[PATCH v3 3/9] efi/libstub: Remove .note.gnu.property

[Fangrui Song]

On 2020-06-23, Kees Cook wrote:
>In preparation for adding --orphan-handling=warn to more architectures,
>make sure unwanted sections don't end up appearing under the .init
>section prefix that libstub adds to itself during objcopy.
>
>Signed-off-by: Kees Cook <keescook at chromium.org>
>---
> drivers/firmware/efi/libstub/Makefile | 3 +++
> 1 file changed, 3 insertions(+)
>
>diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
>index 75daaf20374e..9d2d2e784bca 100644
>--- a/drivers/firmware/efi/libstub/Makefile
>+++ b/drivers/firmware/efi/libstub/Makefile
>@@ -66,6 +66,9 @@ lib-$(CONFIG_X86)		+= x86-stub.o
> CFLAGS_arm32-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
> CFLAGS_arm64-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
>
>+# Remove unwanted sections first.
>+STUBCOPY_FLAGS-y		+= --remove-section=.note.gnu.property
>+
> #
> # For x86, bootloaders like systemd-boot or grub-efi do not zero-initialize the
> # .bss section, so the .bss section of the EFI stub needs to be included in the

arch/arm64/Kconfig enables ARM64_PTR_AUTH by default. When the config is on

ifeq ($(CONFIG_ARM64_BTI_KERNEL),y)
branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET_BTI) := -mbranch-protection=pac-ret+leaf+bti
else
branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pac-ret+leaf
endif

This option creates .note.gnu.property:

% readelf -n drivers/firmware/efi/libstub/efi-stub.o

Displaying notes found in: .note.gnu.property
   Owner                Data size        Description
   GNU                  0x00000010       NT_GNU_PROPERTY_TYPE_0
       Properties: AArch64 feature: PAC

If .note.gnu.property is not desired in drivers/firmware/efi/libstub, specifying
-mbranch-protection=none can override -mbranch-protection=pac-ret+leaf