Principles of Software Security IFN657 Lecture 3
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Principles of Software Security IFN657 Lecture 3

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Questions and Answers

What is the primary function of the 'mov' instruction in x86 assembly?

  • To change the flow of execution in a program
  • To perform arithmetic operations on registers
  • To load the effective address of a memory location
  • To copy data from one location to another (correct)

    • Which instruction is used to load an effective address into a register?

  • pop
  • push
  • mov
  • lea (correct)

    • What does the instruction 'mov eax, [ebx+esi*4]' do?

  • Loads the effective address EBX+ESI into EAX
  • Initializes EAX with a fixed value from EBX
  • Copies the contents of EAX into memory at EBX+ESI
  • Copies data from the memory address computed by EBX+ESI*4 into EAX (correct)

    • Why is 'mov eax, ebx+8' considered invalid in x86 assembly?

    <p>The 'mov' instruction cannot compute memory addresses</p> Signup and view all the answers

    If you want to copy a value from a memory address into a register, which instruction should you use?

    <p>mov</p> Signup and view all the answers

    What does the instruction 'jg loc' do in assembly language?

    <p>Jump if the destination operand is greater than the source operand.</p> Signup and view all the answers

    Which instruction performs a jump if the destination operand is less than the source operand?

    <p>jl loc</p> Signup and view all the answers

    What is the effect of the instruction 'jge loc'?

    <p>Jump if the destination operand is greater than or equal to the source operand.</p> Signup and view all the answers

    What condition does 'jecxz loc' check before performing the jump?

    <p>Jump to location if ECX equals zero.</p> Signup and view all the answers

    Which instruction should be used for an unsigned comparison to check if the destination is greater than the source?

    <p>ja loc</p> Signup and view all the answers

    What is a characteristic of the C programming language that makes it distinct from higher-level languages?

    <p>Manual memory management</p> Signup and view all the answers

    Which section of computer memory grows by making function calls?

    <p>Stack</p> Signup and view all the answers

    What is the primary function of a disassembler?

    <p>Translates binary to assembly language</p> Signup and view all the answers

    How does an assembler differ from a compiler?

    <p>Assemblers generally work in two passes</p> Signup and view all the answers

    Which of the following describes low-level languages?

    <p>Provide a human-readable version of the instruction set</p> Signup and view all the answers

    What is a key feature of interpreted languages?

    <p>Executed within an interpreter after translation to bytecode</p> Signup and view all the answers

    In x86 architecture, what role does microcode play?

    <p>Functions at a level close to firmware</p> Signup and view all the answers

    Which statement is true regarding assembly language?

    <p>It is a class of languages focusing on x86 architecture</p> Signup and view all the answers

    What is the value of argc when the program is executed with the command 'filetestprogram.exe -r filename.txt'?

    <p>3</p> Signup and view all the answers

    What does the statement 'strncmp(argv, "-r", 2) == 0' check for in the program?

    <p>If the first two characters of argv are '-r'</p> Signup and view all the answers

    What will happen if the condition 'argc != 3' evaluates to true?

    <p>The program will return 0 and terminate.</p> Signup and view all the answers

    In the assembly code, which instruction is executed to compare argc with the value 3?

    <p>cmp [ebp+argc], 3</p> Signup and view all the answers

    What is likely to occur if the command 'filetestprogram.exe -r filename.txt' is altered to 'filetestprogram.exe filename.txt'?

    <p>The program will return 0 without doing anything.</p> Signup and view all the answers

    Which assembly syntax reverses the order of operands and uses a % before registers?

    <p>AT&amp;T format</p> Signup and view all the answers

    What does EAX primarily serve as in the context of x86 registers?

    <p>Primary accumulator for input/output and arithmetic</p> Signup and view all the answers

    In a little-endian format, where is the low-order byte stored?

    <p>At the lower memory address</p> Signup and view all the answers

    Which of the following segment registers points to the code segment containing instructions?

    <p>CS</p> Signup and view all the answers

    What is the role of the EIP register in the CPU?

    <p>To track the next instruction address</p> Signup and view all the answers

    What does the CF flag represent in the EFLAGS register?

    <p>It signifies a carry in arithmetic operations</p> Signup and view all the answers

    Which of the following registers is used primarily as a source index for string operations?

    <p>ESI</p> Signup and view all the answers

    Which general register is used for holding loop counts during iterative operations?

    <p>ECX</p> Signup and view all the answers

    What is the purpose of the EBP register in x86 architecture?

    <p>To provide a reference for parameter variables</p> Signup and view all the answers

    Which statement best describes segment registers in x86 architecture?

    <p>They define the logical address space within memory.</p> Signup and view all the answers

    What happens to the EIP when a function is called?

    <p>Current instruction address in EIP is pushed onto the stack.</p> Signup and view all the answers

    Which instruction is equivalent to using 'sub' but only sets the Zero Flag and Carry Flag without modifying the operands?

    <p>cmp</p> Signup and view all the answers

    What does the 'jz' instruction do in a program's control flow?

    <p>Jumps to the specified location if ZF = 1.</p> Signup and view all the answers

    What is the primary purpose of a function restoring local variables and EBP after execution?

    <p>To maintain stack integrity for the calling function.</p> Signup and view all the answers

    What do conditional jumps rely on to determine program control flow?

    <p>Status flags.</p> Signup and view all the answers

    What is the result of the 'test' instruction when used in a program?

    <p>It only sets the Zero Flag based on the result.</p> Signup and view all the answers

    How many different types of conditional jumps are mentioned?

    <p>More than 30</p> Signup and view all the answers

    In the context of stack operations, what must happen before a function call completes successfully?

