The appended README explains how U-Boot and iPXE can be used to boot a diskless system from an iSCSI SAN.
The maintainer for README.efi and README.iscsi is set.
Signed-off-by: Heinrich Schuchardt xypron.glpk@gmx.de --- MAINTAINERS | 2 + doc/README.iscsi | 178 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 180 insertions(+) create mode 100644 doc/README.iscsi
diff --git a/MAINTAINERS b/MAINTAINERS index d459153503..6e94cee5d3 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -286,6 +286,8 @@ EFI PAYLOAD M: Alexander Graf agraf@suse.de S: Maintained T: git git://github.com/agraf/u-boot.git +F: doc/README.efi +F: doc/README.iscsi F: include/efi* F: lib/efi*/ F: test/py/tests/test_efi* diff --git a/doc/README.iscsi b/doc/README.iscsi new file mode 100644 index 0000000000..f095ad1ddf --- /dev/null +++ b/doc/README.iscsi @@ -0,0 +1,178 @@ +# iSCSI booting with U-Boot and iPXE + +## Motivation + +U-Boot has only a reduced set of supported network protocols. A major gap is +the lack of a TCP stack. + +For booting a diskless computer this leaves us with BOOTP or DHCP to get the +address of a boot script. TFTP can be used to load the boot script and the +operating system kernel and initial file system (initrd). + +These protocols are insecure. The client cannot validate the authenticity +of the contacted servers. And the server cannot verify the identity of the +client. + +Furthermore the services providing the operating system loader or kernel are +not the ones that the operating system will use. Especially in a SAN environment +this makes updating the operating system a hassle. After installing a new +kernel version the boot files have to be copied to the TFTP server directory. + +The HTTPS protocol provides certificate based validation of servers. Sensitive +data like passwords can be securely transmitted. + +The iSCSI protocol is used for connecting storage attached networks. It +provides mutual authentication using the CHAP protocol. It typically runs on +a TCP transport. + +Thus a better solution than DHCP/TFTP boot would be to load a boot script via +HTTPS and to download any other files needed for booting via iSCSI. + +An alternative to implementing these protocols in U-Boot is to use an existing +software that can run on top of U-Boot. iPXE is the "swiss army knife" of +network booting. It supports both HTTPS and iSCSI. It has a script engine for +fine grained control of the boot process and can provide a command shell. + +iPXE can be built as an EFI application (named snp.efi) which can be loaded and +run by U-Boot. + +## Boot sequence + +U-Boot loads the EFI application iPXE snp.efi using the bootefi command. This +application has network access via the simple network protocol offered by +U-Boot. + +iPXE executes its internal script. This script may optionally chain load a +secondary boot script via HTTPS or open a shell. + +For the further boot process iPXE connects to the iSCSI server. This includes +the mutual authentication using the CHAP protocol. After the authentication iPXE +has access to the iSCSI targets. + +For a selected iSCSI target iPXE sets up a handle with the block IO protocol. It +uses the ConnectController boot service of U-Boot to request U-Boot to connect a +file system driver. U-Boot reads from the iSCSI drive via the block IO protocol +offered by iPXE. It creates the partition handles and install the simple file +protocol. Now iPXE can call the simple file protocol to load Grub. U-Boot uses +the block IO protocol offered by iPXE to fulfill the request. + +Once Grub is started it uses the same simple file protocol to load Linux. Via +the EFI stub Linux is called as an EFI application. + +``` + +--------+ +--------+ + | | Runs | | + | U-Boot |=========>| iPXE | + | EFI | | snp.efi| ++--------+ | | DHCP | | +| |<====|********|<=========| | +| DHCP | | | Request | | +| Server | | | | | +| |====>|********|=========>| | ++--------+ | | Response | | + | | | | + | | | | ++--------+ | | HTTPS | | +| |<====|********|<=========| | +| HTTPS | | | Request | | +| Server | | | | | +| |====>|********|=========>| | ++--------+ | | Response | | + | | | | + | | | | ++--------+ | | iSCSI | | +| |<====|********|<=========| | +| iSCSI | | | Auth | | +| Server |====>|********|=========>| | +| | | | | | +| | | | Loads | | +| |<====|********|<=========| | +--------+ +| | | | Grub | | Runs | | +| |====>|********|=========>| |=======>| Grub | +| | | | | | | | +| | | | | | | | +| | | | | | Loads | | +| |<====|********|<=========|********|<=======| | +--------+ +| | | | | | Linux | | Runs | | +| |====>|********|=========>|********|=======>| |=====>| Linux | +| | | | | | | | | | ++--------+ +--------+ +--------+ +--------+ | | + | | + | | + | ~ ~ ~ ~| +``` + +## Security + +The iSCSI protocol is not encrypted. The traffic could be secured using IPsec +but iPXE does not support this. So we should at least separate the iSCSI traffic +from all other network traffic. This can be achieved using a virtual local area +network (VLAN). + +``` + +-----------+ + | | + | | + | iSCSI | + | Server | + | | + | | + +-----------+ + | + |iSCSI + | ++-----------+ +-----------+ +-----------+ +| | VLAN 2 | * | | | +| |----------|****** | | | +| Diskless | | Managed | | Firewall | +| Computer | VLAN 1 | Switch | HTTP | | +| |==========|***********|==========|***********|=====$ +| | | | | | ++-----------+ +-----------+ +-----------+ +``` + +## Configuration + +### iPXE + +For running iPXE on arm64 the bin-arm64-efi/snp.efi build target is needed. + + git clone http://git.ipxe.org/ipxe.git + cd ipxe/src + make bin-arm64-efi/snp.efi -j6 EMBED=myscript.ipxe + +The available commands for the boot script are documented at: + +http://ipxe.org/cmd + +Credentials are managed as environment variables. These are described here: + +http://ipxe.org/cfg + +iPXE by default will put the CPU to rest when waiting for input. U-Boot does +not wake it up due to missing interrupt support. To avoid this behavior create +file src/config/local/nap.h. + + /* nap.h */ + #undef NAP_EFIX86 + #undef NAP_EFIARM + #define NAP_NULL + +The supported commands in iPXE are controlled by an include, too. Putting the +following into src/config/local/general.h is sufficient for most use cases. + + /* general.h */ + #define NSLOOKUP_CMD /* Name resolution command */ + #define PING_CMD /* Ping command */ + #define NTP_CMD /* NTP commands */ + #define VLAN_CMD /* VLAN commands */ + #define IMAGE_EFI /* EFI image support */ + #define DOWNLOAD_PROTO_HTTPS /* Secure Hypertext Transfer Protocol */ + #define DOWNLOAD_PROTO_FTP /* File Transfer Protocol */ + #define DOWNLOAD_PROTO_NFS /* Network File System Protocol */ + #define DOWNLOAD_PROTO_FILE /* Local file system access */ + +## Links + +* https://ipxe.org - iPXE open source boot firmware +* https://www.gnu.org/software/grub/ - GNU Grub (Grand Unified Bootloader)