Re: [edk2-devel] [edk2-discuss] GSoC Proposal

["Marvin Häuser" <mhaeuser@posteo.de>]

Hey Brian,

On 15.04.22 18:22, Brian J. Johnson wrote:
> Nate, Andrew, Marvin, Pedro, Ada, et al,
>
> This is a great discussion.  I've been debating where to weigh in...

Personally, I don't think this topic can get enough attention. Thanks! :)

>
> I agree that some sort of library sharing to reduce image size would 
> be very helpful.  Although some parts of the BIOS are built 
> separately, large parts of it are compiled at the same time, so there 
> should be ample opportunity for tool-directed sharing.  Some form of 
> pre-linking modules together may be the easiest way to do that.  But 
> however it gets implemented, we should try to make it automatic:  
> requiring library writers to manually add a lot of metadata or write 
> thunks or shims would be a barrier to adoption.

My suggestion to use a private function array would indeed require 
shims, however this would be the "better than nothing I guess" solution 
where only the most used and most painful to duplicate functions are 
shared, e.g., memory and maybe common string printing functions. This 
would quickly and efficiently achieve the goal of "reduce size". And 
some form of sophisticated prelinking would be my proposal for something 
more systematic, which might come a lot cheaper with the security 
features to be added.

>
> I also agree that PEI has acquired far too much functionality over 
> time, and we badly need to find some way to reverse that.  PEI is 
> pulling in more and more of the h/w initialization, leaving DXE mainly 
> to provide the boot interface (ACPI, UEFI services, setup screens, 
> etc.)  That puts more and more pressure on XIP storage and 
> cache-as-RAM.  How can we encourage a change?

I'm not in the loop enough to comment on the XIP and CAR issues. 
However, HW init moving to PEI (or more generally, into a single stage) 
is not necessarily a bad thing, is it? As I've said before, I'm not sure 
what else to think of PEI than "DXE light". Both "initialise some of the 
hardware" with no clear scope boundary but with similar interfaces. If 
they were sort of fused to provide a minimal "pre-memory PEI" and a more 
DXE-like "post-memory PEI" without having a clear boundary between HW 
init steps, would that be too bad? Now I'm *really* just blindly 
guessing because I barely looked into this project, but isn't that 
somewhat the idea of SlimBootloader?

Your description of DXE sort of is it collapsing into an advanced BDS. 
Nate earlier said he'd like a clear distinction between DXE and BDS, 
which I didn't really get the point of. But if PEI consumed the HW init 
portions of DXE, a more advanced BDS (which also powers e.g. the HID 
stuff on the way) would be the logical remainder stage to separately 
support UEFI booting as a payload (for SlimBootloader, coreboot, ...).

All of that was logically speaking. Even if the development was driven 
to its extreme, PEI and DXE cores would still share a bunch of code and 
it might make sense to share a foundation technically.

