On Fri, Jun 29, 2018 at 11:03 AM Grant Likely grant.likely@arm.com wrote:
Special care is needed when storage is shared between firmware and the OS. Add a chapter that discusses the issues and puts down the requirements for using shared storage.
Resolves: #19
Cc: Daniel Thompson daniel.thompson@linaro.org Signed-off-by: Grant Likely grant.likely@arm.com
source/chapter2-uefi.rst | 44 ------ source/chapter4-firmware-media.rst | 267 +++++++++++++++++++++++++++++++++++++ source/index.rst | 1 + 3 files changed, 268 insertions(+), 44 deletions(-) create mode 100644 source/chapter4-firmware-media.rst
diff --git a/source/chapter2-uefi.rst b/source/chapter2-uefi.rst index 07426a4..05230d2 100644 --- a/source/chapter2-uefi.rst +++ b/source/chapter2-uefi.rst @@ -56,50 +56,6 @@ System Volume Format The system firmware must support all partitioning standards required by the UEFI specification.
-On systems where the system firmware binaries reside on the System Volume then -the System Volume must be pre-configured with a partition table and include -protective partitions to reduce risk of accidental destruction of the system -firmware.
-All pre-installed partition tables must use GPT partitioning unless -some immutable feature of the platform (such as a mask programmed boot ROM) -makes this impossible; on such platforms MBR partitioning may be -used as an alternative.
-GPT partitioning -^^^^^^^^^^^^^^^^
-Any pre-installed partition table must strictly conform to the UEFI -specification and include a protective MBR authored exactly as -described in UEFI specification (hybrid partitioning schemes are not -permitted).
-Pre-installed protective partitions must have the Platform Required -Attribute Flag set.
-It is recommended that automatic system disk partitioning utilities -preserve Platform Required partitions as is, and that manual disk -partitioning utilities provide warnings and/or other safe guards to -reduce risk of accidental removal.
-MBR partitioning -^^^^^^^^^^^^^^^^
-Pre-installed protective partitions should have a partition type of 0xF8 -unless some immutable feature of the platform makes this impossible.
-It is recommended that disk partitioning utilities treat such -partitions in the same manner as GPT partitions with the Platform -Required Attribute Flag set.
-It is recommended that pre-installed protective partitions that are not -type 0xF8 be located wholly within 1MB of the start of the disk.
-Automatic disk partitioning utilities shall not create partitions -within 1MB of the start of the disk. Manual disk partitioning -utilities should avoid recommending that partitions start within -1MB of the start of the disk.
UEFI Boot Services
diff --git a/source/chapter4-firmware-media.rst b/source/chapter4-firmware-media.rst new file mode 100644 index 0000000..f8a03db --- /dev/null +++ b/source/chapter4-firmware-media.rst @@ -0,0 +1,267 @@ +**************** +Firmware Storage +****************
+In general, it is recommended for all platforms to store firmware images +and data on a dedicated storage device which is not accessed by the operating +system. +It is common practice to boot firmware out of a dedicated SPI flash, +while the OS is loaded from another source, whether it be SATA, SD, USB, +Network boot, or something else.
+However, many embedded systems have size, cost, or usage constraints that +make separate firmware storage unfeasible. +On such systems, firmware and the OS reside on the same media.
+Some shared media provides dedicate boot regions, but in many cases
dedicated
perhaps an "(e.g. eMMC)"
+firmware needs to reside in a normal region of storage. +Care must be taken to ensure firmware kept in normal storage does not +conflict with normal usage of the media by an OS.
+* Firmware must be stored on the media in a way that does not conflict
- with normal partitioning and usage by the operating system.
+* Normal operation of the OS must not interfere with firmware files +* Firmware needs a method to modify variable storage at runtime while the
- OS controls access to the device
+Partitioning of Shared Storage +==============================
+Shared storage must use GPT partitioning unless the storage media provides +device-native partitioning [#UFSparts]_, +or if an immutable property of the platform (ex. the masked boot ROM) +is incompatible with the SoC boot ROM). +MBR partitioning shall be used when the platform is incompatible with GPT.
s/when/only when/ ? Though perhaps the rest below is strong enough.
+.. warning::
- MBR partitioning is deprecated and only included for legacy support.
