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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?

VMware by Broadcom, https://www.vmware.com/

What product or service is this for?

Photon OS, https://vmware.github.io/photon/

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

Photon OS is a Linux distribution being used by VMware customers in clouds (vSphere, AWS, Azure, GCE) and on bare-metal. We use shim->grub2->Linux chain for Secure Boot support. It needs to be signed in order to boot the Photon OS on any device using UEFI CA certificate for Secure Boot.

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

Photon OS is a customized operating system and optimized for VMware-specific appliances. We provide our own grub2, kernels and modules that need to be authenticated by VMware CA. Therefore, we cannot use other distro's signed shim for supporting Secure Boot for our customers.

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.

(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.?

(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.

Yes.

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

https://github.com/vmware/photon/tree/5.0/SPECS/shim

What patches are being applied and why:

  • 0001-Enforce-SBAT-presence-in-every-image.patch: Enforce .sbat section in every image (grub, kernel) booted by shim
  • 0001-Add-provision-to-disable-netboot-and-httpboot-in-shi.patch: Limit the boot capability to local disk and disable netboot, httpboot options
  • 0001-Introduce-support-for-revocations-build.patch: Include bare-bones code to generate revocations.efi (.sbata and .sbatl would be added later)

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)

We use downstream Fedora-based GRUB2.

Source - https://github.com/vmware/photon/tree/5.0/SPECS/grub2

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?

The current builds include the grub,4 fixes.

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/

Yes.

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

No. Our shim-v15.4 is not revoked through DBX update but the one before that shim-v15 is revoked. We will invalidate current shim with SBAT generation upgrade and plan to provide hash to Microsoft once we ship the latest signed shim-v15.8.

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

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?

All the above patches are applied to our kernel and we frequently update to latest upstream Linux kernel v6.1.x.

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

Photon OS actively backports features and bugfixes from upstream Linux kernel. We also have various VMware appliance-specific performance and security patches, and patches to enforce kernel lockdown when secure boot is enabled.

Our full patch list is here: https://github.com/vmware/photon/tree/5.0/SPECS/linux

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.

Yes, build time generated ephemeral key.

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.

We don't use this. Our shim trusts photon_sb2020.der certificate from this repo.

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.

SBAT generation upgrade will handle revocation of older binaries. shim SBAT is upgraded from 1 to 4 and grub2 SBAT is upgraded from 1 to 4.

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.

Dockerfile is included to reproduce our 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.

build.log file contains build logs. It was produced with following command.

docker build --progress=plain -t shim-image . --no-cache &>build.log

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..

Last signed Photon shim was 15.4 based. We now have latest upstream release v15.8 to fix security issues. We have also adapted latest 6.1.x kernel and Fedora based grub-2.06.

What is the SHA256 hash of your final SHIM binary?

$ sha256sum shimx64.efi
3c644e2d1f4449fa761c540615f2b59178639ae2fa74c493de71b951afc80e11  shimx64.efi

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

It is stored in HSMs which are operating in FIPS 140-2 level 2 approved mode, only accessible by certain members of the build infrastructure team. They are located in physically secure areas of our datacenters.

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, UKI(s), shim + all child shim binaries )?

Please provide exact SBAT entries for all shim binaries as well as all SBAT binaries that shim will directly boot.

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.photon,1,VMware Photon OS,shim,15.8-1.ph5,https://github.com/vmware/photon

grub2

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.photon,2,VMware Photon OS,grub2,2.06-16.ph5,https://github.com/vmware/photon

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

fat iso9660 part_gpt part_msdos normal boot linux configfile loopback chain efifwsetup efi_gop efi_uga ls search search_label search_fs_uuid search_fs_file gfxterm gfxterm_background gfxterm_menu test all_video loadenv exfat ext2 udf halt gfxmenu png tga lsefi help probe echo lvm

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

No.

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

grub-2.06 based on Fedora https://src.fedoraproject.org/rpms/grub2

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

SHIM only launches signed grub2. To handle future vulnerabilities, we include revocations.efi. It would be read by shim to update SbatLevel and revoke Photon kernel and grub.

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.

GRUB2 will launch only linux kernel, no other component.

How do the launched components prevent execution of unauthenticated code?

grub2 verifies signatures on booted kernels via shim. Kernel is compiled with LOCK_DOWN_KERNEL_FORCE_INTEGRITY when Secure Boot enabled and enforce signatures verification. All modules and kernel images are signed.

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?

We frequently upgrade to latest Linux upstream 6.1.x version. Following patches are included for Secure Boot and kernel lockdown,

  • 0001-kernel-lockdown-when-UEFI-secure-boot-enabled.patch: Lockdown kernel to integrity when Secure Boot detected at boot time
  • 0002-Add-.sbat-section.patch: Insert .sbat section in kernel image
  • 0003-Verify-SBAT-on-kexec.patch: Validate .sbat section of kernel image when using fast-boot (kexec) along with signature

These patches can be found here: https://github.com/vmware/photon/tree/5.0/SPECS/linux/generic

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

Previous version, based on shim 15.4, was approved here rhboot#164

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