Best regards,
Marvin

>
> Thanks,
> Brian J. Johnson
>
>
> On 4/15/22 03:15, Nate DeSimone wrote:
>> Hi Andrew,
>>
>> On 4/14/22, 7:43 PM, "Andrew Fish" <afish@apple.com> wrote:
>>>
>>>
>>>> On Apr 14, 2022, at 6:06 PM, Nate DeSimone 
>>>> <nathaniel.l.desimone@intel.com> wrote:
>>>>
>>>> Hi Marvin,
>>>>
>>>>> -----Original Message-----
>>>>> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Marvin
>>>>> Häuser
>>>>> Sent: Thursday, April 14, 2022 12:56 AM
>>>>> To: discuss@edk2.groups.io; Desimone, Nathaniel L
>>>>> <nathaniel.l.desimone@intel.com>
>>>>> Cc: Pedro Falcato <pedro.falcato@gmail.com>; edk2-devel-groups-io
>>>>> <devel@edk2.groups.io>; adachristine18@gmail.com; Shi, Steven
>>>>> <steven.shi@intel.com>
>>>>> Subject: Re: [edk2-devel] [edk2-discuss] GSoC Proposal
>>>>>
>>>>> I feel like there are so many much easier solutions to this 
>>>>> problem that are at
>>>>> most limited by the clear specification. The UEFI specification 
>>>>> with regards to
>>>>> booting and all of that obviously is of utmost importance.
>>>>
>>>> If you have a better idea that retains compatibility with the 
>>>> existing UEFI PI then I would be happy to hear it. Ultimately 
>>>> anything we do needs to be a pure extension that retains 
>>>> compatibility with old code. Given that restriction having the 
>>>> ability to coalesce all the LibraryClasses into a single module and 
>>>> have cross-module linking seems like the best way to handle it to me.
>>>>
>>>>> The UEFI PI specification parts that deal about internal 
>>>>> structure, as far as I know, are
>>>>> only in place to make it easy to integrate Intel IP.
>>>>
>>>> Its not just for Intel. The biggest reason for it to increase the 
>>>> standardization of the boot flow across the PC ecosystem. We have 
>>>> learned from experience that firmware is super critical to get a 
>>>> product out the door but it is also difficult to write. So we try 
>>>> to make it as reusable as humanly possible.
>>>>
>>>>> In fact, I don’t *know*, but I’m pretty sure the very strict 
>>>>> separation between PEI and DXE was
>>>>> preserved mostly because MRC was 32-bit-only for a long time. Glad 
>>>>> that
>>>>> seems to have been resolved, AMD does memory init by PSP nowadays.
>>>>
>>>> Having less complex early stages chain load more complex later 
>>>> stages is a common design pattern in firmware, not just UEFI. For 
>>>> example, your typical ARM system loads kinda like this:
>>>>
>>>> PBL (SoC ROM) --> SBL (RAM Init) --> ARM Trust Zone --> Hypervisor 
>>>> --> EDK II or U-Boot or LittleKernel (which runs android fastboot)
>>>>
>>>> Comparing relative complexity I believe the Intel UEFI PI design is 
>>>> actually pretty simple when you consider how much it gets done:
>>>>
>>>> Ucode ROM --> SEC + PEI --> DXE + SMM + BDS
>>>>
>>>> My biggest criticism of the design is that the strict separation 
>>>> between PEI and DXE doesn't exist between DXE, SMM, and BDS 😊
>>>>
>>>> There are a few reasons why PEI was 32-bit for quite some time. The 
>>>> biggest one is the code size increase, 64-bit x86 code is 20-30% 
>>>> larger than 32-bit x86 code. Since the only RAM Pre-Memory code has 
>>>> access to is the cache onboard the processor and for security 
>>>> reasons all that code has to fit within that RAM we generally do 
>>>> everything we can to make that image as small as possible. Second, 
>>>> 64-bit requires a page table and since we desired to keep PEI 
>>>> simple we tried to avoid that. Finally, the PI spec didn't allow a 
>>>> 64-bit PEI until recently. MRC is 32-bit code just because that is 
>>>> what PEI happens to be. Porting it to 64-bit is not terribly 
>>>> difficult.
>>>>
>>>> Ultimately the mix of 32/64-bit does cause some difficulties. Any 
>>>> data structures that get shared between PEI and DXE (HOBs, PCDs, 
>>>> etc.) need to resolve to the same size and packing. LibraryClasses 
>>>> need to be written to compile properly in both modes. In the case 
