Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752432AbeAEQmb (ORCPT + 1 other); Fri, 5 Jan 2018 11:42:31 -0500 Received: from smtp-fw-9102.amazon.com ([207.171.184.29]:25226 "EHLO smtp-fw-9102.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752412AbeAEQm2 (ORCPT ); Fri, 5 Jan 2018 11:42:28 -0500 X-Amazon-filename: smime.p7s X-IronPort-AV: E=Sophos;i="5.46,318,1511827200"; d="p7s'?scan'208";a="584397194" Message-ID: <1515170506.29312.149.camel@amazon.co.uk> Subject: Re: [PATCH v3 01/13] x86/retpoline: Add initial retpoline support To: Thomas Gleixner , Borislav Petkov CC: , Paul Turner , LKML , Linus Torvalds , Greg Kroah-Hartman , Tim Chen , "Dave Hansen" , Kees Cook , "Rik van Riel" , Peter Zijlstra , "Andy Lutomirski" , Jiri Kosina , In-Reply-To: <1515160619.29312.126.camel@amazon.co.uk> References: <1515058213.12987.89.camel@amazon.co.uk> <20180104143710.8961-1-dwmw@amazon.co.uk> <1515160619.29312.126.camel@amazon.co.uk> Face: 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 Organization: Amazon Content-Type: multipart/signed; micalg=sha-256; protocol="application/x-pkcs7-signature"; boundary="=-2Tpqvgb2qDK4eHUVB8sK" Date: Fri, 5 Jan 2018 16:41:46 +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: --=-2Tpqvgb2qDK4eHUVB8sK Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2018-01-05 at 13:56 +0000, Woodhouse, David wrote: >=20 > At some point during this whole painful mess, I had come to the > conclusion that having relocations in altinstr didn't work, and that's > why I had X86_xx_NO_RETPOLINE instead of X86_xx_RETPOLINE. I now think > that something else was wrong when I was testing that, and relocs in > altinstr do work. So sure, X86_FEATURE_RETPOLINE ought to work. I can > change that round, and it's simpler for the IBRS patch set to take it > into account and set it when appropriate. +bpetkov Nope, alternatives are broken. Only a jmp as the *first* opcode of altinstr gets handled by recompute_jump(), while any subsequent insn is just copied untouched. To fix that and handle every instruction, the alternative code would need to know about instruction lengths. I think we need to stick with the inverted X86_FEATURE_NO_RETPOLINE flag for the moment, and not tie it to a complex bugfix there. --=-2Tpqvgb2qDK4eHUVB8sK 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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