From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matt Wilson Subject: Re: Is there an issue with turning off "scrubbing free RAM" on boot with Xen 4.1.3 Date: Sun, 10 Nov 2013 14:25:11 -0800 Message-ID: <20131110222511.GA22949@u109add4315675089e695.ant.amazon.com> References: <52559F56.3070901@mokumsolutions.com> <52567676.3010102@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1VfdRY-0002nZ-79 for xen-devel@lists.xenproject.org; Sun, 10 Nov 2013 22:25:20 +0000 Received: by mail-pb0-f43.google.com with SMTP id md4so4377139pbc.2 for ; Sun, 10 Nov 2013 14:25:16 -0800 (PST) Content-Disposition: inline In-Reply-To: <52567676.3010102@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Andrew Cooper Cc: xen-devel@lists.xenproject.org, Roddy Rodstein List-Id: xen-devel@lists.xenproject.org On Thu, Oct 10, 2013 at 10:42:14AM +0100, Andrew Cooper wrote: > On 09/10/13 19:24, Roddy Rodstein wrote: [...] > > Could you please share your comments about turning of RAM scrubbing, > > i.e. have you seen any consequences, security issues and/or threats, > > red flags, etc...? [...] > In the Xen model, domains are responsible for clearing any sensitive > data they have out of memory before shutdown. This isn't strictly true. Memory is scrubbed by Xen when the domain cannot do it for itself (i.e., when a domain is dying during shutdown). However by default domains /are/ responsible for scrubbing pages that are returned to Xen via a reservation adjustment (i.e., pages returned via the balloon driver). --msw > The bootscrub is a preventative measure to ensure that after a crash, > stale domain information is cleared from RAM before that RAM is reused > for a new VM. > > If this is not a concern for you, then you can easily turn bootscrub off > by adding "no-bootscrub" to the Xen command line.