Re: [kernel-hardening] Re: [PATCH 4/3] random: use siphash24 instead of md5 for get_random_int/long

[Jason A. Donenfeld]

Hi again,

On Wed, Dec 14, 2016 at 5:37 PM, Theodore Ts'o <tytso@xxxxxxx> wrote:
> [    3.606139] random benchmark!!
> [    3.606276] get_random_int # cycles: 326578
> [    3.606317] get_random_int_new # cycles: 95438
> [    3.607423] get_random_bytes # cycles: 2653388

Looks to me like my siphash implementation is much faster for
get_random_long, and more or less tied for get_random_int:

[    1.729370] random benchmark!!
[    1.729710] get_random_long # cycles: 349771
[    1.730128] get_random_long_chacha # cycles: 359660
[    1.730457] get_random_long_siphash # cycles: 94255
[    1.731307] get_random_bytes # cycles: 1354894
[    1.731707] get_random_int # cycles: 305640
[    1.732095] get_random_int_chacha # cycles: 80726
[    1.732425] get_random_int_siphash # cycles: 94265
[    1.733278] get_random_bytes # cycles: 1315873

Given the increasing usage of get_random_long for ASLR and related, I
think this makes the siphash approach worth pursuing. The chacha
approach is also not significantly different from the md5 approach in
terms of speed for get_rand_long. Additionally, since siphash is a
PRF, I think this opens up a big window for optimizing it even
further.

Benchmark here:
    https://git.zx2c4.com/linux-dev/commit/?h=rng-bench

Jason