FOG Secure Boot with Shim

KMEH

@jmeyer I haven’t tested it at all myself, but I wonder if that is referring to the fact that if Secure Boot is turned on all binaries (even the chainloaded ones such as the linux kernel) must be Secure Boot compatible. I’ll be interested to hear of your tests.

jmeyer

Here is my first steps.

Install signing tools on your FOG server

apt update
apt install sbsigntool openssl mokutil

Install shim & grub

apt install shim-signed grub-efi-amd64-signed
cp /usr/lib/shim/shimx64.efi.signed /tftpboot/shimx64.efi
cp /usr/lib/grub/x86_64-efi-signed/grubx64.efi.signed /tftpboot/grubx64.efi

I end with this at PXE boot :

Shim signature give this : (sbverify --list shimx64.efi)

warning: data remaining[831016 vs 957136]: gaps between PE/COFF sections?
signature 1
image signature issuers:
 - /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Corporation UEFI CA 2011
image signature certificates:
 - subject: /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Windows UEFI Driver Publisher
   issuer:  /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Corporation UEFI CA 2011
 - subject: /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Corporation UEFI CA 2011
   issuer:  /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Corporation Third Party Marketplace Root

and grub sinature return :

signature 1
image signature issuers:
 - /CN=Debian Secure Boot CA
image signature certificates:
 - subject: /CN=Debian Secure Boot Signer 2022 - grub2
   issuer:  /CN=Debian Secure Boot CA

I tried creating MOK key but I’m stuck with security violation :

mkdir /root/secureboot
cd /root/secureboot
openssl req -new -x509 -newkey rsa:2048 -keyout FOG-MOK.key -out FOG-MOK.crt -nodes -days 3650 -subj "/CN=FOG Secure Boot/"
openssl x509 -in FOG-MOK.crt -outform DER -out FOG-MOK.der

FOG-MOK.key <-- private key (protect!)
FOG-MOK.crt
FOG-MOK.der <-- enroll this on clients

Sign ipxe.efi and rename it to grubx64.efi

cd /tftpboot
cp ipxe.efi ipxe.efi.original
sbsign --key /root/secureboot/FOG-MOK.key --cert /root/secureboot/FOG-MOK.crt /tftpboot/ipxe.efi --output /tftpboot/ipxe-signed.efi
cp ipxe-signed.efi grubx64.efi

I think I need to work more and as Fog default exit type is refind, I’ll make more research.

jmeyer

I remplaced grubx64 by grubnetx64 (not sure if needed but was recommanded for PXE) and create a “grub” directory in tftpboot with “grub.cfg” inside.
Grub signed look for cfg file in a subdir called “grub” by default.

cp /usr/lib/grub/x86_64-efi-signed/grubnetx64.efi.signed /tftpboot/grubx64.efi
mkdir /tftpboot/grub
chmod -R a+rX /tftpboot/grub

I get grub menu.

update (10 am) :
I copied snponly.efi in grub directory and signed it with the FOG-MOK key I generated before.

sbsign --key /root/secureboot/FOG-MOK.key --cert /root/secureboot/FOG-MOK.crt /tftpboot/snponly.efi --output /tftpboot/grub/snponly.efi

I end with “error ; bad shim signature”.
I think I need to import the key on the computer with command “mokutil --import /chemin/vers/FOG-MOK.der”

I keep on searching…

2nd update (12:30 am):

To enroll key :

cp /usr/lib/shim/mmx64.efi.signed /tftpboot/mmx64.efi

and in tftpboot/grub/grub.cfg

menuentry 'Enroll MOK' {
    insmod tftp
    insmod chain
    chainloader (tftp,192.168.69.10)/mmx64.efi
    boot
}

menuentry 'Boot FOG (iPXE)' {
    insmod efinet
    insmod tftp
    insmod chain
    net_bootp
    chainloader (tftp,192.168.69.10)/grub/snponly.efi
    boot
}

Copy the .der on usb key, put it on the computer, run “Enroll MOK” in pxe grub menu then “Enroll from disk”
Reboot and run “Boot FOG” in pxe menu.

