Re: [Xen-devel] [PATCH][ACM] kernel enforcement of vbd policies via blkback driver

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 25 Jul 2006, at 01:21, Reiner Sailer wrote:

> Bryan's differentiation makes sense to me. The hooks serve different 
> purposes:
> The xm tools hook is the "usability hook" that ensures users that 
> domains that get started actually can access their resources.
> The block-backend hook is the "enforcement hook" that independently 
> enforces access control at the time when a resource is mounted.
> Right now, both hooks are in the 'large' Domain0. I can imagine that 
> the xm create resource validation hook eventually moves into a Xen 
> management GUI that verifies at management time if a domain 
> configuration is "policy-conform". The block-backend hook could 
> eventually move together with the block-backend device into a block 
> device domain for run-time policy enforcement.
The tools hook is not just a usability/conformity check. The check 
ensures that the tools will not set up entries in xenstore that would 
allow blkback to create a non-conformant vbd. So there is no way for a 
guest to trick blkback into creating a non-conformant vbd: it can only 
connect to vbds specified in its config file or added later via the 
vbd-add xm hotplug command. The tools stack should perform its 
compiance checks on both 'xm create' and 'xm vbd-add', and that should 
be sufficient.
You have a point about it being nice to check things at the lowest 
possible level, but I'm not inclined to add extra crud into the device 
drivers for this unless more people scream for it. :-)
 -- Keir


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