Re: [TF-A] Proposal: TF-A to adopt hand-off blocks (HOBs) for information passing between boot stages
Adding Andrea
On Wed, 24 Mar 2021 at 13:55, Joanna Farley via TF-A < tf-a@lists.trustedfirmware.org> wrote:
Hi Harb and others,
This thread is now multi-mailing list and I can see some broader needs and opinions on aspects not directly defined by the TF-A project such as differing information exchange formats. However, this is definitely something the TF-A project can try and help provide enablement for to help with the goal of supplying support for single or common TF-A binaries builds for different images. TF-A already have some limited support in this space and are considering how this can be extended given some of the needs expressed here. Folks on the TF-A project are studying the below and will propose soon some ideas on how TF-A could provide more versatile enablement in this space shortly.
Thanks
Joanna
*From: *TF-A tf-a-bounces@lists.trustedfirmware.org on behalf of François Ozog via TF-A tf-a@lists.trustedfirmware.org *Reply to: *François Ozog francois.ozog@linaro.org *Date: *Wednesday, 24 March 2021 at 08:34 *To: *Harb Abdulhamid OS abdulhamid@os.amperecomputing.com *Cc: *"tf-a@lists.trustedfirmware.org" tf-a@lists.trustedfirmware.org, Simon Glass sjg@chromium.org, Boot Architecture Mailman List < boot-architecture@lists.linaro.org>, Paul Isaac's paul.isaacs@linaro.org, Ron Minnich rminnich@google.com *Subject: *Re: [TF-A] Proposal: TF-A to adopt hand-off blocks (HOBs) for information passing between boot stages
On Tue, 23 Mar 2021 at 23:39, Harb Abdulhamid OS < abdulhamid@os.amperecomputing.com> wrote:
Hello Folks,
Appreciate the feedback and replies on this. Glad to see that there is interest in this topic. 😊
I try to address the comments/feedback from Francois and Simon below….
@François Ozog francois.ozog@linaro.org – happy to discuss this on a zoom call. I will make that time slot work, and will be available to attend April 8, 4pm CT.
Note that I’m using the term “HOB” here more generically, as there are typically vendor specific structures beyond the resource descriptor HOB, which provides only a small subset of the information that needs to be passed between the boot phases.
The whole point here is to provide mechanism to develop firmware that we can build ARM Server SoC’s that support **any** BL33 payload (e.g. EDK2, AptioV, CoreBoot, and maybe even directly boot strapping LinuxBoot at some point). In other-words, we are trying to come up with a TF-A that would be completely agnostic to the implementation of BL33 (i.e. BL33 is built completely independently by a separate entity – e.g. an ODM/OEM).
Keep in mind, in the server/datacenter market segment we are not building vertically integrated systems with a single entity compiling firmware/software stacks like most folks in TF-A have become use to. There are two categories of higher level firmware code blobs in the server/datacenter model:
- “SoC” or “silicon” firmware – in TF-A this may map to BL1, BL2,
BL31, and **possibly** one or more BL32 instances 2. “Platform” or “board” firmware – in TF-A this may map to BL33 and * *possibly** one or more BL32 instances.
Even the platform firmware stack could be further fragmented by having multiple entities involved in delivering the entire firmware stack: IBVs, ODMs, OEMs, CSPs, and possibly even device vendor code.
To support a broad range of platform designs with a broad range of memory devices, we need a crisp and clear contract between the SoC firmware that initializes memory (e.g. BL2) and how that platform boot firmware (e.g. BL33) gathers information about what memory that was initialized, at what speeds, NUMA topology, and many other relevant information that needs to be known and comprehended by the platform firmware and eventually by the platform software.
I understand the versatility of DT, but I see two major problems with DT:
- DT requires more complicated parsing to get properties, and even
more complex to dynamically set properties – this HOB structures may need to be generated in boot phases where DDR is not available, and therefore we will be extremely memory constrained.
