|
Speculative Execution
Speculative execution is an optimization (computer science), optimization technique where a computer system performs some task that may not be needed. Work is done before it is known whether it is actually needed, so as to prevent a delay that would have to be incurred by doing the work after it is known that it is needed. If it turns out the work was not needed after all, most changes made by the work are reverted and the results are ignored. The objective is to provide more Concurrency (computer science), concurrency if extra Resource (computer science), resources are available. This approach is employed in a variety of areas, including branch predictor, branch prediction in instruction pipeline, pipelined CPU, processors, value prediction for exploiting value locality, prefetching Instruction prefetch, memory and File system, files, and optimistic concurrency control in Relational database management system, database systems. Speculative multithreading is a special case of specu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optimization (computer Science)
In computer science, program optimization, code optimization, or software optimization is the process of modifying a software system to make some aspect of it work more algorithmic efficiency, efficiently or use fewer resources. In general, a computer program may be optimized so that it executes more rapidly, or to make it capable of operating with less Computer data storage, memory storage or other resources, or draw less power. Overview Although the term "optimization" is derived from "optimum", achieving a truly optimal system is rare in practice, which is referred to as superoptimization. Optimization typically focuses on improving a system with respect to a specific quality metric rather than making it universally optimal. This often leads to trade-offs, where enhancing one metric may come at the expense of another. One popular example is space-time tradeoff, reducing a program’s execution time by increasing its memory consumption. Conversely, in scenarios where memory is l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Memory Dependence Prediction
Memory dependence prediction is a technique, employed by high-performance out-of-order execution microprocessors that execute memory access operations (loads and stores) out of program order, to predict true dependencies between loads and stores at instruction execution Capital punishment, also known as the death penalty and formerly called judicial homicide, is the state-sanctioned killing of a person as punishment for actual or supposed misconduct. The sentence ordering that an offender be punished in ... time. With the predicted dependence information, the processor can then decide to speculatively execute certain loads and stores out of order, while preventing other loads and stores from executing out-of-order (keeping them in-order). Later in the pipeline, memory disambiguation techniques are used to determine if the loads and stores were correctly executed and, if not, to recover. By using the memory dependence predictor to keep most dependent loads and stores ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Out-of-order Execution
In computer engineering, out-of-order execution (or more formally dynamic execution) is an instruction scheduling paradigm used in high-performance central processing units to make use of instruction cycles that would otherwise be wasted. In this paradigm, a processor executes instructions in an order governed by the availability of input data and execution units, rather than by their original order in a program. In doing so, the processor can avoid being idle while waiting for the preceding instruction to complete and can, in the meantime, process the next instructions that are able to run immediately and independently. History Out-of-order execution is a restricted form of dataflow architecture, which was a major research area in computer architecture in the 1970s and early 1980s. Early use in supercomputers The first machine to use out-of-order execution was the CDC 6600 (1964), designed by James E. Thornton, which uses a scoreboard to avoid conflicts. It permits ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anticiparallelism
Anticiparallelism (Anticipatory Parallelism) is a term coined by Bob Metcalfe in 1998. It is a technique of using idle machine cycles to perform useful computing tasks in the background. Such tasks must be readily interrupted for intervals when the computer needs to return to its primary task. An example of such a task is transmitting e-mail. Anticiparalleism is also known as speculative execution, continual computation or optimistic execution. See also * Folding@home, a distributed computing project that uses idle processing resources of personal computers A personal computer, commonly referred to as PC or computer, is a computer designed for individual use. It is typically used for tasks such as Word processor, word processing, web browser, internet browsing, email, multimedia playback, and PC ... owned by volunteers who have installed the software on their systems References Further reading *{{cite journal , first=Bob , last=Metcalfe , date=September 14, 1998 , t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pacman (security Vulnerability)
Pacman is a side-channel vulnerability in certain ARM CPUs that was made public by Massachusetts Institute of Technology security researchers on June 10, 2021. It affects the pointer authentication (PAC) mechanism in many ARMv8.3 chips, including Apple's M1 CPU. Pacman creates an 'oracle' that lets an attacker guess a pointer's PAC signature without crashing the program if the guess is wrong. PAC signatures are typically less than 16 bits wide, so an attacker can use the oracle to guess the signature in 216 tries or fewer. It is unfixable without hardware changes because it is caused by the inherent design of CPU cache A CPU cache is a hardware cache used by the central processing unit (CPU) of a computer to reduce the average cost (time or energy) to access data from the main memory. A cache is a smaller, faster memory, located closer to a processor core, whi ...s and branch predictors. Impact and response Pacman alone is not an exploitable vulnerability. PAC is a ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spectre (security Vulnerability)
