Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754840AbWL1N01 (ORCPT ); Thu, 28 Dec 2006 08:26:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754847AbWL1N00 (ORCPT ); Thu, 28 Dec 2006 08:26:26 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:53064 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754840AbWL1N00 (ORCPT ); Thu, 28 Dec 2006 08:26:26 -0500 Date: Thu, 28 Dec 2006 14:23:25 +0100 From: Ingo Molnar To: Avi Kivity Cc: kvm-devel , linux-kernel , Andrew Morton , Linus Torvalds Subject: Re: [patch, try#2] kvm: fix GFP_KERNEL allocation in atomic section in kvm_dev_ioctl_create_vcpu() Message-ID: <20061228132325.GA2176@elte.hu> References: <45939755.7010603@qumranet.com> <20061228124224.GA28573@elte.hu> <4593BEE6.30206@qumranet.com> <20061228125544.GA31207@elte.hu> <20061228130833.GA555@elte.hu> <4593C345.9040306@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4593C345.9040306@qumranet.com> User-Agent: Mutt/1.4.2.2i X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -2.6 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.6 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.0.3 -2.6 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1945 Lines: 49 * Avi Kivity wrote: > Ingo Molnar wrote: > >Subject: [patch] kvm: fix GFP_KERNEL allocation in atomic section in > >kvm_dev_ioctl_create_vcpu() > >From: Ingo Molnar > > > >fix an GFP_KERNEL allocation in atomic section: > >kvm_dev_ioctl_create_vcpu() called kvm_mmu_init(), which calls > >alloc_pages(), while holding the vcpu. > > > >The fix is to set up the MMU state in two phases: kvm_mmu_create() and > >kvm_mmu_setup(). > > > >(NOTE: free_vcpus does an kvm_mmu_destroy() call so there's no need > > for any extra teardown branch on allocation/init failure here.) > > > >Signed-off-by: Ingo Molnar > > > > Applied, thanks. great! I've got a security related question as well: vcpu_load() sets up a physical CPU's VM registers/state, and vcpu_put() drops that. But vcpu_put() only does a put_cpu() call - it does not tear down any VM state that has been loaded into the CPU. Is it guaranteed that (hostile) user-space cannot use that VM state in any unauthorized way? The state is still loaded while arbitrary tasks execute on the CPU. The next vcpu_load() will then override it, but the state lingers around forever. The new x86 VM instructions: vmclear, vmlaunch, vmresume, vmptrld, vmread, vmwrite, vmxoff, vmxon are all privileged so i guess it should be mostly safe - i'm just wondering whether you thought about this attack angle. ultimately we want to integrate VM state management into the scheduler and the context-switch lowlevel arch code, but right now CPU state management is done by the KVM 'driver' and there's nothing that isolates other tasks from possible side-effects of a loaded VMX/SVN state. Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/