Re: [Xen-devel] (4.5-rc1) Problems using xl migrate

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Nov 25, 2014 at 01:03:34PM -0500, Daniel De Graaf wrote:
> On 11/25/2014 05:07 AM, George Dunlap wrote:
> >On Mon, Nov 24, 2014 at 10:05 PM, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx> 
> >wrote:
> >>>I do. The error is
> >>>(XEN) flask_domctl: Unknown op 72
> >>>
> >>>Incidentally, Flask is running in permissive mode.
> >>>
> >>>      Michael Young
> >>>
> >>
> >>This means that the new domctl needs to be added to the switch statement
> >>in flask/hooks.c.  This error is triggered in permissive mode because it
> >>is a code error rather than a policy error (which is what permissive mode
> >>is intended to debug).
> >
> >If that's the case, should we make that a BUG_ON()?  Or at least an
> >ASSERT() (which will only bug when compiled with debug=y), followed by
> >allow if in permissive mode, and deny if in enforcing mode?
> >
> >Having it default deny, even in permissive mode, breaks the "principle
> >of least surprise", I think. :-)
> >
> >  -George
> Either one of these will allow a guest to crash the hypervisor by requesting
> an undefined domctl, which is not really a good idea.  Linux uses a flag in
> the security policy which defines if unknown permissions are allowed or
> denied; I will send a patch adding this to Xen's security server and using
> it instead of -EPERM in the default case of the switch statements.

Thought I think that for the DEBUG case we want to still be boldly
told about it so we can fix it.
> 
> The patch adding this feature probably shouldn't be applied to 4.5, but I'll
> send it anyway.  I will also send a separate patch adding the 2 domctls.
> 
> -- 
> Daniel De Graaf
> National Security Agency
> 
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