>>>> of FSP API mode you need to resort to thunking between 32 and 
>>>> 64-bit modes during DXE. More or less we decided that the costs are 
>>>> starting to outweigh the advantages.
>>>>
>>>
>>> I’d also point out that x86 VMs use X64 (x86-64) PEI today and it 
>>> works so the 32-bit/64-bit mix has nothing to do with UEFI/PI/edk2.
>>>
>>> In the PC ecosystem a single chipset family can power thousands of 
>>> unique designs. So the  DRAM memory needs to be external, support 
>>> lots of different chipset packages(signal integrity...), support the 
>>> lowest cost through the highest cost DRAM and thousands of different 
>>> board layouts. So programing DRAM takes a masters degree in antenna 
>>> design. I’ve seen MRC (Memory Reference Code) with over a MiB of 
>>> DEBUG prints in it, and it literally is printing histograms of what 
>>> it is tuning. So all this code has to run before the system has any 
>>> DRAM, thus it is running using the cache as RAM. I’ve not looked at 
>>> the x86 architecture specs form the vendors in a while, but back in 
>>> the day they did not support page tables in ROM or pinned cached. 
>>> Now it might work, but if it breaks your CPU vendor blames you so 
>>> you don’t code PEI in X64….
>>>
>>> We contributed the 1st edk2 ARM platform, Beagle Board, and It was a 
>>> long time ago but I seem to remember the mask ROM used a table in 
>>> NOR FLASH to init memory and then copied an image from NOR FLASH 
>>> into DRAM and jumped to it. So PEI is kind of not really needed and 
>>> we implemented a PrePEI and jumped directly to DXE.
>>>
>>> Given I was around back in the day when all this stuff was designed 
>>> I can say SEC was always a place holder for security code, as 
>>> security code always has to run 1st. PEI (Pre EFI) was designed to 
>>> get DRAM programmed and then jump to DXE. It kind of also fell in 
>>> naturally to ACPI S3 flow since that was turning memory back on. 
>>> When we designed PEI we kind of though of it more like a boot loader 
>>> stage for the firmware that turned on memory and all the work would 
>>> happen in DXE. Then reality strikes and the existing BIOS assembly 
>>> programmers start learning C (lots of  cranky people) and they start 
>>> having to learn all about PEI to turn on memory. They had to write a 
>>> big chunk of code for the memory init in PEI. These folks had never 
>>> written any EFI code, so to them it was easier to move a lot of the 
>>> chipset init code into PEI as that is the world they had to figure 
>>> out to get memory turned on. I mean why learn EFI if you don’t have 
>>> to? So that is how we get so much code in IA32 (i386) on some 
>>> platforms. This start kind of biased future choices and how to 
>>> enable non edk2 code bases….
>>
>> One of the big reasons a lot of code that should have been written in 
>> DXE ended up in PEI is unfortunately due to the FSP and its inability 
>> to support DXE code.
>>
>>>
>>> Thanks,
>>>
>>> Andrew Fish
>>>
>>>
>>>>>
>>>>> For many good reasons, Linux does not provide a stable kernel API. 
>>>>> This
>>>>> allows to easily deploy breaking changes across the entire codebase.
>>>>> Obviously, this is infeasible at a large scale when you need to 
>>>>> integrate IP
>>>>> blobs, but it would already help to break the expectation that 
>>>>> UEFI PI is a
>>>>> perfectly forwards- and backwards-compatible system. DXE has 
>>>>> SetMem and
>>>>> CopyMem as part of gBS. Maybe I don’t like it that much as part of 
>>>>> the spec
>>>>> itself, but it’s a good idea technically. I’d probably opt to have 
>>>>> a quickly
>>>>> accessible implementation detail of important function pointers 
>>>>> appended to
>>>>> PEI and DXE services, used by in-tree modules. This may break both
>>>>> forwards- and backwards-compatibility, but as it only applies to 
>>>>> in-tree
>>>>> modules, that is fine so long as we let go of the compatibility 
