Re: [PATCH 0/3] random: add random.rng_seed to bootconfig entry

Rob Herring
2020-02-14T18:15:11Z

On Fri, Feb 14, 2020 at 11:00 AM Mark Salyzyn <salyzyn@android.com> wrote:
>
> On 2/14/20 5:49 AM, Rob Herring wrote:
> > On Fri, Feb 14, 2020 at 12:10 AM Masami Hiramatsu <mhiramat@kernel.org> wrote:
> >> Hi,
> >>
> >> The following series is bootconfig based implementation of
> >> the rng_seed option patch originally from Mark Salyzyn.
> >> Note that I removed unrelated command line fixes from this
> >> series.
> > Why do we need this? There's already multiple other ways to pass
> > random seed and this doesn't pass the "too complex for the command
> > line" argument you had for needing bootconfig.
> >
> > Rob
>
> Android is the use case I can vouch for. But also KVM.
>
> Android Cuttlefish is an emulated device used extensively in the testing
> and development infrastructure for In-house, partner, and system and
> application developers for Android. There is no bootloader, per-se.
> Because of the Android GKI distribution, there is also no rng virtual
> driver built in, it is loaded later as a module, too late for many
> aspects of KASLR and networking. There is no Device Tree, it does
> however have access to the content of the initrd image, and to the
> command line for the kernel. The only convenient way to get early
> entropy is going to have to be one of those two places.

I'm familiar with Cuttlefish somewhat. Guess who got virtio-gpu
working on Android[1]. :) I assume DT doesn't work for you because you
need x86 builds, but doesn't QEMU use UEFI in that case which also has
a mechanism for passing entropy.

To clarify my question: Why do we need random seed in bootconfig
rather than just the kernel command line? I'm not understanding why
things changed from your original patch.

> In addition, 2B Android devices on the planet, especially in light of
> the Android GKI distribution were everything that is vendor created is
> in a module, needs a way to collect early entropy prior to module load
> and pass it to the kernel. Yes, they do have access to the recently
> added Device Tree approach, and we expect them to use it, as I have an
> active backport for the mechanism into the Android 4.19 and 5.4 kernels.
> There may also be some benefit to allowing the 13000 different
> bootloaders an option to use bootconfig as a way of propagating the much
> needed entropy to their kernels. I could make a case to also allow them
> command line as another option to relieve their development stress to
> deliver product, but we can stop there. Regardless, this early entropy
> has the benefit of greatly improving security and precious boot time.

We're going to update 13000 bootloaders to understand bootconfig
rather than use the infrastructure already in place (DT and/or command
line)?

bootconfig is an ftrace feature only IMO. If it's more than that, I
imagine there will be some opinions about that. Adding new
bootloader-kernel interfaces is painful and not something to just add
without much review.

Rob