[PATCH 1/2] efi/zboot: arm64: Inject kernel code size symbol into the zboot payload

From: Ard Biesheuvel <ardb@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: linux-efi@vger.kernel.org, mark.rutland@arm.com,
	catalin.marinas@arm.com, will@kernel.org,
	Ard Biesheuvel <ardb@kernel.org>
Subject: [PATCH 1/2] efi/zboot: arm64: Inject kernel code size symbol into the zboot payload
Date: Wed, 26 Apr 2023 16:11:02 +0200	[thread overview]
Message-ID: <20230426141103.2464423-2-ardb@kernel.org> (raw)
In-Reply-To: <20230426141103.2464423-1-ardb@kernel.org>

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@kernel.org>
---
 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


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