- DT is probably overkill for this purpose – We really just want a
list of pointers to simple C structures that code cast (e.g. JEDEC SPD data blob)
I think that we should not mix the efforts around DT/ACPI specs with what we are doing here, because those specs and concepts were developed for a completely different purpose (i.e. abstractions needed for OS / RTOS software, and not necessarily suitable for firmware-to-firmware hand-offs).
Frankly, I would personally push back pretty hard on defining SMC’s for something that should be one way information passing. Every SMC we add is another attack vector to the secure world and an increased burden on the folks that have to do security auditing and threat analysis. I see no benefit in exposing these boot/HOB/BOB structures at run-time via SMC calls.
Please do let me know if you disagree and why. Look forward to discussing on this thread or on the call.
I am not tied to a particular data representation and using SMC to just pass data structures is overkill as you say. The SMC model seems useful to do complex things like device assignment to secure world. Or something else we don't have yet an idea.
Let's say there is one board with two eMMCs. This board is used by two OEMs. One is fine with all eMMCs in non-secure world, the other wants to assign the eMMC to secure world.
That's something that is related to inter-firmware component communication to be authoritative.
We need to avoid "little arrangements between friends" that exist today, where the Linux provided DT is pruned from the second eMMC to accommodate the use case. We need to think the OS as "immutable" across platforms and adapt to available hardware (not come with its own description of what the board is).
May be a hob would contain a DT overlay or ACPI equivalent that would do the job.
In that case we do not need SMC.
What do you think of this use case?
@Simon Glass sjg@chromium.org - Thanks for the pointer to bloblist. I briefly reviewed and it seems like a good baseline for what we may be looking for.
That being said, I would say that there is some benefit in having some kind of unique identifiers (e.g. UUID or some unique signature) so that we can tie standardized data structures (based on some future TBD specs) to a particular ID. For example, if the TPM driver in BL33 is looking for the TPM structure in the HOB/BOB list, and may not care about the other data blobs. The driver needs a way to identify and locate the blob it cares about.
I guess we can achieve this with the tag, but the problem with tag when you have eco-system with a lot of parties doing parallel development, you can end up with tag collisions and folks fighting about who has rights to what tag values. We would need some official process for folks to register tags for whatever new structures we define, or maybe some tag range for vendor specific structures. This comes with a lot of pain and bureaucracy. On the other hand, UUID has been a proven way to make it easy to just define your own blobs with **either** standard or vendor specific structures without worry of ID collisions between vendors.
We can probably debate whether there is any value in GUID/UUID or not during the call… but again, boblist seems like a reasonable starting point as an alternative to HOB.
Thanks,
--Harb
*From:* François Ozog francois.ozog@linaro.org *Sent:* Tuesday, March 23, 2021 10:00 AM *To:* François Ozog francois.ozog@linaro.org; Ron Minnich < rminnich@google.com>; Paul Isaac's paul.isaacs@linaro.org *Cc:* Simon Glass sjg@chromium.org; Harb Abdulhamid OS < abdulhamid@os.amperecomputing.com>; Boot Architecture Mailman List < boot-architecture@lists.linaro.org>; tf-a@lists.trustedfirmware.org *Subject:* Re: [TF-A] Proposal: TF-A to adopt hand-off blocks (HOBs) for information passing between boot stages
+Ron Minnich rminnich@google.com +Paul Isaac's paul.isaacs@linaro.org
Adding Ron and Paul because I think this interface should be also benefiting LinuxBoot efforts.
On Tue, 23 Mar 2021 at 11:17, François Ozog via TF-A < tf-a@lists.trustedfirmware.org> wrote:
Hi,
I propose we cover the topic at the next Trusted Substrate https://collaborate.linaro.org/display/TS/Trusted+Substrate+Home zoom call https://linaro-org.zoom.us/j/94563644892 on April 8th 4pm CET.
The agenda:
ABI between non-secure firmware and the rest of firmware (EL3, S-EL1, S-EL2, SCP) to adapt hardware description to some runtime conditions.
runtime conditions here relates to DRAM size and topology detection, secure DRAM memory carvings, PSCI and SCMI interface publishing.
