It is not, at least for DDR3: "How Rowhammer Could Be Used to Exploit Weaknesses in Computer Hardware"[0] tested ECC and rowhammered it.

ECC can only reliably detect single and double-bit errors (in 64bit spans, and it can only correct single-bit errors), anything beyond that and detection is up to chance. ECC is a mitigation factor, but ultimately not a protection.

[0] http://www.thirdio.com/rowhammer.pdf

ECC could also help to raise the alarm when you're under attack – the chances of flipping enough bits to evade ECC (and have them be the right bits to pull off your exploit) without getting a few detectable flips in the process must be quite slim.

> ECC could also help to raise the alarm when you're under attack – the chances of flipping enough bits to evade ECC (and have them be the right bits to pull off your exploit) without getting a few detectable flips in the process must be quite slim.

I'd strongly suggest reading the linked paper. The upshot is: no, the chances are actually quite good that ECC won't save you by raising the alarm, because of the poor job most vendors do of surfacing ECC errors.

If you read the paper, you will notice that Micron is the worst here.

the only proper (other than radically redesigning geometry and topology of whole ram chip, probably losing capacity in the process) protection (known in the industry since middle nineties ...) is access counter per row inside the ram module or memory controller. But that would cost additional $0.1 per chip!!!1 :/