From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933697AbeAJKFx (ORCPT + 1 other); Wed, 10 Jan 2018 05:05:53 -0500 Received: from twosheds.infradead.org ([90.155.92.209]:59002 "EHLO twosheds.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751284AbeAJKFv (ORCPT ); Wed, 10 Jan 2018 05:05:51 -0500 Message-ID: <1515578735.22302.91.camel@infradead.org> Subject: Re: [PATCH] x86/retpoline: Fix NOSPEC_JMP for tip From: David Woodhouse To: Linus Torvalds , Andi Kleen , Borislav Petkov Cc: Thomas Gleixner , the arch/x86 maintainers , Linux Kernel Mailing List , Paul Turner , Andrew Lutomirski , Peter Zijlstra , Tom Lendacky , Tim Chen , Greg Kroah-Hartman , Dave Hansen , Jiri Kosina , Andi Kleen In-Reply-To: <1515568506.22302.72.camel@infradead.org> References: <20180110003139.10531-1-andi@firstfloor.org> <1515568506.22302.72.camel@infradead.org> Face: 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 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-4KxbCa6sQdMobkWOE6oF" Date: Wed, 10 Jan 2018 10:05:35 +0000 Mime-Version: 1.0 X-Mailer: Evolution 3.18.5.2-0ubuntu3.2 X-SRS-Rewrite: SMTP reverse-path rewritten from by twosheds.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: --=-4KxbCa6sQdMobkWOE6oF Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2018-01-10 at 07:15 +0000, David Woodhouse wrote: > I'd really like to know what went wrong though. Did we merge Borislav's > attempt to peek at jumps inside alternatives, perchance? Will take a > look... Ah, it only happens if I run in KVM, not with Qemu's CPU; that's why it didn't show up in my testing. And it seems to have been introduced by the addition of '.align 16' at the start of the RETPOLINE_JMP macro. So this fixes it: --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -15,7 +15,6 @@ =C2=A0 * invocation below less ugly. =C2=A0 */ =C2=A0.macro RETPOLINE_JMP reg:req -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0.align=C2=A0=C2=A016 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0call=C2=A0=C2=A0=C2=A0=C2= =A0.Ldo_rop_\@ =C2=A0.Lspec_trap_\@: =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0pause Borislav? Want to take a look at that please? I'm going to go ahead and apply Andi's patches anyway. Once I admit that I shoved the .align in there to precisely match up with Paul's sequence, and since Linus got me to inline the thing at all the call sites instead of using the out-of-line thunk, I don't think an objection of "but it adds some extra bytes for the separate lfence" is going to work... :) But actually, I think I may also rip out the .align there. Because inside alternatives it doesn't make a lot of sense. It may have aligned the code by padding with NOPs in its *original* location, but once it gets copied into the place it's executed from, the alignment could be different. --=-4KxbCa6sQdMobkWOE6oF Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCEFQw ggUxMIIEGaADAgECAhBNRhEyk/HZ7naOeTHWrzuAMA0GCSqGSIb3DQEBCwUAMIGXMQswCQYDVQQG EwJHQjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxmb3JkMRowGAYD VQQKExFDT01PRE8gQ0EgTGltaXRlZDE9MDsGA1UEAxM0Q09NT0RPIFJTQSBDbGllbnQgQXV0aGVu dGljYXRpb24gYW5kIFNlY3VyZSBFbWFpbCBDQTAeFw0xNzEyMjEwMDAwMDBaFw0xODEyMjEyMzU5 NTlaMCQxIjAgBgkqhkiG9w0BCQEWE2R3bXcyQGluZnJhZGVhZC5vcmcwggEiMA0GCSqGSIb3DQEB AQUAA4IBDwAwggEKAoIBAQDgzLNWa18DNpGUj/ZeH0Sgz53ESIbzdPw3OJeuNP6jZhxZojbyfxbM hETscxI/Hj6UZ4a7sHm5BkVjlsB1Af2Za/PXUt8MmLAcPMHkMPGunvkUibEvblDvpqMkQZlaZM+t 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