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  12   <h1>The rEFInd Boot Manager:<br />Managing Secure Boot</h1>
  13
  14   <p class="subhead">by Roderick W. Smith, <a
  15 href="mailto:rodsmith@rodsbooks.com">rodsmith@rodsbooks.com</a></p>
  16
  17 <p>Originally written: 11/13/2012; last Web page update:
  18 12/21/2012, referencing rEFInd 0.6.1</p>
  19
  20
  21 <p>I'm a technical writer and consultant specializing in Linux technologies. This Web page is provided free of charge and with no annoying outside ads; however, I did take time to prepare it, and Web hosting does cost money. If you find this Web page useful, please consider making a small donation to help keep this site up and running. Thanks!</p>
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  86
  87 <hr />
  88
  89 <p>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 <a href="index.html">main page.</a></p>
  90
  91 <hr />
  92
  93 <p class="sidebar"><b>Note:</b> My <a href="http://www.rodsbooks.com/efi-bootloaders/">Managing EFI Boot Loaders for Linux</a> Web page includes a much more detailed description of Secure Boot in its <a href="http://www.rodsbooks.com/efi-bootloaders/secureboot.html">Dealing with Secure Boot</a> sub-page. You should consult this page if you want to disable Secure Boot, generate your own keys, or perform other such tasks.</p>
  94
  95 <p>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 <a href="#basic">secure boot basics</a> and two specific aspects of rEFInd and its interactions with Secure Boot: <a href="#installation">installation issues</a> and <a href="#mok">MOK management.</a> It concludes with a look at <a href="#caveats">known bugs and limitations</a> in rEFInd's Secure Boot features.</p>
  96
  97 <a name="basic">
  98 <h2>Basic Issues</h2>
  99 </a>
 100
 101 <p class="sidebar"><b>Note:</b> You don't <i>have to</i> use Secure Boot.
 102 If you don't want it, you can <a
 103 href="http://www.rodsbooks.com/efi-bootloaders/secureboot.html#disable">disable
 104 it,</a> at least on <i>x</i>86-64 PCs. If an ARM-based computer ships with
 105 Windows 8, this isn't an option for it. Unfortunately, the shim software
 106 described on this page currently supports only <i>x</i>86-64, not
 107 <i>x</i>86 or ARM.</p>
 108
 109 <p>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.</p>
 110
 111 <p>Fortunately, Microsoft will sign third-party binaries with their 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) have all announced plans to take advantage of this system. Unfortunately, using a third-party signing service is an awkward solution for open source software. In fact, for this very reason Red Hat has developed a program that it calls <i>shim</i> that essentially shifts the Secure Boot "train" from Microsoft's proprietary "track" to one that's more friendly to open source authors. Shim is signed by Microsoft and redirects the boot process to another boot loader that can be signed with keys that the distribution maintains and that are built into shim. Fedora 18 is expected to use this system. SUSE has announced that it will use the same system, as does Ubuntu with version 12.10 and later. SUSE has contributed to the shim approach by providing expansions to shim that support a set of keys that users can maintain themselves. These keys are known as Machine Owner Keys (MOKs), and managing them is described later, in <a href="#mok">Managing MOKs.</a> To reiterate, then, there are potentially three ways to sign a binary that will get it launched on a computer that uses shim:</p>
 112
 113 <ul>
 114
 115 <li><b>Secure Boot keys</b>&mdash;These keys are managed by the EFI
 116     firmware. In a default configuration, Microsoft is the only party
 117     that's more-or-less guaranteed to be able to sign boot loaders with
 118     these keys; however, it's possible to <a
