We present Masstree, a fast key-value database designed for SMP machines. Masstree keeps all data in memory. Its main data structure is a trie-like concatenation of B + -trees, each of which handles a fixed-length slice of a variable-length key. This structure effectively handles arbitrary-length possiblybinary keys, including keys with long shared prefixes. B + -tree fanout was chosen to minimize total DRAM delay when descending the tree and prefetching each tree node. Lookups use optimistic concurrency control, a read-copy-update-like technique, and do not write shared data structures; updates lock only affected nodes. Logging and checkpointing provide consistency and durability. Though some of these ideas appear elsewhere, Masstree is the first to combine them. We discuss design variants and their consequences.On a 16-core machine, with logging enabled and queries arriving over a network, Masstree executes more than six million simple queries per second. This performance is comparable to that of memcached, a non-persistent hash table server, and higher (often much higher) than that of VoltDB, MongoDB, and Redis.
The security of many applications relies on the kernel being secure, but history suggests that kernel vulnerabilities are routinely discovered and exploited. In particular, exploitable vulnerabilities in kernel modules are common. This paper proposes LXFI, a system which isolates kernel modules from the core kernel so that vulnerabilities in kernel modules cannot lead to a privilege escalation attack. To safely give kernel modules access to complex kernel APIs, LXFI introduces the notion of API integrity, which captures the set of contracts assumed by an interface. To partition the privileges within a shared module, LXFI introduces module principals. Programmers specify principals and API integrity rules through capabilities and annotations. Using a compiler plugin, LXFI instruments the generated code to grant, check, and transfer capabilities between modules, according to the programmer's annotations. An evaluation with Linux shows that the annotations required on kernel functions to support a new module are moderate, and that LXFI is able to prevent three known privilege-escalation vulnerabilities. Stress tests of a network driver module also show that isolating this module using LXFI does not hurt TCP throughput but reduces UDP throughput by 35%, and increases CPU utilization by 2.2-3.7×.
Avoiding kernel vulnerabilities is critical to achieving security of many systems, because the kernel is often part of the trusted computing base. This paper evaluates the current state-of-the-art with respect to kernel protection techniques, by presenting two case studies of Linux kernel vulnerabilities. First, this paper presents data on 141 Linux kernel vulnerabilities discovered from January 2010 to March 2011, and second, this paper examines how well state-of-the-art techniques address these vulnerabilities. The main findings are that techniques often protect against certain exploits of a vulnerability but leave other exploits of the same vulnerability open, and that no effective techniques exist to handle semantic vulnerabilities-violations of high-level security invariants.
Because embedded interpreters offer flexibility and performance, they are becoming more prevalent, and can be found at nearly every level of the software stack. As one example, the Linux kernel defines languages to describe packet filtering rules and uses embedded interpreters to filter packets at run time. As another example, the RAR archive format allows embedding bytecode in compressed files to describe reversible transformations for decompression. This paper presents an analysis of common pitfalls in embedded interpreter implementations, which can lead to security vulnerabilities, and their impact. We hope that these results are useful both in augmenting existing embedded interpreters and in aiding developers in building new, more secure embedded interpreters.
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