Testing

Testing Secure Boot

Much of this is based on the UEFI work:

Testing infrastructure uses the security team's TestingEnvironment.

Introduction

In brief, Secure Boot works by placing the root of trust in firmware. While other implementations are possible, in practice the chain of trust is achieved via x509 certificates. A root CA is embedded in firmware such that it can then validate the signed bootloader, the signed bootloader can then validate the signed kernel or signed 2nd stage boot loader, and so on. Various key databases are used to provide flexibility and maintain strong security:

  • DB (aka, 'signature database'): contains the trusted keys used for authenticating any applications or drivers executed in the UEFI environment
  • DBX (aka, 'forbidden signature database' or 'signature database blacklist'): contains a set of explicitly untrusted keys and binary hashes. Any application or driver signed by these keys or matching these hashes will be blocked from execution.
  • KEK (key exchange keys database): contains the set of keys trusted for updating DB and DBX
  • PK (platform key - while PK is often referred to simply as a single public key, it could be implemented as a database). Only updates signed with PK can update the KEK database.

The suggested implementation by UEFI:

  • OEM key in PK
  • OS vendor keys in KEK and DB. OEM may also have a key in KEK and DB

Systems shipping with Windows 8 will typically use the following:

  • OEM key in PK
  • 'Microsoft Corporation KEK CA' key in KEK
  • 'Microsoft Windows Production PCA' and 'Microsoft Corporation UEFI CA' keys in DB (note, the 'Microsoft Corporation UEFI CA' is not guaranteed to be present in DB-- while recommended, this is EFI firmware vendor/OEM dependent)

In order to boot on the widest range of systems, Ubuntu uses the following chain of trust:

  1. Microsoft signs Canonical's 'shim' 1st stage bootloader with their 'Microsoft Corporation UEFI CA'. When the system boots and Secure Boot is enabled, firmware verifies that this 1st stage bootloader (from the 'shim-signed' package) is signed with a key in DB (in this case 'Microsoft Corporation UEFI CA')
  2. The second stage bootloader (grub-efi-amd64-signed) is signed with Canonical's 'Canonical Ltd. Secure Boot Signing' key. The shim 1st stage bootloader verifies that the 2nd stage grub2 bootloader is properly signed.
  3. The 2nd stage grub2 bootloader boots an Ubuntu kernel (as of 2012/11, if the kernel (linux-signed) is signed with the 'Canonical Ltd. Secure Boot Signing' key, then grub2 will boot the kernel which will in turn apply quirks and call ExitBootServices. If the kernel is unsigned, grub2 will call ExitBootServices before booting the unsigned kernel)

  4. If signed kernel modules are supported, the signed kernel will verify them during kernel boot

Since the above gives the ability to control boot to the OEM and Microsoft, users may want to:

  • install their own key in PK, KEK and DB, then re-sign grub2 and use it without shim (and optionally sign the kernel with their own key)
  • install their own key in PK and KEK, Canonical's 'Canonical Ltd. Master Certificate Authority' key in KEK and DB and Microsoft's keys in KEK (for updates to DBX). This gives some control of boot to Canonical, but allows for the grub-efi-amd64-signed and linux-signed packages and any DB/DBX updates from Microsoft and Canonical to work without re-signing.
  • install their own key in shim's own keyring, when testing only Canonical- or user-signed grub2 and/or kernel and modules.

When testing, a minimum of shim boot, Canonical-signed grub2 boot and user-signed grub2 boot should be covered.

IMPORTANT: Canonical's Secure Boot implementation in Ubuntu is primarily about hardware-enablement and this page focuses on how to test Secure Boot for common hardware-enablement configurations, not for enabling Secure Boot to harden your system. If you want to use Secure Boot as a security mechanism, an appropriate solution would be to use your own keys (optionally enrolling additional keys, see above) and update the bootloader to prohibit booting an unsigned kernel. Ubuntu 16.04 LTS is planned to enable enforcing secure boot (see LP: #1401532 for details).

VM installation and preparation

  1. Obtain an OVMF image capable of performing Secure Boot by either:
  2. Verify the symlink from /usr/share/ovmf/OVMF.fd to /usr/share/qemu/OVMF.fd and use a relative path to OVMF.fd for now (see LP: #1074207)

  3. Install Ubuntu using the Secure Boot capable UEFI OVMF firmware (downloaded as bios.bin):

    $ uvt new --loader=OVMF.fd --with-ovmf-uefi xenial amd64 sb

    This can also be performed with a virt-install command:

    $ virt-install --connect=qemu:///system --name=sb-xenial-amd64 --arch=x86_64 --ram=2048 \
    --disk=path=<path to>/sb-xenial-amd64.qcow2,size=8,format=qcow2,bus=ide,sparse=True \
    --virt-type=kvm --accelerate --hvm --cdrom=<path to>/xenial-desktop-amd64.iso \
    --os-type=linux --os-variant=generic26 --graphics=vnc --network=network=default,model=virtio \
    --video=cirrus --noreboot --boot=loader=OVMF.fd

Both of the above commands creates the sb-xenial-amd64 machine. Note that when using uvt there is a limitation in that a preseeded ISO cannot be used. uvt will skip the postinstall phase and you will have to perform the install manually. You will know that you are using the OVMF EFI image if the machine comes up with 'Try Ubuntu' (ie, not the graphical install). Using the manual partitioner to create a 250M EFI partition as the first partition and then setting up a '/' and swap partition is known to work.

Caveats:

  • The installer doesn't reboot after install without pressing 'Enter'
  • On Ubuntu releases earlier than 16.04: on reboot and all boots, you must go into the efi config screen to boot from a file off the disk. Eg, from the main EFI configure screen:

     - Boot Maintenance Manager ->
       - Boot From File ->
         - NO VOLUME LABEL,[!PciRoot(0x0)/Pci(0x1,0x1)/Ata(Primary,Master,0x0)/HD(1,GPT,...)] ->
           - <EFI> ->
             - <ubuntu> ->
               - grubx64.efi

    This behavior can be changed by doing booting into the VM and then copying the appropriate files to /boot/efi/EFI/BOOT/BOOTX64.EFI. Eg, for just grub2, copy /boot/efi/EFI/ubuntu/grubx64.efi to /boot/efi/EFI/BOOT/BOOTX64.EFI. For shim, copy /boot/efi/EFI/ubuntu/shimx64.efi to /boot/efi/EFI/BOOT/BOOTX64.EFI and then copy /boot/efi/EFI/ubuntu/grubx64.efi and grub.cfg into /boot/efi/EFI/BOOT. Note: this document assumes that you are using the 'Boot From File' method.

  • Because the postinstall isn't run via uvt, after install, you may want to:

    • sudo apt-get install openssh-server screen vim gnome-panel

    • Use ssh-copy-id to copy your key over

    • Optionally update sources.list for your mirror
  • When using uvt, the intial pristine snapshot is not created. After setting up, use uvt snapshot sb-quantal-amd64

  • Because the firmware needs to be able to interact with the hardware and is limited in what it supports, the following are used when using uvt:

    • IDE disks (ie, can't use virtio)
    • cirrus video driver
    Currently the virtio network driver is used-- if you want to try out PXE booting via EFI, this will likely also need to change.

See https://wiki.ubuntu.com/UEFI/OVMF for other ways of using the OVMF file.

