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Reviews of shim bootloader for IGEL Technology

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IGEL-Technology/shim-review

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This repo is for review of requests for signing shim. To create a request for review:

  • clone this repo (preferably fork it)
  • edit the template below
  • add the shim.efi to be signed
  • add build logs
  • add any additional binaries/certificates/SHA256 hashes that may be needed
  • commit all of that
  • tag it with a tag of the form "myorg-shim-arch-YYYYMMDD"
  • push it to GitHub
  • file an issue at https://github.com/rhboot/shim-review/issues with a link to your tag
  • approval is ready when the "accepted" label is added to your issue

Note that we really only have experience with using GRUB2 or systemd-boot on Linux, so asking us to endorse anything else for signing is going to require some convincing on your part.

Hint: check the docs directory in this repo for guidance on submission and getting your shim signed.

Here's the template:

What organization or people are asking to have this signed?

IGEL Technology GmbH. We are a software company from Germany, building IGEL OS, a managed, Linux-based operating system for thin clients.

What product or service is this for?

IGEL OS.

What's the justification that this really does need to be signed for the whole world to be able to boot it?

Our IGEL OS is rolled out onto large numbers of customer devices. Booting it with UEFI Secureboot enabled must be feasible without rolling out custom keys first.

Why are you unable to reuse shim from another distro that is already signed?

We roll out GRUB and kernel updates frequently, each customized by us. The Linux kernel must fulfill hardware support for most recent devices, and needs therefore be custom-built and signed by us. Hence, GRUB needs to accept our Kernel signatures for SecureBoot. GRUB is also kept up to date and includes minor patches for IGEL OS-specific management and recovery options, therefore is also signed by us frequently.

Who is the primary contact for security updates, etc.?

The security contacts need to be verified before the shim can be accepted. For subsequent requests, contact verification is only necessary if the security contacts or their PGP keys have changed since the last successful verification.

An authorized reviewer will initiate contact verification by sending each security contact a PGP-encrypted email containing random words. You will be asked to post the contents of these mails in your shim-review issue to prove ownership of the email addresses and PGP keys.

  • Name: Kulow, Alexander Fabian
  • Position: Security Architect
  • Email address: [email protected]
  • PGP key fingerprint: D53B9CE1CE8614C6

(Key should be signed by the other security contacts, pushed to a keyserver like keyserver.ubuntu.com, and preferably have signatures that are reasonably well known in the Linux community.)

Who is the secondary contact for security updates, etc.?

  • Name: Müller, Christina
  • Position: Manager Linux Development
  • Email address: [email protected]
  • PGP key fingerprint: 6FCDFA6477566085

(Key should be signed by the other security contacts, pushed to a keyserver like keyserver.ubuntu.com, and preferably have signatures that are reasonably well known in the Linux community.)

Were these binaries created from the 15.8 shim release tar?

Please create your shim binaries starting with the 15.8 shim release tar file: https://github.com/rhboot/shim/releases/download/15.8/shim-15.8.tar.bz2

This matches https://github.com/rhboot/shim/releases/tag/15.8 and contains the appropriate gnu-efi source.

Make sure the tarball is correct by verifying your download's checksum with the following ones:

a9452c2e6fafe4e1b87ab2e1cac9ec00  shim-15.8.tar.bz2
cdec924ca437a4509dcb178396996ddf92c11183  shim-15.8.tar.bz2
a79f0a9b89f3681ab384865b1a46ab3f79d88b11b4ca59aa040ab03fffae80a9  shim-15.8.tar.bz2
30b3390ae935121ea6fe728d8f59d37ded7b918ad81bea06e213464298b4bdabbca881b30817965bd397facc596db1ad0b8462a84c87896ce6c1204b19371cd1  shim-15.8.tar.bz2

Make sure that you've verified that your build process uses that file as a source of truth (excluding external patches) and its checksum matches. Furthermore, there's a detached signature as well - check with the public key that has the fingerprint 8107B101A432AAC9FE8E547CA348D61BC2713E9F that the tarball is authentic. Once you're sure, please confirm this here with a simple yes.

