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doc: uniphier: add simple guide to Verified Boot
Add a simple documentation about how to use the Verified Boot on UniPhier boards. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
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Masahiro Yamada
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@ -107,6 +107,231 @@ Firmware.
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[ARM Trusted Firmware]: https://github.com/ARM-software/arm-trusted-firmware
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Verified Boot
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-------------
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U-Boot supports an image verification method called "Verified Boot".
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This is a brief tutorial to utilize this feature for the UniPhier platform.
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You will find details documents in the doc/uImage.FIT directory.
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Here, we take LD20 reference board for example, but it should work for any
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other boards including 32 bit SoCs.
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1. Generate key to sign with
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$ mkdir keys
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$ openssl genpkey -algorithm RSA -out keys/dev.key \
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-pkeyopt rsa_keygen_bits:2048 -pkeyopt rsa_keygen_pubexp:65537
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$ openssl req -batch -new -x509 -key keys/dev.key -out keys/dev.crt
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Two files "dev.key" and "dev.crt" will be created. The base name is arbitrary,
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but need to match to the "key-name-hint" property described below.
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2. Describe FIT source
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You need to write an FIT (Flattened Image Tree) source file to describe the
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structure of the image container.
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The following is an example for a simple usecase:
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---------------------------------------->8----------------------------------------
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/dts-v1/;
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/ {
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description = "Kernel, DTB and Ramdisk for UniPhier LD20 Reference Board";
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#address-cells = <1>;
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images {
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kernel@0 {
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description = "linux";
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data = /incbin/("PATH/TO/YOUR/LINUX/DIR/arch/arm64/boot/Image.gz");
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type = "kernel";
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arch = "arm64";
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os = "linux";
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compression = "gzip";
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load = <0x82080000>;
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entry = <0x82080000>;
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hash@0 {
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algo = "sha256";
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};
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};
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fdt@0 {
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description = "fdt";
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data = /incbin/("PATH/TO/YOUR/LINUX/DIR/arch/arm64/boot/dts/socionext/uniphier-ld20-ref.dtb");
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type = "flat_dt";
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arch = "arm64";
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compression = "none";
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hash@0 {
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algo = "sha256";
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};
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};
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ramdisk@0 {
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description = "ramdisk";
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data = /incbin/("PATH/TO/YOUR/ROOTFS/DIR/rootfs.cpio");
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type = "ramdisk";
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arch = "arm64";
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os = "linux";
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compression = "none";
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hash@0 {
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algo = "sha256";
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};
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};
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};
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configurations {
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default = "config@0";
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config@0 {
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description = "Configuration0";
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kernel = "kernel@0";
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fdt = "fdt@0";
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ramdisk = "ramdisk@0";
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signature@0 {
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algo = "sha256,rsa2048";
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key-name-hint = "dev";
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sign-images = "kernel", "fdt", "ramdisk";
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};
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};
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};
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};
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---------------------------------------->8----------------------------------------
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You need to change the three '/incbin/' lines, depending on the location of
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your kernel image, device tree blob, and init ramdisk. The "load" and "entry"
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properties also need to be adjusted if you want to change the physical placement
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of the kernel.
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The "key-name-hint" must specify the key name you have created in the step 1.
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The FIT file name is arbitrary. Let's say you saved it into "fit.its".
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3. Compile U-Boot with FIT and signature enabled
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To use the Verified Boot, you need to enable the following two options:
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CONFIG_FIT
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CONFIG_FIT_SIGNATURE
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They are disabled by default for UniPhier defconfig files. So, you need to
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tweak the configuration from "make menuconfig" or friends.
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$ make uniphier_v8_defconfig
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$ make menuconfig
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[ enable CONFIG_FIT and CONFIG_FIT_SIGNATURE ]
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$ make CROSS_COMPILE=aarch64-linux-gnu-
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4. Build the image tree blob
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After building U-Boot, you will see tools/mkimage. With this tool, you can
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create an image tree blob as follows:
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$ tools/mkimage -f fit.its -k keys -K dts/dt.dtb -r -F fitImage
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The -k option must specify the key directory you have created in step 1.
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A file "fitImage" will be created. This includes kernel, DTB, Init-ramdisk,
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hash data for each of the three, and signature data.
