Cpu Security Vulnerabilities: Spectre, Meltdown, And Their Mitigation. – Tracking Specter and Meltdown can be a challenge. This guide includes an in-depth explanation of this particularly dangerous security vulnerability and the best mitigation solutions.
Cpu Security Vulnerabilities: Spectre, Meltdown, And Their Mitigation.
In January 2018, the Specter and Meltdown security vulnerabilities were publicly disclosed, causing widespread concern among security professionals because they can be used to steal data from almost any computer, as well as iPhone and iPad, as well as other mobile devices.
Vector Cpu Icon With Alert Sign. Concept Of Cyber Security And Meltdown And Spectre Critical Vulnerabilities In Modern Processors. Monochrome Flat Ima Stock Vector Image & Art
Specter and Meltdown represent a class of hardware vulnerabilities, each with several variants depending on the specific functionality of the silicon level. Differences between manufacturers (eg Intel vs. AMD) and architectures (eg x86-64 vs. Arm) make some processors susceptible to more variants than others. While this is primarily a hardware design flaw, efforts to correct it at the software level have shown some success.
Understanding of Specter and Meltdown has increased significantly since the initial disclosure, and security researchers continue to study these vulnerabilities. Currently, 13 variants of Specter and 14 variants of Meltdown have been identified. Initially, AMD processors were thought to be immune to Meltdown, although a variant has been successfully demonstrated on AMD systems.
The cheat sheet for Specter and Meltdown is a comprehensive guide to understanding how the vulnerabilities work, as well as a source of up-to-date patching and mitigation information.
Detection Of The Meltdown And Spectre Vulnerabilities
Note: the cheat sheets for Specter and Meltdown use different stratifications, definitions, and explanations from “A Systematic Evaluation of Transient Execution Attacks and Defenses,” by Claudio Canella, Daniel Gruss, Moritz Lipp, Philipp Ortner, Michael Schwarz, and Benjamin von Berg of the University of Technology Graz; Frank Piessens and Jo Van Bulck of KU Leuven; and Dmitry Evtyushkin of the College of William and Mary. The document serves as a further analysis of the original paper presenting Meltdown and Spectre.
At its most basic, Specter is a vulnerability that allows arbitrary locations in a program’s allocated memory to be read. Meltdown is a vulnerability that allows a process to read the entire memory on a given system. Specter and Meltdown are not single vulnerabilities – each represents a closely related class of variants.
Specter and Meltdown are dangerous security vulnerabilities that allow criminals to bypass system security protections built into nearly all modern devices with a CPU—not just PCs, servers, and smartphones, but as well as Internet of Things (IoT) devices such as routers and smart TVs . By using both, it is possible to read protected system memory, gaining access to passwords, encryption keys, and other sensitive information.
Meltdown And Spectre
Specter and Meltdown are representative examples of “transient execution” attacks, which rely on hardware design flaws in the implementation of speculative execution, instruction pipelines, and out-of-order execution on modern CPUs . While all three are essential for the inherent performance optimization of modern processors, their implementation varies between CPU manufacturers and microarchitectures; as a result, not all variants of Specter and Meltdown can be used on all microarchitectures.
Following the Specter and Meltdown disclosures, further research into CPU side-channel vulnerabilities resulted in a new class of vulnerabilities, “Microarchitectural Data Sampling” (MDS), which exploit internal CPU buffers, not in the CPU cache. These targets make attacks using MDS harder to mitigate, but also harder for hackers to exploit.
This cheat sheet cites and contextualizes—or, if necessary, corrects—claims about Specter and Meltdown that do not correspond to real-world events regarding either.
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For cloud computing, Specter and Meltdown can be used by attackers to escape software containers, paravirtualized systems, and virtual machines.
As stand-alone vulnerabilities, Specter and Meltdown are relatively ineffective for mass data exfiltration, as preliminary research shows that Meltdown is capable of accessing data at speeds of around 120 KB/s, while the Specter is at 1.5 to 2 KB/s. Furthermore, Spectre-BTB (Variant 2) takes 10-30 minutes to initialize on a system with 64 GB RAM, which is expected to be “almost linearly” as the host RAM size increases.
