From ee3e00e9e7101c80a2ff2d5672d4b486bf001b88 Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Sun, 15 Jun 2014 16:59:24 -0400 Subject: [PATCH] random: use registers from interrupted code for CPU's w/o a cycle counter MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit For CPU's that don't have a cycle counter, or something equivalent which can be used for random_get_entropy(), random_get_entropy() will always return 0. In that case, substitute with the saved interrupt registers to add a bit more unpredictability. Some folks have suggested hashing all of the registers unconditionally, but this would increase the overhead of add_interrupt_randomness() by at least an order of magnitude, and this would very likely be unacceptable. The changes in this commit have been benchmarked as mostly unaffecting the overhead of add_interrupt_randomness() if the entropy counter is present, and doubling the overhead if it is not present. Signed-off-by: Theodore Ts'o Cc: Jörn Engel --- Reading git-format-patch failed