From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C92DEC48BD6 for ; Wed, 26 Jun 2019 13:10:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AC60F214DA for ; Wed, 26 Jun 2019 13:10:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727492AbfFZNKi (ORCPT ); Wed, 26 Jun 2019 09:10:38 -0400 Received: from mail-wr1-f65.google.com ([209.85.221.65]:37165 "EHLO mail-wr1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726104AbfFZNKi (ORCPT ); Wed, 26 Jun 2019 09:10:38 -0400 Received: by mail-wr1-f65.google.com with SMTP id v14so2686336wrr.4 for ; Wed, 26 Jun 2019 06:10:37 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=bqOWDaCNsHrE1herZzAPunVmKg4cRAUoaCX+z3T2sAM=; b=DUy4QObSVxdhD8sAwnGYd+cmzJb7jM4Uqp74eCKdshNq7kV5Bof+RKfXTH8cZsv1br KVp6olXWFFXHT0FoVfMBLuksbr7IA7QLpeSfq08OoVERj8nq6mlu324qk2UC5geX+J/o KM5UHesEKphBKVLYNYfvbUDy7IwPggwjVRvss9APlQk6YfRWdQ1rZnbtupNR98HVrV8Q 0eDczyuKugspkbFGmm1+3OtiUfgsMsCU29Jf9vNKCuF2M83iKzekFTSRN42lA++9OxbM c6nDmFTVweWT2LSp0flQwSq2MPCkZUKEuhpxJnrysjw8QpVqSBHXe/QmLEx+Q433t8pi wV8A== X-Gm-Message-State: APjAAAW+4Yqia8N+UH9i2Exdjwtlr1PlaL6ALHFaxqqwKs52YBPCMyyM k3uw4rceJxrmbtLrdHmtJ+JUMQ== X-Google-Smtp-Source: APXvYqy/cMPC8Av1yrbGtbve00ZFb/ieRgkL6SpMCmxq4C9XvGvgJpuLHhPLGFVuptpZ/fVy4FDH8w== X-Received: by 2002:adf:fa4c:: with SMTP id y12mr3606968wrr.282.1561554637009; Wed, 26 Jun 2019 06:10:37 -0700 (PDT) Received: from ?IPv6:2001:b07:6468:f312:e88d:856c:e081:f67d? ([2001:b07:6468:f312:e88d:856c:e081:f67d]) by smtp.gmail.com with ESMTPSA id d7sm4766497wrx.37.2019.06.26.06.10.35 (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Wed, 26 Jun 2019 06:10:36 -0700 (PDT) Subject: Re: [PATCH 1/1] kvm/speculation: Allow KVM guests to use SSBD even if host does not To: Thomas Gleixner Cc: Alejandro Jimenez , mingo@redhat.com, Borislav Petkov , rkrcmar@redhat.com, x86@kernel.org, kvm@vger.kernel.org, stable , Jiri Kosina , David Woodhouse , Jon Masters References: <1560187210-11054-1-git-send-email-alejandro.j.jimenez@oracle.com> <1c9d4047-e54c-8d4b-13b1-020864f2f5bf@redhat.com> <56fa2729-52a7-3994-5f7c-bc308da7d710@oracle.com> From: Paolo Bonzini Message-ID: Date: Wed, 26 Jun 2019 15:10:35 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 26/06/19 14:41, Thomas Gleixner wrote: >> I think it's better to leave the guest in control of SSBD even if it's >> globally disabled. The harm cannot escape the guest and in particular >> it cannot escape to the sibling hyperthread. > > SSB allows guest to guest attacks IIRC SSB requires something like p = &foo; ... p = &bar; q = *p; where "p = &foo;" is executed from one privilege domain and the others are executed by another process or privilege domain. Unless two guests share memory, it is not possible to use it for guest-to-guest attacks. Paolo