RE: [Xen-devel] Changing semantics of ioperm() on Xen x86-64?

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> As part of the Xen x86-64 Linux port, we've changed the 
> ioperm() syscall to always modify the IOPL instead of 
> actually modifying the IO bitmap in the TSS like we do on 
> x86-32.  Is there a particular reason for doing this?

I don't believe so. io bitmap support was added to the hypervisor and
the corresponding ioperm support got added on i386, but was never
carried across to x86_64.

We would definitely benefit from someone doing a code review of x86_64
with a view to unifying as many of the xen patches with i386 as
possible. There's certainly some needless/unhelpful divergence.

Ian 
 
> I'm completely guessing here that this may allow us to avoid 
> changing the TR when changing from user/kernel mode but that 
> doesn't seem like that huge of a gain.
> 
> I don't expect that there are many apps that would rely on 
> using ioperm to restrict access to only certain ranges of 
> ports so I don't think this is a security problem but it 
> still is a little discomforting.
> 
> Comments?
> 
> Regards,
> 
> Anthony Liguori
> 
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