 119     href="http://www.rodsbooks.com/efi-bootloaders/secureboot.html#add_keys">replace
 120     Microsoft's keys with your own,</a> in order to take full control of
 121     Secure Boot on your computer. The trouble is that this process is
 122     tedious and varies in details from one computer to another.</li>
 123
 124 <li><b>Shim's built-in keys</b>&mdash;It's possible, but not necessary, to
 125     compile shim with a built-in public key. Its private counterpart can
 126     then be used to sign binaries. In practice, this key type is limited in
 127     utility; it's likely to be used by distribution maintainers to sign
 128     their own version of GRUB and the Linux kernels that it launches,
 129     nothing more. On the plus side, shim's keys require little or no
 130     maintenance by users. One potential complication is that if you swap
 131     out one shim binary for another, its built-in key may change, which
 132     means that the replacement shim might no longer launch its follow-on
 133     boot loader.</li>
 134
 135 <li><b>MOKs</b>&mdash;Versions 0.2 and later of shim support MOKs, which
 136     give you the ability to add your own keys to the computer. If you want
 137     to install multiple Linux distributions in Secure Boot mode, MOKs are
 138     likely to be helpful. They're vital if you want to launch kernels you
 139     compile yourself or use boot managers or boot loaders other than those
 140     provided by your distribution.</li>
 141
 142 </ul>
 143
 144 <p>All three key types are the same in form&mdash;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 <tt>openssl</tt> program, but signing EFI binaries requires a rarer program called <tt>sbsign</tt> or <tt>pesign</tt>. Although it's theoretically possible to use rEFInd without signing your own binaries, this is not yet practical, because distributions don't yet provide their own signed binaries or the public MOK files you must have to enroll their keys. With any luck this will change in 2013. At the very least, many distributions will begin supporting Secure Boot in the near future, and with any luck they'll include their public MOKs for use with other distributions' versions of shim.</p>
 145
 146 <p>Because shim and MOK are being supported by several of the major players in the Linux world, I've decided to do the same with rEFInd. 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 <i>if</i> Secure Boot is disabled in or unsupported by the firmware. (If that's your situation, you needn't bother reading this page.)</p>
 147
 148 <p>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, without public keys for the boot loaders that rEFInd launches, you'll still need to generate keys and sign your boot loaders, as described in the <a href="#mok">Managing Your MOKs</a> section.</p>
 149
 150 <a name="installation">
 151 <h2>Installation Issues</h2>
 152 </a>
 153
 154 <p>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:</p>
 155
 156 <ul>
 157
 158 <li><b>shim</b>&mdash;You can download a version of shim signed with Microsoft's Secure Boot key <a href="http://www.codon.org.uk/~mjg59/shim-signed/">here.</a> 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 <tt>MokManager.efi</tt> program that also ships with the program. Thus, to use this version of shim, you must use MOKs. Ubuntu 12.10 ships with its own shim, but that version doesn't support MOKs and so is useless for launching rEFInd. Future versions of Fedora, SUSE, and probably other distributions will 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 <a href="http://www.rodsbooks.com/efi-bootloaders/installation.html">here.</a> For use in launching rEFInd, it makes sense to install <tt>shim.efi</tt> in <tt>EFI/refind</tt> on your ESP, although of course this detail is up to you.</li>
 159