Meltdown & Spectre Attacks On Cpu Flaws
The Specter and Meltdown exploits can be performed undetected – that is, without leaving evidence of the exploit in the system log. This makes it difficult to detect these pairs in targeted malware attacks, although known malware signatures can still be detected by traditional means.
Specter and Meltdown mechanisms require an understanding of how modern processor microarchitectures are designed.
Performance improvements in modern processors come from several techniques. Limitations in increasing the physical properties of the processor (reducing transistor size and increasing clock frequency) require architectural changes in the way the processor works to produce components with higher performance. These changes are mostly focused on parallelism: Optimization and expansion of the instruction pipeline, allowing multiple operations to be performed in parallel within a logical core (thread), and increasing the number of logical and physical which are cores in a processor.
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Other features in modern processors include virtual (paged) memory, a method that simplifies memory management among processes, privilege levels, which allow the operating system to control which parts of virtual memory can be read by other processes, and the CPU cache, where the data resides. System RAM is cached to reduce latency.
These two independent optimization techniques of modern processors, used together, are key to understanding how Specter and Meltdown represent hardware-level vulnerabilities.
Out-of-sequence execution allows all execution units on a CPU core to be used simultaneously. As explained in the Meltdown paper, “Instead of processing instructions strictly in sequential program order, the CPU executes them as soon as all the necessary resources are available. When the execution unit of the current operation is busy, a different execution unit may run first. Therefore, instructions may be executed in parallel as long as the results conform to the architectural definition.”
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The state of instructions processed out of sequence is stored in the reorder buffer, where they are executed sequentially.
Speculative execution allows the processor to speculate on the future direction of an instruction and actively execute instructions on this path before knowing whether the instruction is correct. An example in the Specter paper, “Consider an example where the control flow of a program relies on an uncached value located in external physical memory. Because this memory is slower than the CPU, it often takes several hundred clock cycles before the value is known. Instead of wasting these cycles in idleness, the CPU tries to predict the direction of the control flow, save the register state its checkpoints, and continue to execute the program speculatively along the predicted path.
When a value is retrieved from memory, the correctness of the prediction is checked. If true, the outcome would be guaranteed, “resulting in significant performance improvements because useful work is completed during the delay.” If false, speculative execution is thrown. Performance-wise, this is transparent—the speed is comparable to idle, as if the speculative execution never took place. Importantly, it is possible to execute speculative instructions in both in-order and out-of-order pipelines.
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In terms of security, speculative execution requires executing a program in a potentially incorrect way. To preserve functional correctness, these false assumptions, or temporary implementations, are intended not to be exposed in the program. They are uncommitted, and removed from the execution path, undoing any architectural effects the instruction might have had.
However, according to the Systematic Evaluation paper, “Even when architectural effects and results of temporary instructions are discarded, microarchitectural effects remain outside of temporary execution. This is the basis of Spectre, Meltdown, and Foreshadow. These attacks exploit the temporary execution and encoding of secrets in microarchitectural side effects (eg, cache state) to deliver them (at the architectural level) to the attacker.”
Spectre, according to the original authors of the Specter paper, “[encourages] victims to speculatively perform operations that would not occur during the processing of strictly sequenced program instructions, and if where the victim’s confidential information is leaked through covert channels to the adversary.”
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Meltdown exploits a race condition between memory accesses and privilege level checks while processing instructions. In conjunction with CPU cache side-channel attacks, privilege level checks can be bypassed, thereby allowing access to memory used by the operating system, or other process running. In certain situations, it can be used to read memory in a paravirtualized software container.
The contents of the attacker’s chosen memory location, which the attacker cannot access, are loaded into a register. Temporary instructions access cache lines based on the secret contents of registers. The attacker uses Flush+Reload to determine which cache line is accessible and therefore the secret stored in the selected memory location. Understand the difference between Specter and Meltdown
Although Specter and Meltdown were published at the same time, they exploit different CPU characteristics; the only similarity between the two
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