下载文档原格式
信息安全模型22:551 计算机体系Computer Architecture •计算机体系结构是指组成计算机的基本组件（fundamental elements）•主要硬件组件:–CPU, memory, input/output devices.22:551.1 中央处理单元CPU–算术逻辑单元Arithmetic Logic Unit (ALU) Performa data transfer, arithmetic, data editing –控制单元Control logic: coordinate, select,interprets of instructions–多个一般寄存器registers–一个指令寄存器instruction register–一个程序计数器program counter–片内内存on-chip local memory•Store instructions and data needed by CPU 22:551.2 CPU•Buffer overflow 缓冲区溢出Data being processed is entered into the CPU in blocks at a time. If the software instructions do not properly set the boundaries for how much data can come in as a block, extra data can slip in and be executed.22:551.3 存储器Memory•高速缓存Cache Memory–Relatively small amount of very high RAM, holds instructions and data used by currently executing program.•随机存取存储器Random Access Memory(RAM)–非永久存储-Is a volatile memory, because when power is lost -> information is lost–Memory where locations can be directly addressed and the data can be altered–动态DRAM-Requires that that data held within it be periodically refreshed because the data dissipates and decays.–静态SRAM uses latches to store each bit.22:55Memory•可编程逻辑设备Programmable Logic Device (PLD)–ROM,PAL (Programmable Array Logic),FPGA•只读存储器Read Only Memory(ROM)–永久性non volatile storage where locations can bedirectly addressed.–Software that is stored within ROM is called firmware –EPROM－Erasable and programmable read-onlymemory–EEPROM－Electrically Erasable Programmable Read Only Memories–EAROM–Flash memories22:551.4 存储器映射Memory Mapping •主存储Real or primary memory–直接可寻址,used for the storage of instructions and data –通常为高速RAM (Random Access Memory)•次级存储Secondary memory–速度较慢(硬盘，软盘，CD-ROM)–永久性Non-volatile storage•时序存储Sequential memory–Info be obtained sequentially.–Example: 磁带(Magnetic tape)22:55存储器映射Memory Mapping•虚存Virtual memory–Uses secondary memory in conjunction with primary memory to present a CPU with a larger, apparentaddress space of the real memory locations–Virtual memory=Real storage + Auxiliary Storage22:55内存寻址Memory addressing•寄存器寻址Register addressing–Addressing the registers within a CPU or special purpose registers•直接寻址Direct addressing–Addressing portion of primary memory by the actual address.Without reference to a storage location containing anotheraddress•绝对寻址Absolute addressing–All of the primary memory space–=relative address+Base address•变址寻址Indexed addressing–By adding the contents of the address to that of an index register. 22:55•隐式寻址Implied addressing–Used such as operations that are internal to theprocessor. The operation is being performed on aninternal register that is specified within the instruction.•间接寻址Indirect addressing–Where the address location that is specified in theprogram instruction contains the address of the finaldesired location.22:55•内存保护Memory protection–防止一个程序访问另一程序的内存空间–由操作系统或硬件实现(by the OS orhardware mechanisms.)•指令执行周期Instruction Execution Cycle –A basic machine cycle consists of two phases:–Fetch and execute.22:55•复杂指令集Complex-Instruction-Set-Computer(CISC)–Instructions that perform many operations per instruction.