>>>>> notions. PPIs
>>>>> and protocols are an option too of course, but they have a lookup
>>>>> performance penalty. Compared to dynamic linking, that should 
>>>>> hopefully be
>>>>> negligible however.
>>>>>
>>>>> Absolutely optional to read, I don’t intend to waste anyone’s time 
>>>>> much,
>>>>> some philosophical stuff about my rationale:
>>>>>
>>>>> If you started UEFI from scratch right now, would it have strictly 
>>>>> separated
>>>>> PEI and DXE?
>>>>
>>>> For sure a clean slate design started today would look a lot 
>>>> different than PEI/DXE... which was a clean slate design circa 1998 
>>>> 😊. In my opinion, if we were to suddenly go back to the drawing 
>>>> board we would build something that is much closer to a full OS now 
>>>> than we did back then. There have been cases where not being able 
>>>> to use interrupt handlers and not having thread scheduling has 
>>>> prevented implementation of desired features. The ARM guys built 
>>>> LittleKernel (https://github.com/littlekernel/lk) for a lot of 
>>>> these reasons. In the data center world some have decided to go to 
>>>> the extreme of putting an entire copy of Linux in SPI so they can 
>>>> do a network boot that downloads the OS image using BitTorrent!
>>>>
>>>>> The duplication between PEI and DXE core, and by extension
>>>>> MM core, would be my most obvious place to start reducing size. I 
>>>>> would
>>>>> probably opt for a PEI/DXE hybrid where it starts in „minimal 
>>>>> mode“ (maybe
>>>>> think of PEI more like a microkernel here) and after memory is 
>>>>> initialised, the
>>>>> rest of DXE is loaded. And MM core would get no loading at all, this
>>>>> requirement has gladly been dropped ages ago. Just one prelinked 
>>>>> snapshot
>>>>> of the address space with a relocation table and a safe 
>>>>> self-relocator on entry
>>>>> (this is needed at the very least for ARM).
>>>>>
>>>>> Ironically, with my idea for MM, dynamic loading would be free as 
>>>>> everything
>>>>> is prelinked anyway. The same is true for PEI XIP, it is prelinked 
>>>>> by nature.
>>>>
>>>> Actually Post-Memory PEI can have non-prelinked PEIMs. And that 
>>>> does get used for the PEI GOP driver.
>>>>
>>>>> What I do not like is the additional dynamic linking code at 
>>>>> load-time for non-
>>>>> XIP modules. Though, the more I think about it, the more I wonder 
>>>>> whether
>>>>> not the entirety of UEFI could be composed of prelinked, relocatable
>>>>> memory snapshots without traditional image loading entirely (for 
>>>>> in-FW
>>>>> stuff). macOS has a similar concept with its “Kernel Collections”. 
>>>>> Well, way
>>>>> too much off-topic now. :)
>>>>
>>>> If you make the assumption that 100% of the code is compiled all at 
>>>> once then yes that works. UEFI was designed so that assumption does 
>>>> not need to be true. There are good use cases for it: OpROMs, 
>>>> generic OS loaders, network boot, etc.
>>>>
>>>> Thanks,
>>>> Nate
>>>>
>>>>>
>>>>> Why am I explaining all this despite the fact everyone knows this 
>>>>> will never
>>>>> happen? Because I don’t like the notion of fixing issues of an 
>>>>> already
>>>>> overcomplicated system by adding even more complicated stuff. 
>>>>> Especially
>>>>> when the existing overcomplicated stuff is already uncomfortably 
>>>>> broken.
>>>>>
>>>>> Best regards,
>>>>> Marvin
>>>>>
>>>>>> For XIP PEI code… it will really help and would be very timely 
>>>>>> since the
>>>>> transition of PEI from 32-bit to 64-bit is going to increase the 
>>>>> size of PEI by
>>>>> ~20%.
>>>>>>
>>>>>> Thanks,
>>>>>> Nate
>>>>>>
>>>>>> From: Pedro Falcato <pedro.falcato@gmail.com>
>>>>>> Sent: Wednesday, April 13, 2022 11:43 AM
>>>>>> To: edk2-devel-groups-io <devel@edk2.groups.io>; Marvin Häuser
>>>>>> <mhaeuser@posteo.de>
>>>>>> Cc: discuss@edk2.groups.io; adachristine18@gmail.com; Desimone,
>>>>>> Nathaniel L <nathaniel.l.desimone@intel.com>; Shi, Steven
