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The cloud computing infrastructure relies on virtualized servers that provide isolation across guest OS's through sandboxing. This isolation was demonstrated to be imperfect in past work which exploited hardware level information leakages to gain access to sensitive information across co-located virtual machines (VMs). In response virtualization companies and cloud services providers have disabled features such as deduplication to prevent such attacks.In this work, we introduce a fine-grain cross-core cache attack that exploits access time variations on the last level cache. The attack exploits huge pages to work across VM boundaries without requiring deduplication. No configuration changes on the victim OS are needed, making the attack quite viable. Furthermore, only machine co-location is required, while the target and victim OS can still reside on different cores of the machine. Our new attack is a variation of the prime and probe cache attack whose applicability at the time is limited to L1 cache. In contrast, our attack works in the spirit of the flush and reload attack targeting the shared L3 cache instead. Indeed, by adjusting the huge page size our attack can be customized to work virtually at any cache level/size. We demonstrate the viability of the attack by targeting an OpenSSL1.0.1f implementation of AES. The attack recovers AES keys in the cross-VM setting on Xen 4.1 with deduplication disabled, being only slightly less efficient than the flush and reload attack. Given that huge pages are a standard feature enabled in the memory management unit of OS's and that besides co-location no additional assumptions are needed, the attack we present poses a significant risk to existing cloud servers.Index Terms-Cross-VM, huge pages, memory deduplication, prime and probe, flush+reload, cache attacks. IEEE Symposium on Security and Privacy

In cloud computing, efficiencies are reaped by resource sharing such as co-location of computation and deduplication of data. This work exploits resource sharing in virtualization software to build a powerful cache-based attack on AES. We demonstrate the vulnerability by mounting Cross-VM Flush+Reload cache attacks in VMware VMs to recover the keys of an AES implementation of OpenSSL 1.0.1 running inside the victim VM. Furthermore, the attack works in a realistic setting where different VMs are located on separate cores. The modified flush+reload attack we present, takes only in the order of seconds to minutes to succeed in a cross-VM setting. Therefore long term co-location, as required by other fine grain attacks in the literature, are not needed. The results of this study show that there is a great security risk to OpenSSL AES implementation running on VMware cloud services when the deduplication is not disabled.

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