efi: libstub: Remove zboot signing from build options

The zboot decompressor series introduced a feature to sign the PE/COFF
kernel image for secure boot as part of the kernel build. This was
necessary because there are actually two images that need to be signed:
the kernel with the EFI stub attached, and the decompressor application.

This is a bit of a burden, because it means that the images must be
signed on the the same system that performs the build, and this is not
realistic for distros.

During the next cycle, we will introduce changes to the zboot code so
that the inner image no longer needs to be signed. This means that the
outer PE/COFF image can be handled as usual, and be signed later in the
release process.

Let's remove the associated Kconfig options now so that they don't end
up in a LTS release while already being deprecated.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/Kconfig

@@ -124,28 +124,6 @@ config EFI_ZBOOT
 	  is supported by the encapsulated image. (The compression algorithm
 	  used is described in the zboot image header)
 
-config EFI_ZBOOT_SIGNED
-	def_bool y
-	depends on EFI_ZBOOT_SIGNING_CERT != ""
-	depends on EFI_ZBOOT_SIGNING_KEY != ""
-
-config EFI_ZBOOT_SIGNING
-	bool "Sign the EFI decompressor for UEFI secure boot"
-	depends on EFI_ZBOOT
-	help
-	  Use the 'sbsign' command line tool (which must exist on the host
-	  path) to sign both the EFI decompressor PE/COFF image, as well as the
-	  encapsulated PE/COFF image, which is subsequently compressed and
-	  wrapped by the former image.
-
-config EFI_ZBOOT_SIGNING_CERT
-	string "Certificate to use for signing the compressed EFI boot image"
-	depends on EFI_ZBOOT_SIGNING
-
-config EFI_ZBOOT_SIGNING_KEY
-	string "Private key to use for signing the compressed EFI boot image"
-	depends on EFI_ZBOOT_SIGNING
-
 config EFI_ARMSTUB_DTB_LOADER
 	bool "Enable the DTB loader"
 	depends on EFI_GENERIC_STUB && !RISCV && !LOONGARCH

drivers/firmware/efi/libstub/Makefile.zboot

@@ -20,18 +20,7 @@ zboot-size-len-y			:= 4
 zboot-method-$(CONFIG_KERNEL_GZIP)	:= gzip
 zboot-size-len-$(CONFIG_KERNEL_GZIP)	:= 0
 
-quiet_cmd_sbsign = SBSIGN  $@
-      cmd_sbsign = sbsign --out $@ $< \
-		   --key $(CONFIG_EFI_ZBOOT_SIGNING_KEY) \
-		   --cert $(CONFIG_EFI_ZBOOT_SIGNING_CERT)
-
-$(obj)/$(EFI_ZBOOT_PAYLOAD).signed: $(obj)/$(EFI_ZBOOT_PAYLOAD) FORCE
-	$(call if_changed,sbsign)
-
-ZBOOT_PAYLOAD-y				 := $(EFI_ZBOOT_PAYLOAD)
-ZBOOT_PAYLOAD-$(CONFIG_EFI_ZBOOT_SIGNED) := $(EFI_ZBOOT_PAYLOAD).signed
-
-$(obj)/vmlinuz: $(obj)/$(ZBOOT_PAYLOAD-y) FORCE
+$(obj)/vmlinuz: $(obj)/$(EFI_ZBOOT_PAYLOAD) FORCE
 	$(call if_changed,$(zboot-method-y))
 
 OBJCOPYFLAGS_vmlinuz.o := -I binary -O $(EFI_ZBOOT_BFD_TARGET) \
@@ -53,18 +42,8 @@ LDFLAGS_vmlinuz.efi.elf := -T $(srctree)/drivers/firmware/efi/libstub/zboot.lds
 $(obj)/vmlinuz.efi.elf: $(obj)/vmlinuz.o $(ZBOOT_DEPS) FORCE
 	$(call if_changed,ld)
 
-ZBOOT_EFI-y				:= vmlinuz.efi
-ZBOOT_EFI-$(CONFIG_EFI_ZBOOT_SIGNED)	:= vmlinuz.efi.unsigned
-
-OBJCOPYFLAGS_$(ZBOOT_EFI-y) := -O binary
-$(obj)/$(ZBOOT_EFI-y): $(obj)/vmlinuz.efi.elf FORCE
+OBJCOPYFLAGS_vmlinuz.efi := -O binary
+$(obj)/vmlinuz.efi: $(obj)/vmlinuz.efi.elf FORCE
 	$(call if_changed,objcopy)
 
 targets += zboot-header.o vmlinuz vmlinuz.o vmlinuz.efi.elf vmlinuz.efi
-
-ifneq ($(CONFIG_EFI_ZBOOT_SIGNED),)
-$(obj)/vmlinuz.efi: $(obj)/vmlinuz.efi.unsigned FORCE
-	$(call if_changed,sbsign)
-endif
-
-targets += $(EFI_ZBOOT_PAYLOAD).signed vmlinuz.efi.unsigned