EFI Shell

Sometimes it might be desirable to go into the EFI shell. This can be done by adjusting the Boot Order in Boot options. Ie:

 - Boot Maintenance Manager ->
   - Boot Options ->
     - Change Boot Order ->
       - Highlight the list, press Enter, go to 'EFI Internal Shell' then press
         '+' until it is above 'EFI Hard Drive'. Press Enter, then select
         Commit Changes and Exit

At this point, press 'Esc' until you get to the main EFI configuration menu and click 'Continue'. This will boot the shell. Use 'exit' to return to the EFI Configuration menu. Useful commands:

  • Shell> ls fs0:\ (directory listing corresponding to /boot/efi)

  • Shell> ls fs0:\EFI\ubuntu\ (directory listing of where our bootloaders are)

  • Shell> fs0:\EFI\ubuntu\grubx64.efi (launch grub2 bootloader)

  • Shell> fs0:\EFI\ubuntu\shimx64.efi (launch shim bootloader)

  • Shell> fs0:\EFI\ubuntu\efilinux.efi -f 0:\EFI\ubuntu\vmlinuz initrd=0:\EFI\ubuntu\initrd root=/dev/sda3 quiet splash (launch eflinux bootloader)

Note: after booting the system via the EFI shell as above, the OVMF firmware will default to EFI Hard Drive and not allow access to the shell. You will have to do a cold reboot to enter the shell again.

Maintenance

uvt update does not work because the boot process requires manual intervention. As such, keeping the VM up to date consists of:

  1. $ sudo start [-rf] <vmname>

  2. Selecting the image to boot
  3. $ uvt cmd -r -p <vmprefix> 'apt-get update && apt-get -y --force-yes dist-upgrade && apt-get autoremove --purge'

  4. $ uvt stop <vmname>

  5. $ uvt snapshot <vmname>

Manual Secure Boot VM setup

Include: Nothing found for "== Basic secure boot setup for testing =="!

Include: Nothing found for "== Resources =="!

What is UEFI Secure Boot?

UEFI Secure boot is a verification mechanism for ensuring that code launched by firmware is trusted.

Proper, secure use of UEFI Secure Boot requires that each binary loaded at boot is validated against known keys, located in firmware, that denote trusted vendors and sources for the binaries, or trusted specific binaries that can be identified via cryptographic hashing.

Most x86 hardware comes from the factory pre-loaded with Microsoft keys. This means we can generally rely on the firmware on these systems to trust binaries that are signed by Microsoft, and the Linux community heavily relies on this assumption for Secure Boot to work. This is the same process used by Red Hat and SUSE, for instance.

Many ARM and other architectures also support UEFI Secure Boot, but may not be pre-loading keys in firmware. On these architectures, it may be necessary to re-sign boot images with a certificate that is loaded in firmware by the owner of the hardware.

Initial implementation plan: Implementation Plan.

Supported architectures

  • amd64: A shim binary signed by Microsoft and grub binary signed by Canonical are provided in the Ubuntu main archive as shim-signed or grub-efi-amd64-signed.

  • arm64: No Microsoft-signed shim is available, but users may sign their own. Canonical-signed grub is available as grub-efi-arm64-signed.

Testing UEFI Secure Boot

If you're interested in testing Secure Boot on your system, consult the how-to here: UEFI/SecureBoot/Testing.

How UEFI Secure Boot works on Ubuntu

On Ubuntu, all pre-built binaries intended to be loaded as part of the boot process, with the exception of the initrd image, are signed by Canonical's UEFI certificate, which itself is implicitly trusted by being embedded in the shim loader, itself signed by Microsoft.

On architectures or systems where pre-loaded signing certificates from Microsoft are not available or loaded in firmware, users may replace the existing signatures on shim or grub and load them as they wish, verifying against their own certificates imported in the system's firmware.

As the system boots, firmware loads the shim binary as specified in firmware BootEntry variables. Ubuntu installs its own BootEntry at installation time and may update it any time the GRUB bootloader is updated. Since the shim binary is signed by Microsoft; it is validated and accepted by the firmware when verifying against certificates already present in firmware. Since the shim binary embeds a Canonical certificate as well as its own trust database, further elements of the boot environment can, in addition to being signed by one of the acceptable certificates pre-loaded in firmware, be signed by Canonical's UEFI key.

The next thing loaded by shim is the second-stage image. This can be one of two things: either GRUB, if the system is booting normally; or MokManager, if key management is required, as configured by firmware variables (usually changed when the system was previously running).

If booting normally; the GRUB binary (grub*.efi) is loaded and its validation is attempted against all previously-known trusted sources. The GRUB binary for Ubuntu is signed by the Canonical UEFI key, so it is successfully validated and the boot process continues.

If booting to proceed with key management tasks, the MokManager binary (mm*.efi) is loaded. This binary is explicitly trusted by shim by being signed by an ephemeral key that only exists while the shim binary is being built. This means only the MokManager binary built with a particular shim binary will be allowed to run and limits the possibility of compromise from the use of compromised tools. MokManager allows any user present at the system console to enroll keys, remove trusted keys, enroll binary hashes and toggle Secure Boot validation at the shim level, but most tasks require a previously set password to be entered to confirm that the user at console is indeed the person who requested changes. Such passwords only survive across a single run of shim / MokManager; and are cleared as soon as the process is completed or cancelled. Once key management is completed, the system is rebooted and does not simply continue with booting, since the key management changes may be required to successfully complete the boot.

Once the system continues booting to GRUB; the GRUB process loads any required configuration (usually loading configuration from the ESP (EFI System Partition), pointing to another configuration file on the root or boot partition), which will point it to the kernel image to load.

EFI applications up to this point having full access to the system firmware, including access to changing trusted firmware variables, the kernel to load must also be validated against the trust database. Official Ubuntu kernels being signed by the Canonical UEFI key, they are successfully validated, and control is handed over to the kernel. Initrd images are not validated.

In the case of unofficial kernels, or kernels built by users, additional steps need to be taken if users wish to load such kernels while retaining the full capabilities of UEFI Secure Boot. All kernels must be signed to be allowed to load by GRUB when UEFI Secure Boot is enabled, so the user will require to proceed with their own signing. Alternatively, users may wish to disable validation in shim while booted with Secure Boot enabled on an official kernel by using 'sudo mokutil --disable-validation', providing a password when prompted, and rebooting; or to disable Secure Boot in firmware altogether.

Up to this point, any failure to validate an image to load is met with a critical error which stops the boot process. The system will not continue booting, and may automatically reboot after a period of time given that other BootEntry variables may contain boot paths that are valid and trusted.

Once loaded, validated kernels will disable the firmware's Boot Services, thus dropping privileges and effectively switching to user mode; where access to trusted variables is limited to read-only. Given the broad permissions afforded to kernel modules, any module not built into the kernel will also need to be validated upon loading. Modules built and shipped by Canonical with the official kernels are signed by the Canonical UEFI key and as such, are trusted. Custom-built modules will require the user to take the necessary steps to sign the modules before they loading them is allowed by the kernel. This can be achieved by using the 'kmodsign' command [see {How to sign} section].

Unsigned modules are simply refused by the kernel. Any attempt to insert them with insmod or modprobe will fail with an error message.

Given that many users require third-party modules for their systems to work properly or for some devices to function; and that these third-party modules require building locally on the system to be fitted to the running kernel, Ubuntu provides tooling to automate and simplify the signing process.

How can I do non-automated signing of drivers?

