Commit 0b2c29fb authored by Ard Biesheuvel's avatar Ard Biesheuvel
Browse files

efi/zboot: Limit compression options to GZIP and ZSTD 



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: default avatarGerd Hoffmann <kraxel@redhat.com>
Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
parent 40384c84

drivers/firmware/efi/Kconfig

+0 −4
Original line number Diff line number Diff line
@@ -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

drivers/firmware/efi/libstub/Makefile.zboot

+6 −12
Original line number Diff line number Diff line
@@ -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))