From mboxrd@z Thu Jan 1 00:00:00 1970 From: poma Subject: Re: KVM SVM(AMD) nested - disabled by default? Date: Tue, 26 Jan 2016 12:00:44 +0100 Message-ID: <56A751DC.2040809@gmail.com> References: <56A39729.8020106@gmail.com> <56A3EB1C.5020605@redhat.com> <56A669F2.1050905@gmail.com> <56A737B4.7030902@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: kvm-devel , Cole Robinson , "Richard W.M. Jones" To: Paolo Bonzini Return-path: Received: from mail-wm0-f45.google.com ([74.125.82.45]:36899 "EHLO mail-wm0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965098AbcAZLAs (ORCPT ); Tue, 26 Jan 2016 06:00:48 -0500 Received: by mail-wm0-f45.google.com with SMTP id n5so123797014wmn.0 for ; Tue, 26 Jan 2016 03:00:47 -0800 (PST) In-Reply-To: <56A737B4.7030902@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 26.01.2016 10:09, Paolo Bonzini wrote: > > > On 25/01/2016 19:31, poma wrote: >> On 23.01.2016 22:05, Paolo Bonzini wrote: >>> >>> >>> On 23/01/2016 16:07, poma wrote: >>>> "KVM: SVM: enable nested svm by default" >>>> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/arch/x86/kvm?id=4b6e4dc >>>> "Nested SVM is (in my experience) stable enough to be enabled by default. So omit the requirement to pass a module parameter." >>>> >>>> I tried to get an explanation of the eventual -default- change here: >>>> https://bugzilla.redhat.com/show_bug.cgi?id=1298244 >>>> >>>> but "... I am *thinking* of changing it ..." ain't explanation, man. >>>> >>>> I've tested "Nested SVM" myself and it works surprisingly well, >>>> therefore what is the -actual- reason to switch it off by default? >>> >>> Neither nested VMX nor nested SVM have ever been audited for security; >>> they could have bugs that let a malicious guest escape L0. In fact I >>> would be surprised if they don't. :( >>> >>> Paolo >>> >> >> >> "In nested virtualization, we have three levels: The host (KVM), which we call >> L0, the guest hypervisor, which we call L1, and its nested guest, which we >> call L2." >> https://www.kernel.org/doc/Documentation/virtual/kvm/nested-vmx.txt >> >> So as long as you don't nestle proprietary crap, no problemos. > > Kind of. Suppose you are a cloud provider, and you think offering > nested virtualization would be cool. Now, a customer (who of course > controls the kernel running in your L1 VM) uses a vulnerability in KVM > to get out of his VM and attack the host. Enorme problema. > > Paolo > Yeah, "closed source" is just a part of problemo. Thanks for the extra explanation/example.