Re: [PATCH v24 00/12] /dev/random - a new approach with full SP800-90B compliance

Stephan Müller
2019-11-12T23:27:51Z

Am Mittwoch, 13. November 2019, 00:03:47 CET schrieb Stephan Müller:

Hi Stephan,

> Am Dienstag, 12. November 2019, 16:33:59 CET schrieb Andy Lutomirski:
>
> Hi Andy,
>
> > On Mon, Nov 11, 2019 at 11:13 AM Stephan Müller <smueller@chronox.de>
wrote:
> > > The following patch set provides a different approach to /dev/random
> > > which
> > > is called Linux Random Number Generator (LRNG) to collect entropy within
> > > the Linux kernel. The main improvements compared to the existing
> > > /dev/random is to provide sufficient entropy during boot time as well as
> > > in virtual environments and when using SSDs. A secondary design goal is
> > > to limit the impact of the entropy collection on massive parallel
> > > systems
> > > and also allow the use accelerated cryptographic primitives. Also, all
> > > steps of the entropic data processing are testable.
> >
> > This is very nice!
> >
> > > The LRNG patch set allows a user to select use of the existing
> > > /dev/random
> > > or the LRNG during compile time. As the LRNG provides API and ABI
> > > compatible interfaces to the existing /dev/random implementation, the
> > > user can freely chose the RNG implementation without affecting kernel or
> > > user space operations.
> > >
> > > This patch set provides early boot-time entropy which implies that no
> > > additional flags to the getrandom(2) system call discussed recently on
> > > the LKML is considered to be necessary.
> >
> > I'm uneasy about this. I fully believe that, *on x86*, this works.
> > But on embedded systems with in-order CPUs, a single clock, and very
> > lightweight boot processes, most or all of boot might be too
> > deterministic for this to work.
>
> I agree that in such cases, my LRNG getrandom(2) would also block until the
> LRNG thinks it collected 256 bits of entropy. However, I am under the
> impression that the LRNG collects that entropy faster that the existing
> /dev/ random implementation, even in this case.
>
> Nicolai is copied on this thread. He promised to have the LRNG tested on
> such a minimalistic system that you describe. I hope he could contribute
> some numbers from that test helping us to understand how much of a problem
> we face.
> > I have a somewhat competing patch set here:
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/log/?h=rand
> > om /kill-it
> >
> > (Ignore the "horrible test hack" and the debugfs part.)
> >
> > The basic summary is that I change /dev/random so that it becomes
> > functionally identical to getrandom(..., 0) -- in other words, it
> > blocks until the CRNG is initialized but is then identical to
> > /dev/urandom.
>
> This would be equal to the LRNG code without compiling the TRNG.
>
> > And I add getrandom(...., GRND_INSECURE) that is
> > functionally identical to the existing /dev/urandom: it always returns
> > *something* immediately, but it may or may not actually be
> > cryptographically random or even random at all depending on system
> > details.
>
> Ok, if it is suggested that getrandom(2) should also have a mode to behave
> exactly like /dev/urandom by not waiting until it is fully seeded, I am
> happy to add that.
>
> > In other words, my series simplifies the ABI that we support. Right
> > now, we have three ways to ask for random numbers with different
> > semantics and we need to have to RNGs in the kernel at all time. With
> > my changes, we have only two ways to ask for random numbers, and the
> > /dev/random pool is entirely gone.
>
> Again, I do not want to stand in the way of changing the ABI if this is the
> agreed way. All I want to say is that the LRNG seemingly is initialized much
> faster than the existing /dev/random. If this is not fast enough for some
> embedded environments, I would not want to stand in the way to make their
> life easier.
>
> > Would you be amenable to merging this into your series (i.e. either
> > merging the code or just the ideas)?
>
> Absolutely. I would be happy to do that.
>
> Allow me to pull your code (I am currently behind a slow line) and review it
> to see how best to integrate it.
>
> > This would let you get rid of
> > things like the compile-time selection of the blocking TRNG, since the
> > blocking TRNG would be entirely gone.
>
> Hm, I am not so sure we should do that.
>
> Allow me to explain: I am also collaborating on the European side with the
> German BSI. They love /dev/random as it is a "NTG.1" RNG based on their AIS
> 31 standard.
>
> In order to seed a deterministic RNG (like OpenSSL, GnuTLS, etc. which are
> all defined to be "DRG.3" or "DRG.2"), BSI mandates that the seed source is
> an NTG.1.
>
> By getting rid of the TRNG entirely and having /dev/random entirely behaving
> like /dev/urandom or getrandom(2) without the GRND_RANDOM flag, the kernel
> would "only" provide a "DRG.3" type RNG. This type of RNG would be
> disallowed to seed another "DRG.3" or "DRG.2".
>
> In plain English that means that for BSI's requirements, if the TRNG is gone
> there would be no native seed source on Linux any more that can satisfy the
> requirement. This is the ultimate reason why I made the TRNG compile-time
> selectable: to support embedded systems but also support use cases like the
> BSI case.
>
> Please consider that I maintain a study over the last years for BSI trying
> to ensure that the NTG.1 property is always met [1] [2]. The sole purpose
> of that study is around this NTG.1.
>
> > Or do you think that a kernel-provided blocking TRNG is a genuinely
> > useful thing to keep around?
>
> Yes, as I hope I explained it appropriately above, there are standardization
> requirements that need the TRNG.
>
> PS: When I was forwarding Linus' email on eliminating the blocking_pool to
> BSI, I saw unhappy faces. :-)
>
> I would like to help both sides here.
>
> [1]
> https://www.bsi.bund.de/SharedDocs/Downloads/EN/BSI/Publications/Studies/
> LinuxRNG/NTG1_Kerneltabelle_EN.pdf?__blob=publicationFile&v=3
>
> [2]
> https://www.bsi.bund.de/SharedDocs/Downloads/EN/BSI/Publications/Studies/
> LinuxRNG/NTG1_Kerneltabelle_EN.pdf?__blob=publicationFile&v=3

Sorry, the copy did not work:

[2] https://bsi.bund.de/SharedDocs/Downloads/EN/BSI/Publications/Studies/
LinuxRNG/LinuxRNG_EN.pdf?__blob=publicationFile&v=16
>
> Ciao
> Stephan

Ciao
Stephan