Am Montag, 2. Mai 2016, 09:48:57 schrieb Theodore Ts'o: Hi Theodore, > On Mon, May 02, 2016 at 08:50:14AM -0400, Theodore Ts'o wrote: > > > - entropy pool draining: when having a timer-based reseeding on a quiet > > > system, the entropy pool can be drained during the expiry of the timer. > > > So, I tried to handle that by increasing the timer by, say, 100 seconds > > > for each new NUMA node. Note, even the baseline of 300 seconds with > > > CRNG_RESEED_INTERVAL is low. When I experimented with that on a KVM > > > test system and left it quiet, entropy pool draining was prevented at > > > around 500 seconds. > > One other thought. If your KVM test system was completely quiet, then > all of the entropy was coming from timer interrupts. It is an open > question whether an adversary could predict the bit of "entropy" you > are generating with better than 50% probability if both the host and > the guest system are quiescent. And if they can, then maybe assuming > one bit of entropy per interrupt might be a too optimistic. It is not entirely quiet -- systemd likes to dump data on the disk once in a while. So, it is no timer interrupt that I see. Note, my test system runs as tickless kernel. > > This is especially true on bare metal where very often, especially on > smaller machines, where there is a single oscillator from which all of > the clocks on the SOC or motherboard are derived. There is a reason > why I was being ultra conservative in sampling 64 interrupts into a > 32-bit fast-mix pool before mixing it into the input pool, and only > crediting the pool with a single bit of entropy each time I did this. As I do not think that we see any timer interrupts, I think this argument may not count. Besides, I have not seen any timer interrupts lately (with or without a tickless kernel). Thus, which interrupt do you think is a timer interrupt? Ciao Stephan -- 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
