Re: [PATCH 1/9] scripts/link-vmlinux.sh: Delay orphan handling warnings until final link

From: Nicholas Piggin <npiggin@gmail.com>
To: Kees Cook <keescook@chromium.org>
Cc: Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@suse.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	clang-built-linux@googlegroups.com,
	"H.J. Lu" <hjl.tools@gmail.com>,
	James Morse <james.morse@arm.com>,
	linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	Russell King <linux@armlinux.org.uk>,
	linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
	Mark Rutland <mark.rutland@arm.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Peter Collingbourne <pcc@google.com>,
	Will Deacon <will@kernel.org>,
	x86@kernel.org
Subject: Re: [PATCH 1/9] scripts/link-vmlinux.sh: Delay orphan handling warnings until final link
Date: Sun, 22 Mar 2020 19:16:29 +1000	[thread overview]
Message-ID: <1584868418.o62lxee8k1.astroid@bobo.none> (raw)
In-Reply-To: <202003201121.8CBD96451B@keescook>

Kees Cook's on March 21, 2020 4:24 am:
> On Fri, Mar 20, 2020 at 12:47:54PM +1000, Nicholas Piggin wrote:
>> Kees Cook's on February 28, 2020 10:22 am:
>> > Right now, powerpc adds "--orphan-handling=warn" to LD_FLAGS_vmlinux
>> > to detect when there are unexpected sections getting added to the kernel
>> > image. There is no need to report these warnings more than once, so it
>> > can be removed until the final link stage.
>> > 
>> > This helps pave the way for other architectures to enable this, with the
>> > end goal of enabling this warning by default for vmlinux for all
>> > architectures.
>> > 
>> > Signed-off-by: Kees Cook <keescook@chromium.org>
>> > ---
>> >  scripts/link-vmlinux.sh | 6 ++++++
>> >  1 file changed, 6 insertions(+)
>> > 
>> > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
>> > index 1919c311c149..416968fea685 100755
>> > --- a/scripts/link-vmlinux.sh
>> > +++ b/scripts/link-vmlinux.sh
>> > @@ -255,6 +255,11 @@ info GEN modules.builtin
>> >  tr '\0' '\n' < modules.builtin.modinfo | sed -n 's/^[[:alnum:]:_]*\.file=//p' |
>> >  	tr ' ' '\n' | uniq | sed -e 's:^:kernel/:' -e 's/$/.ko/' > modules.builtin
>> >  
>> > +
>> > +# Do not warn about orphan sections until the final link stage.
>> > +saved_LDFLAGS_vmlinux="${LDFLAGS_vmlinux}"
>> > +LDFLAGS_vmlinux="$(echo "${LDFLAGS_vmlinux}" | sed -E 's/ --orphan-handling=warn( |$)/ /g')"
>> > +
>> >  btf_vmlinux_bin_o=""
>> >  if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then
>> >  	if gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then
>> > @@ -306,6 +311,7 @@ if [ -n "${CONFIG_KALLSYMS}" ]; then
>> >  	fi
>> >  fi
>> >  
>> > +LDFLAGS_vmlinux="${saved_LDFLAGS_vmlinux}"
>> >  vmlinux_link vmlinux "${kallsymso}" ${btf_vmlinux_bin_o}
>> >  
>> >  if [ -n "${CONFIG_BUILDTIME_TABLE_SORT}" ]; then
>> 
>> That's ugly. Why not just enable it for all archs?
> 
> It is ugly; I agree.
> 
> I can try to do this for all architectures, but I worry there are a
> bunch I can't test. But I guess it would stand out. ;)

It's only warn, so it doesn't break their builds (unless there's a 
linker error on warn option I don't know about?). We had a powerpc bug 
that would have been caught with it as well, so it's not a bad idea to
get everyone using it.

I would just do it. Doesn't take much to fix.

Thanks,
Nick