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

["Mike D. Day" <ncmike@xxxxxxxxxx>]

Keir Fraser wrote:
>
> 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.
Yes, but that relies on the tools being correct and invulnerable to 
attacks like buffer overflow. Further, it does not disallow an 
alternative tool from bypassing or corrupting the conformance and 
authorization policy. Any program with the ability to open a socket to 
xenstore can open the way. Allowing the checks within the hypervisor is 
much safer against these types of attacks or errors.
Mike

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