Re: NVIDIA signed firmware release format

[Ben Skeggs <skeggsb-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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On 02/18/2016 04:03 PM, Alexandre Courbot wrote:
> On 02/18/2016 02:54 PM, Ilia Mirkin wrote:
>> On Thu, Feb 18, 2016 at 12:43 AM, Alexandre Courbot
>> <acourbot-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> wrote:
>>> On 02/18/2016 02:37 PM, Ilia Mirkin wrote:
>>>>
>>>> On Thu, Feb 18, 2016 at 12:06 AM, Alexandre Courbot
>>>> <acourbot-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
>>>> wrote:
>>>>>
>>>>> On 02/18/2016 12:47 PM, Ilia Mirkin wrote:
>>>>>>
>>>>>>
>>>>>> On Wed, Feb 17, 2016 at 10:39 PM, Alexandre Courbot
>>>>>> <acourbot-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
>>>>>> wrote:
>>>>>>>
>>>>>>>
>>>>>>> Hi everyone,
>>>>>>>
>>>>>>> This email is to start a discussion about the format into which
>>>>>>> NVIDIA
>>>>>>> firmware is going to be provided. If you had a look at the
>>>>>>> linux-firmware
>>>>>>> branch we pushed earlier [1] you may already have an idea of the
>>>>>>> general
>>>>>>> organization, but this email is to discuss more specific details.
>>>>>>>
>>>>>>> Official firmware is organized per-chip, with an additional level of
>>>>>>> hierarchy for the different managed subsystems.
>>>>>>>
>>>>>>> For example, gm200 currently has two sub-directories, acr and gr,
>>>>>>> which
>>>>>>> contain the firmware files for secure boot (ACR) and PGRAPH (GR).
>>>>>>>
>>>>>>> ACR is a particular case and comes in the form of self-contained
>>>>>>> units
>>>>>>> (code, data, signature) that can be run on a high-secure falcon
>>>>>>> (currently
>>>>>>> PMU). It consumes a blob that is built by the kernel and contains
>>>>>>> the
>>>>>>> signed
>>>>>>> firmwares of the low-secure falcons to load and manage.
>>>>>>>
>>>>>>> The ACR blob is made of a header describing the managed falcons
>>>>>>> and the
>>>>>>> offses of their bootloader, code and data within the blob, as
>>>>>>> well as
>>>>>>> bootloader/code/data sections for each falcon.
>>>>>>>
>>>>>>> A signed, low-secure falcon firmware in the ACR blob is thus the
>>>>>>> aggregation
>>>>>>> of three different components:
>>>>>>>
>>>>>>> - An image containing the bl, code and data sections
>>>>>>> - A descriptor with the offsets of these sections within the image
>>>>>>> - A signature that the ACR will verify against
>>>>>>>
>>>>>>> These three components can come as files to be directly loaded.
>>>>>>> However
>>>>>>> for
>>>>>>> the current GR firmware we took the approach of splitting the bl,
>>>>>>> code
>>>>>>> and
>>>>>>> data sections into their own files, and building the image and
>>>>>>> descriptor
>>>>>>> on-the-fly, as you can see from gm200/gr:
>>>>>>>
>>>>>>> gm200/gr/fecs_bl.bin
>>>>>>> gm200/gr/fecs_data.bin
>>>>>>> gm200/gr/fecs_inst.bin
>>>>>>> gm200/gr/fecs_sig.bin
>>>>>>>
>>>>>>> The bl, data, and inst files are loaded and combined into an image
>>>>>>> while
>>>>>>> the
>>>>>>> corresponding descriptor is built. This is done in the
>>>>>>> ls_ucode_img_build()
>>>>>>> function.
>>>>>>>
>>>>>>> The main reason for doing this is there is that for a given GPU
>>>>>>> generation,
>>>>>>> the _bl and _inst files are very likely going to be exactly the
>>>>>>> same,
>>>>>>> with
>>>>>>> only the data and signature varying. Splitting the sections allow
>>>>>>> us to
>>>>>>> symlink identical files. For instance, gr/gm200 weights 61KB, while
>>>>>>> gm204/gr, which mostly symlinks to the former, only takes 8.5KB.
>>>>>>>
>>>>>>> Another advantage is that this also allows the code and data to be
>>>>>>> directly
>>>>>>> loaded via the traditional method into a fused non-secure board,
>>>>>>> although
>>>>>>> this advantage is not too relevant for the community.
>>>>>>>
>>>>>>> That's the design we took for now - it is possible to switch to a
>>>>>>> more
>>>>>>> smaller number of files per chip, and remove a bit of kernel
>>>>>>> code, at
>>>>>>> the
>>>>>>> cost of firmware footprint.
>>>>>>>
>>>>>>> I just wanted to make sure this design was ok and take any objection
>>>>>>> into
>>>>>>> account before the planned merge of the kernel support for signed
>>>>>>> firmware,
>>>>>>> hopefully next week.
>>>>>>
>>>>>>
>>>>>>
>>>>>> Since the firmware is completely separate from the kernel, you
>>>>>> need to
>>>>>> think about versioning. The firmware presents an ABI to the kernel,
>>>>>> and unless you promise to never ever ever ever ever change the ABI
>>>>>> with later updates, versioning the firmware files is something you're
>>>>>> going to have to think about. Sometimes it's done via filenames, e.g.
>>>>>> -1, -2, etc. Sometimes it's done by packing multiple data files
>>>>>> into a
>>>>>> single one, allowing the code to pick whichever one it wants.
>>>>>
>>>>>
>>>>>
>>>>> For versioning purposes, I thought about using different filenames.
>>>>> It is
>>>>> simple and effective, and since I cannot predict the scope of changes
>>>>> these
>>>>> files may undergo, it also seems to be the most flexible solution.
>>>>>
>>>>> Note that the format of files named similarly for different GPUs might
>>>>> also
>>>>> be different. What is guaranteed is that a given file will forever
>>>>> remain
>>>>> backward-compatible.
>>>>>
>>>>> There already are differences between the GM20B (Tegra) firmware files
>>>>> and
>>>>> the other GM20X due to GM20B coming from a different tree, so
>>>>> although it
>>>>> may be a little bit confusing this is a necessary evil. And it's
>>>>> not like
>>>>> we
>>>>> are not used to dealing with chip-specific ops in Nouveau anyway. :)
>>>>
>>>>
>>>> I meant more like an update for, say, GM20B, where you want to update
>>>> the ABI between the driver and the firmware. So you have the old
>>>> firmware, and now you have a new version of the same firmware, for a
>>>> particular chip...
>>>
>>>
>>> Right, so for that case GM20B can use different ops than the other
>>> GM20X to
>>> handle its firmware. And if an updated (and incompatible) firmware
>>> lands for
>>> an already existing chip, it will be recorded under a different
>>> filename.
>>> This will ensure that old kernels can keep booting forever. Or am I
>>> missing
>>> something?
>>
>> No, that works. So instead of gm20b/gr/fecs_inst.bin it'll be
>> gm20b/gr/fecs_inst-2.bin and so on?
> 
> That's what I had in mind, yes. New kernels would try to load the newest
> version, while older ones will still find the initial one.
> 
> Of course we will try to prevent this from happening too often, but it
> will be sometimes necessary (one example is if/when we release a newer
> ACR with PMU support - the kernel will use the PMU to start/reset other
> falcons instead of redoing ACR as we currently do).
> 
> In the case of fecs_inst.bin that you listed, I don't expect it to
> change, at least not in incompatible ways.
I'm also fine with the current method of shipping the firmware.
Versioned filenames seem adequate for handling incompatible ABIs also.

Thanks,
Ben.

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