1 .. SPDX-License-Identifier: GPL-2.0+
2 .. Copyright (c) 2018 Heinrich Schuchardt
7 The Unified Extensible Firmware Interface Specification (UEFI) [1] has become
8 the default for booting on AArch64 and x86 systems. It provides a stable API for
9 the interaction of drivers and applications with the firmware. The API comprises
10 access to block storage, network, and console to name a few. The Linux kernel
11 and boot loaders like GRUB or the FreeBSD loader can be executed.
16 The implementation of UEFI in U-Boot strives to reach the requirements described
17 in the "Embedded Base Boot Requirements (EBBR) Specification - Release v1.0"
18 [2]. The "Server Base Boot Requirements System Software on ARM Platforms" [3]
19 describes a superset of the EBBR specification and may be used as further
22 A full blown UEFI implementation would contradict the U-Boot design principle
25 Building U-Boot for UEFI
26 ------------------------
28 The UEFI standard supports only little-endian systems. The UEFI support can be
29 activated for ARM and x86 by specifying::
36 Support for attaching virtual block devices, e.g. iSCSI drives connected by the
37 loaded UEFI application [4], requires::
42 Executing a UEFI binary
43 ~~~~~~~~~~~~~~~~~~~~~~~
45 The bootefi command is used to start UEFI applications or to install UEFI
46 drivers. It takes two parameters::
48 bootefi <image address> [fdt address]
50 * image address - the memory address of the UEFI binary
51 * fdt address - the memory address of the flattened device tree
53 Below you find the output of an example session starting GRUB::
55 => load mmc 0:2 ${fdt_addr_r} boot/dtb
56 29830 bytes read in 14 ms (2 MiB/s)
57 => load mmc 0:1 ${kernel_addr_r} efi/debian/grubaa64.efi
58 reading efi/debian/grubaa64.efi
59 120832 bytes read in 7 ms (16.5 MiB/s)
60 => bootefi ${kernel_addr_r} ${fdt_addr_r}
62 When booting from a memory location it is unknown from which file it was loaded.
63 Therefore the bootefi command uses the device path of the block device partition
64 or the network adapter and the file name of the most recently loaded PE-COFF
65 file when setting up the loaded image protocol.
67 Launching a UEFI binary from a FIT image
68 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
70 A signed FIT image can be used to securely boot a UEFI image via the
71 bootm command. This feature is available if U-Boot is configured with::
75 A sample configuration is provided as file doc/uImage.FIT/uefi.its.
77 Below you find the output of an example session starting GRUB::
79 => load mmc 0:1 ${kernel_addr_r} image.fit
80 4620426 bytes read in 83 ms (53.1 MiB/s)
81 => bootm ${kernel_addr_r}#config-grub-nofdt
82 ## Loading kernel from FIT Image at 40400000 ...
83 Using 'config-grub-nofdt' configuration
84 Verifying Hash Integrity ... sha256,rsa2048:dev+ OK
85 Trying 'efi-grub' kernel subimage
86 Description: GRUB EFI Firmware
87 Created: 2019-11-20 8:18:16 UTC
88 Type: Kernel Image (no loading done)
89 Compression: uncompressed
90 Data Start: 0x404000d0
91 Data Size: 450560 Bytes = 440 KiB
93 Hash value: 4dbee00021112df618f58b3f7cf5e1595533d543094064b9ce991e8b054a9eec
94 Verifying Hash Integrity ... sha256+ OK
95 XIP Kernel Image (no loading done)
96 ## Transferring control to EFI (at address 404000d0) ...
99 See doc/uImage.FIT/howto.txt for an introduction to FIT images.
101 Configuring UEFI secure boot
102 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
104 The UEFI specification[1] defines a secure way of executing UEFI images
105 by verifying a signature (or message digest) of image with certificates.