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The public key needed for the run-time verification is stored in "dts/dt.dtb".
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5. Compile U-Boot again
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Since the "dt.dtb" has been updated in step 4, you need to re-compile the
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U-Boot.
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$ make CROSS_COMPILE=aarch64-linux-gnu-
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The re-compiled "u-boot.bin" is appended with DTB that contains the public key.
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6. Flash the image
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Flash the "fitImage" to a storage device (NAND, eMMC, or whatever) on your
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board.
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Please note the "u-boot.bin" must be signed, and verified by someone when it is
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loaded. For ARMv8 SoCs, the "someone" is generally ARM Trusted Firmware BL2.
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ARM Trusted Firmware supports an image authentication mechanism called Trusted
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Board Boot (TBB). The verification process must be chained from the moment of
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the system reset. If the Chain of Trust has a breakage somewhere, the verified
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boot process is entirely pointless.
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7. Boot verified kernel
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Load the fitImage to memory and run the following from the U-Boot command line.
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> bootm <addr>
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Here, <addr> is the base address of the fitImage.
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If it is successful, you will see messages like follows:
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---------------------------------------->8----------------------------------------
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## Loading kernel from FIT Image at 84100000 ...
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Using 'config@0' configuration
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Verifying Hash Integrity ... sha256,rsa2048:dev+ OK
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Trying 'kernel@0' kernel subimage
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Description: linux
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Created: 2017-10-20 14:32:29 UTC
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Type: Kernel Image
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Compression: gzip compressed
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Data Start: 0x841000c8
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Data Size: 6957818 Bytes = 6.6 MiB
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Architecture: AArch64
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OS: Linux
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Load Address: 0x82080000
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Entry Point: 0x82080000
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Hash algo: sha256
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Hash value: 82a37b7f11ae55f4e07aa25bf77e4067cb9dc1014d52d6cd4d588f92eee3aaad
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Verifying Hash Integrity ... sha256+ OK
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## Loading ramdisk from FIT Image at 84100000 ...
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Using 'config@0' configuration
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Trying 'ramdisk@0' ramdisk subimage
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Description: ramdisk
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Created: 2017-10-20 14:32:29 UTC
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Type: RAMDisk Image
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Compression: uncompressed
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Data Start: 0x847a5cc0
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Data Size: 5264365 Bytes = 5 MiB
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Architecture: AArch64
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OS: Linux
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Load Address: unavailable
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Entry Point: unavailable
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Hash algo: sha256
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Hash value: 44980a2874154a2e31ed59222c9f8ea968867637f35c81e4107a984de7014deb
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Verifying Hash Integrity ... sha256+ OK
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## Loading fdt from FIT Image at 84100000 ...
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Using 'config@0' configuration
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Trying 'fdt@0' fdt subimage
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Description: fdt
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Created: 2017-10-20 14:32:29 UTC
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Type: Flat Device Tree
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Compression: uncompressed
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Data Start: 0x847a2cb0
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Data Size: 12111 Bytes = 11.8 KiB
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Architecture: AArch64
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Hash algo: sha256
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Hash value: c517099db537f6d325e6be46b25c871a41331ad5af0283883fd29d40bfc14e1d
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Verifying Hash Integrity ... sha256+ OK
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Booting using the fdt blob at 0x847a2cb0
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Uncompressing Kernel Image ... OK
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reserving fdt memory region: addr=80000000 size=2000000
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Loading Device Tree to 000000009fffa000, end 000000009fffff4e ... OK
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Starting kernel ...
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---------------------------------------->8----------------------------------------
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Please pay attention to the lines that start with "Verifying Hash Integrity".
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"Verifying Hash Integrity ... sha256,rsa2048:dev+ OK" means the signature check
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passed.
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"Verifying Hash Integrity ... sha256+ OK" (3 times) means the hash check passed
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for kernel, DTB, and Init ramdisk.
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If they are not displayed, the Verified Boot is not working.
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UniPhier specific commands
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--------------------------
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@ -179,4 +404,4 @@ newer SoCs. Even if it is, EA[25] is not connected on most of the boards.
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--
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Masahiro Yamada <yamada.masahiro@socionext.com>
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Sep. 2017
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Oct. 2017
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