On Tue, Jun 23, 2020 at 08:31:42PM -0700, 'Fangrui Song' via Clang Built Linux wrote: > 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 <keesc...@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
We want to keep the branch protection enabled. But since it's not a "regular" ELF, we don't need to keep the property that identifies the feature. -- Kees Cook
