Rowhammer, SGX and IT Security

I am following with interest the developments of the Rowhammer class of attacks and defenses, here there is one of the latest articles. (As far as I know, these are still more research subjects than real-life attacks.)

Already at the time of the Orange Book (or more correctly the “Trusted Computer System Evaluation Criteria – TCSEC”) in the ’80s, it was clear how important the hardware is in building the chain of trust on which IT Security relies.

Rowhammer attacks follow from a hardware security weakness, even if this weakness is also a hardware strength: the increase in density and decrease in size of DRAM cells, which allows to build memory banks with lower energy consumption and higher capacity. Unfortunately this allows the near-location memory bit-flipping that can give rise to a total compromise of the IT system, that is a Rowhammer attack. It is true that there exist memory banks with Error Correction Codes (ECC) which make the Rowhammer attacks quite hard, but these memory banks are more expensive, a little slower and available only on high-end server computers. One can look at it as a hardware feature which carried within an unexpected security weakness.

As it turns out, it seems very hard to find software measures which can detect, block or prevent Rowhammer attacks. Many different software defences have been proposed, but as of today none is really able to completely stop all Rowhammer types of attacks. A hardware weakness seems to require only hardware countermeasures.

To make the situation even more intriguing, the hardware-based Intel SGX security enclaves can be mixed-in in this scenario. Intel SGX is a hardware x86 instruction-set extension which allows to securely and confidentially execute programs in an isolated environment (called a “security enclave”). Nothing can directly look into a SGX security enclave, not even the Operating System, to the point that data can be computed in it even on systems controlled by an adversary (but SGX security enclaves are not immune from side-channel attacks). Rowhammer attacks cannot be performed from outside against programs running in a SGX security enclave. Vice-versa, a SGX security enclave in some conditions can run, without been detected, a Rowhammer software to attack the hardware and programs running on it. Overall it seems that Intel SGX security enclaves can provide extremely interesting IT security features but at the same time can also be abused to defeat IT security itself.

All of this becomes more worrisome when thinking of Virtual Machines and Cloud Services.


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