A short guide on verifying public keys and signatures should be available in the docs directory.

Yes. The build is based on the shim-15.8 linked above.

URL for a repo that contains the exact code which was built to result in your binary:

Hint: If you attach all the patches and modifications that are being used to your application, you can point to the URL of your application here (https://github.com/YOUR_ORGANIZATION/shim-review).

You can also point to your custom git servers, where the code is hosted.

https://github.com/IGEL-Technology/shim

What patches are being applied and why:

Mention all the external patches and build process modifications, which are used during your building process, that make your shim binary be the exact one that you posted as part of this application.

  • Fix for CVE-2024-2312, by Julian Andres Klode
  • Bump SBAT level to 4
  • IGEL-specific change to load igelx64.efi instead of grubx64.efi (required to boot from IGEL USB stick - UDPocket)

Do you have the NX bit set in your shim? If so, is your entire boot stack NX-compatible and what testing have you done to ensure such compatibility?

See https://techcommunity.microsoft.com/t5/hardware-dev-center/nx-exception-for-shim-community/ba-p/3976522 for more details on the signing of shim without NX bit.

No.

What exact implementation of Secure Boot in GRUB2 do you have? (Either Upstream GRUB2 shim_lock verifier or Downstream RHEL/Fedora/Debian/Canonical-like implementation)

Skip this, if you're not using GRUB2.

We're using the Debian implementation.

Do you have fixes for all the following GRUB2 CVEs applied?

Skip this, if you're not using GRUB2, otherwise make sure these are present and confirm with yes.

Yes. CVE-2022-28737 is actually not a GRUB CVE, but fixed in shim upstream here (and thus fixed in our build):

https://github.com/rhboot/shim/commit/159151b6649008793d6204a34d7b9c41221fb4b0 https://github.com/rhboot/shim/commit/e99bdbb827a50cde019393d3ca1e89397db221a7

If shim is loading GRUB2 bootloader, and if these fixes have been applied, is the upstream global SBAT generation in your GRUB2 binary set to 4?

Skip this, if you're not using GRUB2, otherwise do you have an entry in your GRUB2 binary similar to:
grub,4,Free Software Foundation,grub,GRUB_UPSTREAM_VERSION,https://www.gnu.org/software/grub/?

Yes.

Were old shims hashes provided to Microsoft for verification and to be added to future DBX updates?

Does your new chain of trust disallow booting old GRUB2 builds affected by the CVEs?

If you had no previous signed shim, say so here. Otherwise a simple yes will do.

Yes.

If your boot chain of trust includes a Linux kernel:

Is upstream commit 1957a85b0032a81e6482ca4aab883643b8dae06e "efi: Restrict efivar_ssdt_load when the kernel is locked down" applied?

Is upstream commit 75b0cea7bf307f362057cc778efe89af4c615354 "ACPI: configfs: Disallow loading ACPI tables when locked down" applied?

Is upstream commit eadb2f47a3ced5c64b23b90fd2a3463f63726066 "lockdown: also lock down previous kgdb use" applied?

Hint: upstream kernels should have all these applied, but if you ship your own heavily-modified older kernel version, that is being maintained separately from upstream, this may not be the case.
If you are shipping an older kernel, double-check your sources; maybe you do not have all the patches, but ship a configuration, that does not expose the issue(s).

Yes. Our kernel originates from upstream and has the respective patch commits included.

Do you build your signed kernel with additional local patches? What do they do?

We generally backport fixes and features from development kernels to our LTS kernels. For example, we're currently on 6.6.x but have quite a few backports from 6.8+

  • We apply various patches to support also the most recent hardware, e.g.
    • MeteorLake processor generation
    • HP mt645
    • Surface tablets
  • We have IGEL OS-specific features in the kernel
    • IGEL Flash Driver, a kind of logical volume manager optimized for small flash memory devices providing checksum validation, encryption, etc.

Do you use an ephemeral key for signing kernel modules?

If not, please describe how you ensure that one kernel build does not load modules built for another kernel.

