The rEFInd Boot Manager:
Managing Secure Boot

by Roderick W. Smith, rodsmith@rodsbooks.com

Originally written: 11/13/2012; last Web page update: 1/3/2014, referencing rEFInd 0.7.7

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This page is part of the documentation for the rEFInd boot manager. If a Web search has brought you here, you may want to start at the main page.

Note: My Managing EFI Boot Loaders for Linux Web page includes a much more detailed description of Secure Boot in its Dealing with Secure Boot sub-page. You should consult this page if you want to disable Secure Boot, generate your own keys, or perform other such tasks.

If you're using a computer that supports Secure Boot, you may run into extra complications. This feature is intended to make it difficult for malware to insert itself early into the computer's boot process. Unfortunately, it also complicates multi-boot configurations such as those that rEFInd is intended to manage. This page describes some secure boot basics and two specific ways of using rEFInd with Secure Boot: Using the shim program and using the PreLoader program. It concludes with a look at known bugs and limitations in rEFInd's Secure Boot features.

Note: You don't have to use Secure Boot. If you don't want it, you can disable it, at least on x86-64 PCs. If an ARM-based computer ships with Windows 8, this isn't an option for it. Unfortunately, the shim and PreLoader programs described on this page currently support only x86-64, not x86 or ARM.

Through 2012, it became obvious that Secure Boot would be a feature that was controlled, to a large extent, by Microsoft. This is because Microsoft requires that non-server computers that display Windows 8 logos ship with Secure Boot enabled. As a practical matter, this also means that such computers ship with Microsoft's keys in their firmware. In the absence of an industry-standard body to manage the signing of Secure Boot keys, this means that Microsoft's key is the only one that's more-or-less guaranteed to be installed on the computer, thus blocking the ability to boot any OS that lacks a boot path through Microsoft's signing key.

Fortunately, Microsoft will sign third-party binaries with their key—or more precisely, with a key that Microsoft uses to sign third-party binaries. (Microsoft uses another key to sign its own binaries, and some devices, such as the Microsoft Surface tablet, lack the third-party Microsoft key.) A payment of $99 to Verisign enables a software distributor to sign as many binaries as desired. Red Hat (Fedora), Novell (SUSE), and Canonical (Ubuntu) are all using this system to enable their boot loaders to run. Unfortunately, using a third-party signing service is an awkward solution for open source software. In fact, for this very reason two separate programs exist that shift the Secure Boot "train" from Microsoft's proprietary "track" to one that's more friendly to open source authors. Both of these programs (shim and PreLoader) are available in binary form signed by Microsoft's key. Shim enables the computer to launch binaries that are signed by a key that's built into it or that the user adds to a list known as the Machine Owner Key (MOK) list. PreLoader enables the computer to launch binaries that the user has explicitly identified as being OK. Distributions beginning with Ubuntu 12.10 (and 12.04.2), Fedora 18, and OpenSUSE 12.3 use shim, although Ubuntu ships with an early version of shim that's useless for launching rEFInd, at least through Ubuntu 13.04. To the best of my knowledge, no major distribution uses PreLoader, but it may see use on live CDs and is easier to set up if you're not using a distribution that supports shim.

There are three ways to sign a binary that will get it launched on a computer that uses shim:

• Secure Boot keys—These keys are managed by the EFI firmware. In a default configuration, Microsoft is the only party that's more-or-less guaranteed to be able to sign boot loaders with these keys; however, it's possible to replace Microsoft's keys with your own, in order to take full control of Secure Boot on your computer. The trouble is that this process is tedious and varies in details from one computer to another.
• Shim's built-in keys—It's possible, but not necessary, to compile shim with a built-in public key. Its private counterpart can then be used to sign binaries. In practice, this key type is limited in utility; it's likely to be used by distribution maintainers to sign their own version of GRUB and the Linux kernels that it launches, nothing more. On the plus side, shim's keys require little or no maintenance by users. One potential complication is that if you swap out one shim binary for another, its built-in key may change, which means that the replacement shim might no longer launch its follow-on boot loader.
• MOKs—Versions 0.2 and later of shim support MOKs, which give you the ability to add your own keys to the computer. If you want to install multiple Linux distributions in Secure Boot mode, MOKs are likely to be helpful. They're vital if you want to launch kernels you compile yourself or use boot managers or boot loaders other than those provided by your distribution.

All three key types are the same in form—shim's built-in keys and MOKs are both generated using the same tools used to generate Secure Boot keys. The keys can be generated with the common openssl program, but signing EFI binaries requires a rarer program called sbsign or pesign. If you use shim with a distribution that doesn't support this tool, you'll need to either sign the kernels yourself, which can be a hassle, or launch the kernels by way of a boot loader that doesn't check for signatures, such as ELILO.

