Re: [PATCH v3 0/8] Rework random blocking

Andy Lutomirski
2019-12-29T15:08:57Z

> On Dec 29, 2019, at 10:49 PM, Theodore Y. Ts'o <tytso@mit.edu> wrote:
>
> ﻿On Fri, Dec 27, 2019 at 06:06:56PM -0800, Andy Lutomirski wrote:
>>
>> I'm thinking of having a real class device and chardev for each hwrng
>> device. Authentication is entirely in userspace: whatever user code
>> is involved can look at the sysfs hierarchy and decide to what extent
>> it trusts a given source. This could be done based on bus topology or
>> based on anything else.
>
> Yes, that's what I was thinking. Another project on my "when I can
> get a round tuit" list is to change how drivers/char/random.c taps
> into the hwrng devices, mixing in a bit from each of these devies in a
> round-robin fashion, instead of just feeding from a single hwrng.
>
>> The kernel could also separately expose various noise sources, and the
>> user code can do whatever it wants with them. But these should be
>> explicitly unconditioned, un-entropy-extracted sources -- user code
>> can run its favorite algorithm to extract something it believes to be
>> useful. The only conceptually tricky bit is keeping user code like
>> this from interfering with the in-kernel RNG.
>
> The other problem is the unconditioned values of the noise sources may
> leak unacceptable amounts of information about system operation. The
> most obvious example of this would be keyboard and mouse sources,
> where today we mix in not only the timing information, but the actual
> input values (e.g., the keyboard scancodes) into the entropy pool.
> Exposing this to userspace, even if it is via a privileged system
> call, would be... unwise.
>
>

Hmm. We could give only the timing.

We could also say that the official interface for this is to use tracepoints and punt everything into userspace.