Re: [Xen-devel] [Xen-users] UEFI Secure Boot Xen 4.9

["Bill Jacobs (billjac)" <billjac@xxxxxxxxx>]

> -----Original Message-----
> From: Daniel Kiper [mailto:daniel.kiper@xxxxxxxxxx]
> Sent: Monday, May 15, 2017 6:13 AM
> To: Bill Jacobs (billjac) <billjac@xxxxxxxxx>; george.dunlap@xxxxxxxxxx
> Cc: xen-devel@xxxxxxxxxxxxx; xen-users@xxxxxxxxxxxxx
> Subject: Re: [Xen-users] UEFI Secure Boot Xen 4.9
> 
> Hey,
> 
> CC-ing Xen-devel to spread some knowledge about the issue.
> 
> On Mon, May 15, 2017 at 10:42:23AM +0100, George Dunlap wrote:
> > On Wed, May 10, 2017 at 11:36 PM, Bill Jacobs (billjac)
> > <billjac@xxxxxxxxx> wrote:
> > > Hi all
> > >
> > > I gather that with 4.9, UEFI secure boot of Xen should be possible.
> > >
> > > Is this true?
> > >
> > > If so, what are the options for utilizing UEFI secure boot? Do I
> > > need a MSFT-signed shim or grub? Any special changes required for
> > > Xen kernel
> > > (signing?) or has that been done?
> >
> > Bill,
> >
> > I guess in part it depends on what you mean by "utilizing UEFI secure
> > boot".  If you simply want to boot an unsigned Xen on a UEFI system
> > with SecureBoot enabled, then grub would probably work.  If you want
> > to actually do the full SecureBoot thing -- where you have grub check
> > Xen's signature and that of the kernel and initrd, you probably need a
> > bit more.
> >
> > Daniel,
> >
> > Is there any good documentation on this?  The Xen EFI guide
> > (https://wiki.xenproject.org/wiki/Xen_EFI) mentions the shim, but
> > doesn't go into detail about how to sign a binary &c.
> 
> Unfortunately I do not know anything like that. As you said in general shim is
> supported. Sadly, it works only if you load xen.efi directly from EFI.
> __Upstream__ GRUB2 has not have support for shim yet. I am working on it
> (shim support via GRUB2 requires also some changes in Xen). I hope that I will
> have something which works before Xen conf in Budapest.
> 
> If you wish to use shim with xen.efi then you have to sign xen.efi and vmlinux
> with your key using sbsign or pesign. The process works in the same way like 
> in
> case vmlinux alone. Of course you have to install your public key into MOK
> before enabling secure boot.
> 
> Daniel

Yes, there are options in how this is achievable, and the solutions may be 
different. 

We are targeting a secure boot chain from UEFI fw to .ko, using same signing. 
In our case would skip shim and reduce attack surface, but it appears that the 
mechanisms 'out there' for passing pub key (cert) from UEFI db to Linux 
chainring require shim to do the work. Is that accurate? Does it have to be the 
case? I don't see why. 
For us, ideal case is :
UEFI fw -> (signed)GRUB2.efi->Multiboot2->Xen(signed .ko)

I would be happy to work to help achieve this. 
-Bill


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