Shim's author is working on merging it and PreLoader. Thus, future versions of shim may provide the advantages of both programs.

PreLoader is easier to set up on a distribution that doesn't support shim because PreLoader doesn't rely on keys; instead, you tell it which binaries you trust and it will let you launch them. This works well on a system with boot managers, boot loaders, and kernels that seldom change. It's not a good solution for distribution maintainers, though, because it requires that users manually add binaries to PreLoader's list of approved binaries when the OS is installed and every time those binaries change. Also, PreLoader relies on a helper program, HashTool, to enroll hashes. (This is Geek for "tell the computer that a binary is OK.") Unfortunately, HashTool can enroll hashes only from the partition from which it was launched, so if you want to use rEFInd to launch Linux kernels directly, it's easiest if you mount your ESP at /boot in Linux or copy your kernels to the ESP. Another approach is to copy HashTool.efi to the partition that holds your kernel and rename it to almost anything else. rEFInd will then treat it like an OS boot loader and create a menu entry for it, enabling you to launch it as needed.

Beginning with version 0.5.0, rEFInd can communicate with the shim system to authenticate boot loaders. If a boot loader has been signed by a valid UEFI Secure Boot key, a valid shim key, or a valid MOK key, rEFInd will launch it. rEFInd will also launch unsigned boot loaders or those with invalid signatures if Secure Boot is disabled in or unsupported by the firmware. (If that's your situation, you needn't bother reading this page.) PreLoader is designed in such a way that it requires no explicit support in rEFInd to work.

Version 0.5.0 ships signed with my own keys, and I provide the public version of this key with the rEFInd package. This can help simplify setup, since you needn't generate your own keys to get rEFInd working; however, if you lack public keys for the boot loaders that rEFInd launches, you'll need to generate your own keys and sign your boot loaders, as described in the Managing Your MOKs section.

Because several major distributions support shim, I describe it first. You may need to adjust the rEFInd installation process to get it working with shim, especially if you're not using a distribution that uses this software. In addition to installing shim, you should know how to manage your MOKs, so I describe this topic, too. If you don't want to use shim, you can skip ahead to the section on PreLoader.

A working Secure Boot installation of rEFInd involves at least three programs, and probably four or more, each of which must be installed in a specific way:

• shim—You can download a version of shim signed with Microsoft's Secure Boot key here. This version (created by shim's developer, former Red Hat employee Matthew J. Garrett) includes a shim key that's used by nothing but the MokManager.efi program that also ships with the program. Thus, to use this version of shim, you must use MOKs. Fedora 18's and OpenSUSE 12.3's versions of shim include their own keys and can also use MOKs; but to use these packages with rEFInd, you must still enroll rEFInd's MOK. Ubuntu 12.10 and 13.04 ship with an earlier version of shim that version doesn't support MOKs. Ubuntu's shim is useless for launching rEFInd. Future distributions will probably come with their own variants of shim, most of which will no doubt support their own shim keys as well as MOKs. You should install shim just as you would install other EFI boot loaders, as described here. For use in launching rEFInd, it makes sense to install shim.efi in EFI/refind on your ESP, although of course this detail is up to you.
• MokManager—This program is included with shim 0.2 and later (including the versions of shim that ship with Fedora 18 and OpenSUSE 12.3). It presents a crude user interface for managing MOKs, and it's launched by shim if shim can't find its default boot loader (generally grubx64.efi) or if that program isn't properly signed. In principle, this program could be signed with a Secure Boot key or a MOK, but the binary in Garrett's shim 0.2 is signed with a shim key, and I expect that versions distributed with most Linux distributions will also be signed by their respective shim keys. This program should reside in the same directory as shim.efi, under the name MokManager.efi. Although you could theoretically do without MokManager, in practice you'll need it at least temporarily to install the MOK with which rEFInd is signed.
• rEFInd—Naturally, you need rEFInd. Because shim is hard-coded to launch a program called grubx64.efi, you must install rEFInd using that name and to the same directory in which shim.efi resides. In theory, rEFInd could be signed with a Secure Boot key, a shim key, or a MOK; however, because Microsoft won't sign binaries distributed under the GPLv3, I can't distribute a version of rEFInd signed with Microsoft's Secure Boot key; and as I don't have access to the private shim keys used by any distribution, I can't distribute a rEFInd binary signed by them. (If distributions begin including rEFInd in their package sets, though, such distribution-provided binaries could be signed with the distributions' shim keys.) Thus, rEFInd will normally be signed by a MOK. Beginning with version 0.5.0, rEFInd binaries that I provide are signed by me. Beginning with version 0.5.1, the installation script provides an option to sign the rEFInd binary with your own key, provided the necessary support software is installed.
• Your boot loaders and kernels—Your OS boot loaders, and perhaps your Linux kernels, must be signed. They can be signed with any of the three key types. Indeed, your system may have a mix of all three types—a Windows 8 boot loader will most likely be signed with Microsoft's Secure Boot key, GRUB and kernels provided by most distributions will be signed with their own shim keys, and if you use your own locally-compiled kernel or a boot loader from an unusual source you may need to sign it with a MOK. Aside from signing, these files can be installed in exactly the same way as if your computer were not using Secure Boot.

