Hi Peter, some time back when the RDRAND instruction was debated, a patch was offered for driver/char/random.c that in essence turned /dev/random into a frontend for RDRAND in case that instruction was available. The patch kind of monopolized the noise sources such that if a user space "random number hog" pulled data from /dev/random endlessly, the (almost) only noise source was RDRAND. As that patch treated RDRAND to provide entropy, the blocking behavior went away for /dev/random. That patch did not sit well with some developers and it got finally changed such that the output of RDRAND is now just XORed with the output of the "classic" /dev/random behavior -- /dev/random is still blocking. With the current development cycle for 3.15, the function arch_random_refill is added as presented in [1]. It now uses RDSEED instead of RDRAND. Yet, the way this function is called in random_read seems (as I have no system with an RDSEED, I cannot test) to show the very same behavior as the aforementioned RDRAND patch: the blocking behavior of /dev/random will be gone and RDSEED will monopolize the noise sources in case of a user space hog. Note, I do not see an issue with the patch that adds RDSEED as part of add_interrupt_randomness outlined in [2]. The reason is that this patch does not monopolizes the noise sources. I do not want to imply that Intel (or any other chip manufacturer that will hook into arch_random_refill) intentionally provides bad entropy (and this email shall not start a discussion about entropy again), but I would like to be able to only use noise sources that I can fully audit. As it is with hardware, I am not able to see what it is doing. Thus, may I ask that arch_random_refill is revised such that it will not monopolize the noise sources? If somebody wants that, he can easily use rngd. [1] https://lkml.org/lkml/2014/3/4/968 [2] https://lkml.org/lkml/2014/3/4/934 Thanks Stephan -- | Cui bono? | -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