106 This feature on U-Boot is enabled with::
108 CONFIG_EFI_SECURE_BOOT=y
110 To make the boot sequence safe, you need to establish a chain of trust;
111 In UEFI secure boot the chain trust is defined by the following UEFI variables
114 * KEK - Key Exchange Keys
115 * db - white list database
116 * dbx - black list database
118 An in depth description of UEFI secure boot is beyond the scope of this
119 document. Please, refer to the UEFI specification and available online
120 documentation. Here is a simple example that you can follow for your initial
121 attempt (Please note that the actual steps will depend on your system and
124 Install the required tools on your host
130 Create signing keys and the key database on your host:
136 openssl req -x509 -sha256 -newkey rsa:2048 -subj /CN=TEST_PK/ \
137 -keyout PK.key -out PK.crt -nodes -days 365
138 cert-to-efi-sig-list -g 11111111-2222-3333-4444-123456789abc \
140 sign-efi-sig-list -c PK.crt -k PK.key PK PK.esl PK.auth
142 The key exchange keys
146 openssl req -x509 -sha256 -newkey rsa:2048 -subj /CN=TEST_KEK/ \
147 -keyout KEK.key -out KEK.crt -nodes -days 365
148 cert-to-efi-sig-list -g 11111111-2222-3333-4444-123456789abc \
150 sign-efi-sig-list -c PK.crt -k PK.key KEK KEK.esl KEK.auth
152 The whitelist database
156 openssl req -x509 -sha256 -newkey rsa:2048 -subj /CN=TEST_db/ \
157 -keyout db.key -out db.crt -nodes -days 365
158 cert-to-efi-sig-list -g 11111111-2222-3333-4444-123456789abc \
160 sign-efi-sig-list -c KEK.crt -k KEK.key db db.esl db.auth
162 Copy the \*.auth files to media, say mmc, that is accessible from U-Boot.
164 Sign an image with one of the keys in "db" on your host
168 sbsign --key db.key --cert db.crt helloworld.efi
170 Now in U-Boot install the keys on your board::
172 fatload mmc 0:1 <tmpaddr> PK.auth
173 setenv -e -nv -bs -rt -at -i <tmpaddr>:$filesize PK
174 fatload mmc 0:1 <tmpaddr> KEK.auth
175 setenv -e -nv -bs -rt -at -i <tmpaddr>:$filesize KEK
176 fatload mmc 0:1 <tmpaddr> db.auth
177 setenv -e -nv -bs -rt -at -i <tmpaddr>:$filesize db
179 Set up boot parameters on your board::
181 efidebug boot add -b 1 HELLO mmc 0:1 /helloworld.efi.signed ""
183 Since kernel 5.7 there's an alternative way of loading an initrd using
184 LoadFile2 protocol if CONFIG_EFI_LOAD_FILE2_INITRD is enabled.
185 The initrd path can be specified with::
187 efidebug boot add -b ABE0 'kernel' mmc 0:1 Image -i mmc 0:1 initrd
189 Now your board can run the signed image via the boot manager (see below).
190 You can also try this sequence by running Pytest, test_efi_secboot,
195 cd <U-Boot source directory>
196 pytest.py test/py/tests/test_efi_secboot/test_signed.py --bd sandbox
198 UEFI binaries may be signed by Microsoft using the following certificates:
200 * KEK: Microsoft Corporation KEK CA 2011
201 http://go.microsoft.com/fwlink/?LinkId=321185.
202 * db: Microsoft Windows Production PCA 2011
203 http://go.microsoft.com/fwlink/p/?linkid=321192.
204 * db: Microsoft Corporation UEFI CA 2011
205 http://go.microsoft.com/fwlink/p/?linkid=321194.
207 Using OP-TEE for EFI variables
208 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
210 Instead of implementing UEFI variable services inside U-Boot they can
211 also be provided in the secure world by a module for OP-TEE[1]. The
212 interface between U-Boot and OP-TEE for variable services is enabled by
213 CONFIG_EFI_MM_COMM_TEE=y.
215 Tianocore EDK II's standalone management mode driver for variables can
216 be linked to OP-TEE for this purpose. This module uses the Replay
217 Protected Memory Block (RPMB) of an eMMC device for persisting
218 non-volatile variables. When calling the variable services via the
219 OP-TEE API U-Boot's OP-TEE supplicant relays calls to the RPMB driver
220 which has to be enabled via CONFIG_SUPPORT_EMMC_RPMB=y.