Spectre is one of the speculative execution CPU vulnerabilities which involve side-channel attacks. These affect modern microprocessors that perform branch prediction and other forms of speculative execution. On most processors, the speculative execution resulting from a branch misprediction may leave observable side effects that may reveal private data to attackers. For example, if the pattern of memory accesses performed by such speculative execution depends on private data, the resulting state of the data cache constitutes a side channel through which an attacker may be able to extract information about the private data using a timing attack. In addition to vulnerabilities associated with installed applications, JIT engines used for JavaScript were found to be vulnerable. A website can read data stored in the browser for another website, or the browser's memory itself. Two Common Vulnerabilities and Exposures records related to Spectre, (bounds check bypass, Spect ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microarchitectural Data Sampling
The Microarchitectural Data Sampling (MDS) vulnerabilities are a set of weaknesses in Intel x86 microprocessors that use hyper-threading, and leak data across protection boundaries that are architecturally supposed to be secure. The attacks exploiting the vulnerabilities have been labeled Fallout, RIDL (''Rogue In-Flight Data Load''), ZombieLoad., and ZombieLoad 2. Description The vulnerabilities are in the implementation of speculative execution, which is where the processor tries to guess what instructions may be needed next. They exploit the possibility of reading data buffers found between different parts of the processor. * Microarchitectural Store Buffer Data Sampling (MSBDS), * Microarchitectural Load Port Data Sampling (MLPDS), * Microarchitectural Fill Buffer Data Sampling (MFBDS), * Microarchitectural Data Sampling Uncacheable Memory (MDSUM), *Transactional Asynchronous Abort (TAA)CVE-2019-11135 Not all processors are affected by all variants of MDS. History Ac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Meltdown (security Vulnerability)
Meltdown is one of the two original speculative execution CPU vulnerabilities (the other being Spectre). Meltdown affects Intel x86 microprocessors, IBM Power microprocessors, and some ARM-based microprocessors. It allows a rogue process to read all memory, even when it is not authorized to do so. Meltdown affects a wide range of systems. At the time of disclosure (2018), this included all devices running any but the most recent and patched versions of iOS, Linux, macOS, or Windows. Accordingly, many servers and cloud services were impacted, as well as a potential majority of smart devices and embedded devices using ARM-based processors (mobile devices, smart TVs, printers and others), including a wide range of networking equipment. A purely software workaround to Meltdown has been assessed as slowing computers between 5 and 30 percent in certain specialized workloads, although companies responsible for software correction of the exploit reported minimal impact from g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Foreshadow (security Vulnerability)
Foreshadow, known as L1 Terminal Fault (L1TF) by Intel, is a vulnerability that affects modern microprocessors that was first discovered by two independent teams of researchers in January 2018, but was first disclosed to the public on 14 August 2018. The vulnerability is a speculative execution attack on Intel processors that may result in the disclosure of sensitive information stored in personal computers and third-party clouds. There are two versions: the first version (original/Foreshadow) () targets data from SGX enclaves; and the second version (next-generation/Foreshadow-NG) () targets virtual machines (VMs), hypervisors (VMM), operating systems (OS) kernel memory, and System Management Mode (SMM) memory. A listing of affected Intel hardware has been posted. Foreshadow is similar to the Spectre security vulnerabilities discovered earlier to affect Intel and AMD chips, and the Meltdown vulnerability that also affected Intel. AMD products are not affected by the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Privilege (computing)
In computing, privilege is defined as the delegation of authority to perform security-relevant functions on a computer system. A privilege allows a user to perform an action with security consequences. Examples of various privileges include the ability to create a new user, install software, or change kernel functions. Users who have been delegated extra levels of control are called privileged. Users who lack most privileges are defined as unprivileged, regular, or normal users. Theory Privileges can either be automatic, granted, or applied for. An automatic privilege exists when there is no requirement to have permission to perform an action. For example, on systems where people are required to log into a system to use it, logging out will not require a privilege. Systems that do not implement file protection - such as MS-DOS - essentially give unlimited privilege to perform any action on a file. A granted privilege exists as a result of presenting some credential to the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vulnerability (computing)
Vulnerabilities are flaws or weaknesses in a system's design, implementation, or management that can be exploited by a malicious actor to compromise its security. Despite a system administrator's best efforts to achieve complete correctness, virtually all hardware and software contain bugs where the system does not behave as expected. If the bug could enable an attacker to compromise the confidentiality, integrity, or availability of system resources, it can be considered a vulnerability. Insecure software development practices as well as design factors such as complexity can increase the burden of vulnerabilities. Vulnerability management is a process that includes identifying systems and prioritizing which are most important, scanning for vulnerabilities, and taking action to secure the system. Vulnerability management typically is a combination of remediation, mitigation, and acceptance. Vulnerabilities can be scored for severity according to the Common Vulnerability S ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