If you've installed Fedora 18 or OpenSUSE 12.3 and can boot it with Secure Boot active, and if you then install rEFInd using the RPM file that I provide or by running install.sh, chances are you'll end up with a working rEFInd that will start up the first time, with one caveat: You'll have to use MokManager to add rEFInd's MOK to your MOK list, as described shortly. If you don't already have a working copy of shim on your ESP, your task is more complex. Broadly speaking, the procedure should be something like this:

1. Boot the computer. This can be a challenge in and of itself. You may need to use a Secure Boot–enabled Linux emergency disc, temporarily disable Secure Boot, or do the work from Windows.
2. Download rEFInd in binary form (the binary zip or CD-R image file). If you download the binary zip file, unzip it; if you get the CD-R image file, burn it to a CD-R and mount it.
3. Download shim from Matthew J. Garrett's download site or from your distribution. (Don't use Ubuntu's version, though; as noted earlier, it's inadequate for use with rEFInd.)

Tip: If you're running Linux, you can save some effort by using the install.sh script with its --shim /path/to/shim.efi option rather than installing manually, as in steps 4–6 of this procedure. If you've installed openssl and sbsign, using --localkeys will generate local signing keys and re-sign the rEFInd binaries with your own key, too. You can then use sbsign and the keys in /etc/refind.d/keys to sign your kernels or boot loaders.

4. Copy the shim.efi and MokManager.efi binaries to the directory you intend to use for rEFInd—for instance, EFI/refind on the ESP.
5. Follow the installation instructions for rEFInd on the Installing rEFInd page; however, give rEFInd the filename grubx64.efi and register shim.efi with the EFI by using efibootmgr in Linux or bcdedit in Windows. Be sure that rEFInd (as grubx64.efi), shim.efi, and MokManager.efi all reside in the same directory.
6. Copy the refind.cer file from the rEFInd package to your ESP, ideally to a location with few other files. (The rEFInd installation directory should work fine.)
7. Reboot. With any luck, you'll see a simple text-mode user interface with a label of Shim UEFI key management. This is the MokManager program, which shim launched when rEFInd failed verification because its key is not yet enrolled.
8. Press your down arrow key and press Enter to select Enroll key from disk. The screen will clear and prompt you to select a key, as shown here:



9. Each of the lines with a long awkward string represents a disk partition. Select one and you'll see a list of files. Continue selecting subdirectories until you find the refind.cer file you copied to the ESP earlier. (Note that the long lines can wrap and hide valid entries on the next line, so you may need to select a disk whose entry is masked by another one!)
10. Select refind.cer. You can type 1 to view the certificate's details if you like, or skip that and type 0 to enroll the key.
11. Back out of any directories you entered and return to the MokManager main menu.
12. Select Continue boot at the main menu.

At this point the computer may boot into its default OS, reboot, or perhaps even hang. When you reboot it, though, rEFInd should start up in Secure Boot mode. (You can verify this by selecting the About rEFInd tool in the main menu. Check the Platform item in the resulting screen; it should verify that Secure Boot is active.) You should now be able to launch any boot loader signed with a key recognized by the firmware or by shim (including any MOKs you've enrolled). If you want to manage keys in the future, rEFInd displays a new icon in the second (tools) row you can use to launch MokManager. (This icon appears by default if MokManager is installed, but if you edit showtools in refind.conf, you must be sure to include mok_tool as an option in order to gain access to it.)

