Re: [PATCH v3 9/9] arm64/build: Warn on orphan section placement

From: Kees Cook <keescook@chromium.org>
To: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Peter Collingbourne <pcc@google.com>,
	James Morse <james.morse@arm.com>, Borislav Petkov <bp@suse.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Russell King <linux@armlinux.org.uk>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Arnd Bergmann <arnd@arndb.de>,
	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
Subject: Re: [PATCH v3 9/9] arm64/build: Warn on orphan section placement
Date: Wed, 24 Jun 2020 08:36:20 -0700	[thread overview]
Message-ID: <202006240835.E474048BBF@keescook> (raw)
In-Reply-To: <20200624075712.GB5853@willie-the-truck>

On Wed, Jun 24, 2020 at 08:57:12AM +0100, Will Deacon wrote:
> On Tue, Jun 23, 2020 at 06:49:40PM -0700, 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.
> > 
> > Avoid .eh_frame* by making sure both -fno-asychronous-unwind-tables and
> > -fno-unwind-tables are present in both CFLAGS and AFLAGS. Remove one
> > last instance of .eh_frame by removing the needless Call Frame Information
> > annotations from arch/arm64/kernel/smccc-call.S.
> > 
> > Add .plt, .data.rel.ro, .igot.*, and .iplt to discards as they are not
> > actually used. While .got.plt is also not used, it must be included
> > otherwise ld.bfd will fail to link with the error:
> > 
> >     aarch64-linux-gnu-ld: discarded output section: `.got.plt'
> > 
> > However, as it'd be better to validate that it stays effectively empty,
> > add an assert.
> > 
> > Explicitly include debug sections when they're present.
> > 
> > Fix a case of needless quotes in __section(), which Clang doesn't like.
> > 
> > Finally, enable orphan section warnings.
> > 
> > Thanks to Ard Biesheuvel for many hints on correct ways to handle
> > mysterious sections. :)
> 
> Sorry to be a pain, but this patch is doing 3 or 4 independent things at
> once. Please could you split it up a bit?
> e.g.
> 
>  - Removal of cfi directives from smccc macro
>  - Removal of quotes around section name for clang
>  - Avoid generating .eh_frame
>  - Ensure all sections are accounted for in linker script and warn on orphans
> 
> That way it's a bit easier to manage, we can revert/backport bits later if
> necessary and you get more patches in the kernel ;)

Yeah, this one patch did grow a bit. ;) I've split it up now.

> You can also add my Ack on all the patches:
> 
> Acked-by: Will Deacon <will@kernel.org>

Thanks!

-- 
Kees Cook