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>>Pointers CANNOT be counterfeited. .... Anyone else who creates a pointer,
copies a pointer, or
>>modifies a pointer has NO WAY [emphasis added] to turn the tag bits on
and
>>will end up with a useless 16-byte entity."
>
>I know that is what Dr. Frank claims.  I've read the book too.  But I've
also
>read Leif's book.  And before you decide that a pointer CANNOT be
counterfeited,
>and that there is NO WAY to turn the tag bits on, you may want to read
chapters
>6 & 7 of Leif's book.  And follow his instructions to create a program
which
>DOES counterfeit a pointer and DOES turn on the tag bit.

Both Frank and Leif are correct. They just happen to be talking about two
different things. I say this without having read either of their books, but
with knowledge of how the system works.

When Frank Soltis and others say that pointers cannot be counterfeited they
are talking about programs that are created through the machine interface
(MI) by the trusted translator. All of the compilers on the system must use
the trusted translator. It will not create a program that will manufacture
a pointer because the trusted translator enforces the MI and the MI
includes no mechanism for arbitrarily constructing pointers.

When Leif creates a program that manufactures a tagged pointer he is
altering a program created by the trusted translator. He is changing the
program to use hardware instructions in a way that would never be generated
by the trusted translator.

The moral of this is that if you want to ensure the best security and
integrity, you should only use programs that were created by the trusted
translator. You should not allow someone you do not trust to use the DST or
SST (service) interfaces on your system. You should consider retranslating
programs you do not trust, using the CHGPGM or CHGSRVPGM command, for
example. If untrusted programs cannot be retranslated, then you may want to
delete them.

Ed Fishel,
edfishel@US.IBM.COM



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