How do you decide whether or not you trust the hardware RNG? Do you trust RDRAND? Some people do, other people are convinced it may be backdoored by Intel a

How do you decide whether or not you trust the hardware RNG? Do you trust RDRAND? Some people do, other people are convinced it may be backdoored by Intel at the request of the NSA. Worst of all, there is no way to tell which belief is true. So there are potential real problems with hardware RNG's if you are worried about state sponsored attackers who are willing to intercept hardware shipments. Requiring a previous seed requires a way to get access to the seed, early enough in the boot that it is available to kernel users who are trying to use randomness for address space randomization and for stack canaries. But in early boot the kernel may not be sufficiently initialized to read from persistent storage, and there are many, many bootloaders. The reason why there is no file system interface to getrandom(2) is that a file system interface is subject to file descriptor exhaustion attacks. It was OpenBSD which designed the getentropy(2) system call, and getrandom(2) was modelled after it. Basically, getrandom(2) is getentropy(2) with an extra flags parameter added.