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" <af...@apple.com> wrote:On Apr 14, 2022, at 6:06 PM, Nate DeSimone <nathaniel.l.desim...@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: disc...@edk2.groups.io; Desimone, Nathaniel L <nathaniel.l.desim...@intel.com> Cc: Pedro Falcato <pedro.falc...@gmail.com>; edk2-devel-groups-io <devel@edk2.groups.io>; adachristin...@gmail.com; Shi, Steven <steven....@intel.com> Subject: Re: [edk2-devel] [edk2-discuss] GSoC ProposalI 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 tobooting 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, areonly 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 thatseems 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 + BDSMy 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 FishFor many good reasons, Linux does not provide a stable kernel API. Thisallows 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 toPEI and DXE services, used by in-tree modules. This may break bothforwards- 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. PPIsand protocols are an option too of course, but they have a lookupperformance penalty. Compared to dynamic linking, that should hopefully benegligible 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 separatedPEI 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 extensionMM 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, therest of DXE is loaded. And MM core would get no loading at all, thisrequirement 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 whethernot the entirety of UEFI could be composed of prelinked, relocatablememory snapshots without traditional image loading entirely (for in-FW stuff). macOS has a similar concept with its “Kernel Collections”. Well, waytoo 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, NateWhy 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, MarvinFor XIP PEI code… it will really help and would be very timely since thetransition of PEI from 32-bit to 64-bit is going to increase the size of PEI by~20%.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).Thanks, Nate From: Pedro Falcato <pedro.falc...@gmail.com> Sent: Wednesday, April 13, 2022 11:43 AM To: edk2-devel-groups-io <devel@edk2.groups.io>; Marvin Häuser <mhaeu...@posteo.de> Cc: disc...@edk2.groups.io; adachristin...@gmail.com; Desimone, Nathaniel L <nathaniel.l.desim...@intel.com>; Shi, Steven <steven....@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 acomplete operating system, but to try to eliminate the static linking that may be needlessly duplicating code that could instead be put in aOther comments inline. On Wed, Apr 13, 2022 at 4:15 PM Marvin Häuser<mhaeu...@posteo.de<mailto:mhaeu...@posteo.de>> wrote:On 13. Apr 2022, at 16:38, Ada Christine<adachristin...@gmail.com<mailto:adachristin...@gmail.com>> wrote:i was replying via the groups.io<http://groups.io > web interface, I'mguessing that messed up the thread? i haven't used mailing listsbefore 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 ithink 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 ifthis 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. AtAcidanthera, we compile edk2 code in userspace outside the edk2 build system and fuzz with dummy applications.https://llvm.org/docs/LibFuzzer.html ) and is something I could happilyNote: fuzzing is also part of the LLVM instrumentation suite (seementor.some other, more senior, mentor (possibly Steven Shi, which I included inclang integration Pedro and Vitaly are looking for someone to finish ASan: https://edk2.groups.io/g/devel/topic/90010978#87991There 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 andthe task).Anyway, re: ASAN, if the project includes ASAN, UBSAN and possiblysome other sanitizer it's quite possible that it could be considered a largeproject (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 wouldonly work on MMRAM. Also evaluation of how to best avoid pointers in MMcommunication buffers would be nice.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 partThere also is a bunch of other stuff, like working out moving a part ofof a reboot).I personally find all of those projects very important, but I cannotpromise 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<mhaeu...@posteo.de<mailto:mhaeu...@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 <adachristin...@gmail.com<mailto:adachristin...@gmail.com>> wrote: Hi, MarvinIts 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 whena 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 forless 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 dynamiclinking facilities. That would mean the linker itself is shipped with every applicationthat requires it? Otherwise it doesn’t make much sense for it to be anapp and below’s problems apply.If however the whole plan is making the linker as a DXE and includingit with the firmware, that I'm not quite as sure about. That wouldnecessarily tie any applications using dynamic linking to TianoCore orany 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 yearsfrom now. And for in-firmware things, I have a hard time thinking about ause-case that outweighs the drawbacks.To shift the topic slightly back to GSoC, however, I'm willing to workon other items on the task list. Unit testing and an ACPICA application are the alternative projects I had thought about. I needto 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 myown 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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