On Wed, Apr 26, 2023 at 04:11:02PM +0200, Ard Biesheuvel wrote:
> The EFI zboot code is not built as part of the kernel proper, like the
> ordinary EFI stub, but still needs access to symbols that are defined
> only internally in the kernel, and are left unexposed deliberately to
> avoid creating ABI inadvertently that we're stuck with later.
>
> So capture the kernel code size of the kernel image, and inject it as an
> ELF symbol into the object that contains the compressed payload, where
> it will be accessible to zboot code that needs it.
>
> Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
Mark.
> ---
> arch/arm64/boot/Makefile | 3 +++
> arch/arm64/kernel/image-vars.h | 4 ++++
> drivers/firmware/efi/libstub/Makefile.zboot | 2 +-
> drivers/firmware/efi/libstub/zboot.lds | 7 +++++++
> 4 files changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/boot/Makefile b/arch/arm64/boot/Makefile
> index ae645fda90bca574..1761f5972443fc50 100644
> --- a/arch/arm64/boot/Makefile
> +++ b/arch/arm64/boot/Makefile
> @@ -44,4 +44,7 @@ EFI_ZBOOT_BFD_TARGET := elf64-littleaarch64
> EFI_ZBOOT_MACH_TYPE := ARM64
> EFI_ZBOOT_FORWARD_CFI := $(CONFIG_ARM64_BTI_KERNEL)
>
> +EFI_ZBOOT_OBJCOPY_FLAGS = --add-symbol zboot_code_size=0x$(shell \
> + $(NM) vmlinux|grep _kernel_codesize|cut -d' ' -f1)
> +
> include $(srctree)/drivers/firmware/efi/libstub/Makefile.zboot
> diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
> index 8309197c0ebd4a8e..35f3c79595137354 100644
> --- a/arch/arm64/kernel/image-vars.h
> +++ b/arch/arm64/kernel/image-vars.h
> @@ -108,4 +108,8 @@ KVM_NVHE_ALIAS(kvm_protected_mode_initialized);
>
> #endif /* CONFIG_KVM */
>
> +#ifdef CONFIG_EFI_ZBOOT
> +_kernel_codesize = ABSOLUTE(__inittext_end - _text);
> +#endif
> +
> #endif /* __ARM64_KERNEL_IMAGE_VARS_H */
> diff --git a/drivers/firmware/efi/libstub/Makefile.zboot b/drivers/firmware/efi/libstub/Makefile.zboot
> index 0a9dcc2b13736519..1b101d9076fd49e5 100644
> --- a/drivers/firmware/efi/libstub/Makefile.zboot
> +++ b/drivers/firmware/efi/libstub/Makefile.zboot
> @@ -40,7 +40,7 @@ quiet_cmd_compwithsize = $(quiet_cmd_$(zboot-method-y))
> $(obj)/vmlinuz: $(obj)/vmlinux.bin FORCE
> $(call if_changed,compwithsize)
>
> -OBJCOPYFLAGS_vmlinuz.o := -I binary -O $(EFI_ZBOOT_BFD_TARGET) \
> +OBJCOPYFLAGS_vmlinuz.o := -I binary -O $(EFI_ZBOOT_BFD_TARGET) $(EFI_ZBOOT_OBJCOPY_FLAGS) \
> --rename-section .data=.gzdata,load,alloc,readonly,contents
> $(obj)/vmlinuz.o: $(obj)/vmlinuz FORCE
> $(call if_changed,objcopy)
> diff --git a/drivers/firmware/efi/libstub/zboot.lds b/drivers/firmware/efi/libstub/zboot.lds
> index 93d33f68333b2b68..ac8c0ef851581f5d 100644
> --- a/drivers/firmware/efi/libstub/zboot.lds
> +++ b/drivers/firmware/efi/libstub/zboot.lds
> @@ -2,6 +2,8 @@
>
> ENTRY(__efistub_efi_zboot_header);
>
> +PROVIDE(zboot_code_size = ABSOLUTE(0));
> +
> SECTIONS
> {
> .head : ALIGN(4096) {
> @@ -17,6 +19,11 @@ SECTIONS
> *(.gzdata)
> __efistub__gzdata_end = .;
> *(.rodata* .init.rodata* .srodata*)
> +
> + . = ALIGN(4);
> + __efistub_code_size = .;
> + LONG(zboot_code_size);
> +
> _etext = ALIGN(4096);
> . = _etext;
> }
> --
> 2.39.2
>
