Domain 3 Security Engineering Flashcards
Program Status Word (PSW)
The program status word (PSW) holds different condition bits. One of the bits indicates whether the CPU should be working in user mode (also called problem state) or privileged mode (also called kernel or supervisor mode).
Symmetric mode and asymmetric mode of multiprocessing
When a processor is dedicated, as in this example, the system is working in asymmetric mode. This usually means the computer has some type of time-sensitive application that needs its own personal processor. So, the system scheduler will send instructions from the time-sensitive application to CPU 4 and send all the other instructions (from the operating system and other applications) to CPU 3.
SDRAM, EDO DRAM, BEDO DRAM, DDR SDRAM
Synchronous DRAM (SDRAM) Synchronizes itself with the system’s CPU and synchronizes signal input and output on the RAM chip. It coordinates its activities with the CPU clock so the timing of the CPU and the timing of the memory activities are synchronized. This increases the speed of transmitting and executing data.
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Extended data out DRAM (EDO DRAM) This is faster than DRAM because DRAM can access only one block of data at a time, whereas EDO DRAM can capture the next block of data while the first block is being sent to the CPU for processing. It has a type of “look ahead” feature that speeds up memory access.
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Burst EDO DRAM (BEDO DRAM) Works like (and builds upon) EDO DRAM in that it can transmit data to the CPU as it carries out a read option, but it can send more data at once (burst). It reads and sends up to four memory addresses in a small number of clock cycles.
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Double data rate SDRAM (DDR SDRAM) Carries out read operations on the rising and falling cycles of a clock pulse. So instead of carrying out one operation per clock cycle, it carries out two and thus can deliver twice the throughput of SDRAM. Basically, it doubles the speed of memory activities, when compared to SDRAM, with a smaller number of clock cycles. Pretty groovy.
L1, L2, L3 Cache
Different motherboards have different types of cache. Level 1 (L1) is faster than Level 2 (L2), and L2 is faster than L3. Some processors and device controllers have cache memory built into them. L1 and L2 are usually built into the processors and the controllers themselves.
Absolute address, logical address, relative address
The physical memory addresses that the CPU uses are called absolute addresses. The indexed memory addresses that software uses are referred to as logical addresses. And relative addresses are based on a known address with an offset value applied.
Memory Manager
the memory manager allows the application to use its own addressing scheme—the logical addresses. When the application makes a call to one of these “phantom” logical addresses, the memory manager must map this address to the actual physical address
Buffer Overflow
Since the stack grows downward in most operating systems, putting too many characters into the stack will eventually lead to overwriting the RP. Why? Because the RP is written to the stack first whenever a function is called. Depending on how much memory you have between the vulnerable variable and the RP, you could insert malicious code all the way up to the RP and then overwrite the RP to point to the start of the malicious code you just inserted. This allows the malicious instructions to be executed in the security context of the requesting application
Memory protection techniques: address space layout randomization (ASLR) and data execution prevention (DEP)
If an attacker wants to maliciously interact with a process, he needs to know what memory address to send his attack inputs to. If the operating system changes these addresses continuously, which is what ASLR accomplishes, the potential success of his attack is greatly reduced. You can’t mess with something if you don’t know where it is.
Many of the main operating systems use some form of data execution prevention (DEP), which can be implemented via hardware (CPU) or software (operating system). The actual implementations of DEP vary, but the main goal is to help ensure that executable code does not function within memory segments that could be dangerous.
Counter measures for memory leak
Two main countermeasures can protect against memory leaks: developing better code that releases memory properly, and using a garbage collector, software that runs an algorithm to identify unused committed memory and then tells the operating system to mark that memory as “available.”
Process State
A process can be in a running state (CPU is executing its instructions and data), ready state (waiting to send instructions to the CPU), or blocked state (waiting for input data, such as keystrokes, from a user).
Cooperative Multitasking vs. Preemptive Multitasking
Cooperative multitasking, used in Windows 3.x and early Macintosh systems, required the processes to voluntarily release resources they were using. This was not necessarily a stable environment because if a programmer did not write his code properly to release a resource when his application was done using it, the resource would be committed indefinitely to his application and thus be unavailable to other processes. With preemptive multitasking, used in Windows 9x and later versions and in Unix systems, the operating system controls how long a process can use a resource. The system can suspend a process that is using the CPU and allow another process access to it through the use of time sharing.
Why process isolation
With process isolation, if one process hangs for some reason, it will not affect the other software running. (Process isolation is required for preemptive multitasking.)
How to enforce process isolation
- Encapsulation of objects -Encapsulation provides data hiding
- Time multiplexing of shared resources -Although it seems as though all applications are running (executing their instructions) simultaneously, the operating system is splitting up time shares between each process. Multiplexing means there are several data sources and the individual data pieces are piped into one communication channel.
- Naming distinctions -Naming distinctions just means that the different processes have their own name or identification value. Processes are usually assigned process identification (PID) values, which the operating system and other processes use to call upon them
- Virtual memory mapping - Virtual address mapping allows the different processes to have their own memory space; the operating system ensures no processes improperly interact with another process’s memory. This provides integrity and confidentiality for the individual processes and their data and an overall stable processing environment for the operating system.
Memory Manager - 5 functionalities
Relocation, Protection,Sharing, Logical organization, Physical organization
Software I/O procedures
• Programmed I/O • Interrupt-driven I/O • I/O using DMA • Premapped I/O • Fully mapped I/O
