This document describes the OpenBmc software implementing the secure flash update mechanism.

The primary details are here.

This repo contains a host-tool implementation for talking to the corresponding BMC blob handler.

The host-tool depends on ipmi-blob-tool and pciutils.

Check out the xorg-macros source.

Then run these commands in the source directory.

./autogen.sh --prefix=/usr
make install

Check out the libpciaccess source.

Then run these commands in the source directory.

./autogen.sh
make
make install

Check out the ipmi-blob-tool source.

Then run these commands in the source directory.

./bootstrap.sh
./configure
make
make install

Check out the stdplus source.

Then run these commands in the source directory.

meson setup -Dexamples=false -Dtests=disabled builddir
ninja -C builddir
ninja -C builddir install

Check out the phosphor-ipmi-flash source.

Then run these commands in the source directory.

./bootstrap.sh
./configure --disable-build-bmc-blob-handler
make
make install

NOTE: When building from the OpenBMC SDK your configuration call will be:

./configure --enable-oe-sdk --host "$(uname -m)" --disable-build-bmc-blob-handler AR=x86_64-openbmc-linux-gcc-ar RANLIB=x86_64-openbmc-linux-gcc-ranlib

The host-tool has parameters that let the caller specify every required detail.

The required parameters are:

If you're using an LPC data transfer mechanism, you'll need two additional parameters: address and length. These values indicate where on the host you've reserved memory to be used for the transfer window.

If you're using a net data transfer mechanism, you'll also need two additional parameters: hostname and port. These specify which address and port the tool should attempt to connect to the BMC using. If unspecified, the port option defaults to 623, the same port as IPMI LAN+.

This supports three methods of providing the image to stage. You can send the file over IPMI packets, which is a very slow process. A 32-MiB image can take ~3 hours to send via this method. This can be done in <1 minutes via the PCI or net bridge, or just a few minutes via LPC depending on the size of the mapped area.

This is implemented as a phosphor blob handler.

The image must be signed via the production or development keys, the former being required for production builds. The image itself and the image signature are separately sent to the BMC for verification. The verification package source is beyond the scope of this design.

Basically the IPMI OEM handler receives the image in one fashion or another and then triggers the verify_image service. Then, the user polls until the result is reported. This is because the image verification process can exceed 10 seconds.

The image flashing mechanism itself is the initramfs stage during reboot. It will check for files named "image-*" and flash them appropriately for each name to section. The IPMI command creates a file /run/initramfs/bmc-image and writes the contents there. It was found that writing it in /tmp could cause OOM errors moving it on low memory systems, whereas renaming a file within the same folder seems to only update the directory inode's contents.

The staging file path can be controlled via software configuration. The image is assumed to be the tarball contents and is written into /tmp/{tarball_name}.gz

TODO: Flesh out the UBI approach.

To use phosphor-ipmi-flash a platform must provide a configuration. A platform can configure multiple interfaces, such as both lpc and pci. However, a platform should only configure either static layout updates, or ubi. If enabling lpc, the platform must specify either aspeed or nuvoton. The system also supports receiving BIOS updates.

The following are the two primary configuration options, which control how the update is treated.

The following are configuration options for how the host and BMC are meant to transfer the data. By default, the data-in-IPMI mechanism is enabled.

There are three configurable data transport mechanisms, either staging the bytes via the LPC memory region, the PCI-to-AHB memory region, or sending over a network connection. Because there is only one MAPPED_ADDRESS variable at present, a platform should not configure LPC and P2A at the same time. The platform's device-tree may have the region locked to a specific driver (lpc-aspeed-ctrl), preventing the region from other use.

NOTE: It will likely be possible to configure both LPC and P2A in the near future.

There are two kinds of PCI device-id for NPCM7xx and NPCM8xx respectively. For NPCM7xx the device-id is using 0x0750 and NPCM8xx is using 0x0850. Use this variable that can help to build host tool burn_my_bmc compatible with different platforms and make in-band firmware update work well.

If a platform enables p2a as the transport mechanism, a specific vendor must be selected via the following configuration option. Currently, only one is supported.

If a platform enables lpc as the transport mechanism, a specific vendor must be selected via the following configuration option. Currently, only two are supported.

A platform may also enable the network transport mechanism.

NOTE: This mechanism is only intended to be used in-band and not exposed externally, as it doesn't implement any encryption or integrity verification.

There are also options to control an optional clean up mechanism.

If the update mechanism desired is simply a BMC reboot, a platform can just enable that directly.

If you would like the update status to be tracked with a status file, this option can be enabled. Note that --enable-update-status option and the above --enable-reboot-update option cannot be enabled at the same time.

If you would like to use host memory access to update on a PPC platform, this configuration option needs to be enabled.

The following variables can be set to whatever you wish, however they have usable default values.

Read the details of the json configuration. The json configurations are used to configure the BMC's flash handler behaviors.

This document describes the details of the state machine implemented and how different interactions with it will respond. This also describes how a host-side tool is expected to talk to it (triggering different states and actions).