Some projects may require the use of custom kernel drivers that are not set up in such a way as to work with DKMS. In these cases, people should make use of the tools included in the shim-signed package: the update-secureboot-policy script is available to generate a new MOK (if no DKMS-built modules have triggered generating one already).

Use the following command to enroll an existing key into shim:

sudo update-secureboot-policy --enroll-key

If no MOK exists, the script will exit with a message to that effect. If the key is already enrolled, the script will exit, doing nothing. If the key exists but it not shown to be enrolled, the user will be prompted for a password to use after reboot, so that the key can be enrolled.

One can generate a new MOK using the following command:

sudo update-secureboot-policy --new-key

And then enroll the newly-generated key into shim with the previously-mentioned command for that task.

Kernel modules can then be signed with the kmodsign command (see UEFI/SecureBoot/Signing) as part of their build process.

Security implications in Machine-Owner Key management

The MOK generated at installation time or on upgrade is machine-specific, and only allowed by the kernel or shim to sign kernel modules, by use of a specific KeyUsage OID (1.3.6.1.4.1.2312.16.1.2) denoting the limitations of the MOK.

Recent shim versions include logic to follow the limitations of module-signing-only keys. These keys will be allowed to be enrolled in the firmware in shim's trust database, but will be ignored when shim or GRUB validate images to load in firmware. Shim's verify() function will only successfully validate images signed by keys that do not include the "Module-signing only" (1.3.6.1.4.1.2312.16.1.2) KeyUsage OID. The Ubuntu kernels use the global trust database (which includes both shim's and the firmware's) and will accept any of the included keys as signing keys when loading kernel modules.

Given the limitations imposed on the automatically generated MOK and the fact that users with superuser access to the system and access to the system console to enter the password required when enrolling keys already have high-level access to the system; the generated MOK key is kept on the filesystem as regular files owned by root with read-only permissions. This is deemed sufficient to limit access to the MOK for signing by malicious users or scripts, especially given that no MOK exists on the system unless it requires third-party drivers. This limits the possibility of compromise from the misuse of a generated MOK key to signing a malicious kernel module. This is equivalent to compromise of the userland applications which would already be possible with superuser access to the system, and securing this is out of the scope of UEFI Secure Boot.

Previous systems may have had Secure Boot validation disabled in shim. As part of the upgrade process, these systems will be migrated to re-enabling Secure Boot validation in shim and enrolling a new MOK key when applicable.

MOK generation and signing process

The key generation and signing process is slightly different based on whether we are dealing with a brand new installation or an upgrade of system previously running Ubuntu; these two cases are clearly marked below.

In all cases, if the system is not booting in UEFI mode, no special kernel module signing steps or key generation will happen.

If Secure Boot is disabled, MOK generation and enrollment still happens, as the user may later enable Secure Boot. They system should work properly if that is the case.

The user installs Ubuntu on a new system

The user steps through the installer. Early on, when preparing to install and only if the system requires third-party modules to work, the user is prompted for a system password that is clearly marked as being required after the install is complete, and while the system is being installed, a new MOK is automatically generated without further user interaction.

Third-party drivers or kernel modules required by the system will be automatically built when the package is installed, and the build process includes a signing step. The signing step automatically uses the MOK generated earlier to sign the module, such that it can be immediately loaded once the system is rebooted and the MOK is included in the system's trust database.

Once the installation is complete and the system is restarted, at first boot the user is presented with the MokManager program (part of the installed shim loader), as a set of text-mode panels that all the user to enroll the generated MOK. The user selects "Enroll MOK", is shown a fingerprint of the certificate to enroll, and is prompted to confirm the enrollment. Once confirmed, the new MOK will be entered in firmware and the user will be asked to reboot the system.

When the system reboots, third-party drivers signed by the MOK just enrolled will be loaded as necessary.

The user upgrades an UEFI-enabled Ubuntu system to a new release where the system requires third-party drivers

On upgrade, the shim and shim-signed packages are upgraded. The shim-signed package's post-install tasks proceeds to generate a new MOK, and prompts the user for a password that is clearly mentioned as being required once the upgrade process is completed and the system rebooted.

During the upgrade, the kernel packages and third-party modules are upgraded. Third-party modules are rebuilt for the new kernels and their post-build process proceeds to automatically sign them with the MOK.

After upgrade, the user is recommended to reboot their system.

On reboot, the user is presented with the MokManager program (part of the installed shim loader), as a set of text-mode panels that all the user to enroll the generated MOK. The user selects "Enroll MOK", is shown a fingerprint of the certificate to enroll, and is prompted to confirm the enrollment. The user is also presented with a prompt to re-enable Secure Boot validation (in the case it was found to be disabled); and MokManager again requires confirmation from the user. Once all steps are confirmed, shim validation is re-enabled, the new MOK will be entered in firmware and the user will be asked to reboot the system.

When the system reboots, third-party drivers signed by the MOK just enrolled will be loaded as necessary.

In all cases, once the system is running with UEFI Secure Boot enabled and a recent version of shim; the installation of any new DKMS module (third-party driver) will proceed to sign the built module with the MOK. This will happen without user interaction if a valid MOK key exists on the system and appears to already be enrolled.

If no MOK exists or the existing MOK is not enrolled, a new key will automatically created just before signing and the user will be prompted to enroll the key by providing a password which will be required upon reboot.

Assisted Secure Boot VM setup

Bootloader signed with user key

This emulates a configuration where a user or enterprise is using its own keys in PK, KEK and DB and follows the procedures in http://jk.ozlabs.org/docs/sbkeysync-maintaing-uefi-key-databases/. This configuration allows the greatest flexibility in testing as we control PK and KEK, so we can update all aspects of Secure Boot as needed. The key database is configured with (each entry in firmware has the same GUID):

  • User key in PK
  • User key in KEK
  • User key in DB

Steps to configure:

  1. Boot an OVMF virtual UEFI machine (see above)
  2. Install some packages:

    $ sudo apt-get install sbsigntool openssl grub-efi-amd64-signed fwts linux-signed-generic
  3. Install the signed bootloader:

    $ sudo grub-install --uefi-secure-boot
  4. Reboot the VM and 'Boot from File' as above (continue to use 'grubx64.efi')
  5. Download sb-setup and keys/ from https://git.launchpad.net/qa-regression-testing:/notes_testing/secure-boot/ to /tmp/sb-setup and /tmp/keys

  6. Enroll the user keys (output may vary):

    $ /tmp/sb-setup enroll
    Creating keystore...
      mkdir '/etc/secureboot/keys'
      mkdir '/etc/secureboot/keys/PK'
      mkdir '/etc/secureboot/keys/KEK'
      mkdir '/etc/secureboot/keys/db'
      mkdir '/etc/secureboot/keys/dbx'
    done
    
    Creating keys... done
    
    Generating key updates for PK...
      using GUID=1d5bd2fb-f597-4315-b3bc-dfe84b594ce7
      creating EFI_SIGNATURE_LIST (test-cert.der.siglist)...
      creating signed update (test-cert.der.siglist.PK.signed)...
    done
    Generating key updates for KEK...
      using GUID=1d5bd2fb-f597-4315-b3bc-dfe84b594ce7
      creating EFI_SIGNATURE_LIST (test-cert.der.siglist)...
      creating signed update (test-cert.der.siglist.KEK.signed)...
    done
    Generating key updates for db...
      using GUID=1d5bd2fb-f597-4315-b3bc-dfe84b594ce7
      creating EFI_SIGNATURE_LIST (test-cert.der.siglist)...
      creating signed update (test-cert.der.siglist.db.signed)...
    done
    Initializing keystore...
      adding to /etc/secureboot/keys/PK/
      adding to /etc/secureboot/keys/KEK/
      adding to /etc/secureboot/keys/db/
    done
    