>>>>>> <steven.shi@intel.com>
>>>>>> Subject: Re: [edk2-devel] [edk2-discuss] GSoC Proposal
>>>>>>
>>>>>> Hi Marvin, Ada,
>>>>>>
>>>>>> Some comments:
>>>>>>
>>>>>> I don't think the purpose of the dynamic linker is to treat EFI as a
>>>>>> complete operating system, but to try to eliminate the static 
>>>>>> linking
>>>>>> that may be needlessly duplicating code that could instead be put 
>>>>>> in a
>>>>> single dynamic library. For instance, MdePkg and MdeModulePkg are 
>>>>> linked
>>>>> into a *lot* of .efi, instead of being just a library. It'd be 
>>>>> nice to see some
>>>>> numbers on this (something like Google's bloaty could be run on 
>>>>> every .efi
>>>>> file, in order to understand how much file space we would actually 
>>>>> save).
>>>>>>
>>>>>> Other comments inline.
>>>>>>
>>>>>> On Wed, Apr 13, 2022 at 4:15 PM Marvin Häuser
>>>>> <mhaeuser@posteo.de<mailto:mhaeuser@posteo.de>> wrote:
>>>>>>
>>>>>> On 13. Apr 2022, at 16:38, Ada Christine
>>>>> <adachristine18@gmail.com<mailto:adachristine18@gmail.com>> wrote:
>>>>>> i was replying via the groups.io<http://groups.io > web 
>>>>>> interface, I'm
>>>>>> guessing that messed up the thread? i haven't used mailing lists
>>>>>> before and don't know how they work. I'll use my mail client from 
>>>>>> here on.
>>>>>>
>>>>>> I'm on board with not treating EFI as an operating system. the 
>>>>>> more i
>>>>>> think about it the more it looks like scope creep.
>>>>>>
>>>>>> Agreed.
>>>>>>
>>>>>>
>>>>>> I'm not quite as enthusiastic
>>>>>> about it as i was at first glance.
>>>>>>
>>>>>> I'm still keen on doing my gsoc proposal for edk, though, and 
>>>>>> even if
>>>>>> this task and the acpica application are decided to be out of scope
>>>>>> unit testing,
>>>>>>
>>>>>> How about fuzz-testing? This is also something edk2 needs quite 
>>>>>> badly. At
>>>>> Acidanthera, we compile edk2 code in userspace outside the edk2 build
>>>>> system and fuzz with dummy applications.
>>>>>>
>>>>>> Note: fuzzing is also part of the LLVM instrumentation suite (see
>>>>> https://llvm.org/docs/LibFuzzer.html ) and is something I could 
>>>>> happily
>>>>> mentor.
>>>>>> clang integration
>>>>>>
>>>>>> Pedro and Vitaly are looking for someone to finish ASan:
>>>>>> https://edk2.groups.io/g/devel/topic/90010978#87991
>>>>>> There are working UBSan concepts, but they also need to be 
>>>>>> mainlined.
>>>>>>
>>>>>> Is Vitaly going to be a mentor? I was assuming it was going to be 
>>>>>> me and
>>>>> some other, more senior, mentor (possibly Steven Shi, which I 
>>>>> included in
>>>>> the task).
>>>>>> Anyway, re: ASAN, if the project includes ASAN, UBSAN and possibly
>>>>>> some other sanitizer it's quite possible that it could be 
>>>>>> considered a large
>>>>> project (which means more hours but a larger stipend too). Fuzzing +
>>>>> coverage could be very nice additions to this project idea.
>>>>>> Also, is stress-testing a decent idea?
>>>>>>
>>>>>>
>>>>>> and source-level debugging are all relevant to my interests.
>>>>>>
>>>>>> how about your ideas for security stuff?
>>>>>>
>>>>>> I want the entirety of MM to leverage SmmMemLib and to support SMAP.
>>>>> SmmMemLib would then handle UEFI->MMRAM and BaseMemoryLib would
>>>>> only work on MMRAM. Also evaluation of how to best avoid pointers 
>>>>> in MM
>>>>> communication buffers would be nice.
>>>>>>
>>>>>> There also is a bunch of other stuff, like working out moving a 
>>>>>> part of
>>>>> CpuDxe into DxeCore to have memory protection live immediately, 
>>>>> memory
>>>>> protection in PEI, a replacement for the TE format (it’s buggy and 
>>>>> most
>>>>> platforms mostly abandoned it over various issues), and 
>>>>> alternatives to
>>>>> guarding critical code with SMM (like allowing NVRAM commits only 
>>>>> as part
>>>>> of a reboot).
>>>>>>
>>>>>> I personally find all of those projects very important, but I cannot
>>>>>> promise many people agree. Especially those that impose global 