- All new platforms are expected to use either GPT or device-native
- partitioning.
- GPT partitioning supports a much larger number of partitions, and
- has build in redundancy by storing two copies of the partition table.
built in
- A future issue of this specification will remove the MBR allowance.
+All firmware images and data stored in normal media should be contained +in a regular partition,
Only 1 allowed?
+which can either be a dedicated firmware partition, +or the UEFI System Partition (ESP).
+The system should locate firmware by reading the partition table. +Using a fixed offset into the storage media is deprecated and should not +be used for new SoC designs. +If a fixed offset is required by the hardware, then it is strongly recommended +for the firmware location to be covered by a protective partition to protect +against accidentally overwriting system firmware.
+.. warning::
- Fixed offsets to firmware data is supported only for legacy reasons.
- All new platforms are expected to use partitions to locate firmware files.
- A future issues of this specification will disallow the use of fixed
- offsets.
+GPT partitioning +----------------
+Any pre-installed partition table must strictly conform to the UEFI +specification and include a protective MBR authored exactly as +described in UEFI specification (hybrid partitioning schemes are not +permitted).
Section number?
+Pre-installed protective partitions must have the Platform Required +Attribute Flag set.
+It is recommended that automatic system disk partitioning utilities +preserve Platform Required partitions as is, and that manual disk +partitioning utilities provide warnings and/or other safe guards to +reduce risk of accidental removal.
+The system should locate firmware images by searching for partitions with +the following UUIDs in order:
+.. table::
- ==================================== ======== ========================
- UUID Priority Description
- ==================================== ======== ========================
- Vendor defined UUID 1 (Not recommended)
Proprietary vendordedicated firmwarepartition. Should onlybe used if firmwarecannot use a FATfilesystem.- TBD 2 EBBR compliant dedicated
firmware partition- C12A7328-F81F-11D2-BA4B-00A0C93EC93B 3 UEFI System Partition
as defined inUEFI ยง 5.3.3- ==================================== ======== ========================
+.. note::
- Should the vendor defined UUID be included in this table at all?
+MBR partitioning +^^^^^^^^^^^^^^^^
+Pre-installed protective partitions should have a partition type of 0xF8 +unless some immutable feature of the platform makes this impossible.
+It is recommended that disk partitioning utilities treat such +partitions in the same manner as GPT partitions with the Platform +Required Attribute Flag set.
+It is recommended that pre-installed protective partitions that are not +type 0xF8 be located wholly within 1MB of the start of the disk.
+Automatic disk partitioning utilities shall not create partitions +within 1MB of the start of the disk. Manual disk partitioning +utilities should avoid recommending that partitions start within +1MB of the start of the disk.
+.. [#UFSParts] For example, Universal Flash Storage (UFS) provides
- device-native partitioning and does not require a discrete MBR or
- GPT partition table.
+Firmware Partition Filesystem +=============================
Do we need to clarify what firmware this is? Do we want or care if say WiFi firmware is here.
+Where possible, firmware images and data should be stored in a filesystem. +Firmware can be stored either in a dedicated firmware partition, +or in certain circumstances in the UEFI System Partition (ESP). +Using a filesystem makes it simpler to manage multiple firmware file and
s/file/files/
+makes it possible for a single disk image to contain firmware for multiple +platforms.
+Dedicated firmware partitions are recommended to be formatted with a FAT +filesystem as defined by the UEFI specification. +However, dedicated firmware partition must not be used as an ESP. +EFI binaries in a dedicated firmware partition should be ignored +by default.
+When firmware is stored in the ESP, the ESP must contain a partition named +``/FIRMWARE`` in the root directory. +Dedicated firmware partitions should use the same ``/FIRMWARE`` hierarchy. +All firmware images and data must be stored in platform vendor +subdirectories under ``/FIRMWARE``.
+Vendors may choose their own subdirectory name under ``/FIRMWARE``, +but must choose names the do not conflict with other vendors. +Normally the vendor name will be the name of the SoC vendor, because the +firmware directory name will be hard coded in the SoC's boot ROM. +Vendors are recommended to use their Devicetree vendor prefix as their
s/Devicetree/DeviceTree/
Perhaps the whole doc needs a consistency check. I'll check if I don't get distracted...
+vendor subdirectory name.
