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efi/zboot: Limit compression options to GZIP and ZSTD

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For historical reasons, the legacy decompressor code on various
architectures supports 7 different compression types for the compressed
kernel image.

EFI zboot is not a compression library museum, and so the options can be
limited to what is likely to be useful in practice:

- GZIP is tried and tested, and is still one of the fastest at
  decompression time, although the compression ratio is not very high;
  moreover, Fedora is already shipping EFI zboot kernels for arm64 that
  use GZIP, and QEMU implements direct support for it when booting a
  kernel without firmware loaded;

- ZSTD has a very high compression ratio (although not the highest), and
  is almost as fast as GZIP at decompression time.

Reducing the number of options makes it less of a hassle for other
consumers of the EFI zboot format (such as QEMU today, and kexec in the
future) to support it transparently without having to carry 7 different
decompression libraries.

Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
This commit is contained in:
Ard Biesheuvel 2024-12-06 11:41:40 +01:00
parent 40384c840e
commit 0b2c29fb68
2 changed files with 6 additions and 16 deletions
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4
drivers/firmware/efi/Kconfig
View File

@ -76,10 +76,6 @@ config EFI_ZBOOT
bool "Enable the generic EFI decompressor"
depends on EFI_GENERIC_STUB && !ARM
select HAVE_KERNEL_GZIP
select HAVE_KERNEL_LZ4
select HAVE_KERNEL_LZMA
select HAVE_KERNEL_LZO
select HAVE_KERNEL_XZ
select HAVE_KERNEL_ZSTD
help
Create the bootable image as an EFI application that carries the

18
drivers/firmware/efi/libstub/Makefile.zboot
View File

@ -12,22 +12,16 @@ quiet_cmd_copy_and_pad = PAD $@
$(obj)/vmlinux.bin: $(obj)/$(EFI_ZBOOT_PAYLOAD) FORCE
$(call if_changed,copy_and_pad)
comp-type-$(CONFIG_KERNEL_GZIP) := gzip
comp-type-$(CONFIG_KERNEL_LZ4) := lz4
comp-type-$(CONFIG_KERNEL_LZMA) := lzma
comp-type-$(CONFIG_KERNEL_LZO) := lzo
comp-type-$(CONFIG_KERNEL_XZ) := xzkern
comp-type-$(CONFIG_KERNEL_ZSTD) := zstd22
# in GZIP, the appended le32 carrying the uncompressed size is part of the
# format, but in other cases, we just append it at the end for convenience,
# causing the original tools to complain when checking image integrity.
# So disregard it when calculating the payload size in the zimage header.
zboot-method-y := $(comp-type-y)_with_size
zboot-size-len-y := 4
comp-type-y := gzip
zboot-method-y := gzip
zboot-size-len-y := 0
zboot-method-$(CONFIG_KERNEL_GZIP) := gzip
zboot-size-len-$(CONFIG_KERNEL_GZIP) := 0
comp-type-$(CONFIG_KERNEL_ZSTD) := zstd
zboot-method-$(CONFIG_KERNEL_ZSTD) := zstd22_with_size
zboot-size-len-$(CONFIG_KERNEL_ZSTD) := 4
$(obj)/vmlinuz: $(obj)/vmlinux.bin FORCE
$(call if_changed,$(zboot-method-y))