On Wed, 24 Jun 2020 at 12:44, Will Deacon <will@xxxxxxxxxx> wrote: > > On Tue, Jun 23, 2020 at 09:44:11PM -0700, Kees Cook wrote: > > 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 <keescook@xxxxxxxxxxxx> > > > > --- > > > > 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. > > For the kernel Image, how do we remove these sections? The objcopy flags > in arch/arm64/boot/Makefile look both insufficient and out of date. My > vmlinux ends up with both a ".notes" and a ".init.note.gnu.property" > segment. > The latter is the fault of the libstub make rules, that prepend .init to all section names. I'm not sure if there is a point to having PAC and/or BTI in the EFI stub, given that it runs under the control of the firmware, with its memory mappings and PAC configuration etc.
