From patchwork Tue Feb 25 16:56:18 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kashyap Chamarthy X-Patchwork-Id: 11404247 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 475CC92A for ; Tue, 25 Feb 2020 16:57:41 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 1E90020CC7 for ; Tue, 25 Feb 2020 16:57:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="h/a22QBt" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1E90020CC7 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Received: from localhost ([::1]:60374 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j6dWd-0004fI-VS for patchwork-qemu-devel@patchwork.kernel.org; Tue, 25 Feb 2020 11:57:40 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:44527) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j6dVf-0003e5-OE for qemu-devel@nongnu.org; Tue, 25 Feb 2020 11:56:42 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1j6dVe-0002m4-0l for qemu-devel@nongnu.org; Tue, 25 Feb 2020 11:56:39 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:35005 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1j6dVd-0002ls-T1 for qemu-devel@nongnu.org; Tue, 25 Feb 2020 11:56:37 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1582649797; 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=noIQUvmu88Gj9chmSxQ6cb8p2IeY9lN+BsMm7RyT4EA=; b=h/a22QBtlOs+JfEC92C1SIb+8T8d/54u9hdul8xOrhLHjvvRZs8cgraoeRgQS15qEdjrPH m5BLhquJiVjpUgFmfXxDld5HOcowd/5TpZhq5Xd1Vt2RI1vJ2SMcoMsDChK9YtlLeMKNB9 px5b4XZVPY+OxABStLqzDA8NUf2VtE4= 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-488-wdxD5feWMRquyUHk9bQNkA-1; Tue, 25 Feb 2020 11:56:29 -0500 X-MC-Unique: wdxD5feWMRquyUHk9bQNkA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0D9BC1005512; Tue, 25 Feb 2020 16:56:28 +0000 (UTC) Received: from paraplu.redhat.com (ovpn-117-203.ams2.redhat.com [10.36.117.203]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3525E90519; Tue, 25 Feb 2020 16:56:24 +0000 (UTC) From: Kashyap Chamarthy To: qemu-devel@nongnu.org Subject: [PATCH v4 2/2] qemu-cpu-models.rst: Document -noTSX, mds-no, taa-no, and tsx-ctrl Date: Tue, 25 Feb 2020 17:56:18 +0100 Message-Id: <20200225165618.6571-3-kchamart@redhat.com> In-Reply-To: <20200225165618.6571-1-kchamart@redhat.com> References: <20200225165618.6571-1-kchamart@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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: 205.139.110.120 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 , berrange@redhat.com, Eduardo Habkost , kchamart@redhat.com, Paolo Bonzini , Richard Henderson Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.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 --- v4: - Fix two minor rST-related things [pbonzini] --- docs/system/qemu-cpu-models.rst | 57 +++++++++++++++++++++++++++++++-- 1 file changed, 55 insertions(+), 2 deletions(-) diff --git a/docs/system/qemu-cpu-models.rst b/docs/system/qemu-cpu-models.rst index 2bf635ecab..6ad572c509 100644 --- a/docs/system/qemu-cpu-models.rst +++ b/docs/system/qemu-cpu-models.rst @@ -61,10 +61,15 @@ 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. -``Skylake-Server``, ``Skylake-Server-IBRS`` +``Cascadelake-Server``, ``Cascadelake-Server-noTSX`` + 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*.) + +``Skylake-Server``, ``Skylake-Server-IBRS``, ``Skylake-Server-IBRS-noTSX`` Intel Xeon Processor (Skylake, 2016) -``Skylake-Client``, ``Skylake-Client-IBRS`` +``Skylake-Client``, ``Skylake-Client-IBRS``, ``Skylake-Client-noTSX-IBRS}`` Intel Core Processor (Skylake, 2015) ``Broadwell``, ``Broadwell-IBRS``, ``Broadwell-noTSX``, ``Broadwell-noTSX-IBRS`` @@ -160,6 +165,54 @@ 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 + 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 + mitigating 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 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~