Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753295AbeAINsK (ORCPT + 1 other); Tue, 9 Jan 2018 08:48:10 -0500 Received: from smtp-fw-9102.amazon.com ([207.171.184.29]:57317 "EHLO smtp-fw-9102.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751647AbeAINsH (ORCPT ); Tue, 9 Jan 2018 08:48:07 -0500 X-Amazon-filename: smime.p7s X-IronPort-AV: E=Sophos;i="5.46,335,1511827200"; d="p7s'?scan'208";a="585115561" Message-ID: <1515505210.22302.37.camel@amazon.co.uk> Subject: Re: [PATCH v6 01/10] x86/retpoline: Add initial retpoline support To: Peter Zijlstra , Thomas Gleixner , "Van De Ven, Arjan" CC: Josh Poimboeuf , Andi Kleen , Paul Turner , LKML , "Linus Torvalds" , Greg Kroah-Hartman , Tim Chen , "Dave Hansen" , Kees Cook , "Rik van Riel" , Andy Lutomirski , Jiri Kosina , In-Reply-To: <20180109123631.GH6176@hirez.programming.kicks-ass.net> References: <1515363085-4219-1-git-send-email-dwmw@amazon.co.uk> <1515363085-4219-2-git-send-email-dwmw@amazon.co.uk> <20180108134220.2for3pwgqbmkkq2s@treble> <20180109123631.GH6176@hirez.programming.kicks-ass.net> Face: 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 Organization: Amazon Content-Type: multipart/signed; micalg=sha-256; protocol="application/x-pkcs7-signature"; boundary="=-k+clNWUsGkL7Ei/Kx2QL" Date: Tue, 9 Jan 2018 13:40:10 +0000 X-Mailer: Evolution 3.18.5.2-0ubuntu3.2 MIME-Version: 1.0 From: "Woodhouse, David" X-Evolution-Source: 1481217574.17989.4@uc8d3ff76b9bc5848a9cc Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: --=-k+clNWUsGkL7Ei/Kx2QL Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 2018-01-09 at 13:36 +0100, Peter Zijlstra wrote: > On Mon, Jan 08, 2018 at 02:46:32PM +0100, Thomas Gleixner wrote: > > On Mon, 8 Jan 2018, Josh Poimboeuf wrote: >=20 > > > I wonder if an error might be more appropriate than a warning.=C2=A0 = I > > > learned from experience that a lot of people don't see these Makefile > > > warnings, and this would be a dangerous one to miss. > > >=C2=A0 > > > Also if this were an error, you could get rid of the RETPOLINE define= , > > > and that would be one less define cluttering up the already way-too-l= ong > > > GCC arg list. > >=C2=A0 > > It still allows to get the ASM part covered. If that's worth it I can't= tell. >=20 > So elsewhere you stated we're dropping support for GCC without asm-goto > (<4.5), does it then make sense to make one more step and mandate a > retpoline capable compiler, which would put us at >=3D4.9 (for x86). >=20 > That would get rid of this weird case as well. Yeah... I don't have strong feelings there. Arjan (IIRC) had asked me to keep it this way. The idea was that those were the *easy* targets for an attacker to find; especially in entry_64.S it's asm all the way to the indirect branch. A rootkit might be targeted at entirely unpatched systems which leave that vulnerable, and *even* though there are other targets which could be found with more work, doing just the asm code might well end up protecting from such an attack in practice. The CONFIG_RETPOLINE/!RETPOLINE case isn't really *that* much complexity; I don't really care about that either. On the whole, I'm inclined to leave it as it is without further bikeshedding for now. We can change it later once all those GCC releases have been made with the backports, perhaps. --=-k+clNWUsGkL7Ei/Kx2QL Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCEE4w ggUuMIIEFqADAgECAhEApEtL31g6H7ROXdOiQnA9RjANBgkqhkiG9w0BAQsFADCBlzELMAkGA1UE BhMCR0IxGzAZBgNVBAgTEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4GA1UEBxMHU2FsZm9yZDEaMBgG A1UEChMRQ09NT0RPIENBIExpbWl0ZWQxPTA7BgNVBAMTNENPTU9ETyBSU0EgQ2xpZW50IEF1dGhl bnRpY2F0aW9uIGFuZCBTZWN1cmUgRW1haWwgQ0EwHhcNMTcxMjIxMDAwMDAwWhcNMTgxMjIxMjM1 OTU5WjAiMSAwHgYJKoZIhvcNAQkBFhFkd213QGFtYXpvbi5jby51azCCASIwDQYJKoZIhvcNAQEB BQADggEPADCCAQoCggEBAKdGKgXuwKMg2r+i/4BZZC0ddRxNq3xIKTakie/VCSzoO7P17A36ZzUc VMEYPfqDt/65xoc6Tdih+qkY2pNDppZ1DZ8mVrAX6O2O60ZhmXB60wMoDvXPZInvkMOW4drqnje/ 7/NOypn/XQAY+ln4KT+3tHG3TfryyJFMedqC/r29KJlCeeCxIzdtq2j5mN42tvPVv4+p+Kr77uui 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