Re: some other memory considerations.

[Bas Wijnen]

Espen Skoglund wrote:
> [Rian Hunter]
>
> > By the way, is it even possible for two arbitrary tasks in L4 to map
> > memory to each other, assuming not one of them are pagers to the
> > other?  I'm not entirely sure but I don't think so.
>
>
> Yes.  It is possible.

L4 allows it, indeed.  However, our current ideas of the Hurd don't.  In 
fact, they don't allow it even if you are a pager.

Mapping memory to an other task costs kernel memory.  Therefore, it can 
be used for a denial of service attack against the system.  Because of 
that, it must be a restricted operation, which can only be performed by 
trusted tasks (and will in practice only be performed by physmem, I 
think.)  Note also that pagers are not trusted tasks.  So for a pager to 
map memory to a task, it has to ask physmem to do it.  Granting memory 
is not a problem, and will be allowed.  I'm not sure if it would be used 
much, though.

Thanks,
Bas

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