222 EDK2 Build instructions
223 ***********************
227 $ git clone https://github.com/tianocore/edk2.git
228 $ git clone https://github.com/tianocore/edk2-platforms.git
230 $ git submodule init && git submodule update --init --recursive
232 $ export WORKSPACE=$(pwd)
233 $ export PACKAGES_PATH=$WORKSPACE/edk2:$WORKSPACE/edk2-platforms
234 $ export ACTIVE_PLATFORM="Platform/StandaloneMm/PlatformStandaloneMmPkg/PlatformStandaloneMmRpmb.dsc"
235 $ export GCC5_AARCH64_PREFIX=aarch64-linux-gnu-
236 $ source edk2/edksetup.sh
237 $ make -C edk2/BaseTools
238 $ build -p $ACTIVE_PLATFORM -b RELEASE -a AARCH64 -t GCC5 -n `nproc`
240 OP-TEE Build instructions
241 *************************
245 $ git clone https://github.com/OP-TEE/optee_os.git
247 $ ln -s ../Build/MmStandaloneRpmb/RELEASE_GCC5/FV/BL32_AP_MM.fd
249 $ CROSS_COMPILE32=arm-linux-gnueabihf- make -j32 CFG_ARM64_core=y \
250 PLATFORM=<myboard> CFG_STMM_PATH=BL32_AP_MM.fd CFG_RPMB_FS=y \
251 CFG_RPMB_FS_DEV_ID=0 CFG_CORE_HEAP_SIZE=524288 CFG_RPMB_WRITE_KEY=y \
252 CFG_CORE_DYN_SHM=y CFG_RPMB_TESTKEY=y CFG_REE_FS=n \
253 CFG_CORE_ARM64_PA_BITS=48 CFG_TEE_CORE_LOG_LEVEL=1 \
254 CFG_TEE_TA_LOG_LEVEL=1 CFG_SCTLR_ALIGNMENT_CHECK=n
256 U-Boot Build instructions
257 *************************
259 Although the StandAloneMM binary comes from EDK2, using and storing the
260 variables is currently available in U-Boot only.
264 $ git clone https://github.com/u-boot/u-boot.git
266 $ export CROSS_COMPILE=aarch64-linux-gnu-
268 $ make <myboard>_defconfig
271 Enable ``CONFIG_OPTEE``, ``CONFIG_CMD_OPTEE_RPMB`` and ``CONFIG_EFI_MM_COMM_TEE``
275 - Your OP-TEE platform port must support Dynamic shared memory, since that's
276 the only kind of memory U-Boot supports for now.
278 [1] https://optee.readthedocs.io/en/latest/building/efi_vars/stmm.html
280 Enabling UEFI Capsule Update feature
281 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
283 Support has been added for the UEFI capsule update feature which
284 enables updating the U-Boot image using the UEFI firmware management
285 protocol (FMP). The capsules are not passed to the firmware through
286 the UpdateCapsule runtime service. Instead, capsule-on-disk
287 functionality is used for fetching capsules from the EFI System
288 Partition (ESP) by placing capsule files under the directory::
292 The directory is checked for capsules only within the
293 EFI system partition on the device specified in the active boot option,
294 which is determined by BootXXXX variable in BootNext, or if not, the highest
295 priority one within BootOrder. Any BootXXXX variables referring to devices
296 not present are ignored when determining the active boot option.
