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

[Doug O'Neil]

> -----Original Message-----
> From: openib-general-bounces at openib.org [mailto:openib-general-
> bounces at openib.org] On Behalf Of Talpey, Thomas
> Sent: Monday, March 20, 2006 5:00 PM
> To: Roland Dreier
> Cc: openib-general at openib.org
> Subject: Re: [openib-general] mthca FMR correctness (and memory
windows)
> 
> 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. 

>From iWarp RDMA Verbs Section 5.2

  "When a data transfer takes place, if the STag refers to an
  MR, then the PD ID of the MR is validated against the PD ID of the
  QP. If they do not match, the data transfer generates an error and
  no data transfer takes place. If the STag refers to an MW, then the
  PD ID of the MW is validated against the PD ID of the QP when the MW
  is Bound to the QP. When a data transfer takes place, the QP ID of
  the MW is validated against the QP ID of the QP."

Tom, I read the above as an STag that represents a MR can be used by any
QP with the same PD ID. STags that represent a MW must be used on the
same QP that created them.
 
- Doug

> This leverages the IP security model and provides correctness.
> 
> It is true that IB implementations generally don't do this. They
should.
> 
> Tom.
> 
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