Re: CTF: UEFI HTTP boot support

> On Wed, Jun 17, 2020 at 11:53 AM Rodney W. Grimes <
> freebsd-rwg_at_gndrsh.dnsmgr.net> wrote:
> 
> > > Rodney W. Grimes <freebsd-rwg_at_gndrsh.dnsmgr.net> wrote:
> > > > > The "fake cd drive" is in the kernel, loader just copies the iso into
> > > > > memory like any other module, and by the time that's done you just
> > > > > reboot into the newly installed system, which again uses
> > > > >
> > > > > vfs.root.mountfrom="cd9660:/dev/md0.uzip"
> > > >                                   ^^^
> > > >
> > > > Argh, the cd9660 confused me, I think your doing a
> > > > "root on mfs/md"?
> > >
> > > loader.conf says
> > >
> > > rootfs_load="yes"
> > > rootfs_name="contents.izo"
> > > rootfs_type="md_image"
> > > vfs.root.mountfrom="cd9660:/dev/md0.uzip"
> > >
> > > contents.izo is uzip'd contents.iso which file(1)
> > > describes as ISO 9660 CD-ROM filesystem data ''
> > >
> > > That's for normal boot, for the loader 'install' command
> > > it expects an uncompressed iso for rootfs.
> >
> > Ok, now the puzzle is how much work to get from a stock FreeBSD .iso
> > image to something that works with this.  Obviously we need a non-stock
> > /boot/loader.conf file, or to type some commands manually at a loader
> > prompt.  I believe the stock GENERIC kernel has the md_root support
> > for this already, so it may not be that hard to do.
> >
> 
> Looking at the code, I think MD_ROOT alone is insufficient here...

I was a bit worried about that, but hopefull.  We do work out of the
box with a NFS root as long as the NIC is found during boot.  And
given that I load the loader over NFS the loader can also find my
/boot/ directory and the files in it, so that part is already solved.

> If there's no MD root provided, we look for the symbols mfs_root and
> mfs_root_end, which I think means that rootfs_ in the above example needs
> to be md_root_ instead so that we find it.

Isnt this all handled by the loader?  I think we have 2 slightly
different cases here.  THe one sjg shows up, where you actually
load the md_image from a  seperate file, and the case your talking
about where you actually embed the kernel and image into a single
file.

> 
> You may need to have a custom kernel with 'options MD_ROOT_READONLY'
> because isofs is read-only.
> 
> And there's a small chance you may need to define ROOTDEVNAME in the build
> as well to be "cd9660:/dev/md0.uzip"

I do not think that is necessesary but I'll keep it in mind, at present
I do over ride the vfs.root.mountfrom to point to my version specific
root file system using some ipxe variables.

> 
> Every time I do stuff like this I have to re-puzzle it out, alas, but these
> should give you some guide posts. It should be better documented in md(4),
> but isn't at the moment.

Thanks for exposing what may be some pointy sticks to stumble on.

> 
> I'd honestly try to get this setup working first loading all the files off
> a local disk before layering in the networking on top of that.

Probalby a good idea, as the usually failure mode in the diskless
word is black screens leaving little detail about what went wrong.

> Warner
-- 
Rod Grimes                                                 rgrimes_at_freebsd.org