Security problem with DIAGNOSE mode on IBM 370's 
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IBM 370, 30xx DIAGNOSE gives access to everything

System:       IBM 370, 30xx Mainframes

Summary:      The diagnose instruction allegedly has no limits on what
              you can do with it.

Interest-To:  IBM Mainframe Security People

Capsule:      Apparently the DIAGNOSE instruction can be used to do
              untraced, undetected I/O and thus you can get away with
              anything from that point.

Comments:     DIAGNOSE is a priveleged instruction on IBM Mainframes.
              I believe that it is used in some cases by VM Guest 
              Operating Systems to tell VM some information.  I believe
              it is also used in Multiprocessor configurations to allow
              one processor to send information to another.  I think
              one of the uses is the same as the "machine check" e.g.
              system failure warning that is internal to the 370.

              In the case of VM 370 this may or may not be a problem,
              because according to the literature I have read, guest 
              operating systems running under VM do not get "real" 
              priveleges; VM checks to see if the particular caller
              is the Guest O/S and if it is, emulates the priveleged
              instruction (usually to do I/O on a disk, tape or terminal.)

Repair or Correction:  Not yet known.