Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965652AbeAJMaH (ORCPT + 1 other); Wed, 10 Jan 2018 07:30:07 -0500 Received: from twosheds.infradead.org ([90.155.92.209]:40252 "EHLO twosheds.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965508AbeAJMaD (ORCPT ); Wed, 10 Jan 2018 07:30:03 -0500 Message-ID: <1515587384.22302.132.camel@infradead.org> Subject: Re: [patch RFC 5/5] x86/speculation: Add basic speculation control code From: David Woodhouse To: Andrea Arcangeli Cc: Peter Zijlstra , Dave Hansen , Thomas Gleixner , LKML , Linus Torvalds , x86@kernel.org, Borislav Petkov , Tim Chen , Andi Kleen , Greg KH , Andy Lutomirski , Arjan Van De Ven In-Reply-To: <20180110121755.GD9706@redhat.com> References: <20180110010652.404145126@linutronix.de> <20180110011350.855878109@linutronix.de> <20180110092234.GY29822@worktop.programming.kicks-ass.net> <1515576479.22302.81.camel@infradead.org> <20180110115419.GA9706@redhat.com> <1515585534.22302.122.camel@infradead.org> <20180110120158.GB9706@redhat.com> <1515586174.22302.126.camel@infradead.org> <20180110121755.GD9706@redhat.com> Face: 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 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-/qi/wPbwbpLTTiU9tzDm" Date: Wed, 10 Jan 2018 12:29:44 +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: --=-/qi/wPbwbpLTTiU9tzDm Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2018-01-10 at 13:17 +0100, Andrea Arcangeli wrote: > On Wed, Jan 10, 2018 at 12:09:34PM +0000, David Woodhouse wrote: > > That is not consistent with the documentation I've seen, which Intel > > have so far utterly failed to publish AFAICT. > >=C2=A0 > > "a near indirect jump/call/return may be affected by code in a less pri= vileged > > prediction mode that executed AFTER IBRS mode was last written with a v= alue of 1" >=20 > You must have misunderstood the context there, or the above text is > wrong to begin with. That's a quote from the Intel documentation for the IBRS feature. Go read it, please. > > The kernel is only protected from branch targets set in userspace > > *BEFORE* the IBRS mode was last set to 1. If you set it to 1, then > > leave it like that while you run userspace and then kernel code again, > > you are not protected. >=20 > I'm sure you've got it wrong, that would be crazy if it would be the > case. Andrea, what part of this whole fucking mess isn't entirely batshit insane to start with? :) I think you are confused with the future IBRS_ATT option which will exist on new hardware.=C2=A0 Right now, IBRS works as I described it because that's the best they could do with microcode. --=-/qi/wPbwbpLTTiU9tzDm 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 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