    Filesystem keystore:
      /etc/secureboot/keys/db/test-cert.der.siglist.db.signed [2116 bytes]
      /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed [2116 bytes]
      /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed [2116 bytes]
    firmware keys:
      PK:
      KEK:
      db:
      dbx:
    filesystem keys:
      PK:
        /CN=test-key
         from /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed
      KEK:
        /CN=test-key
         from /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed
      db:
        /CN=test-key
         from /etc/secureboot/keys/db/test-cert.der.siglist.db.signed
      dbx:
    New keys in filesystem:
     /etc/secureboot/keys/db/test-cert.der.siglist.db.signed
     /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed
     /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed
    Commit to keystore? (y|N) y
    Filesystem keystore:
      /etc/secureboot/keys/db/test-cert.der.siglist.db.signed [2116 bytes]
      /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed [2116 bytes]
      /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed [2116 bytes]
    firmware keys:
      PK:
      KEK:
      db:
      dbx:
    filesystem keys:
      PK:
        /CN=test-key
         from /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed
      KEK:
        /CN=test-key
         from /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed
      db:
        /CN=test-key
         from /etc/secureboot/keys/db/test-cert.der.siglist.db.signed
      dbx:
    New keys in filesystem:
     /etc/secureboot/keys/db/test-cert.der.siglist.db.signed
     /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed
     /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed
    Inserting key update /etc/secureboot/keys/db/test-cert.der.siglist.db.signed into db
    Inserting key update /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed into KEK
    Inserting key update /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed into PK
    Signing '/boot/efi/EFI/ubuntu/grubx64.efi'
    warning: overwriting existing signature
  7. Reboot and verify Secure Boot is enabled:

     - Device Manager ->
       - Secure Boot Configuration ->
         - Verify 'Attempt Secure Boot' is selected and 'Secure Boot Mode' is in
           'Standard Mode' ('Custom Mode' is also ok)
         - Change 'Secure Boot Mode' to 'Custom Mode' by highlighting 'Standard
           Mode' and pressing 'Enter'
         - Select Custom Boot Options ->
           - PK Options ->
             - Verify 'Enroll PK' is grayed out. Delete PK should have '[ ]' (or
               possibly a GUID).
             - Press Esc
           - KEK Options ->
             - Delete KEK ->
               - Verify GUID from sb-setup is listed
               - Press 'Esc', twice
           - DB Options
             - Delete signature ->
               - Verify GUID from sb-setup is listed
               - Press 'Esc', twice
           - DBX Options
             - Delete signature ->
               - Verify no GUIDs are listed
               - Press 'Esc', twice
  8. Press 'Esc' until at the main EFI configure screen, then 'Boot from File' normally (notice now there is a grubx64.efi.bak listed-- this is the grubx64.efi as installed by 'sudo grub-install --uefi-secure-boot'. Ie, the one signed with Canonical's key)
  9. Verify the machine booted with Secure Boot (note, can also use sbsigdb from newer versions of sbsigntool if it is available):

    $ sudo fwts uefidump - | grep Secure
    Name: SecureBoot.
      Value: 0x01 (Secure Boot Mode On).

In the above, a CA is setup in /etc/secureboot/key-material (private key: test-key.rsa, public pem: test-cert.pem, public der: test-cert.der). A keystore is created in /etc/secureboot/keys/ and signed updates (using the keys in /etc/secureboot/key-material) are created for PK, KEK and DB.

Shim bootloader signed with Microsoft key

This is the expected configuration for new machines with default hardware and has Microsoft keys in KEK and DB (user key still in PK and KEK). The key database configuration is with (user key in PK and KEK has the same GUID, each Microsoft key has a different GUID):

  • User key in PK
  • User key and 'Microsoft Corporation KEK CA' key in KEK
  • 'Microsoft Corporation UEFI CA' key and 'Microsoft Windows Production PCA' key in DB

Steps to configure:

  1. Boot an OVMF virtual UEFI machine (see above)
  2. Install some packages:

    $ sudo apt-get install sbsigntool openssl grub-efi-amd64-signed fwts shim-signed linux-signed-generic
  3. Install the signed bootloader:

    $ sudo grub-install --uefi-secure-boot
  4. Reboot the VM and 'Boot from File' as above, except choose 'shimx64.efi' instead of 'grubx64.efi'
  5. Download sb-setup and keys/ from https://git.launchpad.net/qa-regression-testing:/notes_testing/secure-boot/ to /tmp/sb-setup and /tmp/keys

  6. Enroll the keys (output may vary):

    $ /tmp/sb-setup enroll microsoft
    Creating keystore...
      mkdir '/etc/secureboot/keys'
      mkdir '/etc/secureboot/keys/PK'
      mkdir '/etc/secureboot/keys/KEK'
      mkdir '/etc/secureboot/keys/db'
      mkdir '/etc/secureboot/keys/dbx'
    done
    
    Creating keys... done
    
    Generating key updates for PK...
      using GUID=2b6a3c26-eeca-405d-bdc1-1e8c133253e1
      creating EFI_SIGNATURE_LIST (test-cert.der.siglist)...
      creating signed update (test-cert.der.siglist.PK.signed)...
    done
    Generating key updates for KEK...
      using GUID=2b6a3c26-eeca-405d-bdc1-1e8c133253e1
      creating EFI_SIGNATURE_LIST (test-cert.der.siglist)...
      creating signed update (test-cert.der.siglist.KEK.signed)...
    done
    Generating key updates for KEK...
      using GUID=dc072709-eb81-4b97-b1c1-3c48dc4202e1
      creating EFI_SIGNATURE_LIST (microsoft-kekca-public.der.siglist)...
      creating signed update (microsoft-kekca-public.der.siglist.KEK.signed)...
    done
    Generating key updates for db...
      using GUID=7fbf5694-f148-4051-8bd2-f36794ee2a54
      creating EFI_SIGNATURE_LIST (microsoft-pca-public.der.siglist)...
      creating signed update (microsoft-pca-public.der.siglist.db.signed)...
    done
    Generating key updates for db...
      using GUID=68386fb9-f8a6-4bfa-8868-adfd534a628a
      creating EFI_SIGNATURE_LIST (microsoft-uefica-public.der.siglist)...
      creating signed update (microsoft-uefica-public.der.siglist.db.signed)...
    done
    Initializing keystore...
      adding to /etc/secureboot/keys/PK/
      adding to /etc/secureboot/keys/KEK/
      adding to /etc/secureboot/keys/db/
    done
    
