Clémentine Maurice

Hardware is often considered as an abstract layer that behaves correctly, just executing instructions and outputting a result. However, the internal state of the hardware leaks information about the programs that are executing. In this talk, we focus on how to extract information from the execution of simple x86 instructions that do not require any privileges. Beyond classical cache-based side-channel attacks, we demonstrate how to perform cache attacks without a single memory access, as well as how to bypass kernel ASLR. This talk does not require any knowledge about assembly. We promise.

When hunting for bugs, the focus is mostly on the software layer. On the other hand, hardware is often considered as an abstract layer that behaves correctly, just executing instructions and outputing a result. However, the internal state of the hardware leaks information about the programs that are running. Unlike software bugs, these bugs are not easy to patch on current hardware, and manufacturers are also reluctant to fix them in future generations, as they are tightly tied with performance optimizations. In this talk, we focus on how to extract information from the execution of simple x86 instructions that do not require any privileges. The most studied microarchitectural attacks are beyond doubt cache attacks. Indeed, the timing of a memory access depends heavily on the state of the CPU cache. But beyond memory accesses that are the base of classical cache-based side-channel attacks, other x86 instructions leak information about the internal state of the hardware, and thus about running programs. First, we present side channels caused by the "clflush" instruction, that flushes all content of the cache. We will explain how it can be used to perform side-channel attacks that are faster and stealthier than their classical counterpart, without performing so much as a single memory access [1]. Second, we present side channels caused by the prefetch instructions. We will explain how these instructions can be used to translate virtual addresses to physical addresses - without the use of the proc interface that is restricted today -, and to bypass kernel ASLR [2]. This talk does not require any knowledge about assembly. We promise. The talk will be given as a joint presentation by Clémentine Maurice and Moritz Lipp. [1] Daniel Gruss, Clémentine Maurice, Klaus Wagner and Stefan Mangard, "Flush+Flush: A Fast and Stealthy Cache Attack", DIMVA 2016 [2] Daniel Gruss, Clémentine Maurice, Anders Fogh, Moritz Lipp, Stefan Mangard, "Prefetch Side-Channel Attacks: Bypassing SMAP and Kernel ASLR", CCS 2016

Other people: Moritz Lipp

"Insanity: doing the same thing over and over again and expecting different results." Albert Einstein - Who did not live long enough to see Rowhammer Recent studies have found that repeated accesses to DRAM rows can cause random bit flips, resulting in the so called Rowhammer vulnerability. We present Rowhammer.js, the first remote software-induced hardware-fault attack, from JavaScript. We also extend our presentation with an overview of cache side-channel attacks, that use the same technique to evict data from the cache.

Last year, studies demonstrated Rowhammer, a fault attack that can cause random bit flips by repeatedly accessing DRAM rows. This vulnerability has already been exploited to gain root privileges and to evade a sandbox, showing the severity of faulting single bits for security. However, these exploits are written in native code and use special instructions that flush data from the cache. In this talk we present Rowhammer.js [1], a JavaScript-based implementation of the Rowhammer attack. After presenting the native attack, we underline the challenges we faced to trigger the vulnerability from JavaScript, without any special instruction. Beyond DRAM, this attack also requires a very fine understanding of CPU cache internals, that are largely undocumented. We detail our findings on these undocumented parts, and the different steps that led to the attack from JavaScript. We also give an outlook on possible exploits, including gaining root privileges from JavaScript and performing fault attacks on cryptography. In the last part, we extend our presentation with an overview of cache attacks, bridging the gap between hardware-fault attacks and side channels. In side-channel attacks, the attacker doesn't rely on a direct software compromise, but rather on passive observation of hardware characteristics when a victim process runs. In common with Rowhammer.js, these attacks use techniques to evict data from the last-level cache. [1] Daniel Gruss, Clémentine Maurice, Stefan Mangard. Rowhammer.js: A Remote Software-Induced Fault Attack in JavaScript. http://arxiv.org/abs/1507.06955

Other people: Daniel Gruss