    <p>The EIP must be restored.</p> Signup and view all the answers

    Study Notes

    QUT Acknowledgement of Traditional Owners

    • QUT recognizes the Turrbal and Yugara peoples as the First Nations owners of the land.
    • Respect is paid to Elders, customs, lores, and creation spirits.
    • The land has always been a place of learning, teaching, and research.
    • QUT acknowledges the important role of Aboriginal and Torres Strait Islander people within their community.

    Principles of Software Security (IFN657 Lecture 3)

    • Key Points from Last Lecture (C and C#):
      • C is efficient but error-prone, closely related to the machine model with flexible memory management.
      • C# is type-safe, with built-in bounds and string checks, and automatic memory management.
      • Computer memory is divided into sections (stack, heap).
      • Stack grows as function calls are made.
      • Heap grows dynamically as memory is allocated.

    x86 Architecture - Assembly Basics

    • x86 architecture and assembly basics

    Machine vs. Assembly vs. C

    • Shows the relationship between C code, compiled machine code, and assembly code.
    • Demonstrates the translation process from a high-level language (C) to low-level machine code.
    • Includes example C code, generated machine code (in hexadecimal format), and assembly instructions.

    Levels of Abstraction

    • Hardware: Basic electrical circuits implementing logical operations (XOR, AND, OR, NOT).
    • Microcode (Firmware): Lower-level instructions.
    • Machine code: Opcodes (hexadecimal digits) that tell the processor what to do.
    • Low-level languages: Human-readable versions of an architecture's instruction set.
    • High-level languages: Transformed into machine code at compilation (e.g., C/C++).
    • Interpreted languages: Translated to bytecode, then executed.

    Assembly Language

    • Assembly is the highest-level language reliably recovered from machine code.
    • Vulnerable code or malware is typically stored in binary at the machine code level.
    • Disassemblers convert binary to assembly language code.
    • Assembly language is a class of languages, with x86 as a specific focus (explained in more detail).

    Assemblers and Linkers

    • Assemblers and linkers are tools used in software development that manipulate object files and libraries in creating and managing executable code.
    • Assembly files are transformed into object files by assemblers.
    • Object files are linked into an executable file by a linker that also incorporates libraries.

    Assembler vs. Compiler

    • Compilers translate high-level languages to machine code in a single step.
    • Assemblers translate assembly language to machine code in multiple steps.
    • A compiler checks and converts the entire code simultaneously, whereas an assembler typically works in multiple passes.
    • Compilers may include a lexical analyzer (scanning), syntax analyzer, semantic analyzer, code optimizer, code generator, and produce mnemonic versions.

    AT&T vs. Intel Syntax (NASM)

    • Two main assembly language syntax forms.
    • NASM format uses a different order, and symbols before registers/literals.
    • AT&T format, uses the reverse order, and includes % before registers and $ before literal values.

    Fundamental Data Types

    • Binary representations of data types (bytes).

    Memory

    • Memory addresses and their corresponding data.

    Data in Memory (Little-Endian Format)

    • How data is stored in memory using little-endian format

    CPU Registers

    • A small amount of data storage directly accessible by the CPU.
    • Registers are faster accessible than memory.

    x86 Registers

    • Categorizes x86 registers into General, Segment, Status, and Instruction Pointer registers.

    General Registers

    • Storing data or memory addresses and functions like storing data.

    x64 Registers

    • A further division of x86 registers based on 64-bit architecture

    Data Registers

    • Functions of EAX, EBX, ECX, EDX registers (explained in more detail).

    Index Registers

    • Functions of ESI (source) and EDI (destination) registers.

    Segment Registers

    • Functions of CS (Code Segment), DS (Data Segment), SS (Stack Segment) for referencing code, global data and stack, respectively.
    • ES, FS, and GS provide additional segments.
    • Memory address are relative to the starting address of the segment.

    Status Registers

    • Functions of ZF, CF, SF, TF flags (zero, carry, sign, trap).

    Instruction Pointer (EIP)

    • Points to the next instruction to be executed.
    • The complete address consists of a segment selector and offset.

    Other Pointer Registers

    • ESP (Stack Pointer) and EBP (Base Pointer) are described.
    • ESP points to the top of the stack, while EBP points to the current stack frame or local variables in current functions.

    Simple Instructions

    • Functions and uses of various instructions like MOV, LEA, arithmetic instructions (e.g., ADD, SUB, INC, DEC, MUL, DIV), logic instructions(e.g., XOR, OR, SHR, ROR), and the 'nop' instruction.

    Stack Layout

    • Visual representation of the stack with multiple stack frames.

    Function Calls

    • Process of calling and returning from a function explained.

    Conditionals

    • Functions of test and cmp instructions and how they use flags (ZF, CF).

    Branching

    • Types of unconditional jumps (JMP) and conditional jumps (e.g., JZ, JNZ, JG, JGE).

    Examples of Conditional Jumps

    • A variety of conditional jumps.

    C Main Method and Offsets

    • How C programs organize arguments using the main method (argc, argv array).

    A Simple C Program (and compiled form)

    • C program demonstrating the usage of file operations.
    • Shows assembly code after compilation.

    Home Readings

    • List of resources for additional learning about NASM Assembly.

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    Quiz Team

    Related Documents

    Principles of Software Security IFN657 Lecture 3 PDF

    Description

    This quiz covers key points from Lecture 3 of Principles of Software Security. It focuses on the programming languages C and C#, highlighting their memory management differences and safety features. Additionally, it delves into foundational concepts essential for understanding assembly language in the context of x86 architecture.

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