arXiv subjects

Boris Köpf

Publications and source records attributed to Boris Köpf.

23 records · Page 2Linked to original sources

arXiv2018

Theory and Practice of Finding Eviction Sets

Many micro-architectural attacks rely on the capability of an attacker to efficiently find small eviction sets: groups of virtual addresses that map to the same cache set. This capability has become a decisive primitive for cache side-channel, rowhammer, and speculative execution attacks. Despite their importance, algorithms for finding small eviction sets have not been systematically studied in the literature. In this paper, we perform such a systematic study. We begin by formalizing the problem and analyzing the probability that a set of random virtual addresses is an eviction set. We then present novel algorithms, based on ideas from threshold group testing, that reduce random eviction sets to their minimal core in linear time, improving over the quadratic state-of-the-art. We complement the theoretical analysis of our algorithms with a rigorous empirical evaluation in which we identify and isolate factors that affect their reliability in practice, such as adaptive cache replacement strategies and TLB thrashing. Our results indicate that our algorithms enable finding small eviction sets much faster than before, and under conditions where this was previously deemed impractical.

cs.CR↗

arXiv2017

A Language-theoretic View on Network Protocols

Input validation is the first line of defense against malformed or malicious inputs. It is therefore critical that the validator (which is often part of the parser) is free of bugs. To build dependable input validators, we propose using parser generators for context-free languages. In the context of network protocols, various works have pointed at context-free languages as falling short to specify precisely or concisely common idioms found in protocols. We review those assessments and perform a rigorous, language-theoretic analysis of several common protocol idioms. We then demonstrate the practical value of our findings by developing a modular, robust, and efficient input validator for HTTP relying on context-free grammars and regular expressions.

cs.FL↗

arXiv2017

Loophole: Timing Attacks on Shared Event Loops in Chrome

Event-driven programming (EDP) is the prevalent paradigm for graphical user interfaces, web clients, and it is rapidly gaining importance for server-side and network programming. Central components of EDP are {\em event loops}, which act as FIFO queues that are used by processes to store and dispatch messages received from other processes. In this paper we demonstrate that shared event loops are vulnerable to side-channel attacks, where a spy process monitors the loop usage pattern of other processes by enqueueing events and measuring the time it takes for them to be dispatched. Specifically, we exhibit attacks against the two central event loops in Google's Chrome web browser: that of the I/O thread of the host process, which multiplexes all network events and user actions, and that of the main thread of the renderer processes, which handles rendering and Javascript tasks. For each of these loops, we show how the usage pattern can be monitored with high resolution and low overhead, and how this can be abused for malicious purposes, such as web page identification, user behavior detection, and covert communication.

cs.CR↗

arXiv2017

Rigorous Analysis of Software Countermeasures against Cache Attacks

CPU caches introduce variations into the execution time of programs that can be exploited by adversaries to recover private information about users or cryptographic keys. Establishing the security of countermeasures against this threat often requires intricate reasoning about the interactions of program code, memory layout, and hardware architecture and has so far only been done for restricted cases. In this paper we devise novel techniques that provide support for bit-level and arithmetic reasoning about memory accesses in the presence of dynamic memory allocation. These techniques enable us to perform the first rigorous analysis of widely deployed software countermeasures against cache attacks on modular exponentiation, based on executable code.

cs.CR↗

arXiv2017

Security Analysis of Cache Replacement Policies

Modern computer architectures share physical resources between different programs in order to increase area-, energy-, and cost-efficiency. Unfortunately, sharing often gives rise to side channels that can be exploited for extracting or transmitting sensitive information. We currently lack techniques for systematic reasoning about this interplay between security and efficiency. In particular, there is no established way for quantifying security properties of shared caches. In this paper, we propose a novel model that enables us to characterize important security properties of caches. Our model encompasses two aspects: (1) The amount of information that can be absorbed by a cache, and (2) the amount of information that can effectively be extracted from the cache by an adversary. We use our model to compute both quantities for common cache replacement policies (FIFO, LRU, and PLRU) and to compare their isolation properties. We further show how our model for information extraction leads to an algorithm that can be used to improve the bounds delivered by the CacheAudit static analyzer.

cs.CR↗