From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kees Cook Subject: Re: [PATCH v3 3/9] efi/libstub: Remove .note.gnu.property Date: Tue, 23 Jun 2020 21:44:11 -0700 Message-ID: <202006232143.66828CD3@keescook> References: <20200624014940.1204448-1-keescook@chromium.org> <20200624014940.1204448-4-keescook@chromium.org> <20200624033142.cinvg6rbg252j46d@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45192 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727862AbgFXEoO (ORCPT ); Wed, 24 Jun 2020 00:44:14 -0400 Received: from mail-pj1-x1041.google.com (mail-pj1-x1041.google.com [IPv6:2607:f8b0:4864:20::1041]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CB6D6C0613ED for ; Tue, 23 Jun 2020 21:44:13 -0700 (PDT) Received: by mail-pj1-x1041.google.com with SMTP id jz3so624702pjb.0 for ; Tue, 23 Jun 2020 21:44:13 -0700 (PDT) Content-Disposition: inline In-Reply-To: <20200624033142.cinvg6rbg252j46d@google.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Fangrui Song Cc: Will Deacon , 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 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. -- Kees Cook