298 Please note that capsules will be applied in the alphabetic order of
301 Creating a capsule file
302 ***********************
304 A capsule file can be created by using tools/mkeficapsule.
305 To build this tool, enable::
307 CONFIG_TOOLS_MKEFICAPSULE=y
308 CONFIG_TOOLS_LIBCRYPTO=y
310 Run the following command
312 .. code-block:: console
315 --index 1 --instance 0 \
316 [--fit <FIT image> | --raw <raw image>] \
319 Performing the update
320 *********************
322 Put capsule files under the directory mentioned above.
323 Then, following the UEFI specification, you'll need to set
324 the EFI_OS_INDICATIONS_FILE_CAPSULE_DELIVERY_SUPPORTED
325 bit in OsIndications variable with
327 .. code-block:: console
329 => setenv -e -nv -bs -rt -v OsIndications =0x04
331 Since U-boot doesn't currently support SetVariable at runtime, its value
332 won't be taken over across the reboot. If this is the case, you can skip
333 this feature check with the Kconfig option (CONFIG_EFI_IGNORE_OSINDICATIONS)
336 Finally, the capsule update can be initiated by rebooting the board.
338 Enabling Capsule Authentication
339 *******************************
341 The UEFI specification defines a way of authenticating the capsule to
342 be updated by verifying the capsule signature. The capsule signature
343 is computed and prepended to the capsule payload at the time of
344 capsule generation. This signature is then verified by using the
345 public key stored as part of the X509 certificate. This certificate is
346 in the form of an efi signature list (esl) file, which is embedded in
349 The capsule authentication feature can be enabled through the
350 following config, in addition to the configs listed above for capsule
353 CONFIG_EFI_CAPSULE_AUTHENTICATE=y
355 The public and private keys used for the signing process are generated
356 and used by the steps highlighted below.
358 1. Install utility commands on your host
362 2. Create signing keys and certificate files on your host
364 .. code-block:: console
366 $ openssl req -x509 -sha256 -newkey rsa:2048 -subj /CN=CRT/ \
367 -keyout CRT.key -out CRT.crt -nodes -days 365
368 $ cert-to-efi-sig-list CRT.crt CRT.esl
370 3. Run the following command to create and sign the capsule file
372 .. code-block:: console
374 $ mkeficapsule --monotonic-count 1 \
375 --private-key CRT.key \
376 --certificate CRT.crt \
377 --index 1 --instance 0 \
378 [--fit | --raw | --guid <guid-string] \
379 <image_blob> <capsule_file_name>
381 4. Insert the signature list into a device tree in the following format::
385 capsule-key = [ <binary of signature list> ];
390 You can do step-4 manually with
392 .. code-block:: console
394 $ dtc -@ -I dts -O dtb -o signature.dtbo signature.dts
395 $ fdtoverlay -i orig.dtb -o new.dtb -v signature.dtbo
397 where signature.dts looks like::
401 capsule-key = /incbin/("CRT.esl");
405 Executing the boot manager
406 ~~~~~~~~~~~~~~~~~~~~~~~~~~
408 The UEFI specification foresees to define boot entries and boot sequence via
409 UEFI variables. Booting according to these variables is possible via::
411 bootefi bootmgr [fdt address]
413 As of U-Boot v2020.10 UEFI variables cannot be set at runtime. The U-Boot
414 command 'efidebug' can be used to set the variables.
416 Executing the built in hello world application
417 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
419 A hello world UEFI application can be built with::
421 CONFIG_CMD_BOOTEFI_HELLO_COMPILE=y
423 It can be embedded into the U-Boot binary with::
425 CONFIG_CMD_BOOTEFI_HELLO=y
427 The bootefi command is used to start the embedded hello world application::
429 bootefi hello [fdt address]
431 Below you find the output of an example session::
433 => bootefi hello ${fdtcontroladdr}
434 ## Starting EFI application at 01000000 ...
435 WARNING: using memory device/image path, this may confuse some payloads!
440 Load options: root=/dev/sdb3 init=/sbin/init rootwait ro
441 ## Application terminated, r = 0
443 The environment variable fdtcontroladdr points to U-Boot's internal device tree
446 Executing the built-in self-test
447 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
449 An UEFI self-test suite can be embedded in U-Boot by building with::
451 CONFIG_CMD_BOOTEFI_SELFTEST=y
453 For testing the UEFI implementation the bootefi command can be used to start the
456 bootefi selftest [fdt address]
458 The environment variable 'efi_selftest' can be used to select a single test. If
459 it is not provided all tests are executed except those marked as 'on request'.
