Re: [PATCH 0/6] arm64: make kexec_file able to load zboot image

[Ard Biesheuvel]

(cc Mark)

Hello Pingfan,

Thanks for working on this.

On Mon, 6 Mar 2023 at 04:03, Pingfan Liu <kernelfans@xxxxxxxxx> wrote:
>
> After introducing zboot image, kexec_file can not load and jump to the
> new style image. Hence it demands a method to load the new kernel.
>
> The crux of the problem lies in when and how to decompress the Image.gz.
> There are three possible courses to take: -1. in user space, but hard to
> achieve due to the signature verification inside the kernel.

That depends. The EFI zboot image encapsulates another PE/COFF image,
which could be signed as well.

So there are at least three other options here:
- sign the encapsulated image with the same key as the zboot image
- sign the encapsulated image with a key that is only valid for kexec boot
- sign the encapsulated image with an ephemeral key that is only valid
for a kexec'ing an image that was produced by the same kernel build

>  -2. at the
> boot time, let the efi_zboot_entry() handles it, which means a simulated
> EFI service should be provided to that entry, especially about how to be
> aware of the memory layout.

This is actually an idea I intend to explore: with the EFI runtime
services regions mapped 1:1, it wouldn't be too hard to implement a
minimal environment that can run the zboot image under the previous
kernel up to the point where it call ExitBootServices(), after which
kexec() would take over.

>  -3. in kernel space, during the file load
> of the zboot image. At that point, the kernel masters the whole memory
> information, and easily allocates a suitable memory for the decompressed
> kernel image. (I think this is similar to what grub does today).
>

GRUB just calls LoadImage(), and the decompression code runs in the EFI context.

> The core of this series is [5/6].  [3,6/6] handles the config option.
> The assumption of [3/6] is kexec_file_load is independent of zboot,
> especially it can load kernel images compressed with different
> compression method.  [6/6] is if EFI_ZBOOT, the corresponding
> decompression method should be included.
>
>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Cc: kexec@xxxxxxxxxxxxxxxxxxx
> To: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> To: linux-kernel@xxxxxxxxxxxxxxx
>
> Pingfan Liu (6):
>   arm64: kexec: Rename kexec_image.c to kexec_raw_image.c
>   lib/decompress: Introduce decompress_method_by_name()
>   arm64: Kconfig: Pick decompressing method for kexec file load
>   lib/decompress: Keep decompress routines based on selection
>   arm64: kexec: Introduce zboot image loader
>   init/Kconfig: Select decompressing method if compressing kernel
>
>  arch/arm64/Kconfig                            |  59 ++++++
>  arch/arm64/include/asm/kexec.h                |   4 +-
>  arch/arm64/kernel/Makefile                    |   2 +-
>  .../{kexec_image.c => kexec_raw_image.c}      |   2 +-
>  arch/arm64/kernel/kexec_zboot_image.c         | 186 ++++++++++++++++++
>  arch/arm64/kernel/machine_kexec.c             |   1 +
>  arch/arm64/kernel/machine_kexec_file.c        |   3 +-
>  include/linux/decompress/generic.h            |   2 +
>  include/linux/decompress/mm.h                 |   9 +-
>  include/linux/zboot.h                         |  26 +++
>  init/Kconfig                                  |   7 +
>  lib/Kconfig                                   |   3 +
>  lib/decompress.c                              |  17 +-
>  13 files changed, 314 insertions(+), 7 deletions(-)
>  rename arch/arm64/kernel/{kexec_image.c => kexec_raw_image.c} (98%)
>  create mode 100644 arch/arm64/kernel/kexec_zboot_image.c
>  create mode 100644 include/linux/zboot.h
>
> --
> 2.31.1
>