No. The kernel loads only modules signed off by us. We're not using ephemeral keys, yet, but plan to use them in the future. In the meantime, loading kernel modules built for another kernel is almost impossible because both kernel and modules are delivered in one closed system. If additional modules are provided to the system, they will be loaded from a directory matching the kernel version, thereby preventing different versions from being loaded, too.

Other than that, only modules signed by us will be loaded, thus it's not possible to inject modules from other distributions.

If you use vendor_db functionality of providing multiple certificates and/or hashes please briefly describe your certificate setup.

If there are allow-listed hashes please provide exact binaries for which hashes are created via file sharing service, available in public with anonymous access for verification.

No.

If you are re-using the CA certificate from your last shim binary, you will need to add the hashes of the previous GRUB2 binaries exposed to the CVEs mentioned earlier to vendor_dbx in shim. Please describe your strategy.

This ensures that your new shim+GRUB2 can no longer chainload those older GRUB2 binaries with issues.

If this is your first application or you're using a new CA certificate, please say so here.

We use a new CA certificate.

Is the Dockerfile in your repository the recipe for reproducing the building of your shim binary?

A reviewer should always be able to run docker build . to get the exact binary you attached in your application.

Hint: Prefer using frozen packages for your toolchain, since an update to GCC, binutils, gnu-efi may result in building a shim binary with a different checksum.

If your shim binaries can't be reproduced using the provided Dockerfile, please explain why that's the case, what the differences would be and what build environment (OS and toolchain) is being used to reproduce this build? In this case please write a detailed guide, how to setup this build environment from scratch.

N/A. You can just use the provided Dockerfile.

Which files in this repo are the logs for your build?

This should include logs for creating the buildroots, applying patches, doing the build, creating the archives, etc.

build.log: attached is the full container log, including debuild will all build steps, comparing against upstream shim15.8, and so on. The last step outputs the resulting sha256sum on the submitted shimx64.efi.

What changes were made in the distro's secure boot chain since your SHIM was last signed?

For example, signing new kernel's variants, UKI, systemd-boot, new certs, new CA, etc..

Skip this, if this is your first application for having shim signed.

  • We updated GRUB to 2.06
  • We introduced new certificates for Kernel and GRUB signatures
  • updated shim to 15.8.

What is the SHA256 hash of your final shim binary?

90ce33685c5ac241b582bdf27d0ae872b72263a5ae8271ef7f738bd1d13e8e63  shimx64.efi

How do you manage and protect the keys used in your shim?

Describe the security strategy that is used for key protection. This can range from using hardware tokens like HSMs or Smartcards, air-gapped vaults, physical safes to other good practices.

The keys are generated on a NitroKey HSM, which is stored in a safe in the company's facility.

Do you use EV certificates as embedded certificates in the shim?

A yes or no will do. There's no penalty for the latter.

No.

Do you add a vendor-specific SBAT entry to the SBAT section in each binary that supports SBAT metadata ( GRUB2, fwupd, fwupdate, systemd-boot, systemd-stub, shim + all child shim binaries )?

Please provide the exact SBAT entries for all binaries you are booting directly through shim.

Hint: The history of SBAT and more information on how it works can be found here. That document is large, so for just some examples check out SBAT.example.md

If you are using a downstream implementation of GRUB2 (e.g. from Fedora or Debian), make sure you have their SBAT entries preserved and that you append your own (don't replace theirs) to simplify revocation.

Remember to post the entries of all the binaries. Apart from your bootloader, you may also be shipping e.g. a firmware updater, which will also have these.

