On Fri, Dec 06, 2024 at 09:03:30AM +0100, Ard Biesheuvel wrote: Also cc Jan, Philipp, who are also engaged in related topic (UKI) > (cc Peter, Gerd) > > On Fri, 6 Dec 2024 at 03:10, Pingfan Liu <piliu@xxxxxxxxxx> wrote: > > > > At present, the kexec_file_load of either zboot or UKI kernel relies on > > the user space to parse and extract the Image, and then pass the Image > > through that syscall. During this process, the outmost signature on > > zboot or UKI kernel is stripped and discarded. > > > > On the other hand, a secure boot platform enforces the signature > > verfiication on the kernel image passed through the kexec_file_load > > syscall. To cater to this requirement, this patch applies signature on > > the PE format 'Image' before padding. > > > > The whole point of the EFI zboot format was avoiding the need to sign > the compressed payload. > > Now, we are back to signing the payload along with the full image > using PE based tools, even though the payload is intended to be booted > as a raw image. > I remember that I sent out a zboot image parser in the kernel to tackle with this signature issue. But that will complicate the kernel image parser, as a result, we defer resolving it, and finally we have it implemented in the user space kexec-tools. The emergence of UKI makes things more complicated. Jan introduced "UKI format parser in linux kernel". For arm64, the UKI support in kernel means that a UKI format parser should be followed by a zboot format parser. So we tried emulator solution instead of parser. ( I have a summary on: https://github.com/rhkdump/kexec_uefi/blob/main/overview.md) But either of the emulator methods have their own drawback: -1.the purgatory-style method has trouble in the hardware scaling. -2.the user space emulator can not ensure the security. (also I think it can not resolve the hardware issue since at that time, it can not alter the hardware status arbitrarily) > I'm not sure I see the point of this: EFI zboot is a trivial container > format which records the compression type and the start and length of > the payload in its header at a known offset. > > Perhaps we should just make EFI zboot gzip-only, rather than > supporting 7 different compression methods because that is what the > legacy decompressors on ARM and x86 support - I struggle to see the > point of that tbh (even though I implemented that myself) > > That way, the kernel can authenticate the outer PE zboot image as > usual, and perform the decompression itself, without having to carry > code for all compression formats it might encounter. > It is always good to keep things simple. But this seems helpless to step around the kexec_file_load issue. > (Apologies if we are sending you in circles, but if we get this wrong > now, we're stuck with another kexec-related maintenance nightmare so I > really don't want to commit to something tooo hastily) > Although this issue has come full circle, we now have a clear understanding of its solutions' limitations, advantages, and disadvantages. Unlike the forecast of this issue about three years ago, we are now facing real customer pressure. Thanks, Pingfan > -- > Ard.