    Filesystem keystore:
      /etc/secureboot/keys/db/microsoft-pca-public.der.siglist.db.signed [2850 bytes]
      /etc/secureboot/keys/db/microsoft-uefica-public.der.siglist.db.signed [2907 bytes]
      /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed [2116 bytes]
      /etc/secureboot/keys/KEK/microsoft-kekca-public.der.siglist.KEK.signed [2867 bytes]
      /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed [2116 bytes]
    firmware keys:
      PK:
      KEK:
      db:
      dbx:
    filesystem keys:
      PK:
        /CN=test-key
         from /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed
      KEK:
        /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Corporation KEK CA 2011
         from /etc/secureboot/keys/KEK/microsoft-kekca-public.der.siglist.KEK.signed
        /CN=test-key
         from /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed
      db:
        /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Corporation UEFI CA 2011
         from /etc/secureboot/keys/db/microsoft-uefica-public.der.siglist.db.signed
        /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Windows Production PCA 2011
         from /etc/secureboot/keys/db/microsoft-pca-public.der.siglist.db.signed
      dbx:
    New keys in filesystem:
     /etc/secureboot/keys/db/microsoft-pca-public.der.siglist.db.signed
     /etc/secureboot/keys/db/microsoft-uefica-public.der.siglist.db.signed
     /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed
     /etc/secureboot/keys/KEK/microsoft-kekca-public.der.siglist.KEK.signed
     /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed
    Commit to keystore? (y|N) y
    Filesystem keystore:
      /etc/secureboot/keys/db/microsoft-pca-public.der.siglist.db.signed [2850 bytes]
      /etc/secureboot/keys/db/microsoft-uefica-public.der.siglist.db.signed [2907 bytes]
      /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed [2116 bytes]
      /etc/secureboot/keys/KEK/microsoft-kekca-public.der.siglist.KEK.signed [2867 bytes]
      /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed [2116 bytes]
    firmware keys:
      PK:
      KEK:
      db:
      dbx:
    filesystem keys:
      PK:
        /CN=test-key
         from /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed
      KEK:
        /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Corporation KEK CA 2011
         from /etc/secureboot/keys/KEK/microsoft-kekca-public.der.siglist.KEK.signed
        /CN=test-key
         from /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed
      db:
        /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Corporation UEFI CA 2011
         from /etc/secureboot/keys/db/microsoft-uefica-public.der.siglist.db.signed
        /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Windows Production PCA 2011
         from /etc/secureboot/keys/db/microsoft-pca-public.der.siglist.db.signed
      dbx:
    New keys in filesystem:
     /etc/secureboot/keys/db/microsoft-pca-public.der.siglist.db.signed
     /etc/secureboot/keys/db/microsoft-uefica-public.der.siglist.db.signed
     /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed
     /etc/secureboot/keys/KEK/microsoft-kekca-public.der.siglist.KEK.signed
     /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed
    Inserting key update /etc/secureboot/keys/db/microsoft-pca-public.der.siglist.db.signed into db
    Inserting key update /etc/secureboot/keys/db/microsoft-uefica-public.der.siglist.db.signed into db
    Inserting key update /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed into KEK
    Inserting key update /etc/secureboot/keys/KEK/microsoft-kekca-public.der.siglist.KEK.signed into KEK
    Inserting key update /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed into PK
    Skipping bootloader signing for 'microsoft'
  7. Reboot and verify Secure Boot is enabled and configured like 'Bootloader signed with user key' above, except with:
    • 2 different keys in KEK (should match GUIDs for KEK from sb-setup)
    • 2 different keys in db (should match GUIDs for db from sb-setup)
  8. 'Boot from File' normally (notice shimx64.efi and grubx64.efi are listed-- this is the grubx64.efi as installed by 'sudo grub-install --uefi-secure-boot'. Ie, the one signed with Canonical's key)
  9. Verify the machine booted with Secure Boot (note, can also use sbsigdb from newer versions of sbsigntool if it is available):

    $ sudo fwts uefidump - | grep Secure
    Name: SecureBoot.
      Value: 0x01 (Secure Boot Mode On).
  10. Reboot and try to boot grubx64.efi (Ie, the one signed with Canonical's key). This should fail to boot (ie, when you press 'Enter' to select it, nothing happens).

Bootloader signed with Canonical key

This emulates a configuration which supports machines with Canonical's key in KEK and DB (user key still in PK and KEK). The key database is configured with (user key in PK and KEK has the same GUID, Canonical key in KEK and db has the same GUID):

  • User key in PK
  • User key and 'Canonical Ltd. Master Certificate Authority' key in KEK
  • 'Canonical Ltd. Master Certificate Authority' key in DB

Steps to configure:

  1. Boot an OVMF virtual UEFI machine (see above)
  2. Install some packages:

    $ sudo apt-get install sbsigntool openssl grub-efi-amd64-signed fwts linux-signed-generic
  3. Install the signed bootloader:

    $ sudo grub-install --uefi-secure-boot
  4. Reboot the VM and 'Boot from File' as above
  5. Download sb-setup and keys/ from https://git.launchpad.net/qa-regression-testing:/notes_testing/secure-boot/ to /tmp/sb-setup and /tmp/keys

  6. Enroll the keys (output may vary):

    $ /tmp/sb-setup enroll canonical
      mkdir '/etc/secureboot/keys'
      mkdir '/etc/secureboot/keys/PK'
      mkdir '/etc/secureboot/keys/KEK'
      mkdir '/etc/secureboot/keys/db'
      mkdir '/etc/secureboot/keys/dbx'
    done
    
    Creating keys... done
    
    Generating key updates for PK...
      using GUID=55077d9d-6ca8-427a-9291-c60425c676e2
      creating EFI_SIGNATURE_LIST (test-cert.der.siglist)...
      creating signed update (test-cert.der.siglist.PK.signed)...
    done
    Generating key updates for KEK...
      using GUID=55077d9d-6ca8-427a-9291-c60425c676e2
      creating EFI_SIGNATURE_LIST (test-cert.der.siglist)...
      creating signed update (test-cert.der.siglist.KEK.signed)...
    done
    Generating key updates for KEK...
      using GUID=6a43e12f-b589-40c3-a332-a15eac86e3f5
      creating EFI_SIGNATURE_LIST (canonical-master-public.der.siglist)...
      creating signed update (canonical-master-public.der.siglist.KEK.signed)...
    done
    Generating key updates for db...
      using GUID=6a43e12f-b589-40c3-a332-a15eac86e3f5
      creating EFI_SIGNATURE_LIST (canonical-master-public.der.siglist)...
      creating signed update (canonical-master-public.der.siglist.db.signed)...
    done
    Initializing keystore...
      adding to /etc/secureboot/keys/PK/
      adding to /etc/secureboot/keys/KEK/
      adding to /etc/secureboot/keys/db/
    done
    
