From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964971AbeBLQas (ORCPT ); Mon, 12 Feb 2018 11:30:48 -0500 Received: from twosheds.infradead.org ([90.155.92.209]:43122 "EHLO twosheds.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964886AbeBLQaq (ORCPT ); Mon, 12 Feb 2018 11:30:46 -0500 Message-ID: <1518453038.11483.4.camel@infradead.org> Subject: Re: [tip:x86/pti] x86/speculation: Use IBRS if available before calling into firmware From: David Woodhouse To: afzal mohammed , mingo@kernel.org, hpa@zytor.com, tglx@linutronix.de, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, peterz@infradead.org Cc: linux-tip-commits@vger.kernel.org, "Wieczorkiewicz, Pawel" In-Reply-To: <20180212055948.GA3281@afzalpc> References: <1518362359-1005-1-git-send-email-dwmw@amazon.co.uk> <20180212055948.GA3281@afzalpc> Face: 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 Content-Type: multipart/signed; micalg="sha-256"; protocol="application/x-pkcs7-signature"; boundary="=-C9RprgktzT98ks2EWIVw" Date: Mon, 12 Feb 2018 16:30:38 +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 --=-C9RprgktzT98ks2EWIVw Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2018-02-12 at 11:29 +0530, afzal mohammed wrote: > Hi, >=20 > On Sun, Feb 11, 2018 at 11:19:10AM -0800, tip-bot for David Woodhouse wro= te: >=20 > >=20 > > x86/speculation: Use IBRS if available before calling into firmware > >=20 > > Retpoline means the kernel is safe because it has no indirect branches. > > But firmware isn't, so use IBRS for firmware calls if it's available. > > afaui, so only retpoline means still mitigation not enough. >=20 > Also David W has mentioned [1] that even with retpoline, IBPB is also > required (except Sky Lake). Retpoline is sufficient to protect the *kernel*, which is the biggest target. (Except on Skylake, where IBRS is the only full mitigation and people are still working trying to come up with a "good enough" mitigation that isn't IBRS.) On all CPUs, you need IBPB to protect userspace processes from each other, although since it's slow we don't actually *do* that for every context switch; only when switching to non-dumpable processes. That IBPB requirement for protecting userspace is true even on the next generation of CPUs with the "Enhanced IBRS" (IBRS_ALL) feature. It only goes away in CPUs which are even *further* in the future, when Intel manage to fix it completely in hardware. They haven't even documented the feature bit they're going to advertise to indicate that fix yet! > If IBPB & IBRS is not supported by ucode, shouldn't the below indicate > some thing on the lines of Mitigation not enough ? >=20 > >=20 > > - return sprintf(buf, "%s%s%s\n", spectre_v2_strings[spectre_v2_enabled= ], > > + return sprintf(buf, "%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabl= ed], > > =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0boot_cpu_has(X86_FEAT= URE_USE_IBPB) ? ", IBPB" : "", > > + =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0boot_cpu_has(X86_FEATURE_U= SE_IBRS_FW) ? ", IBRS_FW" : "", > > =C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0spectre_v2_module_str= ing()); > On 4.16-rc1, w/ GCC 7.3.0, >=20 > /sys/devices/system/cpu/vulnerabilities/meltdown:Mitigation: PTI > /sys/devices/system/cpu/vulnerabilities/spectre_v1:Mitigation: __user poi= nter sanitization > /sys/devices/system/cpu/vulnerabilities/spectre_v2:Mitigation: Full gener= ic retpoline >=20 > Here for the user (at least for me), it is not clear whether the > mitigation is enough. In the present system (Ivy Bridge), as ucode > update is not available, IBPB is not printed along with > "spectre_v2:Mitigation", so unless i am missing something, till then > this system should be considered vulnerable, but for a user not > familiar with details of the issue, it cannot be deduced. >=20 > Perhaps an additional status field [OKAY,PARTIAL] to Mitigation in > sysfs might be helpful. All these changes are in the air for me, this > is from a user perspective, sorry if my feedback seems idiotic. Given that we only do it for non-dumpable processes, it's *always* going to be only=C2=A0partial. (Although I think Thomas was looking at a command line option to =C2=A0make that happen on every context switch?) And on Skylake the current plan is that strictly speaking it would also be partial. I understand the concern, but I'm not sure that there's much we can do to improve it. If it says "Mitigation:" that's generally OK, and if it says anything else, it's not. --=-C9RprgktzT98ks2EWIVw 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 5PqFmWkbehLaEvbpNY7dmEAAeKh4klTzJzrr5AAzaCQ32cA2e3+DEIv5O5l9ViMIjy/JM+xMQrfX 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