From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kees Cook Subject: Re: [PATCH v2 3/3] x86/boot: Warn on orphan section placement Date: Mon, 22 Jun 2020 15:35:39 -0700 Message-ID: <202006221534.D22F51D37@keescook> References: <20200622205341.2987797-1-keescook@chromium.org> <20200622205341.2987797-4-keescook@chromium.org> <20200622220628.t5fklwmbtqoird5f@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48266 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730826AbgFVWfm (ORCPT ); Mon, 22 Jun 2020 18:35:42 -0400 Received: from mail-pl1-x642.google.com (mail-pl1-x642.google.com [IPv6:2607:f8b0:4864:20::642]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 28D36C061795 for ; Mon, 22 Jun 2020 15:35:42 -0700 (PDT) Received: by mail-pl1-x642.google.com with SMTP id 35so8230572ple.0 for ; Mon, 22 Jun 2020 15:35:42 -0700 (PDT) Content-Disposition: inline In-Reply-To: <20200622220628.t5fklwmbtqoird5f@google.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Fangrui Song Cc: Borislav Petkov , Thomas Gleixner , Ingo Molnar , x86@kernel.org, Arnd Bergmann , Nick Desaulniers , Nathan Chancellor , clang-built-linux@googlegroups.com, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org On Mon, Jun 22, 2020 at 03:06:28PM -0700, Fangrui Song wrote: > On 2020-06-22, Kees Cook wrote: > > We don't want to depend on the linker's orphan section placement > > heuristics as these can vary between linkers, and may change between > > versions. All sections need to be explicitly named in the linker > > script. > > > > Add the common debugging sections. Discard the unused note, rel, plt, > > dyn, and hash sections that are not needed in the compressed vmlinux. > > Disable .eh_frame generation in the linker and enable orphan section > > warnings. > > > > Signed-off-by: Kees Cook > > --- > > arch/x86/boot/compressed/Makefile | 3 ++- > > arch/x86/boot/compressed/vmlinux.lds.S | 11 +++++++++++ > > 2 files changed, 13 insertions(+), 1 deletion(-) > > > > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile > > index 7619742f91c9..646720a05f89 100644 > > --- a/arch/x86/boot/compressed/Makefile > > +++ b/arch/x86/boot/compressed/Makefile > > @@ -48,6 +48,7 @@ GCOV_PROFILE := n > > UBSAN_SANITIZE :=n > > > > KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE) > > +KBUILD_LDFLAGS += $(call ld-option,--no-ld-generated-unwind-info) > > # Compressed kernel should be built as PIE since it may be loaded at any > > # address by the bootloader. > > ifeq ($(CONFIG_X86_32),y) > > @@ -59,7 +60,7 @@ else > > KBUILD_LDFLAGS += $(shell $(LD) --help 2>&1 | grep -q "\-z noreloc-overflow" \ > > && echo "-z noreloc-overflow -pie --no-dynamic-linker") > > endif > > -LDFLAGS_vmlinux := -T > > +LDFLAGS_vmlinux := --orphan-handling=warn -T > > > > hostprogs := mkpiggy > > HOST_EXTRACFLAGS += -I$(srctree)/tools/include > > diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S > > index 8f1025d1f681..6fe3ecdfd685 100644 > > --- a/arch/x86/boot/compressed/vmlinux.lds.S > > +++ b/arch/x86/boot/compressed/vmlinux.lds.S > > @@ -75,5 +75,16 @@ SECTIONS > > . = ALIGN(PAGE_SIZE); /* keep ZO size page aligned */ > > _end = .; > > > > + STABS_DEBUG > > + DWARF_DEBUG > > + > > DISCARDS > > + /DISCARD/ : { > > + *(.note.*) > > + *(.rela.*) *(.rela_*) > > + *(.rel.*) *(.rel_*) > > + *(.plt) *(.plt.*) > > + *(.dyn*) > > + *(.hash) *(.gnu.hash) > > + } > > } > > -- > > 2.25.1 > > LLD may report warnings for 3 synthetic sections if they are orphans: > > ld.lld: warning: :(.symtab) is being placed in '.symtab' > ld.lld: warning: :(.shstrtab) is being placed in '.shstrtab' > ld.lld: warning: :(.strtab) is being placed in '.strtab' > > Are they described? Ah, hm. I see gcc is just silent about these. It looks like both regular and debug kernels end up with those sections for both GCC and Clang. How would you expect them to be described? -- Kees Cook