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I have a VM running Debian Jessie (Linux 3.16) that has very low entropy available (cat /proc/sys/kernel/random/entropy_avail returns <200 most of the time) eve
by praseodym 11y ago
I have a VM running Debian Jessie (Linux 3.16) that has very low entropy available (cat /proc/sys/kernel/random/entropy_avail returns <200 most of the time) even though the Intel RDRAND instruction is available. Shouldn't it be using that to fill up the entropy pool, or am I misunderstanding how the entropy_avail value works?
- Freaky 11y agoLinux is very conservative with how much entropy it credits to things like RDRAND since they can't be easily trusted. Looks like you get one extra bit per interrupt: https://github.com/torvalds/linux/blob/master/drivers/char/random.c#L937 https://github.com/torvalds/linux/blob/master/drivers/char/r... You'll note no other use of arch_get_random_* throws anything at credit_entropy_bits(). Linux 3.17 did bump up the assumed quality of virtio-rnd: https://github.com/torvalds/linux/commit/34679ec7a0c45da8161507e1f2e1f72749dfd85c https://github.com/torvalds/linux/commit/34679ec7a0c45da8161...