460 If the environment variable is set to 'list' a list of all tests is shown.
462 Below you can find the output of an example session::
464 => setenv efi_selftest simple network protocol
466 Testing EFI API implementation
467 Selected test: 'simple network protocol'
468 Setting up 'simple network protocol'
469 Setting up 'simple network protocol' succeeded
470 Executing 'simple network protocol'
472 DHCP reply received from 192.168.76.2 (52:55:c0:a8:4c:02)
473 as broadcast message.
474 Executing 'simple network protocol' succeeded
475 Tearing down 'simple network protocol'
476 Tearing down 'simple network protocol' succeeded
477 Boot services terminated
479 Preparing for reset. Press any key.
484 After the U-Boot platform has been initialized the UEFI API provides two kinds
490 The API can be extended by loading UEFI drivers which come in two variants:
495 UEFI drivers are installed with U-Boot's bootefi command. With the same command
496 UEFI applications can be executed.
498 Loaded images of UEFI drivers stay in memory after returning to U-Boot while
499 loaded images of applications are removed from memory.
501 An UEFI application (e.g. an operating system) that wants to take full control
502 of the system calls ExitBootServices. After a UEFI application calls
505 * boot services are not available anymore
506 * timer events are stopped
507 * the memory used by U-Boot except for runtime services is released
508 * the memory used by boot time drivers is released
510 So this is a point of no return. Afterwards the UEFI application can only return
511 to U-Boot by rebooting.
513 The UEFI object model
514 ---------------------
516 UEFI offers a flexible and expandable object model. The objects in the UEFI API
517 are devices, drivers, and loaded images. These objects are referenced by
520 The interfaces implemented by the objects are referred to as protocols. These
521 are identified by GUIDs. They can be installed and uninstalled by calling the
522 appropriate boot services.
524 Handles are created by the InstallProtocolInterface or the
525 InstallMultipleProtocolinterfaces service if NULL is passed as handle.
527 Handles are deleted when the last protocol has been removed with the
528 UninstallProtocolInterface or the UninstallMultipleProtocolInterfaces service.
530 Devices offer the EFI_DEVICE_PATH_PROTOCOL. A device path is the concatenation
531 of device nodes. By their device paths all devices of a system are arranged in a
534 Drivers offer the EFI_DRIVER_BINDING_PROTOCOL. This protocol is used to connect
535 a driver to devices (which are referenced as controllers in this context).
537 Loaded images offer the EFI_LOADED_IMAGE_PROTOCOL. This protocol provides meta
538 information about the image and a pointer to the unload callback function.
543 In the UEFI terminology an event is a data object referencing a notification
544 function which is queued for calling when the event is signaled. The following
545 types of events exist:
547 * periodic and single shot timer events
548 * exit boot services events, triggered by calling the ExitBootServices() service
549 * virtual address change events
550 * memory map change events
551 * read to boot events
552 * reset system events
553 * system table events
554 * events that are only triggered programmatically
556 Events can be created with the CreateEvent service and deleted with CloseEvent
559 Events can be assigned to an event group. If any of the events in a group is
560 signaled, all other events in the group are also set to the signaled state.
562 The UEFI driver model
563 ---------------------
565 A driver is specific for a single protocol installed on a device. To install a
566 driver on a device the ConnectController service is called. In this context
567 controller refers to the device for which the driver is installed.
569 The relevant drivers are identified using the EFI_DRIVER_BINDING_PROTOCOL. This
570 protocol has has three functions:
572 * supported - determines if the driver is compatible with the device
573 * start - installs the driver by opening the relevant protocol with
574 attribute EFI_OPEN_PROTOCOL_BY_DRIVER
575 * stop - uninstalls the driver
577 The driver may create child controllers (child devices). E.g. a driver for block
578 IO devices will create the device handles for the partitions. The child
579 controllers will open the supported protocol with the attribute
580 EFI_OPEN_PROTOCOL_BY_CHILD_CONTROLLER.
582 A driver can be detached from a device using the DisconnectController service.
584 U-Boot devices mapped as UEFI devices
585 -------------------------------------
587 Some of the U-Boot devices are mapped as UEFI devices
594 As of U-Boot 2018.03 the logic for doing this is hard coded.
596 The development target is to integrate the setup of these UEFI devices with the
597 U-Boot driver model [5]. So when a U-Boot device is discovered a handle should
598 be created and the device path protocol and the relevant IO protocol should be
599 installed. The UEFI driver then would be attached by calling ConnectController.