>>>>>> changes
>>>>>> (most notably the TE replacement) may be very tedious to submit.
>>>>>> Gladly, I believe you can submit multiple proposals (?)
>>>>>>
>>>>>> Best regards,
>>>>>> Marvin
>>>>>>
>>>>>>
>>>>>> I'm not very knowledgeable about
>>>>>> trusted platform or secure boot but I'm willing to learn whatever is
>>>>>> necessary to get something spun up for my proposal.
>>>>>>
>>>>>> On Wed, Apr 13, 2022, 12:05 Marvin Häuser
>>>>> <mhaeuser@posteo.de<mailto:mhaeuser@posteo.de>> wrote:
>>>>>>
>>>>>>
>>>>>> Do you use the “reply all” option in your mail client? Looks like my
>>>>>> CCs have been dropped again. Comments inline.
>>>>>>
>>>>>> On 13. Apr 2022, at 12:54, Ada Christine
>>>>>> <adachristine18@gmail.com<mailto:adachristine18@gmail.com>>
>>>>>> wrote:
>>>>>> Hi, Marvin
>>>>>>
>>>>>> Its similarity to my own latest experiment is the key to what 
>>>>>> grabbed
>>>>>> my attention. I have no particular use case in mind for it, but I 
>>>>>> see
>>>>>> its potential for anybody developing larger applications in that 
>>>>>> when
>>>>>> a library is changed there's no need to distribute a new version of
>>>>>> the whole binary, just the relevant library module.
>>>>>>
>>>>>> I really do not like the trend of treating UEFI as a full-fledged 
>>>>>> OS -
>>>>>> it is not. The most used UEFI applications, OS loaders, are 
>>>>>> really not
>>>>>> that huge and are distributed as part of the OS image anyway. 
>>>>>> Even for
>>>>>> less used applications, you will always get a full snapshot anyhow.
>>>>>> Gladly we don’t have auto-update and package management yet. :)
>>>>>>
>>>>>>
>>>>>> I slept on it and it occurred to me that the whole thing could 
>>>>>> operate
>>>>>> similarly to the shell protocol in that the linker/loader is 
>>>>>> itself an
>>>>>> application that does a LoadImage() on the application needing 
>>>>>> dynamic
>>>>>> linking facilities.
>>>>>>
>>>>>> That would mean the linker itself is shipped with every application
>>>>>> that requires it? Otherwise it doesn’t make much sense for it to 
>>>>>> be an
>>>>>> app and below’s problems apply.
>>>>>>
>>>>>> If however the whole plan is making the linker as a DXE and 
>>>>>> including
>>>>>> it with the firmware, that I'm not quite as sure about. That would
>>>>>> necessarily tie any applications using dynamic linking to 
>>>>>> TianoCore or
>>>>>> any firmware distribution that derives from it.
>>>>>>
>>>>>> I think that was the idea referred to as “edk2 core” by Steven, but
>>>>>> I’d like to hear his proposal to be sure. Virtually everyone uses
>>>>>> edk2, so that itself is not the problem, but versioning is. Vendors
>>>>>> are slow to update their snapshots or have just given up doing that
>>>>>> entirely. Distributing it for external applications like OS loaders
>>>>>> would mean this can be leveraged probably no earlier than 10 years
>>>>>> from now. And for in-firmware things, I have a hard time thinking 
>>>>>> about a
>>>>> use-case that outweighs the drawbacks.
>>>>>>
>>>>>>
>>>>>> To shift the topic slightly back to GSoC, however, I'm willing to 
>>>>>> work
>>>>>> on other items on the task list. Unit testing and an ACPICA
>>>>>> application are the alternative projects I had thought about. I need
>>>>>> to choose fairly soon as the proposal deadline is next Tuesday. I 
>>>>>> know
>>>>>> a tiny bit about porting ACPICA as I also have plans to 
>>>>>> incorporate it into my
>>>>> own project.
>>>>>>
>>>>>> I have a few more ideas for security stuff, but Nate did not confirm
>>>>>> them as appropriate yet and I’m not here to drive you away from this
>>>>>> specific task (or the others). However, I’m still curious and
>>>>>> concerned. :)
>>>>>>
>>>>>> Best regards,
>>>>>> Marvin
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> -- 
>>>>>> Pedro Falcato
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
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