•精简指令集Reduced-Instruction-Set-Computer(RISC)–Simpler and require fewer clock cycles toexecute.22:55•标量处理器Scalar Processor–Executes one instruction at a time.•超标量处理器Superscalar Processor–Enable concurrent execution of multiple instructions in the same pipeline stage as well as in different pipeline stages.•Very-Long Instruction-Word Processor(VLIW)–A single instruction specifies more than oneconcurrent operation.22:55•多程序Multiprogramming–一个处理器Executes two or more programssimultaneously on a single processor(CPU) byaltaernating execution among the programs.•多任务Multitasking–一个处理器Executes two or more subprograms ortasks at the same time on a CPU by alternatingexecution among the tasks.•多处理Multiprocessing–多个处理器Exe two or more programs at the same time on multiple processors.22:551.5 输入输出结构Input/Output Structures•I/O接口适配器interface adapters–A processor communicates with outside devicesthrough which.–Provide data buffering, timing and interrupt controls.–Adapters have addresses on the computer bus22:551.6 软件Software•1GL-machine language 机器语言•2GL-assembly language 汇编语言•3GL-FORTRAN, BASIC, PL/1, and C 高级语言•4GL-NATURAL, FOCUS, and DB query languages. 自然语言•5GL-Prolog, LISP, and other artificial intelligence languages that process symbols or implement predicate logic.人工智能语言22:55Software•源码Source code,•目标代码object code, code generated by assembler •Resident assembler.•Cross assembler•反汇编Disassember,–If assembler is being run on another computer–Reverse function•Macro–A group of assembly language statements used to perform a specific function.–can be used to represent several functions inassembly22:551.7 CPU模式和保护环(CPU Modes and Protection Rings)0 OS核123保护环：0环：操作系统内核1环：操作系统其余部分2环：I/O驱动和工具3环：应用和程序22:55Process进程•Process–正在执行的程序•Thread–一段在某个进程中执行的代码22:55操作状态operating states •ready state,就绪进程已就绪，等待新指令•problem state, 运行正在执行程序•supervisory state,管理执行系统程序•wait state, 等待等待中断22:552 系统体系结构•TCB可信计算基础•Security Perimeter 安全边界•Reference Monitor 参考监控器•Security Kernel 安全核心•Domains 域•Resource isolation 资源隔离•Security policy 安全策略•Least privilege 最小特权22:552.1 TCB 可信计算基础•TCB -Trusted Computing Base:–TCB 在TCSEC 中的定义是：一个计算机系统中的保护机制的全体，它们共同负责实施一个安全政策，它们包括硬件、固件和软件；一个TCB 由在一个产品或系统上共同实施一个统一的安全政策的一个或多个组件构成。
安全模型和体系结构一、快速提示·系统可以有完全相同的硬件、软件和应用，但却会因为系统建立在不同的安全策略和安全模型之上而提供不同的保护级别。
·CPU包括一个控制单元，它控制指令和数据执行的时序；一个ALU（算术逻辑单元)，它执行算术功能和逻辑操作。
·绝大多数系统部使用保护环(protection ring）。
进程的特权级别越高，则运行在编号越小的保护环中，它就能访问全部或者大部分的系统资源。
应用运行在编号越大的保护环中．它能访问的资源就越少。
·操作系统的进程运行在特权或监控模式中，应用运行在用户模式中，也称为“问题”状态。
·次级存储(second storage)是永久性的，它可以是硬盘、CD—ROM、软驱、磁带备份或者Zip驱动器。
·虚存（virtual storage)由RAM和次级存储所构成，系统因此显得具有很大一块存储器。
·当两个进程试图同时访问相同的资源，或者一个进程占据着某项资源而且不释放的时候，就发生了死锁情况。
·安全机制着眼于不同的问题，运行于不同的层次，复杂性也不尽相同。
·安全机制越复杂，它能提供的保险程度就越低。
·并不是所有的系统组成部分都要处于TCB范围内：只有那些直接以及需要实施安全策略的部件才是。
·构成TCB的组成部分有硬件、软件、回件，因为它们都提供了某种类型的安全保护功能。
·安全边界(security perimeter)是一个假想的边界线，可信的部件位子其中(那些构成TCB 的部件)，而不可信的部件则处于边界之外。
·引用监控器(reference monitor)是一个抽象机，它能确保所有的主体在访问客体之前拥有必要的访问权限。
因此，它是主体对客体所有访问的中介。
·安全核心(security kernel)是实际落实引用监控器规则的机制。