 160 <li><b>MokManager</b>&mdash;This program is included with shim 0.2 and later. 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 <tt>grubx64.efi</tt>) 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 <tt>shim.efi</tt>, under the name <tt>MokManager.efi</tt>. 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.</li>
 161
 162 <li><b>rEFInd</b>&mdash;Naturally, you need rEFInd. Because shim is hard-coded to launch a program called <tt>grubx64.efi</tt>, you must install rEFInd using that name and to the same directory in which <tt>shim.efi</tt> 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.</li>
 163
 164 <li><b>Your boot loaders and kernels</b>&mdash;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&mdash;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.</li>
 165
 166 </ul>
 167
 168 <p>Because of variables such as which version of shim you're using and whether you're installing a pre-signed version of rEFInd or want to sign it yourself, I can't provide an absolutely complete procedure for installing rEFInd to work with Secure Boot. Broadly speaking, though, the procedure should be something like this:</p>
 169
 170 <ol>
 171
 172 <li>Boot the computer. This can be a challenge in and of itself. You may
 173     need to use a Secure Boot&ndash;enabled Linux emergency disc,
 174     temporarily disable Secure Boot, or do the work from Windows.</li>
 175
 176 <li><a href="getting.html">Download rEFInd</a> in binary form (the binary
 177     zip or CD-R image file). If you download the binary zip file, unzip it;
 178     if you get the CD-R image file, burn it to a CD-R and mount it.</li>
 179
 180 <li>Download shim from <a
 181     href="http://www.codon.org.uk/~mjg59/shim-signed/">Matthew J. Garrett's
 182     download site</a> or from your distribution. (Don't use Ubuntu 12.10's
 183     version, though; as noted earlier, it's inadequate for use with
 184     rEFInd.)</li>
 185
 186 <p class="sidebar"><b>Tip:</b> If you're running Linux, you can save some effort by using the <tt>install.sh</tt> script with its <tt>--shim <tt class="variable">/path/to/shim.efi</tt></tt> option rather than installing manually, as in steps 4&ndash;6 of this procedure. If you've installed <tt>openssl</tt> and <tt>sbsign</tt>, using <tt>--localkeys</tt> will generate local signing keys and re-sign the rEFInd binaries with your own key, too. You can then use <tt>sbsign</tt> and the keys in <tt>/etc/refind.d/keys</tt> to sign your kernels or boot loaders.</p>
 187
 188 <li>Copy the <tt>shim.efi</tt> and <tt>MokManager.efi</tt> binaries to the
 189     directory you intend to use for rEFInd&mdash;for instance,
 190     <tt>EFI/refind</tt> on the ESP.</li>
 191
 192 <li>Follow the installation instructions for rEFInd on the <a
 193     href="installing.html">Installing rEFInd</a> page; however, give rEFInd
 194     the filename <tt>grubx64.efi</tt> and register <tt>shim.efi</tt> with
 195     the EFI by using <tt>efibootmgr</tt> in Linux or <tt>bcdedit</tt> in
 196     Windows. Be sure that rEFInd (as <tt>grubx64.efi</tt>),
 197     <tt>shim.efi</tt>, and <tt>MokManager.efi</tt> all reside in the same
 198     directory.</li>
 199
 200 <li>Copy the <tt>refind.cer</tt> file from the rEFInd package to your ESP,
 201     ideally to a location with few other files. (The rEFInd installation
 202     directory should work fine.)</li>
 203
 204 <li>Reboot. With any luck, you'll see a simple text-mode user interface
 205     with a label of <tt>Shim UEFI key management</tt>. This is the
 206     MokManager program, which shim launched when rEFInd failed verification
 207     because its key is not yet enrolled.</li>
 208
 209 <li>Press your down arrow key and press Enter to select <tt>Enroll key from
 210     disk</tt>. The screen will clear and prompt you to select a key, as
 211     shown here:</li>
 212
 213     <br /><IMG SRC="MokManager1.png" ALIGN="CENTER" WIDTH="676"
