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Rohde-Schwarz / shim-review

Reviews of shim

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

  • clone this repo
  • 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 that 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.

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?

Rohde & Schwarz Cybersecurity GmbH

What product or service is this for?

Trusted Disk full-disk encryption

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

Trusted Disk provides full-disk encryption for internal and external storage devices and protects data from unauthorized access. With a signed SHIM bootloader we are able to use the secure boot feature to ensure that each of the files in the boot chain is unmodified.

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

No Linux distribution is used in our product.

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.

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

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.

We are using https://github.com/rhboot/shim/releases/download/15.8/shim-15.8.tar.bz2

URL for a repo that contains the exact code which was built to get this binary:

Please use the Dockerfile in https://github.com/Rohde-Schwarz/shim-review/tree/rohdeschwarz-shim-x64-20240219 to build and verify our shim bootloader.

What patches are being applied and why:

msabi.patch Using the ms_abi calling convention for the SHIM_LOCK protocol function invocation.
bypass_bootoptions.patch Bypass bootoption parsing and second stage loader name assembly.

We added a patch to bypass the bootoption parsing and second stage loader name assembly. This code failed on some systems and produced a non-bootable name for the second stage loader. Because we are using a hardcoded path and filename for the second stage loader, we just bypass this code with this patch.

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.

NX bit is not set.

If shim is loading GRUB2 bootloader what exact implementation of Secureboot in GRUB2 do you have? (Either Upstream GRUB2 shim_lock verifier or Downstream RHEL/Fedora/Debian/Canonical-like implementation)

No GRUB bootloader is used.

If shim is loading GRUB2 bootloader and your previously released shim booted a version of GRUB2 affected by any of the CVEs in the July 2020, the March 2021, the June 7th 2022, the November 15th 2022, or 3rd of October 2023 GRUB2 CVE list, have fixes for all these CVEs been applied?

No GRUB bootloader is used.

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?

The entry should look similar to: grub,4,Free Software Foundation,grub,GRUB_UPSTREAM_VERSION,https://www.gnu.org/software/grub/

No GRUB bootloader is used.

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?

All older signed shims are using SBAT revocation. No GRUB bootloader is used.

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?

No Linux kernel is used.

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

No Linux kernel is used.

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 Linux kernel is used.

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 vendor_db is used.

If you are re-using a previously used (CA) certificate, you will need to add the hashes of the previous GRUB2 binaries exposed to the CVEs to vendor_dbx in shim in order to prevent GRUB2 from being able to chainload those older GRUB2 binaries. If you are changing to a new (CA) certificate, this does not apply.

Please describe your strategy.

No GRUB bootloader is used.

What OS and toolchain must we use to reproduce this build? Include where to find it, etc. We're going to try to reproduce your build as closely as possible to verify that it's really a build of the source tree you tell us it is, so these need to be fairly thorough. At the very least include the specific versions of gcc, binutils, and gnu-efi which were used, and where to find those binaries.

If the shim binaries can't be reproduced using the provided Dockerfile, please explain why that's the case and what the differences would be.

Please use the included Dockerfile to build and verify our shim bootloader.

Use the command:

docker build https://github.com/Rohde-Schwarz/shim-review.git

to reproduce this build.

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.

https://github.com/Rohde-Schwarz/shim-review/blob/rohdeschwarz-shim-x64-20240219/build.log

What changes were made in the distor'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..

No changes were made.

What is the SHA256 hash of your final SHIM binary?

6A887C457F51CEE59855C4B98834E9EAB273A6400AB9137BCD0A99DBAE1AAA60

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

The private key is stored on hardware token with restricted access.

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

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 exact SBAT entries for all SBAT binaries you are booting or planning to boot directly through shim.

Where your code is only slightly modified from an upstream vendor's, please also preserve their SBAT entries to simplify revocation.

If you are using a downstream implementation of GRUB2 or systemd-boot (e.g. from Fedora or Debian), please preserve the SBAT entry from those distributions and only append your own. More information on how SBAT works can be found here.

shim

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.rscs,1,Rohde & Schwarz Cybersecurity GmbH,shim,15.8,https://www.rohde-schwarz.com/cybersecurity

trusted disk

sbat,1,SBAT Version,sbat,1,https://github.com/rhboot/shim/blob/main/SBAT.md
tdisk.rscs,1,Rohde & Schwarz Cybersecurity GmbH,tdisk,1,https://www.rohde-schwarz.com/cybersecurity

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

No GRUB bootloader is used.

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

No systemd-boot on arm64 or riscv is used.

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

No GRUB bootloader is used.

If your SHIM launches any other components, please provide further details on what is launched.

The SHIM launches our pre-boot authentication component that decrypts the system and boots a Windows operating system.

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.

No GRUB bootloader is used.

How do the launched components prevent execution of unauthenticated code?

The integrity of each file in our boot chain is verified by checking the validity of the digital signature when using the LoadImage/StartImage functions.

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

No.

What kernel are you using? Which patches does it includes to enforce Secure Boot?

No Linux kernel is used.

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

No.

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