't have > >> that feature yet? > > > > I am worried about gcc versions that don't have this feature, yes.
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