From: Stephan Mueller Subject: Re: [PATCH 3/3] random: add interrupt callback to VMBus IRQ handler Date: Mon, 02 May 2016 11:14:25 +0200 Message-ID: <1465960.gVT9QnQ1pA@tauon.atsec.com> References: <1462170413-7164-1-git-send-email-tytso@mit.edu> <1462170413-7164-4-git-send-email-tytso@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: Theodore Ts'o , linux-kernel@vger.kernel.org, Herbert Xu , andi@firstfloor.org, Sandy Harris , cryptography@lakedaemon.net, jsd@av8n.com, hpa@zytor.com, linux-crypto@vger.kernel.org To: noloader@gmail.com Return-path: Received: from mail.eperm.de ([89.247.134.16]:54432 "EHLO mail.eperm.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752459AbcEBJO2 (ORCPT ); Mon, 2 May 2016 05:14:28 -0400 In-Reply-To: Sender: linux-crypto-owner@vger.kernel.org List-ID: Am Montag, 2. Mai 2016, 05:00:47 schrieb Jeffrey Walton: Hi Jeffrey, > On Mon, May 2, 2016 at 2:26 AM, Theodore Ts'o wrote: > > From: Stephan Mueller > > > > The Hyper-V Linux Integration Services use the VMBus implementation for > > communication with the Hypervisor. VMBus registers its own interrupt > > handler that completely bypasses the common Linux interrupt handling. > > This implies that the interrupt entropy collector is not triggered. > > ... > > Stephan correctly identified the problem of virtualized environments > in his paper, but there does not appear to be any real defenses in > place for VM rollback attacks. The issue the patch addresses is only that on Hyper-V with para-virt drivers, the /dev/random implementation does not receive interrupts. The issue of rollback (if you refer to activating an earlier saved image of the guest) is a real issue the guest cannot do anything about it that is effective (i.e. the guest can do without the help of the VMM). Note, rollback is just a special case of a much broader issue of the duplication of the RNG state by the VMM (be it snapshots, move of a guest to another VMM, suspend/resume, ...). However, the patch to enable interrupts does not seem to be related to that issue as interrupts are not re-issued in case of rollbacks, are they? Ciao Stephan