If you're using Ubuntu, you can't use its version of shim, but you can replace it with Garrett's shim. If you do so, though, you'll have to add Ubuntu's public key as a MOK, at least if you intend to launch Ubuntu's version of GRUB or launch Ubuntu-provided signed kernels. Ubuntu's public key is available in the shim_0~20120906.bcd0a4e8-0ubuntu4.debian.tar.gz tarball, as canonical-uefi-ca.der. (The filename extensions .cer and .der are interchangeable for most purposes.) I've also included this key with rEFInd, in the refind/keys subdirectory of its package file. To use this key, copy it to your ESP and enroll it with MokManager. See this blog post for further details on Ubuntu 12.10's handling of Secure Boot. In principle, you should be able to use shim 0.2 or later from future distributions that include it; but you must be sure that whatever you use supports MokManager.

The preceding instructions provided the basics of getting rEFInd up and running, including using MokManager to enroll a MOK on your computer. If you need to sign binaries, though, you'll have to use additional tools. The OpenSSL package provides the cryptographic tools necessary, but actually signing EFI binaries requires additional software. Two packages for this are available: sbsigntool and pesign. Both are available in binary form from this OpenSUSE Build Service (OBS) repository. The following procedure uses sbsigntool. To sign your own binaries, follow these steps (you can skip the first five steps if you've used install.sh's --localkeys option):

1. If it's not already installed, install OpenSSL on your computer. (It normally comes in a package called openssl.)
2. If you did not re-sign your rEFInd binaries with install.sh's --localkeys option, type the following two commands to generate your public and private keys:

   $ openssl req -new -x509 -newkey rsa:2048 -keyout refind_local.key \
     -out refind_local.crt -nodes -days 3650 -subj "/CN=Your Name/"
   $ openssl x509 -in refind_local.crt -out refind_local.cer -outform DER
   

   Change Your Name to your own name or other identifying characteristics, and adjust the certificate's time span (set via -days) as you see fit. If you omit the -nodes option, the program will prompt you for a passphrase for added security. Remember this, since you'll need it to sign your binaries. The result is a private key file (refind_local.key), which is highly sensitive since it's required to sign binaries, and two public keys (refind_local.crt and refind_local.cer), which can be used to verify signed binaries' authenticity. The two public key files are equivalent, but are used by different tools—sbsigntool uses refind_local.crt to sign binaries, but MokManager uses refind_local.cer to enroll the key. If you used install.sh's --localkeys option, this step is unnecessary, since these keys have already been created and are stored in /etc/refind.d/keys.
3. Copy the three key files to a secure location and adjust permissions such that only you can read refind_local.key. You'll need these keys to sign future binaries, so don't discard them.
4. Copy the refind_local.cer file to your ESP, ideally to a location with few other files. (MokManager's user interface becomes unreliable when browsing directories with lots of files.)
5. Download and install the sbsigntool package. Binary links for various distributions are available from the OpenSUSE Build Service, or you can obtain the source code by typing git clone git://kernel.ubuntu.com/jk/sbsigntool.
6. Sign your binary by typing sbsign --key refind_local.key --cert refind_local.crt --output binary-signed.efi binary.efi, adjusting the paths to the keys and the binary names.
7. Copy your signed binary to a suitable location on the ESP for rEFInd to locate it. Be sure to include any support files that it needs, too.
8. Check your refind.conf file to ensure that the showtools option is either commented out or includes mok_tool among its options.
9. Reboot. You can try launching the boot loader you just installed, but chances are it will generate an Access Denied message. For it to work, you must launch MokManager using the tool that rEFInd presents on its second row. You can then enroll your refind_local.cer key just as you enrolled the refind.cer key.

At this point you should be able to launch the binaries you've signed. Unfortunately, there can still be problems at this point....

If you want to use Secure Boot with a distribution that doesn't come with shim but the preceding description exhausts you, take heart: PreLoader is easier to set up and use for your situation! Unfortunately, it's still not as easy to use as not using Secure Boot at all, and it's got some drawbacks, but it may represent an acceptable middle ground. To get started, proceed as follows:

1. Boot the computer. As with shim, this can be a challenge; you may need to boot with Secure Boot disabled, use a Secure Boot–enabled live CD, or do the installation from Windows.
2. Download rEFInd in binary form (the binary zip or CD-R image file). If you download the binary zip file, unzip it; if you get the CD-R image file, burn it to a CD-R and mount it.
3. Download PreLoader from its release page or by clicking the following links. Be sure to get both the PreLoader.efi and HashTool.efi files.
4. Copy the PreLoader.efi and HashTool.efi binaries to the directory you intend to use for rEFInd—for instance, EFI/refind on the ESP.
5. Follow the installation instructions for rEFInd on the Installing rEFInd page; however, give rEFInd the filename loader.efi and register PreLoader.efi with the EFI by using efibootmgr in Linux or bcdedit in Windows. Be sure that rEFInd (as loader.efi), PreLoader.efi, and HashTool.efi all reside in the same directory.
6. Reboot. With any luck, you'll see HashTool appear with a warning message stating that it was unable to launch loader.efi and declaring that it will launch HashTool.efi. Press the Enter key to continue.
7. HashTool should now appear. It should give you three or four options, including Enroll Hash, as shown here. Select this option



8. You can now select the binary you want to authorize. You should first select loader.efi, since that's rEFInd. The program presents the hash (a very long number) and asks for confirmation. Be sure to select Yes.