 214     HEIGHT="186" ALT="MokManager's user interface is crude but effective."
 215     BORDER=2> <br />
 216
 217 <li>Each of the lines with a long awkward string represents a disk
 218     partition. Select one and you'll see a list of files. Continue
 219     selecting subdirectories until you find the <tt>refind.cer</tt> file
 220     you copied to the ESP earlier.</li>
 221
 222 <li>Select <tt>refind.cer</tt>. You can type <tt class="userinput">1</tt>
 223     to view the certificate's details if you like, or skip that and type
 224     <tt class="userinput">0</tt> to enroll the key.</li>
 225
 226 <li>Back out of any directories you entered and return to the MokManager
 227     main menu.</li>
 228
 229 <li>Select <tt>Continue boot</tt> at the main menu.</li>
 230
 231 </ol>
 232
 233 <p>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 <i>About rEFInd</i> tool in the main menu. Check the <i>Platform</i> 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 <tt>showtools</tt> in <tt>refind.conf</tt>, you must be sure to include <tt>mok_tool</tt> as an option in order to gain access to it.)</p>
 234
 235 <p>If you're using Ubuntu 12.10, 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 <a href="http://archive.ubuntu.com/ubuntu/pool/main/s/shim/shim_0~20120906.bcd0a4e8-0ubuntu4.debian.tar.gz">shim_0~20120906.bcd0a4e8-0ubuntu4.debian.tar.gz</a> tarball, as <tt>canonical-uefi-ca.der</tt>. (The filename extensions <tt>.cer</tt> and <tt>.der</tt> are interchangeable for most purposes.) I've also included this key with rEFInd, in the <tt>refind/keys</tt> subdirectory of its package file. To use this key, copy it to your ESP and enroll it with MokManager. See <a href="http://falstaff.agner.ch/2012/12/12/secure-boot-implementation-of-ubuntu-12-10-quantal-quetzal/">this blog post</a> 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.</p>
 236
 237 <a name="mok">
 238 <h2>Managing Your MOKs</h2>
 239 </a>
 240
 241 <p>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: <tt>sbsigntool</tt> and <tt>pesign</tt>. Both are available in binary form from <a href="https://build.opensuse.org/project/show?project=home%3Ajejb1%3AUEFI">this OpenSUSE Build Service (OBS)</a> repository. The following procedure uses <tt>sbsigntool</tt>. To sign your own binaries, follow these steps (you can skip the first five steps if you've used <tt>install.sh</tt>'s <tt>--localkeys</tt> option):</p>
 242
 243 <ol>
 244
 245 <li>If it's not already installed, install OpenSSL on your computer. (It
 246     normally comes in a package called <tt>openssl</tt>.)</li>
 247
 248 <li>If you did <i>not</i> re-sign your rEFInd binaries with
 249     <tt>install.sh</tt>'s <tt>--localkeys</tt> option, type the following
 250     two commands to generate your public and private keys:
 251
 252 <pre class="listing">
 253 $ <tt class="userinput">openssl req -new -x509 -newkey rsa:2048 -keyout refind_local.key \
 254   -out refind_local.crt -nodes -days 3650 -subj "/CN=Your Name/"</tt>
 255 $ <tt class="userinput">openssl x509 -in refind_local.crt -out refind_local.cer -outform DER</tt>
 256 </pre>
 257
 258     Change <tt>Your Name</tt> to your own name or other identifying
 259     characteristics, and adjust the certificate's time span (set via
 260     <tt>-days</tt>) as you see fit. If you omit the <tt>-nodes</tt> option,
 261     the program will prompt you for a passphrase for added security.
 262     Remember this, since you'll need it to sign your binaries. The result
 263     is a private key file (<tt>refind_local.key</tt>), which is highly
 264     sensitive since it's required to sign binaries, and two public keys
 265     (<tt>refind_local.crt</tt> and <tt>refind_local.cer</tt>), which can be
 266     used to verify signed binaries' authenticity. The two public key files
 267     are equivalent, but are used by different
 268     tools&mdash;<tt>sbsigntool</tt> uses <tt>refind_local.crt</tt> to sign
 269     binaries, but MokManager uses <tt>refind_local.cer</tt> to enroll the
 270     key. If you used <tt>install.sh</tt>'s <tt>--localkeys</tt> option,
 271     this step is unnecessary, since these keys have already been created
 272     and are stored in <tt>/etc/refind.d/keys</tt>.</li>
 273
 274 <li>Copy the three key files to a secure location and adjust permissions
 275     such that only you can read <tt>refind_local.key</tt>. You'll need
 276     these keys to sign future binaries, so don't discard them.</li>
 277
 278 <li>Copy the <tt>refind_local.cer</tt> file to your ESP, ideally to a
 279     location with few other files. (MokManager's user interface becomes
