Re: IBM-MAIN Digest - 4 Mar 2012 to 5 Mar 2012 (#2012-65)

2012-03-07 Thread Shmuel Metz (Seymour J.) 
In
,
on 03/06/2012
   at 08:39 PM, "Pate, Gene"  said:

>By PCFLIH backdoor I mean a routine whose address replaced the
>address of the IBM supplied PCFLIH.

That's not what the others were using the term to mean.
 
-- 
 Shmuel (Seymour J.) Metz, SysProg and JOAT
 ISO position; see  
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Re: IBM-MAIN Digest - 4 Mar 2012 to 5 Mar 2012 (#2012-65)

2012-03-06 Thread Tom Marchant 
On Tue, 6 Mar 2012 20:39:02 +, Pate, Gene wrote:

>By PCFLIH backdoor I mean a routine whose address 
>replaced the address of the IBM supplied PCFLIH.

That would be a hook or an intercept.
"Backdoor" means something else entirely.

>The backdoor routine received control every time a 
>PC interrupt

ITYM a program interruption.

>occurred and, based on the reason for the PC 
>interrupt it either emulated the failing instruction 
>using available instructions and returned control to 
>the next sequential instruction or passed control to
>the IBM supplied PCFLIH routine for it to process 
>the PC interrupt. I believe that this is also what 
>the vendor routine being discussed did.

That is certainly not what the vendor routine being 
discussed is alleged to have done.  It is alleged to 
return to the program that was interrupted in supervisor 
state.  It is further alleged that it is relatively easy for 
any program to exploit this and to get put into 
supervisor state.

-- 
Tom Marchant

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Re: IBM-MAIN Digest - 4 Mar 2012 to 5 Mar 2012 (#2012-65)

2012-03-06 Thread Pate, Gene 
on 03/05/2012 at 20:54:38, "Shmuel Metz (Seymour J.)" 
 said:

> What do you mean by backdoor? I don't believe that it is what others
were referring to.

By PCFLIH backdoor I mean a routine whose address replaced the address of the 
IBM supplied PCFLIH. The backdoor routine received control every time a PC 
interrupt occurred and, based on the reason for the PC interrupt it either 
emulated the failing instruction using available instructions and returned 
control to the next sequential instruction or passed control to the IBM 
supplied PCFLIH routine for it to process the PC interrupt. I believe that this 
is also what the vendor routine being discussed did. 

As I said, the PCFLIH backdoor is just a technique and if it is not the 
appropriate technique to use then the vendor should be beat about the head and 
shoulders and made to use whatever technique is appropriate for what their 
product needs to accomplish. 

Gene Pate
CSX Technology
Enterprise Architecture



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