Hint: run objcopy --only-section .sbat -O binary YOUR_EFI_BINARY /dev/stdout to get these entries. Paste them here. Preferably surround each listing with three backticks (```), so they render well.

shimx64.efi

sbat,1,SBAT Version,sbat,1,https://github.com/rhboot/shim/blob/main/SBAT.md
shim,4,UEFI shim,shim,1,https://github.com/rhboot/shim
shim.igel,1,Igel,shim,15.8,https://www.igel.com

igelx64.efi

sbat,1,SBAT Version,sbat,1,https://github.com/rhboot/shim/blob/main/SBAT.md
grub,4,Free Software Foundation,grub,2.06,https://www.gnu.org/software/grub/
grub.debian,4,Debian,grub2,2.06-13+deb12u1,https://tracker.debian.org/pkg/grub2
grub.igel,4,Igel,grub2,2.06-13+deb12u1igel1721912063,https://www.igel.com

fwupdx64.efi

sbat,1,UEFI shim,sbat,1,https://github.com/rhboot/shim/blob/main/SBAT.md
fwupd-efi,1,Firmware update daemon,fwupd-efi,1.6,https://github.com/fwupd/fwupd-efi
fwupd-efi.debian,1,Debian,fwupd,1:1.6-1,https://tracker.debian.org/pkg/fwupd

If shim is loading GRUB2 bootloader, which modules are built into your signed GRUB2 image?

Skip this, if you're not using GRUB2.

Hint: this is about those modules that are in the binary itself, not the .mod files in your filesystem.

boot
bufio
cat
chain
configfile
datetime
disk
diskfilter
echo
efi_gop
efi_uga
efinet
eval
ext2
extcmd
fat
file
font
gcry_rsa
gcry_sha256
gcry_sha512
gfxmenu
gfxterm
gfxterm_background
gfxterm_menu
gzio
halt
hfsplus
http
jpeg
linux
linux16
linuxefi
ls
lzopio
memdisk
minicmd
mmap
msdospart
net
normal
ntfs
part_gpt
part_msdos
password_pbkdf2
pgp
png
priority_queue
progress
regexp
relocator
search
search_fs_file
search_fs_uuid
search_label
terminal
test
tftp
tpm
tr
true
udf
video
video_bochs
video_cirrus
video_colors
video_fb
videoinfo
videotest
xzio

If you are using systemd-boot on arm64 or riscv, is the fix for unverified Devicetree Blob loading included?

N/A

What is the origin and full version number of your bootloader (GRUB2 or systemd-boot or other)?

GRUB2 2.06, Debian Bookworm.

If your shim launches any other components apart from your bootloader, please provide further details on what is launched.

Hint: The most common case here will be a firmware updater like fwupd.

We launch fwupd during BIOS updates.

If your GRUB2 or systemd-boot launches any other binaries that are not the Linux kernel in SecureBoot mode, please provide further details on what is launched and how it enforces Secureboot lockdown.

Skip this, if you're not using GRUB2 or systemd-boot.

  • fwupd

How do the launched components prevent execution of unauthenticated code?

Summarize in one or two sentences, how your secure bootchain works on higher level.

  • GRUB2 checks the launched components and only boots into kernels signed off by us.
  • Our kernel is built with security lockdown patches, and only boots from read-only partitions also signed by us.
  • Newer versions of IGEL OS containing the updated bootloader will have LOCKDOWN_FORCE_INTEGRITY enabled.

Does your shim load any loaders that support loading unsigned kernels (e.g. certain GRUB2 configurations)?

No.

What kernel are you using? Which patches and configuration does it include to enforce Secure Boot?

Upstream 6.6.32. The following module configuration will be present in the version with the updated shim:

CONFIG_SECURITY_LOCKDOWN_LSM=y
CONFIG_SECURITY_LOCKDOWN_LSM_EARLY=y
CONFIG_MODULE_SIG_FORCE=y
CONFIG_MODULE_SIG_ALL=y
CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY=y

What contributions have you made to help us review the applications of other applicants?

The reviewing process is meant to be a peer-review effort and the best way to have your application reviewed faster is to help with reviewing others. We are in most cases volunteers working on this venue in our free time, rather than being employed and paid to review the applications during our business hours.

A reasonable timeframe of waiting for a review can reach 2-3 months. Helping us is the best way to shorten this period. The more help we get, the faster and the smoother things will go.

For newcomers, the applications labeled as easy to review are recommended to start the contribution process.

None so far.

Add any additional information you think we may need to validate this shim signing application.

N/A.

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