    Filesystem keystore:
      /etc/secureboot/keys/db/canonical-master-public.der.siglist.db.signed [2431 bytes]
      /etc/secureboot/keys/KEK/canonical-master-public.der.siglist.KEK.signed [2431 bytes]
      /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed [2116 bytes]
      /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed [2116 bytes]
    firmware keys:
      PK:
      KEK:
      db:
      dbx:
    filesystem keys:
      PK:
        /CN=test-key
         from /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed
      KEK:
        /CN=test-key
         from /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed
        /C=GB/ST=Isle of Man/L=Douglas/O=Canonical Ltd./CN=Canonical Ltd. Master Certificate Authority
         from /etc/secureboot/keys/KEK/canonical-master-public.der.siglist.KEK.signed
      db:
        /C=GB/ST=Isle of Man/L=Douglas/O=Canonical Ltd./CN=Canonical Ltd. Master Certificate Authority
         from /etc/secureboot/keys/db/canonical-master-public.der.siglist.db.signed
      dbx:
    New keys in filesystem:
     /etc/secureboot/keys/db/canonical-master-public.der.siglist.db.signed
     /etc/secureboot/keys/KEK/canonical-master-public.der.siglist.KEK.signed
     /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed
     /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed
    Commit to keystore? (y|N) y
    Filesystem keystore:
      /etc/secureboot/keys/db/canonical-master-public.der.siglist.db.signed [2431 bytes]
      /etc/secureboot/keys/KEK/canonical-master-public.der.siglist.KEK.signed [2431 bytes]
      /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed [2116 bytes]
      /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed [2116 bytes]
    firmware keys:
      PK:
      KEK:
      db:
      dbx:
    filesystem keys:
      PK:
        /CN=test-key
         from /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed
      KEK:
        /CN=test-key
         from /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed
        /C=GB/ST=Isle of Man/L=Douglas/O=Canonical Ltd./CN=Canonical Ltd. Master Certificate Authority
         from /etc/secureboot/keys/KEK/canonical-master-public.der.siglist.KEK.signed
      db:
        /C=GB/ST=Isle of Man/L=Douglas/O=Canonical Ltd./CN=Canonical Ltd. Master Certificate Authority
         from /etc/secureboot/keys/db/canonical-master-public.der.siglist.db.signed
      dbx:
    New keys in filesystem:
     /etc/secureboot/keys/db/canonical-master-public.der.siglist.db.signed
     /etc/secureboot/keys/KEK/canonical-master-public.der.siglist.KEK.signed
     /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed
     /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed
    Inserting key update /etc/secureboot/keys/db/canonical-master-public.der.siglist.db.signed into db
    Inserting key update /etc/secureboot/keys/KEK/canonical-master-public.der.siglist.KEK.signed into KEK
    Inserting key update /etc/secureboot/keys/KEK/test-cert.der.siglist.KEK.signed into KEK
    Inserting key update /etc/secureboot/keys/PK/test-cert.der.siglist.PK.signed into PK
    Skipping bootloader signing for 'canonical'
  7. Reboot and verify Secure Boot is enabled and configured like 'Bootloader signed with user key' above, except with:
    • 2 different keys in KEK (should match GUIDs for KEK from sb-setup)
    • 2 different keys in db (should match GUIDs for db from sb-setup)
  8. 'Boot from File' normally (notice only grubx64.efi listed-- this is the grubx64.efi as installed by 'sudo grub-install --uefi-secure-boot'. Ie, the one signed with Canonical's key)
  9. Verify the machine booted with Secure Boot (note, can also use sbsigdb from newer versions of sbsigntool if it is available):

    $ sudo fwts uefidump - | grep Secure
    Name: SecureBoot.
      Value: 0x01 (Secure Boot Mode On).

efilinux bootloader

Warning /!\ It is highly recommended to use shim and grub2 instead of efilinux for the bootloader.

In theory, should be able to do:

$ sudo apt-get install efilinux efilinux-signed
$ sudo cp /usr/lib/efilinux/efilinux.efi /boot/efi/EFI/ubuntu
$ sudo cp /boot/vmlinuz-3.5.0-19-generic.efi.signed /boot/efi/EFI/ubuntu/vmlinuz
$ sudo cp /boot/initrd-3.5.0-19-generic /boot/efi/EFI/ubuntu/initrd
$ sudo cp /usr/lib/efilinux-signed/efilinux.efi.signed /boot/efi/EFI/ubuntu/efilinux-signed.efi
$ sudo sh -c 'cat > /boot/efi/EFI/ubuntu/efilinux.cfg << EOM
# efilinux menu 1
EFILINUX MENU
Ubuntu EFILINUX
0:\EFI\ubuntu\vmlinuz initrd=0:\EFI\ubuntu\initrd root=... ...
EOM
'

Then reboot, select one of 'efilinux.efi' or 'efilinux-signed.efi' from Boot From File and get a menu. Unfortunately, with current OVMF images, this does not work (though it apparently works on USB install images).

Shim should try to boot anything named grubx64.efi, so we can play a trick on shim by naming efilinux.efi.signed as grubx64.efi, like so:

  1. Boot an OVMF virtual UEFI machine (see above)
  2. Install some packages:

    $ sudo apt-get install sbsigntool openssl grub-efi-amd64-signed fwts shim-signed linux-signed-generic efilinux-signed
  3. Install the signed bootloader (shim and grub2):

    $ sudo grub-install --uefi-secure-boot
  4. Backup grub2:

    $ sudo cp /boot/efi/EFI/ubuntu/grubx64.efi /boot/efi/EFI/ubuntu/grubx64-orig.efi
  5. Install the signed efilinux bootloader as grubx64.efi:

    $ sudo cp /usr/lib/efilinux-signed/efilinux.efi.signed /boot/efi/EFI/ubuntu/efilinux-signed.efi
    $ sudo cp /usr/lib/efilinux-signed/efilinux.efi.signed /boot/efi/EFI/ubuntu/grubx64.efi
    $ sudo cp /boot/vmlinuz-3.5.0-19-generic.efi.signed /boot/efi/EFI/ubuntu/vmlinuz
    $ sudo cp /boot/initrd-3.5.0-19-generic /boot/efi/EFI/ubuntu/initrd
    $ sudo sh -c 'cat > /boot/efi/EFI/ubuntu/efilinux.cfg << EOM
    # efilinux menu 1
    EFILINUX MENU
    Ubuntu text boot
    0:\EFI\ubuntu\vmlinuz initrd=0:\EFI\ubuntu\initrd root=/dev/sda3
    Ubuntu graphical boot
    0:\EFI\ubuntu\vmlinuz initrd=0:\EFI\ubuntu\initrd root=/dev/sda3 quiet splash
    Ubuntu recovery
    0:\EFI\ubuntu\vmlinuz initrd=0:\EFI\ubuntu\initrd root=/dev/sda3 single
    EOM
    '
  6. Reboot the VM and 'Boot from File' as above, except choose 'shimx64.efi' instead of 'grubx64.efi'

Unfortunately, this doesn't work either and it seems to be a bug in the OVMF implementation. Copying efilinux-signed.efi to /boot/efi/EFI/BOOT/BOOTX64.EFI (and efilinux.cfg in /boot/efi/EFI/BOOT) also doesn't work. With the above configuration, you can boot efilinux via the EFI shell like so:

Shell> fs0:\EFI\ubuntu\efilinux-signed.efi

However, you can't setup Secure Boot using sb-setup since it requires a reboot and you aren't able to boot into the EFI shell with a warm reboot and a cold reboot resets the Secure Boot configuration. It should be possible to enlist the keys manually by copying the DER files into /boot/efi somewhere and manually enlisting them via the EFI configuration (but even then, it is only good for that one boot).

Miscellaneous

Disabling Secure Boot

If you already committed your changes to the keystore (which enrolls PK and toggles Secure Boot to enabled) and want to disable Secure Boot, you can reboot and go into the Device Manager/Secure Boot Configuration in the EFI firmware configuration, then 'Unenroll PK' (highlight '[ ]' and press Enter). You can then delete the signatures in KEK, DB and DBX. You should also be able to unenroll PPK and disable Secure Boot with:

$ /tmp/sb-setup reset

Disabling Secure Boot validation in shim

With the VM installed, you can start a terminal and run the following commands, which will ask you to choose a password:

$ sudo mokutil --disable-validation

To enable validation again use:

$ sudo mokutil --enable-validation

Reboot, and you will be starting in MokManager, a blue screen with prompts that will walk you through enabling or disabling validation. You will need to type in some of the characters of the password again.

