svn commit: r346250 - in head: share/man/man4 share/man/man9 sys/dev/random sys/kern sys/libkern sys/sys

[Warner Losh]

On Wed, Apr 17, 2019 at 10:06 AM John Baldwin <jhb at freebsd.org> wrote:

> On 4/16/19 4:48 PM, Conrad Meyer wrote:
> > On Tue, Apr 16, 2019 at 4:31 PM John Baldwin <jhb at freebsd.org> wrote:
> >> bhyveload is effectively the loader in this case.  It runs the normal
> loader
> >> scripts and logic and so would load the guests's /boot/entropy and pass
> it
> >> to the guest kernel as metadata just like the regular loader.
> >
> > Right, except it doesn't seem to do things like nuke /boot/nextboot.conf
> :-(.
>
> It just needs a disk write method I think for that to work, but I'm not
> sure
> that's currently in the userboot interface.
>

It isn't. Write support was added to the boot loader after bhyveload was
forked. It hasn't been updated.


> >> In addition, bhyve also supports virtio-rng which is another way to
> provide
> >> entropy to guest OS's.  That's why in my reply I focused on qemu for
> mips
> >> (or riscv) as for x86 hypervisors there are existing,
> somewhat-standarized
> >> solutions for the hypervisor to provide entropy to the guest.
> >
> > Perhaps cryptographically random stack-protector cookies are simply
> > inappropriate for MIPS or RISCV.  Do we have any other examples of
> > kernel random consumers blocking after that immediate hiccup is
> > overcome?
>
> There may be MIPS and RISCV designs that do have suitable entropy available
> (especially I would expect future RISCV designs to have them), so I think
> blacklisting stack protector wholesale on those architectures is overboard.
> I think some sort of off-by-default knob (even a compile option) is fine
> for
> people who need fast and loose vs safe as you already agreed to earlier.
>
> Also, for development testing we still want coverage of using stack cookies
> on MIPS and RISCV even if the simulator environment gives not-very-strong
> cookie values.


I'm going to put a very fine point on this: any hard-requirement of entropy
sources is a non-starter. If you require that, your commit will be backed
out and/or hacked around by the addition of a nob in the future. It will
happen. Don't pretend you can say 'but things weren't random enough' will
carry the day. It will not.

That's why I specifically requested a MD routine to be called when there's
no source of entropy: that will let special needs folks do the right thing.
It's also why I asked for a way to say "don't ever block waiting for
entropy, soldier on the best you can, but set some variable that can be
exposed to userland so that early in /etc/rc automation can be written to
decide what to do when that condition exists: generate entropy and reboot,
report it to some central control, nothing" since that will give the tools
for different reactions.

For our application it is *NEVER* OK to block the boot because there's not
enough randomness. We'd rather solider on with crappy randomness and want
the boot to proceed not matter what. We want the information that we had to
make compromises along the way to make it happen so we can decide the right
course of action for our appliances.

Warner