Yes, the instruction that returns random bits returns a flag indicating that the bits were successfully obtained. I guarantee you somebody somewhere is going to forget to check that flag.
Sounds like that is built into the RdRand instruction. From the article:
"We really like to sleep well at night, so we've built in additional circuitry that tests to make sure that the concentrating machinery is always working with bit streams that aren't too biased. If it detects a biased output, we tag it as unhealthy and refine it to meet our standards. This way, only healthy pairs of bit streams are combined."