Resetting the keystore

The keystore and key material are stored in /etc/secureboot. If you have not committed your changes to the keystore, you can:

$ sudo rm -rf /etc/secureboot
$ /tmp/sb-setup enroll ...
  • If you have committed your changes to the keystore, disable Secure Boot (see above) and empty all the key databases in firmware.
  • Enabling Secure Boot after unenrolling PK: if you unenrolled PK, then you can re-enable it again with (uses existing keys):

    $ /tmp/sb-setup enroll microsoft

Converting a DER formatted certificate to PEM

sbverify takes a PEM formatted certificate. You can convert the Canonical master DER formatted certificate like so:

$ openssl x509 -inform DER -in ~/keys/canonical-master-public.der \
               -outform PEM -out ~/keys/canonical-master-public.pem

and the Microsoft one:

$ openssl x509 -inform DER -in ~/keys/microsoft-uefica-public.der \
               -outform PEM -out ~/keys/microsoft-uefica-public.pem

Creating a PEM certificate chain from DER formatted certificates

To create a PEM certificate chain suitable for use with sbverify, you convert all the DER certificates to PEM, then concatenate them in one certificate. Eg, to create the Canonical certificate chain file:

$ openssl x509 -inform DER -in ~/keys/canonical-master-public.der \
               -outform PEM -out ~/keys/canonical-master-public.pem
$ openssl x509 -inform DER -in ~/keys/canonical-signing-public.der \
               -outform PEM -out ~/keys/canonical-signing-public.pem
$ cat ~/keys/canonical-master-public.pem ~/keys/canonical-signing-public.pem \
      > ~/keys/canonical-master-signing-public-chain.pem

Verifying the signature on a signed PE/COFF or signed kernel image

  • To verify Microsoft's signature on the signed shim bootloader (must first create the PEM certificate, above):

    $ sbverify --cert ~/keys/microsoft-uefica-public.pem /boot/efi/EFI/ubuntu/shimx64.efi
    Signature verification OK
  • To verify Canonical's signature on the signed grub bootloader (must first create the PEM certificate, above):

    $ sbverify --cert ~/keys/canonical-master-public.pem /boot/efi/EFI/ubuntu/grubx64.efi
    Signature verification OK
  • To verify Ubuntu signature on the signed kernel, you must first extract the signature from the kernel image, then use sbverify to verify the image with the detached signature (must first create the PEM certificate chain, above):

    $ sbattach --detach /tmp/vmlinuz-3.5.0-27-generic.efi.signature \
      /boot/vmlinuz-3.5.0-27-generic.efi.signed
    $ sbverify --cert ~/keys/canonical-master-signing-public-chain.pem \
               --detached /tmp/vmlinuz-3.5.0-27-generic.efi.signature \
               /boot/vmlinuz-3.5.0-27-generic.efi.signed 
    Signature verification OK

Updating key databases

Inserting keys in shim's keyring

To insert your own keys in shim's keyring, use:

$ sudo mokutil --import <path to cert in DER format>

Removing an enrolled key from shim's keyring

You can remove certificates from shim's keyring if you still have access to the DER-format certificate by using:

$ sudo mokutil --delete <path to DER cert>

If you don't have access to the certificate, your other option is to completely reset shim's keyring:

$ sudo mokutil --reset

Certificates

To create an entry for a key database:

  1. create a signature list variable with the thing you want to blacklist using sbsiglist
  2. sign the signature list variable with a key pair that is in KEK or PK using sbvarsign
  3. add the signed update to a keystore
  4. use sbkeysync to add the signed update to the key database

Eg, if using the user key generated above, we can add create a signed update to the blacklist database (dbx) for the Microsoft Corporation UEFI CA like so:

$ guid=$(uuidgen)
$ sbsiglist --owner $guid --type x509 \
            --output microsoft_uefica_dbx-test.siglist \
            ~/keys/microsoft-uefica-public.der
$ sbvarsign --key /etc/secureboot/key-material/test-key.rsa \
            --cert /etc/secureboot/key-material/test-cert.pem \
            --output microsoft_uefica_dbx-test.siglist.signed \
            dbx \
            microsoft_uefica_dbx-test.siglist

$ ls -1
microsoft_uefica_dbx-test.siglist
microsoft_uefica_dbx-test.siglist.signed
$ sudo cp microsoft_uefica_dbx-test.siglist.signed /etc/secureboot/keys/dbx
$ sudo sbkeysync --verbose

If you have the secureboot-db package installed, you can copy to the system wide updates keystore:

$ sudo cp microsoft_uefica_dbx-test.siglist.signed /usr/share/secureboot/updates/dbx
$ sudo dpkg-reconfigure secureboot-db
Filesystem keystore:
  /usr/share/secureboot/updates/dbx/microsoft_uefica_dbx-test.siglist.signed [2907 bytes]
firmware keys:
  PK:
    /CN=test-key
  KEK:
    /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Corporation KEK CA 2011
    /CN=test-key
  db:
    /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Corporation UEFI CA 2011
    /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Windows Production PCA 2011
  dbx:
filesystem keys:
  PK:
  KEK:
  db:
  dbx:
    /C=US/ST=Washington/L=Redmond/O=Microsoft Corporation/CN=Microsoft Corporation UEFI CA 2011
     from /usr/share/secureboot/updates/dbx/microsoft_uefica_dbx-test.siglist.signed
New keys in filesystem:
 /usr/share/secureboot/updates/dbx/microsoft_uefica_dbx-test.siglist.signed
Inserting key update /usr/share/secureboot/updates/dbx/microsoft_uefica_dbx-test.siglist.signed into dbx

sha256 hashes

TODO (needs sbtools support): Ultimately this should be in sbsign since the hash of PE/COFF image is the has of everything except the embedded signature. We'd like to do something like this, but it doesn't work because it doesn't exclude the embedded signature (and if it wasn't signed, there is no point blacklisting it):

$ echo -n "0x`sha256sum grubx64.efi | cut -d ' ' -f 1`" |
          | xxd -r -g 1 -c 64 > /tmp/sha256.bin

Then would create a signed update with:

$ sbsiglist --owner $guid --type sha256 \
            --output /tmp/sha256.bin.siglist \
            /tmp/sha256.bin
$ sbvarsign --key /etc/secureboot/key-material/test-key.rsa \
            --cert /etc/secureboot/key-material/test-cert.pem \
            --output /tmp/sha256.bin.siglist.signed \
            dbx \
            /tmp/sha256.bin.siglist

Testing signed updates via secureboot-db

Updates to db and dbx will need to be performed as keys are rotated and things are blacklisted. This will be handled by the secureboot-db package. In essence, secureboot-db will ship a keystore in /usr/share/secureboot/updates for updating db and dbx and then in package postinst run:

# keystore=/usr/share/secureboot/updates sbkeysync --no-default-keystores --keystore "$keystore" --verbose

sbkeysync will only add new updates so management of secureboot-db is simple and updates primarily consist of adding the signed updates to the keystore. Please see debian/README.source and debian/README.Debian for details.

Notes:

  • IMPORTANT improperly updating secureboot-db could result in all systems with Secure Boot enabled failing to boot.