Note: Unfortunately, HashTool's file selector can't change filesystems. Thus, if you want to boot a Linux kernel using rEFInd and PreLoader, you'll need to copy the kernel to the ESP, at least temporarily. Alternatively, as noted earlier, you can copy HashTool.efi to the directory that holds the kernels or to another directory on that partition that rEFInd scans—but be sure to rename HashTool.efi or rEFInd will ignore it. You'll then see a boot loader entry for HashTool.

9. Repeat the preceding two steps for any additional binaries you might want to enroll. These include any EFI filesystem drivers you're using, any boot loaders you're launching from rEFInd (other than those that are already signed, such as Microsoft's boot loader), and possibly your Linux kernel.
10. At the HashTool main menu, select Exit. rEFInd should launch.

If you did everything right, rEFInd should now launch follow-on boot loaders and kernels, including both programs signed with the platform's Secure Boot keys and binaries that you've authorized with HashTool. If you need to authorize additional programs, you can do so from rEFInd by using the MOK utility tool icon that launches HashTool.efi from the second row of icons. (This icon should appear by default, but if you uncomment the showtools token in refind.conf, be sure that mok_tool is present among the options.)

rEFInd's Secure Boot support is brand-new with version 0.5.0 of the program, and was revamped for version 0.6.2. I believe rEFInd 0.6.2's Secure Boot support to be significantly superior to that of previous versions, but you might still run into problems. Some issues you might encounter include the following:

• rEFInd uses the same EFI "hooks" as PreLoader. This method, however, is part of an optional EFI subsystem, so in theory some EFIs might not support it. For months, I knew of no such implementation, but this SuperUser question indicates that at least one such implementation exists. The board in question is old enough that it might not support Secure Boot at all, though, so I'm not sure if this report indicates a serious limitation or just a stray error message on a computer that doesn't need this feature at all.
• Under certain circumstances, the time required to launch a boot loader can increase. This is unlikely to be noticeable for the average small boot loader, but could be significant for larger boot loaders on slow filesystems, such as Linux kernels on ext2fs, ext3fs, or ReiserFS partitions.
• As of version 0.6.2, rEFInd's own Secure Boot support is theoretically able to work on non-x86-64 platforms; however, shim 0.2 and PreLoader both work only on x86-64, and rEFInd is dependent upon these tools. Thus, you'll have to wait for future developments if you want to use Secure Boot on x86 or ARM computers.
• In theory, signing Microsoft's boot loader with a MOK should work. This might be handy if you want to replace your computer's built-in keys with your own but still boot Windows—but be aware that if Windows replaces its boot loader, it will then stop working.

If you launch a boot loader or other program from rEFInd that relies on the EFI's standard program-launching code, that program should take advantage of shim and its MOKs. For instance, if you launch gummiboot from rEFInd (and rEFInd from shim), gummiboot should be able to launch shim/MOK-signed Linux kernels. This is not currently true if you launch gummiboot directly from shim. (You can launch gummiboot from PreLoader and it should work, though, because of technical differences between how shim and PreLoader work.)

My focus in testing rEFInd's Secure Boot capabilities has been on getting Linux kernels with EFI stub loaders to launch correctly. I've done some minimal testing with GRUB 2, though. I've also tested some self-signed binaries, such as an EFI shell and MokManager. (The EFI shell launches, but will not itself launch anything that's not been signed with a UEFI Secure Boot key, even with rEFInd 0.6.2. This of course limits its utility.)

At the moment, I consider rEFInd's shim/MOK support to be of late alpha quality. I'm releasing it in this state in the hope of getting feedback from adventurous early adopters. Some of the usability improvements are dependent upon MOK-capable versions of shim being released with major distributions; such versions of shim, with kernels signed with the key that matches the one built into shim, will greatly reduce the need for users to sign boot loaders.

copyright © 2012–2014 by Roderick W. Smith

This document is licensed under the terms of the GNU Free Documentation License (FDL), version 1.3.

If you have problems with or comments about this Web page, please e-mail me at rodsmith@rodsbooks.com. Thanks.

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