600 When a U-Boot device is removed DisconnectController should be called.
602 UEFI devices mapped as U-Boot devices
603 -------------------------------------
605 UEFI drivers binaries and applications may create new (virtual) devices, install
606 a protocol and call the ConnectController service. Now the matching UEFI driver
607 is determined by iterating over the implementations of the
608 EFI_DRIVER_BINDING_PROTOCOL.
610 It is the task of the UEFI driver to create a corresponding U-Boot device and to
611 proxy calls for this U-Boot device to the controller.
613 In U-Boot 2018.03 this has only been implemented for block IO devices.
618 An UEFI uclass driver (lib/efi_driver/efi_uclass.c) has been created that
619 takes care of initializing the UEFI drivers and providing the
620 EFI_DRIVER_BINDING_PROTOCOL implementation for the UEFI drivers.
622 A linker created list is used to keep track of the UEFI drivers. To create an
623 entry in the list the UEFI driver uses the U_BOOT_DRIVER macro specifying
624 UCLASS_EFI_LOADER as the ID of its uclass, e.g::
626 /* Identify as UEFI driver */
627 U_BOOT_DRIVER(efi_block) = {
628 .name = "EFI block driver",
629 .id = UCLASS_EFI_LOADER,
633 The available operations are defined via the structure struct efi_driver_ops::
635 struct efi_driver_ops {
636 const efi_guid_t *protocol;
637 const efi_guid_t *child_protocol;
638 int (*bind)(efi_handle_t handle, void *interface);
641 When the supported() function of the EFI_DRIVER_BINDING_PROTOCOL is called the
642 uclass checks if the protocol GUID matches the protocol GUID of the UEFI driver.
643 In the start() function the bind() function of the UEFI driver is called after
645 The stop() function of the EFI_DRIVER_BINDING_PROTOCOL disconnects the child
646 controllers created by the UEFI driver and the UEFI driver. (In U-Boot v2013.03
647 this is not yet completely implemented.)
652 The UEFI block IO driver supports devices exposing the EFI_BLOCK_IO_PROTOCOL.
654 When connected it creates a new U-Boot block IO device with interface type
655 IF_TYPE_EFI_LOADER, adds child controllers mapping the partitions, and installs
656 the EFI_SIMPLE_FILE_SYSTEM_PROTOCOL on these. This can be used together with the
657 software iPXE to boot from iSCSI network drives [4].
659 This driver is only available if U-Boot is configured with::
670 The load file 2 protocol can be used by the Linux kernel to load the initial
671 RAM disk. U-Boot can be configured to provide an implementation with::
673 EFI_LOAD_FILE2_INITRD=y
675 When the option is enabled the user can add the initrd path with the efidebug
678 Load options Boot#### have a FilePathList[] member. The first element of
679 the array (FilePathList[0]) is the EFI binary to execute. When an initrd
680 is specified the Device Path for the initrd is denoted by a VenMedia node
681 with the EFI_INITRD_MEDIA_GUID. Each entry of the array is terminated by the
682 'end of entire device path' subtype (0xff). If a user wants to define multiple
683 initrds, those must by separated by the 'end of this instance' identifier of
686 So our final format of the FilePathList[] is::
688 Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff)
693 * [1] http://uefi.org/specifications - UEFI specifications
694 * [2] https://github.com/ARM-software/ebbr/releases/download/v1.0/ebbr-v1.0.pdf -
695 Embedded Base Boot Requirements (EBBR) Specification - Release v1.0
696 * [3] https://developer.arm.com/docs/den0044/latest/server-base-boot-requirements-system-software-on-arm-platforms-version-11 -
697 Server Base Boot Requirements System Software on ARM Platforms - Version 1.1
699 * [5] :doc:`../driver-model/index`