From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8A87BC43464 for ; Fri, 18 Sep 2020 21:40:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3EB7320848 for ; Fri, 18 Sep 2020 21:40:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726168AbgIRVkZ (ORCPT ); Fri, 18 Sep 2020 17:40:25 -0400 Received: from jabberwock.ucw.cz ([46.255.230.98]:36612 "EHLO jabberwock.ucw.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726139AbgIRVkY (ORCPT ); Fri, 18 Sep 2020 17:40:24 -0400 Received: by jabberwock.ucw.cz (Postfix, from userid 1017) id 19EEE1C0B78; Fri, 18 Sep 2020 23:40:21 +0200 (CEST) Date: Fri, 18 Sep 2020 23:40:20 +0200 From: Pavel Machek To: "Yu, Yu-cheng" Cc: Randy Dunlap , x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Peter Zijlstra , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang Subject: Re: [PATCH v12 1/8] x86/cet/ibt: Add Kconfig option for user-mode Indirect Branch Tracking Message-ID: <20200918214020.GF4304@duo.ucw.cz> References: <20200918192312.25978-1-yu-cheng.yu@intel.com> <20200918192312.25978-2-yu-cheng.yu@intel.com> <20200918205933.GB4304@duo.ucw.cz> <019b5e45-b116-7f3d-f1f2-3680afbd676c@intel.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="AH+kv8CCoFf6qPuz" Content-Disposition: inline In-Reply-To: <019b5e45-b116-7f3d-f1f2-3680afbd676c@intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org --AH+kv8CCoFf6qPuz Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri 2020-09-18 14:25:12, Yu, Yu-cheng wrote: > On 9/18/2020 1:59 PM, Pavel Machek wrote: > > On Fri 2020-09-18 13:24:13, Randy Dunlap wrote: > > > Hi, > > >=20 > > > If you do another version of this: > > >=20 > > > On 9/18/20 12:23 PM, Yu-cheng Yu wrote: > > > > Introduce Kconfig option X86_INTEL_BRANCH_TRACKING_USER. > > > >=20 > > > > Indirect Branch Tracking (IBT) provides protection against CALL-/JM= P- > > > > oriented programming attacks. It is active when the kernel has this > > > > feature enabled, and the processor and the application support it. > > > > When this feature is enabled, legacy non-IBT applications continue = to > > > > work, but without IBT protection. > > > >=20 > > > > Signed-off-by: Yu-cheng Yu > > > > --- > > > > v10: > > > > - Change build-time CET check to config depends on. > > > >=20 > > > > arch/x86/Kconfig | 16 ++++++++++++++++ > > > > 1 file changed, 16 insertions(+) > > > >=20 > > > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > > > > index 6b6dad011763..b047e0a8d1c2 100644 > > > > --- a/arch/x86/Kconfig > > > > +++ b/arch/x86/Kconfig > > > > @@ -1963,6 +1963,22 @@ config X86_INTEL_SHADOW_STACK_USER > > > > If unsure, say y. > > > > +config X86_INTEL_BRANCH_TRACKING_USER > > > > + prompt "Intel Indirect Branch Tracking for user-mode" > > > > + def_bool n > > > > + depends on CPU_SUP_INTEL && X86_64 > > > > + depends on $(cc-option,-fcf-protection) > > > > + select X86_INTEL_CET > > > > + help > > > > + Indirect Branch Tracking (IBT) provides protection against > > > > + CALL-/JMP-oriented programming attacks. It is active when > > > > + the kernel has this feature enabled, and the processor and > > > > + the application support it. When this feature is enabled, > > > > + legacy non-IBT applications continue to work, but without > > > > + IBT protection. > > > > + > > > > + If unsure, say y > > >=20 > > > If unsure, say y. > >=20 > > Actually, it would be "If unsure, say Y.", to be consistent with the > > rest of the Kconfig. > >=20 > > But I wonder if Yes by default is good idea. Only very new CPUs will > > support this, right? Are they even available at the market? Should the > > help text say "if your CPU is Whatever Lake or newer, ...." :-) ? >=20 > I will revise the wording if there is another version. But a CET-capable > kernel can run on legacy systems. We have been testing that combination. Yes, but enabling CET is unneccessary overhead on older systems. And Kconfig is great place to explain that. Best regards, Pavel --=20 (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo= g.html --AH+kv8CCoFf6qPuz Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iF0EABECAB0WIQRPfPO7r0eAhk010v0w5/Bqldv68gUCX2UpRAAKCRAw5/Bqldv6 8tKaAJoCjw1dkJHdYlkUkB4fM1+kRrBkbACfTbioBaGJ8ZtKgM0RqUOnLeG0ipE= =cAzW -----END PGP SIGNATURE----- --AH+kv8CCoFf6qPuz--