Initializing the entropy pool using RDRAND and friends

Random number generation in the kernel has garnered a lot of attention over the years. The tensions between the need for cryptographic-strength random numbers versus getting strong random numbers more quickly—along with the need to avoid regressions—has led to something of a patchwork of APIs. While it is widely agreed that waiting for a properly initialized random number generator (RNG) before producing random numbers is the proper course, opinions differ on what "properly" means exactly. Beyond that, waiting, especially early in the boot process, can be problematic as well. One solution would be to trust the RNG instructions provided by most modern processors, but that comes with worries of its own.

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