+Vendors are free to decide how to structure subdirectories under their +own vendor directory, but they must use a naming convention that allows +multiple SoCs to be supported in the same filesystem.
+For example, a vendor named Acme with two SoCs, ACME100 & AM300, could +choose to use the SoC part number as a subdirectory in the firmware path::
- /FIRMWARE
- /ACME
I guess originally vendor prefixes were upper case ticker symbols, but these days most are lower case. So is this the vendor prefix as-is or converted to uppercase.
/ACME100fw.img/ACME300fw.img+It is also recommended for dedicated firmware partitions to use the +``/FIRMWARE`` file hierarchy.
Including the FIRMWARE part or just below it?
+The following is a sample directory structure for firmware files::
- /FIRMWARE
- /<Vendor 1 Directory>
/<SoC A Directory><Firmware image><Firmware data>/<SoC B Directory><Firmware image><Firmware data>- /<Vendor 2 Directory>
<Common Firmware image><Common Firmware data>- /<Vendor 3 Directory>
/<SoC E Directory><Firmware image>+Operating systems and installers should not manipulate any files in the +``/FIRMWARE`` hierarchy during normal operation.
+.. todo:
- Recommend failover A/B image layout to protect against corrupted
firmware.
- Define firmware update procedure. In what circumstances could an
OS automatically update firmware files in ``/FIRMWARE``?+The sections below discuss the requirements when using both fixed and +removable storage. +However, it should be noted that the recommended behaviour of firmware +should be identical regardless of storage type. +In both cases, the recommended boot sequence is to first search for firmware +in a dedicated firmware partition, and second search for firmware in the +ESP. +The only difference between fixed and removable storage is the recommended +factory settings for the platform.
+Fixed Shared Storage +--------------------
+Fixed storage is storage that is permanently attached to the platform, +and cannot be moved between systems. +eMMC and Universal Flash Storage (UFS) device are often used as +shared fixed storage for both firmware and the OS.
+Where possible, it is prefered for the system to boot from a dedicated boot +region on media that provides one (ex. eMMC) that is sufficiently large. +Otherwise, the platform storage should be pre-formatted in the factory with +a partition table, a dedicated firmware partition, and firmware binaries +installed.
+Operating systems must not use the dedicated firmware partition,
What does 'use' mean? Installing f/w updates would be using.
+but shall instead create a normal ESP for installing the EFI applications +including the OS loader.
To clarify, I'd rearrange like this:
Operating systems must not use the dedicated firmware partition for installing the EFI applications including the OS loader or OS specific files, but shall instead create a normal ESP.
+OS partitioning tools must take care not to modify or delete dedicated +firmware partitions.
+Removable Shared Storage +------------------------
+Removable storage is any media that can be physically removed from +the system and moved to another machine as part of normal operation +(ex. SD cards, USB thumb drives, and CDs).
+There are two primary scenarios for storing firmware on removable media.
+1. Platforms that only have removable media (ex. The Raspberry Pi has an
- SD card slot, but no fixed storage).
+2. Recovery when on-board firmware has been corrupted. If firmware on
- fixed media has been corrupted, some platforms support loading firmware
- from removable media which can then be used to recover the platform.
+In both cases, it is desirable to start with a stock OS boot image, +copy it to the media (SD or USB), and then add the necessary firmware files +to make the platform bootable. +Typically, OS boot images won't include a dedicated firmware partition, +and it is inconvenient to repartition the media to add one. +It is simpler and easier for the user if they are able to copy +the required firmware files into the ``/FIRMWARE`` directory tree on the ESP +using the basic file manager tools provided by all desktop operating systems.
+On removable media, firmware should be stored in the ESP under the +``/FIRMWARE`` directory structure as described above.
Perhaps an anchor and reference instead of "above".
+Platform vendors should support their platform by providing a single +.zip file that places all the required firmware files in the correct +locations when extracted in the ESP ``/FIRMWARE`` directory. +For simplicity sake, it is expected the same .zip file will recover the +firmware files in a dedicated firmware partition.
Do we really care if it is a .zip file vs. some other archive format? I guess it is a case of if we don't specify it, we'll get to deal with all the possibilities needlessly.
Doesn't this also apply for fixed shared storage for firmware updates (or does capsule update define something already)?
Rob