For additional background on existing metadata: UEFI Platform Initialization Specification Version 1.7 https://uefi.org/sites/default/files/resources/PI_Spec_1_7_final_Jan_2019.pdf , 5.5 Resource Descriptor HOB
Out of the ResourceType we care about is EFI_RESOURCE_SYSTEM_MEMORY.
This HOB lacks memory NUMA attachment or something that could be related to fill SRAT table for ACPI or relevant DT proximity domains.
HOB is not consistent accros platforms: some platforms (Arm) lists memory from the booting NUMA node, other platforms (x86) lists all memory from all NUMA nodes. (At least this is the case on the two platforms I tested).
There are two proposals to use memory structures from SPL/BLx up to the handover function (as defined in the Device Tree technical report https://docs.google.com/document/d/1CLkhLRaz_zcCq44DLGmPZQFPbYHOC6nzPowaL0XmRk0/edit?usp=sharing) which can be U-boot (BL33 or just U-Boot in case of SPL/U-Boot scheme) or EDK2.
I would propose we also discuss possibility of FF-A interface to actually query information or request actions to be done (this is a model actually used in some SoCs with proprietary SMC calls).
Requirements (to be validated):
ACPI and DT hardware descriptions.
agnostic to boot framework (SPL/U-Boot, TF-A/U-Boot, TF-A/EDK2)
agnostic to boot framework (SPL/U-Boot, TF-A/U-Boot, TF-A/EDK2,
TF-A/LinuxBoot)
- at least allows complete DRAM description and "persistent" usage
(reserved areas for secure world or other usages)
- support secure world device assignment
Cheers
FF
On Mon, 22 Mar 2021 at 19:56, Simon Glass sjg@chromium.org wrote:
Hi,
Can I suggest using bloblist for this instead? It is lightweight, easier to parse, doesn't have GUIDs and is already used within U-Boot for passing info between SPL/U-Boot, etc.
Docs here: https://github.com/u-boot/u-boot/blob/master/doc/README.bloblist Header file describes the format: https://github.com/u-boot/u-boot/blob/master/include/bloblist.h
Full set of unit tests: https://github.com/u-boot/u-boot/blob/master/test/bloblist.c
Regards, Simon
On Mon, 22 Mar 2021 at 23:58, François Ozog francois.ozog@linaro.org wrote:
+Boot Architecture Mailman List boot-architecture@lists.linaro.org
standardization is very much welcomed here and need to accommodate a very diverse set of situations. For example, TEE OS may need to pass memory reservations to BL33 or "capture" a device for the secure world.
I have observed a number of architectures:
- pass information from BLx to BLy in the form of a specific object
- BLx called by BLy by a platform specific SMC to get information
- BLx called by BLy by a platform specific SMC to perform Device Tree
fixups
I also imagined a standardized "broadcast" FF-A call so that any firmware element can either provide information or "do something".
My understanding of your proposal is about standardizing on architecture
with the HOB format.
The advantage of the HOB is simplicity but it may be difficult to
implement
schemes such as pruning a DT because device assignment in the secure
world.
In any case, it looks feasible to have TF-A and OP-TEE complement the
list
of HOBs to pass information downstream (the bootflow).
It would be good to start with building the comprehensive list of information that need to be conveyed between firmware elements:
information. | authoritative entity | reporting entity | information exchanged: dram | TFA | TFA | <format to be detailed, NUMA topology to build the SRAT table or DT equivalent?> PSCI | SCP | TFA? | SCMI | SCP or TEE-OS | TFA? TEE-OS?| secure SRAM | TFA. | TFA. | secure DRAM | TFA? TEE-OS? | TFA? TEE-OS? | other? | | |
Cheers
FF
On Mon, 22 Mar 2021 at 09:34, Harb Abdulhamid OS via TF-A < tf-a@lists.trustedfirmware.org> wrote:
Hello Folks,
I'm emailing to start an open discussion about the adoption of a
concept
known as "hand-off blocks" or HOB to become a part of the TF-A Firmware Framework Architecture (FFA). This is something that is a pretty major pain point when it comes to the adoption of TF-A in ARM Server SoC’s designed to enable a broad range of highly configurable datacenter platforms.
