On Mon, Dec 11, 2023 at 12:30 PM Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx> wrote: > > On Mon, Dec 11, 2023 at 10:57:58AM +0100, Lennart Poettering wrote: > > On Fr, 08.12.23 17:59, Eric Curtin (ecurtin@xxxxxxxxxx) wrote: > > > > > Here is the boot sequence with initoverlayfs integrated, the > > > mini-initramfs contains just enough to get storage drivers loaded and > > > storage devices initialized. storage-init is a process that is not > > > designed to replace init, it does just enough to initialize storage > > > (performs a targeted udev trigger on storage), switches to > > > initoverlayfs as root and then executes init. > > > > > > ``` > > > fw -> bootloader -> kernel -> mini-initramfs -> initoverlayfs -> rootfs > > > > > > fw -> bootloader -> kernel -> storage-init -> init -----------------> > > > ``` > > > > I am not sure I follow what these chains are supposed to mean? Why are > > there two lines? > > > > So, I generally would agree that the current initrd scheme is not > > ideal, and we have been discussing better approaches. But I am not > > sure your approach really is useful on generic systems for two > > reasons: > > > > 1. no security model? you need to authenticate your initrd in > > 2023. There's no execuse to not doing that anymore these days. Not > > in automotive, and not anywhere else really. > > > > 2. no way to deal with complex storage? i.e. people use FDE, want to > > unlock their root disks with TPM2 and similar things. People use > > RAID, LVM, and all that mess. > > > > Actually the above are kinda the same problem in a way: you need > > complex storage, but if you need that you kinda need udev, and > > services, and then also systemd and all that other stuff, and that's > > why the system works like the system works right now. > > > > Whenever you devise a system like yours by cutting corners, and > > declaring that you don't want TPM, you don't want signed initrds, you > > don't want to support weird storage, you just solve your problem in a > > very specific way, ignoring the big picture. Which is OK, *if* you can > > actually really work without all that and are willing to maintain the > > solution for your specific problem only. > > > > As I understand you are trying to solve multiple problems at once > > here, and I think one should start with figuring out clearly what > > those are before trying to address them, maybe without compromising on > > security. So my guess is you want to address the following: > > > > 1. You don't want the whole big initrd to be read off disk on every > > boot, but only the parts of it that are actually needed. > > > > 2. You don't want the whole big initrd to be fully decompressed on every > > boot, but only the parts of it that are actually needed. > > > > 3. You want to share data between root fs and initrd > > > > 4. You want to save some boot time by not bringing up an init system > > in the initrd once, then tearing it down again, and starting it > > again from the root fs. > > > > For the items listed above I think you can find different solutions > > which do not necessarily compromise security as much. > > > > So, in the list above you could address the latter three like this: > > > > 2. Use an erofs rather than a packed cpio as initrd. Make the boot > > loader load the erofs into contigous memory, then use memmap=X!Y on > > the kernel cmdline to synthesize a block device from that, which > > you then mount directly (without any initrd) via > > root=/dev/pmem0. This means yout boot loader will still load the > > whole image into memory, but only decompress the bits actually > > neeed. (It also has some other nice benefits I like, such as an > > immutable rootfs, which tmpfs-based initrds don't have.) > > > > 3. Simply never transition to the root fs, don't marke the initrds in > > systemd's eyes as an initrd (specifically: don't add an > > /etc/initrd-release file to it). Instead, just merge resources of > > the root fs into your initrd fs via overlayfs. systemd has > > infrastructure for this: "systemd-sysext". It takes immutable, > > authenticated erofs images (with verity, we call them "DDIs", > > i.e. "discoverable disk images") that it overlays into /usr/. [You > > could also very nicely combine this approach with systemd's > > portable services, and npsawn containers, which operate on the same > > authenticated images]. At MSFT we have a major product that works > > exactly like this: the OS runs off a rootfs that is loaded as an > > initrd, and everything that runs on top of this are just these > > verity disk images, using overlayfs and portable services. > > > > 4. The proposal in 3 also addresses goal 4. > > > > Which leaves item 1, which is a bit harder to address. We have been > > discussing this off an on internally too. A generic solution to this > > is hard. My current thinking for this could be something like this, > > covering the UEFI world: support sticking a DDI for the main initrd in > > the ESP. The ESP is per definition unencrypted and unauthenticated, > > but otherwise relatively well defined, i.e. known to be vfat and > > discoverable via UUID on a GPT disk. So: build a minimal > > single-process initrd into the kernel (i.e. UKI) that has exactly the > > storage to find a DDI on the ESP, and set it up. i.e. vfat+erofs fs > > drivers, and dm-verity. Then have a PID 1 that does exactly enough to > > jump into the rootfs stored in the ESP. That latter then has proper > > file system drivers, storage drivers, crypto stack, and can unlock the > > real root. This would still be a pretty specific solution to one set > > of devices though, as it could not cover network boots (i.e. where > > there is just no ESP to boot from), but I think this could be kept > > relatively close, as the logic in that case could just fall back into > > loading the DDI that normally would still in the ESP fully into > > memory. > > I don't think this is "a pretty specific solution to one set of devices" > _at all_. To the contrary, it is _exactly_ what I want to see desktop > systems moving to in the future. > > It solves the problem of large firmware images. It solves the problem > of device-specific configuration, because one can use a file on the EFI > system partition that is read by userspace and either treated as > untrusted or TPM-signed. It means that one have a complete set of > recovery tools in the event of a problem, rather than being limited to > whatever one can squeese into an initramfs. One can even include a full > GUI stack (with accessibility support!), rather than just Plymouth. For > Qubes OS, one can include enough of the Xen and Qubes toolstack to even > launch virtual machines, allowing the use of USB devices and networking > for recovery purposes. It even means that one can use a FIDO2 token to > unlock the hard drive without a USB stack on the host. And because the > initramfs _only_ needs to load the boot extension volume, it can be > very, _very_ small, which works great with using Linux as a coreboot > payload. > > The only problem I can see that this does not solve is network boot, but > that is very much a niche use case when compared to the millions of > Fedora or Debian desktop installs, or even the tens of thousands of > Qubes OS installs. Furthermore, I would _much_ rather network boot be > handled by userspace and kexec, rather than the closed source UEFI network > stack. > Network boot is fairly common in some industries for workstations. In particular, the film industry does this a fair bit to leverage switching between workstation and renderfarm modes for workstation hardware. -- 真実はいつも一つ！/ Always, there's only one truth!
