[openib-general] mthca FMR correctness (and memory windows)

[Talpey, Thomas]

At 07:50 PM 3/20/2006, Roland Dreier wrote:
>    Thomas> Yes, I know about binding on a separate queue. That
>    Thomas> doesn't work, because windows are semantically not
>    Thomas> fungible (for security reasons).
>
>Can you elaborate on the issue of fungibility?  If one entity has two
>QPs, one of which it's using for traffic and one of which it's using
>for MW binds, I don't see any security issue (beyond the fact that
>you've now given up ordering of operations between the QPs).

If I can snoop or guess rkeys (not a huge challenge with 32 bits), and
if I can use them on an arbitrary queuepair, then I can handily peek and
poke at memory that does not belong to me.

For this reason, iWARP requires its steering tags to be scoped to a single
connection. This leverages the IP security model and provides correctness.

It is true that IB implementations generally don't do this. They should.

Tom.