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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=no 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 6A9D9C433DB for ; Thu, 14 Jan 2021 17:35:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3D15823B3E for ; Thu, 14 Jan 2021 17:35:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727011AbhANRfj (ORCPT ); Thu, 14 Jan 2021 12:35:39 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48712 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726266AbhANRfi (ORCPT ); Thu, 14 Jan 2021 12:35:38 -0500 Received: from mail-pj1-x1032.google.com (mail-pj1-x1032.google.com [IPv6:2607:f8b0:4864:20::1032]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 746E5C061574 for ; Thu, 14 Jan 2021 09:34:58 -0800 (PST) Received: by mail-pj1-x1032.google.com with SMTP id b5so3599900pjk.2 for ; Thu, 14 Jan 2021 09:34:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=7+wptAskGDjPCM/rtSd9GeVD54civZ0IhTr0BYervcE=; b=h0Vzkd89olpKGDIiVF7JgUQgbc4qq8f54PO9VAiv0SLf1yToAF7HSVm+dfVS+xVSZS WxtVjR2//GZX/ZlQ51FRTqE/QHI+r0wK3jmdp+3H2wphXOR+fcrAThHeW0vyNAB9VDQK GbVu7xyxJqYpqNiokerPhHZOh88Y4ZI9HYPOZ314YtvsDzbvgaV/F3UDhJ7/0mVrPpKX 9Rm0H9zOnH62+L0x/Yf7kBuc4GUmrT5Wm5TYh55eWunlNuKkivQevoYLyp/UPzLO8mO5 eJVZP6nW7c5MWru5b+OvjRblx6sWfNJUsOI6LUvkTen+BJKAj7gvYnqOAhOQvzQuDDqm j82A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=7+wptAskGDjPCM/rtSd9GeVD54civZ0IhTr0BYervcE=; b=saiIx2iQJ2ZTjbKMRpiC5Yfk3LI7R+fCJMPwWh2gax/As28Gepd6Oa1jURRcMXpJpR dvMqoDW52KNeERJs2NbGhJIMTNxwQ4IGPXtdNsx2oCXpYzTrhVlQkVeAw6C5pH1gQJGg R4XxbMy9FD5t3rooJpsPbNYpybxOSqkp0bJmLtWP0mC7CYtKGPWhtgZ3BscUPL4ZDMi/ zb+7rEoSypdOWcRC9KHOvqibh1Va2ANIST11Kdq4I8V7UrjuCGM+NrvTUc1olKHBQQJL rY/YAVw6wtAjpRd2aI7YTop+YlqMPtcKgHlVUTm6b/af8iTtzckqc7sP56JmCZ0dUbGG OO1w== X-Gm-Message-State: AOAM533tYnsbmWEMVgOKQ84GxfwtICgOzTHEpJ1fJCS4M8ez5b5nxIuq rZlvyJdxV2Ga/rANK1Mc6Pa1XA== X-Google-Smtp-Source: ABdhPJyWu31+NHrAEdDgt75PYbXBAWB13kUeru9konpXj1/8XYbvlOH+vGoiZx5eczD5HHbL9dqtxA== X-Received: by 2002:a17:902:ee05:b029:dd:f952:db11 with SMTP id z5-20020a170902ee05b02900ddf952db11mr8409438plb.42.1610645697892; Thu, 14 Jan 2021 09:34:57 -0800 (PST) Received: from google.com ([2620:15c:f:10:1ea0:b8ff:fe73:50f5]) by smtp.gmail.com with ESMTPSA id 84sm6194330pfy.9.2021.01.14.09.34.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 14 Jan 2021 09:34:57 -0800 (PST) Date: Thu, 14 Jan 2021 09:34:50 -0800 From: Sean Christopherson To: Vitaly Kuznetsov Cc: kvm@vger.kernel.org, Paolo Bonzini , Wanpeng Li , Jim Mattson Subject: Re: [PATCH 6/7] KVM: x86: hyper-v: Make Hyper-V emulation enablement conditional Message-ID: References: <20210113143721.328594-1-vkuznets@redhat.com> <20210113143721.328594-7-vkuznets@redhat.com> <87v9bz7sdk.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87v9bz7sdk.fsf@vitty.brq.redhat.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Jan 14, 2021, Vitaly Kuznetsov wrote: > Sean Christopherson writes: > > > On Wed, Jan 13, 2021, Vitaly Kuznetsov wrote: > >> Hyper-V emulation is enabled in KVM unconditionally. This is bad at least > >> from security standpoint as it is an extra attack surface. Ideally, there > >> should be a per-VM capability explicitly enabled by VMM but currently it > > > > Would adding a module param buy us anything (other than complexity)? > > > > A tiny bit, yes. This series is aimed at protecting KVM from 'curious > guests' which can try to enable Hyper-V emulation features even when > they don't show up in CPUID. A module parameter would help to protect > against a malicious VMM which can still enable all these features. What > I'm not sure about is how common Linux-guests-only deployments (where > the parameter can actually get used) are as we'll have to keep it > 'enabled' by default to avoid breaking existing deployments. I always forget that these "optional" features aren't so optional for Windows guests. Given that, it does seem like a module param would be of dubious value. What I really want for my own personal development is a Kconfig option to turn it off completely and shave a few cycles of build time, but I can't even justify that to myself :-)