What is a HOB (Background)?
UEFI PI spec describes a particular definition for how HOB may be used
for
transitioning between the PEI and DXE boot phases, which is a good reference point for this discussion, but not necessarily the exact
solution
appropriate for TF-A.
A HOB is simply a dynamically generated data structure passed in
between
two boot phases. This is information that was obtained through
discovery
and needs to be passed forward to the next boot phase *once*, with no
API
needed to call back (e.g. no call back into previous firmware phase is needed to fetch this information at run-time - it is simply passed one
time
during boot).
There may be one or more HOBs passed in between boot phases. If there
are
more than one HOB that needs to be passed, this can be in a form of a
"HOB
table", which (for example) could be a UUID indexed array of pointers
to
HOB structures, used to locate a HOB of interest (based on UUID). In
such
cases, instead of passing a single HOB, the boot phases may rely on
passing
the pointer to the HOB table.
This has been extremely useful concept to employ on highly configurable systems that must rely on flexible discovery mechanisms to initialize
and
boot the system. This is especially helpful when you have multiple
Why do we need HOBs in TF-A?:
It is desirable that EL3 firmware (e.g. TF-A) built for ARM Server SoC
in
a way that is SoC specific *but* platform agnostic. This means that a single ARM SoC that a SiP may deliver to customers may provide a single TF-A binary (e.g. BL1, BL2, BL31) that could be used to support a broad range of platform designs and configurations in order to boot a
platform
specific firmware (e.g. BL33 and possibly even BL32 code). In order to achieve this, the platform configuration must be *discovered* instead
of
statically compiled as it is today in TF-A via device tree based enumeration. The mechanisms of discovery may differ broadly depending
on
the relevant industry standard, or in some cases may have rely on SiP specific discovery flows.
For example: On server systems that support a broad range DIMM memory population/topologies, all the necessary information required to boot
is
fully discovered via standard JEDEC Serial Presence Detect (SPD) over
an
I2C bus. Leveraging the SPD bus, may platform variants could be
supported
with a single TF-A binary. Not only is this information required to initialize memory in early boot phases (e.g. BL2), the subsequent boot phases will also need this SPD info to construct a system physical
address
map and properly initialize the MMU based on the memory present, and
where
the memory may be present. Subsequent boot phases (e.g. BL33 / UEFI)
may
need to generate standard firmware tables to the operating systems,
such as
SMBIOS tables describing DIMM topology and various ACPI tables (e.g.
SLIT,
SRAT, even NFIT if NVDIMM's are present).
In short, it all starts with a standardized or vendor specific
discovery
flow in an early boot stage (e.g. BL1/BL2), followed by the passing of information to the next boot stages (e.g. BL31/BL32/BL33).
Today, every HOB may be a vendor specific structure, but in the future there may be benefit of defining standard HOBs. This may be useful for memory discovery, passing the system physical address map, enabling TPM measured boot, and potentially many other common HOB use-cases.
It would be extremely beneficial to the datacenter market segment if
the
TF-A community would adopt this concept of information passing between
all
boot phases as opposed to rely solely on device tree enumeration.
This is
not intended to replace device tree, rather intended as an alternative
way
to describe the info that must be discovered and dynamically generated.
Conclusion:
We are proposing that the TF-A community begin pursuing the adoption of HOBs as a mechanism used for information exchange between each boot
stage
(e.g. BL1->BL2, BL2->BL31, BL31->BL32, and BL31->BL33)? Longer term we want to explore standardizing some HOB structures for the BL33 phase
(e.g.
UEFI HOB structures), but initially would like to agree on this being a useful mechanism used to pass information between each boot stage.
Thanks,
--Harb
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Bill Fletcher