From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH v3 3/9] efi/libstub: Remove .note.gnu.property Date: Wed, 24 Jun 2020 11:43:56 +0100 Message-ID: <20200624104356.GA6134@willie-the-truck> References: <20200624014940.1204448-1-keescook@chromium.org> <20200624014940.1204448-4-keescook@chromium.org> <20200624033142.cinvg6rbg252j46d@google.com> <202006232143.66828CD3@keescook> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail.kernel.org ([198.145.29.99]:60664 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388421AbgFXKoD (ORCPT ); Wed, 24 Jun 2020 06:44:03 -0400 Content-Disposition: inline In-Reply-To: <202006232143.66828CD3@keescook> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Kees Cook Cc: Fangrui Song , Catalin Marinas , Mark Rutland , Ard Biesheuvel , Peter Collingbourne , James Morse , Borislav Petkov , Thomas Gleixner , Ingo Molnar , Russell King , Masahiro Yamada , Arvind Sankar , Nick Desaulniers , Nathan Chancellor , Arnd Bergmann , x86@kernel.org, clang-built-linux@googlegroups.com, linux-arch@vger.kernel.org, linux-efi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org 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 > > > --- > > > 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. Will