| ==Phrack Inc.== |
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| Volume One, Issue Four, Phile #6 of 11 |
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| Crashing DEC-10's |
| by The Mentor |
| 3-13-86 |
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| Occasionally there will be a time when destruction is necessary. |
| Whether it is revenge against a tyrannical system operator or against |
| a particular company, sometimes it is desirable to strike at the heart of a |
| company...their computer. |
| What follows is a fairly detailed explanation of how to go about |
| crashing a DEC-10 computer running any operating system. The user will have |
| to be able to create and execute assembly level and high level language |
| files, as well as having a good working knowledge of programming. |
| The first step is to obtain an account. Whether this be a default |
| account like 5,30 (pw: GAMES) or an account that you hacked by some other |
| method, you have to be able to access the system. Superuser access is not |
| necessary, however, for this method to work. |
| At the heart of every mainframe computer is the central processing |
| unit. The CPU handles all instructions, fetching them from memory, decoding |
| them, and executing them. A DEC has what is called a DMA (Direct Memory |
| Access) Controller that functions as a small CPU handling all the input and |
| output from memory and peripherals, freeing the main CPU to execute instruc- |
| tions. We take advantage of this fact in crashing the system. |
| Theory: The CPU depends on the DMA Controller to handle all memory |
| access. If the DMA can be crashed, the CPU grinds to a halt and the sysop |
| has to run DSK:RAT to restore all the files on the system (a one hour process, |
| deadly at peak operating time.) We cause the DMA to crash by slowing it down |
| incredibly and overflowing the system stack. |
| Practice- |
| There exists an area known as 'Job Data Area' at octal 20 through 140 |
| of the user's memory. This stores all relevant information about the current |
| task executing. The individual locations each have a 6-bit mnemonic starting |
| with .JB in each case. These must be introduced into a symbol table as ext- |
| ernal references. |
| The highest core address available to the user is stored at .JBREL |
| in the Job Data Area. If you try to access more core than you are allowed, |
| you will get an interrupt and it will crash. The first step is to disable |
| the interrupt. This is done by setting bit 22 in the AC to 1. This is done |
| with a mask as follows... |
| APRENB AC |
| MOVEI AC,20000 (octal) |
| The interrupt is now shut out. Next, you must start snatching up all |
| available system core. This cannot be done by directly meddling with .JBREL. |
| Instead, you must alter AC (accumulator) to contain the highest desired |
| address and then move it into .JBREL. This can be done with the following |
| subroutine. |
| CORE AC, |
| TOP: MOVE AC,.JBREL## |
| AOJA AC,.+1 |
| CORE AC, |
| BRA TOP |
| At first, incrementing only by one looks like a slow way to grab core, |
| but since it is only allocated in chunks of either 1K or 2K words, you can |
| quickly suck up a lot of memory. (Following this file is a complete sample |
| program in MACRO-10 showing how to increase the core to a certain limit.) |
| Now that we have all the core we can get, the system is already more |
| than likely slowing down. This is good. Now we put in the fatal blow. |
| You should already have prepared a program that relies heavily on recursion. |
| The choice languages for this are either C or Pascal. Simply set up a simple |
| recursive program (Towers of Hanoi with 100 rings, for instance), and tell it |
| to execute. |
| What will begin to happen is that the DMA stack will start filling up, |
| slowing the system down even further. Eventually, after between 5 minutes and |
| 15 minutes (longest it's ever taken me), you get the nice beep and... |
| ;;OPSER- DEC SYSTEM-10 NOT RUNNING |
| I've only had to do this on three systems that the sysop really |
| pissed me off (not counting the system where I go to school, on which I do |
| it all the time when I'm bored...) It's kind of an extreme measure, but |
| it can be an effective one. |
| The following program is a sample for those not familiar with MACRO-10 |
| assembly language. |
| 32 |
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| START: TITLE SAMPLE |
| MOVE P,[IOWD 3,MEM] |
| MOVE [PUSHJ P,PDLOV] |
| MOVEM .JBAPR## |
| MOVEI AC,600000 |
| APRENB AC, |
| SETZB CT |
| MOVEM AC |
| AOS |
| PUSHJ P,S1 |
| JRST .-3 |
| S1: IDIVI AC,10 |
| HRLM N,(P) |
| JUMPE AC,.+3 |
| PUSHJ P,S1 |
| SKIPA |
| PUSHJ P,S2 |
| HLRZ N,(P) |
| ADDI N,60 |
| OUTCHR N |
| POPJ P, |
| S2: SOJG CT,.+4 |
| OUTCHR [15] |
| OUTCHR [12] |
| MOVEI CT,10 |
| MOVE T,P |
| OUTCHR [40] |
| AOBJN T,.-1 |
| POPJ P, |
| PDLOV: PUSHJ P,LIMIT |
| SUB P,[1,,0] |
| JRSTF @.JBTPC## |
| LIMIT: CAIL 1000 ;CHANGE TO WHATEVER YOU WANT! |
| EXIT |
| POPJ P, |
| MEM: BLOCK 10 |
| END START |
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