24,013 research outputs found
Linux kernel compaction through cold code swapping
There is a growing trend to use general-purpose operating systems like Linux in embedded systems. Previous research focused on using compaction and specialization techniques to adapt a general-purpose OS to the memory-constrained environment, presented by most, embedded systems. However, there is still room for improvement: it has been shown that even after application of the aforementioned techniques more than 50% of the kernel code remains unexecuted under normal system operation. We introduce a new technique that reduces the Linux kernel code memory footprint, through on-demand code loading of infrequently executed code, for systems that support virtual memory. In this paper, we describe our general approach, and we study code placement algorithms to minimize the performance impact of the code loading. A code, size reduction of 68% is achieved, with a 2.2% execution speedup of the system-mode execution time, for a case study based on the MediaBench II benchmark suite
Security Through Amnesia: A Software-Based Solution to the Cold Boot Attack on Disk Encryption
Disk encryption has become an important security measure for a multitude of
clients, including governments, corporations, activists, security-conscious
professionals, and privacy-conscious individuals. Unfortunately, recent
research has discovered an effective side channel attack against any disk
mounted by a running machine\cite{princetonattack}. This attack, known as the
cold boot attack, is effective against any mounted volume using
state-of-the-art disk encryption, is relatively simple to perform for an
attacker with even rudimentary technical knowledge and training, and is
applicable to exactly the scenario against which disk encryption is primarily
supposed to defend: an adversary with physical access. To our knowledge, no
effective software-based countermeasure to this attack supporting multiple
encryption keys has yet been articulated in the literature. Moreover, since no
proposed solution has been implemented in publicly available software, all
general-purpose machines using disk encryption remain vulnerable. We present
Loop-Amnesia, a kernel-based disk encryption mechanism implementing a novel
technique to eliminate vulnerability to the cold boot attack. We offer
theoretical justification of Loop-Amnesia's invulnerability to the attack,
verify that our implementation is not vulnerable in practice, and present
measurements showing our impact on I/O accesses to the encrypted disk is
limited to a slowdown of approximately 2x. Loop-Amnesia is written for x86-64,
but our technique is applicable to other register-based architectures. We base
our work on loop-AES, a state-of-the-art open source disk encryption package
for Linux.Comment: 13 pages, 4 figure
Caching in Multidimensional Databases
One utilisation of multidimensional databases is the field of On-line
Analytical Processing (OLAP). The applications in this area are designed to
make the analysis of shared multidimensional information fast [9]. On one hand,
speed can be achieved by specially devised data structures and algorithms. On
the other hand, the analytical process is cyclic. In other words, the user of
the OLAP application runs his or her queries one after the other. The output of
the last query may be there (at least partly) in one of the previous results.
Therefore caching also plays an important role in the operation of these
systems. However, caching itself may not be enough to ensure acceptable
performance. Size does matter: The more memory is available, the more we gain
by loading and keeping information in there. Oftentimes, the cache size is
fixed. This limits the performance of the multidimensional database, as well,
unless we compress the data in order to move a greater proportion of them into
the memory. Caching combined with proper compression methods promise further
performance improvements. In this paper, we investigate how caching influences
the speed of OLAP systems. Different physical representations (multidimensional
and table) are evaluated. For the thorough comparison, models are proposed. We
draw conclusions based on these models, and the conclusions are verified with
empirical data.Comment: 14 pages, 5 figures, 8 tables. Paper presented at the Fifth
Conference of PhD Students in Computer Science, Szeged, Hungary, 27 - 30 June
2006. For further details, please refer to
http://www.inf.u-szeged.hu/~szepkuti/papers.html#cachin
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