1.. SPDX-License-Identifier: GPL-2.0+ 2.. Copyright (c) 2018 Heinrich Schuchardt 3 4iSCSI booting with U-Boot and iPXE 5================================== 6 7Motivation 8---------- 9 10U-Boot has only a reduced set of supported network protocols. The focus for 11network booting has been on UDP based protocols. A TCP stack and HTTP support 12are expected to be integrated in 2018 together with a wget command. 13 14For booting a diskless computer this leaves us with BOOTP or DHCP to get the 15address of a boot script. TFTP or NFS can be used to load the boot script, the 16operating system kernel and the initial file system (initrd). 17 18These protocols are insecure. The client cannot validate the authenticity 19of the contacted servers. And the server cannot verify the identity of the 20client. 21 22Furthermore the services providing the operating system loader or kernel are 23not the ones that the operating system typically will use. Especially in a SAN 24environment this makes updating the operating system a hassle. After installing 25a new kernel version the boot files have to be copied to the TFTP server 26directory. 27 28The HTTPS protocol provides certificate based validation of servers. Sensitive 29data like passwords can be securely transmitted. 30 31The iSCSI protocol is used for connecting storage attached networks. It 32provides mutual authentication using the CHAP protocol. It typically runs on 33a TCP transport. 34 35Thus a better solution than DHCP/TFTP/NFS boot would be to load a boot script 36via HTTPS and to download any other files needed for booting via iSCSI from the 37same target where the operating system is installed. 38 39An alternative to implementing these protocols in U-Boot is to use an existing 40software that can run on top of U-Boot. iPXE[1] is the "swiss army knife" of 41network booting. It supports both HTTPS and iSCSI. It has a scripting engine for 42fine grained control of the boot process and can provide a command shell. 43 44iPXE can be built as an EFI application (named snp.efi) which can be loaded and 45run by U-Boot. 46 47Boot sequence 48------------- 49 50U-Boot loads the EFI application iPXE snp.efi using the bootefi command. This 51application has network access via the simple network protocol offered by 52U-Boot. 53 54iPXE executes its internal script. This script may optionally chain load a 55secondary boot script via HTTPS or open a shell. 56 57For the further boot process iPXE connects to the iSCSI server. This includes 58the mutual authentication using the CHAP protocol. After the authentication iPXE 59has access to the iSCSI targets. 60 61For a selected iSCSI target iPXE sets up a handle with the block IO protocol. It 62uses the ConnectController boot service of U-Boot to request U-Boot to connect a 63file system driver. U-Boot reads from the iSCSI drive via the block IO protocol 64offered by iPXE. It creates the partition handles and installs the simple file 65protocol. Now iPXE can call the simple file protocol to load GRUB[2]. U-Boot 66uses the block IO protocol offered by iPXE to fulfill the request. 67 68Once GRUB is started it uses the same block IO protocol to load Linux. Via 69the EFI stub Linux is called as an EFI application:: 70 71 +--------+ +--------+ 72 | | Runs | | 73 | U-Boot |========>| iPXE | 74 | EFI | | snp.efi| 75 +--------+ | | DHCP | | 76 | |<===|********|<========| | 77 | DHCP | | | Get IP | | 78 | Server | | | Address | | 79 | |===>|********|========>| | 80 +--------+ | | Response| | 81 | | | | 82 | | | | 83 +--------+ | | HTTPS | | 84 | |<===|********|<========| | 85 | HTTPS | | | Load | | 86 | Server | | | Script | | 87 | |===>|********|========>| | 88 +--------+ | | | | 89 | | | | 90 | | | | 91 +--------+ | | iSCSI | | 92 | |<===|********|<========| | 93 | iSCSI | | | Auth | | 94 | Server |===>|********|========>| | 95 | | | | | | 96 | | | | Loads | | 97 | |<===|********|<========| | +--------+ 98 | | | | GRUB | | Runs | | 99 | |===>|********|========>| |======>| GRUB | 100 | | | | | | | | 101 | | | | | | | | 102 | | | | | | Loads | | 103 | |<===|********|<========|********|<======| | +--------+ 104 | | | | | | Linux | | Runs | | 105 | |===>|********|========>|********|======>| |=====>| Linux | 106 | | | | | | | | | | 107 +--------+ +--------+ +--------+ +--------+ | | 108 | | 109 | | 110 | ~ ~ ~ ~| 111 112Security 113-------- 114 115The iSCSI protocol is not encrypted. The traffic could be secured using IPsec 116but neither U-Boot nor iPXE does support this. So we should at least separate 117the iSCSI traffic from all other network traffic. This can be achieved using a 118virtual local area network (VLAN). 119 120Configuration 121------------- 122 123iPXE 124~~~~ 125 126For running iPXE on arm64 the bin-arm64-efi/snp.efi build target is needed:: 127 128 git clone http://git.ipxe.org/ipxe.git 129 cd ipxe/src 130 make bin-arm64-efi/snp.efi -j6 EMBED=myscript.ipxe 131 132The available commands for the boot script are documented at: 133 134http://ipxe.org/cmd 135 136Credentials are managed as environment variables. These are described here: 137 138http://ipxe.org/cfg 139 140iPXE by default will put the CPU to rest when waiting for input. U-Boot does 141not wake it up due to missing interrupt support. To avoid this behavior create 142file src/config/local/nap.h: 143 144.. code-block:: c 145 146 /* nap.h */ 147 #undef NAP_EFIX86 148 #undef NAP_EFIARM 149 #define NAP_NULL 150 151The supported commands in iPXE are controlled by an include, too. Putting the 152following into src/config/local/general.h is sufficient for most use cases: 153 154.. code-block:: c 155 156 /* general.h */ 157 #define NSLOOKUP_CMD /* Name resolution command */ 158 #define PING_CMD /* Ping command */ 159 #define NTP_CMD /* NTP commands */ 160 #define VLAN_CMD /* VLAN commands */ 161 #define IMAGE_EFI /* EFI image support */ 162 #define DOWNLOAD_PROTO_HTTPS /* Secure Hypertext Transfer Protocol */ 163 #define DOWNLOAD_PROTO_FTP /* File Transfer Protocol */ 164 #define DOWNLOAD_PROTO_NFS /* Network File System Protocol */ 165 #define DOWNLOAD_PROTO_FILE /* Local file system access */ 166 167Open-iSCSI 168~~~~~~~~~~ 169 170When the root file system is on an iSCSI drive you should disable pings and set 171the replacement timer to a high value in the configuration file [3]:: 172 173 node.conn[0].timeo.noop_out_interval = 0 174 node.conn[0].timeo.noop_out_timeout = 0 175 node.session.timeo.replacement_timeout = 86400 176 177Links 178----- 179 180* [1] https://ipxe.org - iPXE open source boot firmware 181* [2] https://www.gnu.org/software/grub/ - 182 GNU GRUB (Grand Unified Bootloader) 183* [3] https://github.com/open-iscsi/open-iscsi/blob/master/README - 184 Open-iSCSI README 185