Re: Fw: Xen on /. again

[Jacob Gorm Hansen <jacobg@diku.dk>]

Mark Williamson wrote:

> Well domains are not aware of each other's memory usage, so I wouldn't have 
> thought that allocation / exposing real page tables would matter.  (Except 
> dom0 can of course see everything if it wants).

Microkernel people like to make the argument that you could create a 
low-bandwidth covert channel by systematically allocating and freeing a 
set of pages, and because domains see real page frame numbers they can 
learn the state of the other guy by looking at what pages they get in 
return from an alloc call. I suppose you could randomize the 
page-allocator, but then you will have to leave a certain amount of 
pages unused at all times, to have enough random pages to choose from.

(For myself, I would much rather have the real page tables and find a 
way to live with the covert channels, but I am not building 
military-grade systems).

Jacob


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