From patchwork Thu Feb 20 14:02:10 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kashyap Chamarthy X-Patchwork-Id: 1241442 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Authentication-Results: ozlabs.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=dw+SFEAr; dkim-atps=neutral Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 48NbsF2wxzz9sPk for ; Fri, 21 Feb 2020 01:03:13 +1100 (AEDT) Received: from localhost ([::1]:43008 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j4mQ3-0004zW-9U for incoming@patchwork.ozlabs.org; Thu, 20 Feb 2020 09:03:11 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:37390) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j4mPQ-0004rs-O8 for qemu-devel@nongnu.org; Thu, 20 Feb 2020 09:02:37 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1j4mPL-0007uX-Fm for qemu-devel@nongnu.org; Thu, 20 Feb 2020 09:02:32 -0500 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:31485 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1j4mPL-0007tp-Bt for qemu-devel@nongnu.org; Thu, 20 Feb 2020 09:02:27 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1582207346; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Z6YmwN7BQesNWvl/e1ATsqXxfhRdFSw9Rf2vpl2YuV8=; b=dw+SFEAr+FiogqZdRFhjXttkM6OPzcOr3rO5dWS3mHTkb0BpdFp07sSoCHv57o+VfCqu2S wOVW9/QhkrsgH25MuUHrrVyVQ892tIb0kbZvgxqkCd6TnoGN1aBVz31HB5EHE8NjJK7mdF 3J7NrJdIL8jvYr4fHr2DZtN6EUjlvEQ= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-80-vA59OkpDOGGTJFCk5j0PuA-1; Thu, 20 Feb 2020 09:02:19 -0500 X-MC-Unique: vA59OkpDOGGTJFCk5j0PuA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0D3C8801E5C; Thu, 20 Feb 2020 14:02:18 +0000 (UTC) Received: from paraplu.localdomain (unknown [10.36.118.120]) by smtp.corp.redhat.com (Postfix) with ESMTP id 957F65C114; Thu, 20 Feb 2020 14:02:16 +0000 (UTC) From: Kashyap Chamarthy To: kchamart@redhat.com, qemu-devel@nongnu.org Subject: [PATCH v3 2/2] qemu-cpu-models.rst: Document -noTSX, mds-no, taa-no, and tsx-ctrl Date: Thu, 20 Feb 2020 15:02:10 +0100 Message-Id: <20200220140210.14209-3-kchamart@redhat.com> In-Reply-To: <20200220140210.14209-1-kchamart@redhat.com> References: <20200220140210.14209-1-kchamart@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: peter.maydell@linaro.org, berrange@redhat.com, ehabkost@redhat.com Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" - Add the '-noTSX' variants for CascadeLake and SkyLake. - Document the three MSR bits: 'mds-no', 'taa-no', and 'tsx-ctrl' Two confusing things about 'mds-no' (and the first point applies to the other two MSRs too): (1) The 'mds-no' bit will _not_ show up in the guest's /proc/cpuinfo. Rather it is used to fill in the guest's sysfs: /sys/devices/system/cpu/vulnerabilities/mds:Not affected Paolo confirmed on IRC as such. (2) There are _three_ variants[+] of CascadeLake CPUs, with different stepping levels: 5, 6, and 7. To quote wikichip.org[*]: "note that while steppings 6 & 7 are fully mitigated, earlier stepping 5 is not protected against MSBDS, MLPDS, nor MDSUM" The above is also indicated in the Intel's document[+], as indicated by "No" under the three columns of MFBDS, MSBDS, and MLPDS. I've expressed this in the docs without belabouring the details. [+] https://software.intel.com/security-software-guidance/insights/processors-affected-microarchitectural-data-sampling [*] https://en.wikichip.org/wiki/intel/microarchitectures/cascade_lake#Key_changes_from_Skylake Signed-off-by: Kashyap Chamarthy --- docs/system/qemu-cpu-models.rst | 57 +++++++++++++++++++++++++++++++++ 1 file changed, 57 insertions(+) diff --git a/docs/system/qemu-cpu-models.rst b/docs/system/qemu-cpu-models.rst index a189d6a9da..946e90e1dc 100644 --- a/docs/system/qemu-cpu-models.rst +++ b/docs/system/qemu-cpu-models.rst @@ -61,15 +61,24 @@ mixture of host CPU models between machines, if live migration compatibility is required, use the newest CPU model that is compatible across all desired hosts. +* Intel Xeon Processor (Cascade Lake, 2019), with "stepping" levels 6 or + 7 only. (The Cascade Lake Xeon processor with *stepping 5 is + vulnerable to MDS variants*.) + + * ``Cascadelake-Server`` + * ``Cascadelake-Server-noTSX`` + * Intel Xeon Processor (Skylake, 2016) * ``Skylake-Server`` * ``Skylake-Server-IBRS`` + * ``Skylake-Server-IBRS-noTSX`` * Intel Core Processor (Skylake, 2015) * ``Skylake-Client`` * ``Skylake-Client-IBRS`` + * ``Skylake-Client-noTSX-IBRS}`` * Intel Core Processor (Broadwell, 2014) @@ -182,6 +191,54 @@ features are included if using "Host passthrough" or "Host model". Requires the host CPU microcode to support this feature before it can be used for guest CPUs. +``mds-no`` + Recommended to inform the guest OS that the host is *not* vulnerable + to any of the MDS variants ([MFBDS] CVE-2018-12130, [MLPDS] + CVE-2018-12127, [MSBDS] CVE-2018-12126). + + This is an MSR (Model-Specific Register) feature rather than a CPUID feature, + so it will not appear in the Linux ``/proc/cpuinfo`` in the host or + guest. Instead, the host kernel uses it to populate the MDS + vulnerability file in ``sysfs``. + + So it should only be enabled for VMs if the host reports @code{Not + affected} in the ``/sys/devices/system/cpu/vulnerabilities/mds`` file. + +``taa-no`` + Recommended to inform that the guest that the host is ``not`` + vulnerable to CVE-2019-11135, TSX Asynchronous Abort (TAA). + + This too is an MSR feature, so it does not show up in the Linux + ``/proc/cpuinfo`` in the host or guest. + + It should only be enabled for VMs if the host reports ``Not affected`` + in the ``/sys/devices/system/cpu/vulnerabilities/tsx_async_abort`` + file. + +``tsx-ctrl`` + Recommended to inform the guest that it can disable the Intel TSX + (Transactional Synchronization Extensions) feature; or, if the + processor is vulnerable, use the Intel VERW instruction (a + processor-level instruction that performs checks on memory access) as + a mitigation for the TAA vulnerability. (For details, refer to this + `Intel's deep-dive into + MDS `_.) + + Expose this to the guest OS if and only if: (a) the host has TSX + enabled; *and* (b) the guest has ``rtm`` CPU flag enabled. + + By disabling TSX, KVM-based guests can avoid paying the price of + mitigting TSX-based attacks. + + Note that ``tsx-ctrl`` too is an MSR feature, so it does not show + up in the Linux ``/proc/cpuinfo`` in the host or guest. + + To validate that Intel TSX is indeed disabled for the guest, there are + two ways: (a) check for the *absence* of ``rtm`` in the guest's + ``/proc/cpuinfo``; or (b) the + ``/sys/devices/system/cpu/vulnerabilities/tsx_async_abort`` file in + the guest should report ``Mitigation: TSX disabled``. + Preferred CPU models for AMD x86 hosts ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~