Re: [Xen-devel] Is there an issue with turning off "scrubbing free RAM" on boot with Xen 4.1.3

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Sun, 2013-11-10 at 14:25 -0800, Matt Wilson wrote:
> 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).

Isn't this only when the domain is killed by the toolstack or crashes
etc. On a graceful shutdown I thought the guest was still responsible
for clearing any memory it cared about.

>  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.
> 
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