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      CS 211編程代做、代寫c/c++,Java程序

      時間:2024-04-04  來源:  作者: 我要糾錯



      CS 211 - Computer Architecture
      Instructor: Prof. Santosh Nagarakatte
      Assignment 4
      Disassembling and Defusing a Binary Bomb
      March 25, 2024
      Due by April 10, 2024 - 5:00PM
      dis·as·sem·ble (vt)
      take apart: to take something such as a piece of machinery apart.
      – Bing Dictionary
      0 Overview
      The purpose of Assignment 4 (PA4) is for you to become familiar with x86 64 Instruction Set Architecture (ISA).
      The nefarious Dr. Evil has planted a slew of ”binary bombs” on our machines. A binary bomb is a program
      that consists of a sequence of phases. Each phase expects you to type a particular string on stdin. If you type the
      correct string, then the phase is defused and the bomb proceeds to the next phase. Otherwise, the bomb explodes
      by printing ”BOOM!!!” and then terminating. The bomb is defused when every phase has been defused.
      There are too many bombs for us to deal with, so we are giving everyone a bomb to defuse. Your mission,
      which you have no choice but to accept, is to defuse your bomb before the due date. Good luck, and welcome to
      the bomb squad!
      1 Instructions
      The bombs were constructed specifically for the Linux operating system. You must do this assignment on the iLab
      machines. You will not defuse the bomb otherwise and will not get credit.
      In fact, there is a rumor that Dr. Evil has ensured the bomb will always blow up if run elsewhere. There are
      several other tamper-proofing devices built into the bomb as well, or so they say.
      Open an Internet Browser and go to the URL: http://skylake.cs.rutgers.edu:17300. This address is only “visible” when you access it on iLab machines through weblogin. Fill the form up with your NetID
      and your email address to get your bomb package. The file that you will get is in the format bombN.tar, where N is
      your bomb ID, i.e. ID.
      If you haven’t downloaded it in the iLab machines, copy the file to there and untar your bomb into your home
      directory.
      We recommend that you download no more than two bombs. Copy the bomb that you downloaded into your
      iLab account and work with it.
      $ tar -xvf bomb<ID>.tar
      It will create a directory bomb< ID > that should contain the following files:
      1
      • bomb: The executable binary bomb
      • bomb.c: Source file with the bomb’s main routine
      • README: File with the bomb ID and extra information
      Your job is to defuse the bomb. You can use many tools to help you with this; please look at the tools section
      for some tips and ideas. The best way is to use a debugger to step through the disassembled binary.
      The bomb has 9 phases. The phases get progressively harder to defuse, but the expertise you gain as you move
      from phase to phase should offset this difficulty. Nonetheless, the latter phases are not easy, so please don’t wait
      until the last minute to start. (If you’re stumped, check the hints section at the end of this document.)
      The bomb ignores blank input lines. If you run your bomb with a command line argument, for example,
      ./bomb mysolution.txt
      then it will read the input lines from mysolution.txt until it reaches EOF (end of file), and then switch over to
      stdin (standard input from the terminal). In a moment of weakness, Dr. Evil added this feature so you don’t have
      to keep retyping the solutions to phases you have already defused.
      To avoid accidentally detonating the bomb, you will need to learn how to single-step through the assembly code
      and how to set breakpoints. You will also need to learn how to inspect both the registers and the memory states.
      One of the nice side-effects of doing the lab is that you will get very good at using a debugger. This is a crucial
      skill that will pay big dividends the rest of your career.
      IMPORTANT: Every time that the bomb explodes, you will lose 0.5 points. It is important that you use
      breakpoints and avoid those unnecessary explosions.
      2 Resources
      There are a number of online resources that will help you understand any assembly instructions you may encounter
      while examining the bomb. In particular, the programming manuals for x86 processors distributed by Intel and
      AMD can be valuable. They both describe the same ISA, but sometimes one may be easier to understand than the
      other.
      It is important to realize that the assembly syntax of the instructions on the Intel manual follows the Intel
      assembly language, while in the book, in gcc, and in gdb they all use the AT&T assembly language. They are
      perfectly interchangable, you can identify the differences in this webpage:
      http://asm.sourceforge.net/articles/linasm.html
      2.1 Checking your Work
      We provided a webpage where you can check your work. Access:
      http://skylake.cs.rutgers.edu:17300/scoreboard to verify how many points you have, up to
      which phase you have defused the bomb, and so on. You have to be on the iLab machines to access the above link.
      3 Tools
      There are many ways of defusing your bomb. You can examine it in great detail without ever running the program,
      and figure out exactly what it does. This is a useful technique, but it not always easy to do. You can also run it
      under a debugger, watch what it does step by step, and use this information to defuse it. This is probably the fastest
      way of defusing it.
      2
      We do make one request, please do not use brute force! You could write a program that will try every possible
      key to find the right one, but the number of possibilities is so large that you won’t be able to try them all in time.
      There are many tools which are designed to help you figure out both how programs work, and what is wrong
      when they don’t work. Here is a list of some of the tools you may find useful in analyzing your bomb, and hints on
      how to use them.
      • gdb: The GNU debugger is a command line debugger tool available on virtually every platform. You can
      trace through a program line by line, examine memory and registers, look at both the source code and
      assembly code (we are not giving you the source code for most of your bomb), set breakpoints, set memory
      watch points, and write scripts. Here are some tips for using gdb.
      – To keep the bomb from blowing up every time you type in a wrong input, you’ll want to learn how to
      set breakpoints.
      – The CS:APP Student Site has a very handy gdb summary (there is also a more extensive tutorial).
      – For other documentation, type help at the gdb command prompt, or type ”man gdb”, or ”info gdb” at a
      Unix prompt. Some people also like to run gdb under gdb-mode in emacs.
      • objdump -t bomb: This will print out the bomb’s symbol table. The symbol table includes the names of all
      functions and global variables in the bomb, the names of all the functions the bomb calls, and their addresses.
      You may learn something by looking at the function names!
      • objdump -d bomb: Use this to disassemble all of the code in the bomb. You can also just look at individual
      functions. Reading the assembler code can tell you how the bomb works. Although objdump -d gives you a
      lot of information, it doesn’t tell you the whole story. Calls to system-level functions may look cryptic. For
      example, a call to sscanf might appear as:
      8048c36: e8 99 f c ff ff call 80488d4 < init + 0x1a0 >
      To determine that the call was to sscanf, you would need to disassemble within gdb.
      • strings -t x bomb: This utility will display the printable strings in your bomb and their offset within the
      bomb.
      Looking for a particular tool? How about documentation? Don’t forget, the commands apropos and man
      are your friends. In particular, man ascii is more useful than you’d think. If you get stumped, use the course’s
      discussion board on Canvas.
      4 Submission
      You have to e-submit the assignment using Canvas. Your submission should be a tar file named bomb < ID > .tar
      that can be extracted using the command:
      tar -xf bomb<ID>.tar
      Extracting your tar file must give a directory called bomb < ID >. This directory should contain the same
      files that you downloaded, along with the file mysolution.txt to defuse the bomb.
      To create the tar file that you will submit after finishing your programming assignment, you will use the following command line, in the parent directory of bomb < ID >:
      tar -cvf bomb<ID>.tar bomb<ID>/
      3
      5 Grading
      Your grade will be based on how many stages of the bomb you have defused. Be careful to follow all instructions.
      If something doesn’t seem right, ask.
      6 Collaboration
      You are not supposed to assist your friends or other students in solving the bombs. You are required not to use any
      online resource other than ones explicitly described above. If in doubt, ask. Keep in mind that your final will test
      you based on the skills learned in this assignment.

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