 280     unreliable when browsing directories with lots of files.)</li>
 281
 282 <li>Download and install the <tt>sbsigntool</tt> package. Binary links for
 283     various distributions are available from the <a
 284     href="https://build.opensuse.org/package/show?package=sbsigntools&project=home%3Ajejb1%3AUEFI">OpenSUSE
 285     Build Service</a>, or you can obtain the source code by typing <tt
 286     class="userinput">git clone
 287     git://kernel.ubuntu.com/jk/sbsigntool</tt>.</li>
 288
 289 <li>Sign your binary by typing <tt class="userinput">sbsign --key
 290     refind_local.key --cert refind_local.crt --output <tt
 291     class="variable">binary-signed.efi binary.efi</tt></tt>, adjusting the
 292     paths to the keys and the binary names.</li>
 293
 294 <li>Copy your signed binary to a suitable location on the ESP for rEFInd to
 295     locate it. Be sure to include any support files that it needs,
 296     too.</li>
 297
 298 <li>Check your <tt>refind.conf</tt> file to ensure that the
 299     <tt>showtools</tt> option is either commented out or includes
 300     <tt>mok_tool</tt> among its options.</li>
 301
 302 <li>Reboot. You can try launching the boot loader you just installed, but
 303     chances are it will generate an <tt>Access Denied</tt> message. For it
 304     to work, you must launch MokManager using the tool that rEFInd presents
 305     on its second row. You can then enroll your <tt>refind_local.cer</tt>
 306     key just as you enrolled the <tt>refind.cer</tt> key.</li>
 307
 308 </ol>
 309
 310 <p>At this point you should be able to launch the binaries you've signed. Unfortunately, there can still be problems at this point....</p>
 311
 312 <a name="caveats">
 313 <h2>Secure Boot Caveats</h2>
 314 </a>
 315
 316 <p>rEFInd's Secure Boot support is brand-new with version 0.5.0 of the program. Unfortunately, rEFInd, like shim, must essentially bypass UEFI security features, and must simultaneously not create security problems, in order to work. Unfortunately, the procedures that rEFInd uses to do this (which were lifted straight from shim) play "fast and loose" with the UEFI rules. This fact creates a number of limitations, which include (but are almost certainly not limited to) the following:</p>
 317
 318 <ul>
 319
 320 <li>rEFInd can launch <i>one</i> shim/MOK-signed driver, no more. If you
 321     try to launch two drivers, rEFInd throws up an <tt>Access Denied</tt>
 322     error for the second driver.</li>
 323
 324 <li>Signing the Windows boot loader with a MOK won't work; it hangs.
 325     Fortunately, the Windows 8 boot loader should work because it should be
 326     verified and launched via EFI calls rather than via the new
 327     shim-derived code. (I lack a Windows 8 installation for testing,
 328     though.) This limitation could affect you if you want to boot Windows 7
 329     with Secure Boot active.</li>
 330
 331 <li>Under certain circumstances, the time required to launch a boot loader
 332     can increase. This is unlikely to be noticeable for the average small
 333     boot loader, but could be significant for larger boot loaders on slow
 334     filesystems, such as Linux kernels on ext2fs, ext3fs, or ReiserFS
 335     partitions.</li>
 336
 337 <li>Secure Boot mode doesn't work on <i>x</i>86 (IA32) or ARM systems, just
 338     on <i>x</i>86-64 (AMD64) computers. This is largely because shim has
 339     the same limitations.</li>
 340
 341 </ul>
 342
 343 <p>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. This of course limits its utility.)</p>
 344
 345 <p>At the moment, I consider rEFInd's shim/MOK support to be of alpha quality. I'm releasing it in this state in the hope of getting feedback from adventurous early adopters. I expect to improve the installation procedure, and with any luck fix some of the known bugs, in the next couple of versions. 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.</p>
 346
 347 <hr />
 348
 349 <p>copyright &copy; 2012 by Roderick W. Smith</p>
 350
 351 <p>This document is licensed under the terms of the <a href="FDL-1.3.txt">GNU Free Documentation License (FDL), version 1.3.</a></p>
 352
 353 <p>If you have problems with or comments about this Web page, please e-mail me at <a href="mailto:rodsmith@rodsbooks.com">rodsmith@rodsbooks.com.</a> Thanks.</p>
 354
 355 <p><a href="index.html">Go to the main rEFInd page</a></p>
 356
 357 <p><a href="revisions.html">Learn about rEFInd's history</a></p>
 358
 359
 360   <p><a href="http://www.rodsbooks.com/">Return</a> to my main Web page.</p>
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