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

Hi Ard,

Thanks for sharing your idea. Please see the comment.

On Mon, Mar 06, 2023 at 09:08:03AM +0100, Ard Biesheuvel wrote:

(cc Mark)

Hello Pingfan,

Thanks for working on this.

On Mon, 6 Mar 2023 at 04:03, Pingfan Liu [off-list ref] wrote:

quoted

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

quoted

 -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

The idea of the minimal environment lools amazing. After digging
more deeply into it, I think it means to implement most of the function
members in efi_boot_services, besides that, some UEFI protocols due to
the reference of efi_call_proto(). So a clear boundary between zboot and
its dependent EFI service is demanded before the work.

kernel up to the point where it call ExitBootServices(), after which
kexec() would take over.

IIUC, after kexec switches to efi_zboot_entry(), it will not return,
right?

quoted

 -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.

Ah, thanks for the correcting. I had made an wrong assumption of grub
based on [1], from which, I thought that grub is the case "For
compatibility with non-EFI loaders, the payload can be decompressed and
executed by the loader as well, provided that the loader implements the
decompression algorithm and that non-EFI boot is supported by the
encapsulated image" 


[1]: https://www.phoronix.com/news/Linux-6.1-Generic-EFI-Zboot


Eager to find a solution to kexec a zboot image. Hope it will come soon.


Thanks,

	Pingfan

quoted

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@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: kexec@lists.infradead.org
To: linux-arm-kernel@lists.infradead.org
To: linux-kernel@vger.kernel.org

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

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