  • As mentioned, when Secure Boot is enabled, updates to DB and DBX must be signed by something that verifies via the chain of trust to something in KEK. As a result, when testing secureboot-db, expect sbkeysign to complain when adding a signed update from Microsoft on a machine that does not have the Microsoft key in KEK but does have Secure Boot enabled.
  • sbkeysync (and therefore secureboot-db) will add the updates to DB and DBX unconditionally when Secure Boot is disabled

Test cases

Functional tests

  • Booting with Secure Boot disabled
    • for each of grub2-signed only and shim-signed
      • install bootloader
      • reboot and verify the machine boots with Secure Boot disabled
  • Booting with Secure Boot enabled
    • for each of linux-generic (unsigned) and linux-signed-generic
      • for each of microsoft/shim-signed, canonical/grub2-signed and user signed
        • verify vendor's (or when test user keys, user's) keys are in KEK and DB and Secure Boot is enabled
        • reboot and verify the machine still boots
        • install updated secureboot-db, verifying:
          • package installation succeeded
          • secureboot-db properly used 'Breaks' and pulled in necessary packages
          • the updates were added to firmware (check EFI configuration, as well as output from sbkeysync)
          • reboot and verify the machine still boots

Verification tests

Additionally, with Secure Boot enabled with shim and using Microsoft keys:

  • shim validation (tests firmware properly verifies our signed shim):
    • TODO: add a dbx entry for an old shim and try booting (should fail)
    • add a dbx entry for the 'Microsoft Corporation UEFI CA' and try booting (should fail):

      $ guid=$(uuidgen)
      $ sbsiglist --owner $guid --type x509 \
                  --output microsoft_uefica_dbx-test.siglist \
                  ~/keys/microsoft-uefica-public.der
      $ sbvarsign --key /etc/secureboot/key-material/test-key.rsa \
                  --cert /etc/secureboot/key-material/test-cert.pem \
                  --output microsoft_uefica_dbx-test.siglist.signed \
                  dbx \
                  microsoft_uefica_dbx-test.siglist
      $ sudo cp microsoft_uefica_dbx-test.siglist.signed /etc/secureboot/keys/dbx
      $ sudo sbkeysync --verbose

      Now try to 'boot from file' shimx64.efi (succeed if sb disabled, fail if enabled). To reset back to a working signed grub2, delete the signature from the DBX database in firmware, and then on reboot:

      $ sudo rm -f /etc/secureboot/keys/dbx/*signed
    • replace shim with unsigned shim (should fail):

      $ sudo apt-get install shim
      $ sudo cp /usr/lib/shim/shim.efi /boot/efi/EFI/ubuntu/
      Now try to 'boot from file' shim.efi (succeed if sb disabled, fail if enabled)
    • replace shim with signed shim using a key not in DB (should fail):

      $ sudo apt-get install shim
      $ sudo sbsign --key /etc/secureboot/key-material/test-key.rsa \
                    --cert /etc/secureboot/key-material/test-cert.pem \
                    --output /boot/efi/EFI/ubuntu/shim_user-signed.efi \
                    /usr/lib/shim/shim.efi
      Now try to 'boot from file' shimx64.efi (succeed if sb disabled, fail if enabled)
    • OPTIONAL: replace signed shim with a bit-flipped/fuzzed shim (should fail)
  • grub2 validation (tests shim properly verifies our bootloader):
    • try to boot grub2 directly, without shim (should fail)
    • TODO: add a dbx entry for an old grub2 and try booting (should fail)
    • add a dbx entry for the 'Canonical Ltd. Master Certificate Authority' and try booting (should fail):

      $ guid=$(uuidgen)
      $ sbsiglist --owner $guid --type x509 \
                  --output canonical_ca_dbx-test.siglist \
                  ~/keys/canonical-master-public.der
      $ sbvarsign --key /etc/secureboot/key-material/test-key.rsa \
                  --cert /etc/secureboot/key-material/test-cert.pem \
                  --output canonical_ca_dbx-test.siglist.signed \
                  dbx \
                  canonical_ca_dbx-test.siglist
      $ sudo cp canonical_ca_dbx-test.siglist.signed /etc/secureboot/keys/dbx
      $ sudo sbkeysync --verbose

      Now try to 'boot from file' shim_user-signed.efi (succeed if sb disabled, fail if enabled). To reset back to a working signed grub2, delete the signature from the DBX database in firmware and then on reboot:

      $ sudo rm -f /etc/secureboot/keys/dbx/*signed
    • add a dbx entry for the 'Canonical Ltd. Secure Boot Signing' key and try booting (should fail):

      $ guid=$(uuidgen)
      $ sbsiglist --owner $guid --type x509 \
                  --output canonical_signing_dbx-test.siglist \
                  ~/keys/canonical-signing-public.der
      $ sbvarsign --key /etc/secureboot/key-material/test-key.rsa \
                  --cert /etc/secureboot/key-material/test-cert.pem \
                  --output canonical_signing_dbx-test.siglist.signed \
                  dbx \
                  canonical_signing_dbx-test.siglist
      $ sudo cp canonical_signing_dbx-test.siglist.signed /etc/secureboot/keys/dbx
      $ sudo sbkeysync --verbose

      Now try to 'boot from file' shimx64.efi (succeed if sb disabled, fail if enabled). To reset back to a working signed grub2, delete the signature from the DBX database in firmware, and then on reboot:

      $ sudo rm -f /etc/secureboot/keys/dbx/*signed
    • replace grub2 with unsigned grub2 (should fail):

      $ sudo grub-install --no-uefi-secure-boot

      Try to 'boot from file' shimx64.efi (succeed if sb disabled, fail if enabled). Run the following to reset to working signed grub2:

      $ sudo grub-install --uefi-secure-boot
    • replace grub2 with signed grub2 using a key not in DB (should fail):

      $ sudo grub-install --uefi-secure-boot
      $ sudo sbsign --key /etc/secureboot/key-material/test-key.rsa \
                    --cert /etc/secureboot/key-material/test-cert.pem \
                    --output /boot/efi/EFI/ubuntu/grubx64.efi \
                    /usr/lib/grub/x86_64-efi-signed/grubx64.efi.signed

      Try to 'boot from file' shimx64.efi (succeed if sb disabled, fail if enabled). Run the following to reset to working signed grub2:

      $ sudo grub-install --uefi-secure-boot
    • OPTIONAL: replace signed grub2 with a bit-flipped/fuzzed grub2 (should fail)
  • kernel (tests grub2 verification of kernel and fallback mechanism)
    • TODO: add a dbx entry for an old kernel and try booting (should fail)
    • replace kernel with unsigned kernel (should succeed):

      $ sudo apt-get remove --purge linux-signed*

      Try to 'boot from file' shimx64.efi (succeeds if sb disabled or enabled). Run the following to reset to working signed kernel:

      sudo apt-get install linux-signed-generic
    • replace kernel with signed kernel using a key not in DB (should succeed):

      $ sudo cp /boot/vmlinuz-<version>-generic.efi.signed \
                /boot/vmlinuz-<version>-generic.efi.signed.bak
      $ sudo sbsign --key /etc/secureboot/key-material/test-key.rsa \
                    --cert /etc/secureboot/key-material/test-cert.pem \
                    --output /boot/vmlinuz-<version>-generic.efi.signed \
                    /boot/vmlinuz-<version>-generic.efi.signed.bak

      Try to 'boot from file' shimx64.efi (succeeds if sb disabled or enabled). Run the following to reset to working signed kernel:

      $ sudo apt-get remove --purge linux-signed*
      $ sudo apt-get install linux-signed-generic
    • OPTIONAL: replace signed kernel with a bit-flipped/fuzzed kernel (should fail)

UEFI/SecureBoot/Testing (last edited 2017-12-04 22:03:02 by cyphermox)