And at least I have the FOG menu !
I think I’m in the right way.

Let’s keep on working.

KMEH

@jmeyer Good work. So far looks very similar to what I was doing above but with grub instead. I’m guessing you’re aiming for something along the lines of the archived project you mentioned earlier that did this. Make sure you modify your ipxe scripts to load the shim with the shim command, and then sign whatever you’re booting from ipxe and you should be more or less there.

It’s worth noting if you want you should be able to skip the grub stage entirely, if you load the shim directly and name your ipxe binary what you’re grub binary currently is you should be able to net boot any shim pretty easily, from there the shim can automatically call mok manager as long as it’s in the same directory as your shim.

Sorry for responding so late. I’m out on training this week.

KMEH

So, somehow this slipped by my radar, but this guide is now largely obsolete! Pretty much everything done here now seems to be automatically handled by FOG after the transition to iPXE 2.0. FOG will now generate it’s own signing keys and seemingly sign the kernels for you, and provides a dedicated boot menu entry to enroll keys via MOK! I’ve yet to test this myself so happy to be corrected if I’m missing anything here.

Additionally, it looks like you can pretty easily migrate existing keys into this setup with some install parameters. I’ll be updating my ansible role to acomodate these changes soon!

Tom Elliott

@KMEH This wasn’t somehow. partly it was yours (among all the others) requests for secure boot and some max access to claude that really helped get this more flushed out more properly.

And a lot of mind tossing to get there.

Hopefully you enjoy it and like it (everyone).

KMEH

@Tom-Elliott Haha thank you! I was more referring to it slipping past my radar… I’m not sure how I missed it being added to be honest, I’d even read the patchnotes for that version of FOG and missed it.

I’m glad my attempts were able to help get this implemented one way or another. I’m going to update my ansible role as it’s currently broken due to the changes (it manually rebuilt iPXE itself with some files from the FOG repo which have now been removed due to the transition to 2.0 so that no longer works), and then I’ll give it a whirl.

Out of interest, I assume that like the other install time parameters this can be set by the .fogsettings file rather than the command line. I had a look in the docs and I can’t see a matching parameter listed, but I’m not sure if that’s because it isn’t supported or just the docs having not been updated yet.

The role uses templating with the .fogsettings file for the majority of the settings (it’s easier than conditionally setting command line parameters), so I’d much prefer to be able to adjust this from the file if I can!

Tom Elliott

@KMEH This might be able to help:
https://docs.fogproject.org/en/latest/management/server/install-fogsettings/

KMEH

@Tom-Elliott Ah yes, thanks. That’s what I was looking for. I was checking on that page but I couldn’t find it, even did a ctrl+f for secure boot. I wonder if it was an old cache or something, weird!

KMEH

@Tom-Elliott Just a thought, was reading through the docs and I noticed that because of the adhereance to stock iPXE 2.0 netbooting with HTTPS is disabled by default. This may be a little too complicated so I’d get avoiding this, but you could probably work around this by nesting shim and iPXE to boot a custom signed iPXE. It would work something like this:

Netboot iPXE 2.0 normally with it’s shim
Use autoexec.ipxe with the shim command to reload that shim
Using autoexec.ipxe chainload a custom build of iPXE 2.0 that has the FOG certificate bundled and trusted.

If the binary chained isn’t already trusted, I believe you should be able to use some scripting to then automatically chain in mokmanager or fallback to chaining via http.

Provided you use the normal FOG signing keys, this should work fine, though it does mean having two shims. It may be worth it to close that small gap in HTTPS. Both the shim and custom iPXE could be chain loaded via TFTP. It does add a little more complexity to the signing and boot process but I figured it was worth mentioning, as having HTTPS wherever possible does seem valuable.

FOG Secure Boot with Shim

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