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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Wed, 18 Nov 2020 15:05:45 -0800
Message-ID: <CAKwvOdnauFdUgS0Ww=O-PHrXWhXQEEYd806NUcy8_7MOG0Uo2g@mail.gmail.com>
Subject: Re: [PATCH] kbuild: Always link with '-z norelro'
To:     Nathan Chancellor <natechancellor@gmail.com>
Cc:     Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Russell King <linux@armlinux.org.uk>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Abbott Liu <liuwenliang@huawei.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Jian Cai <jiancai@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Fangrui Song <maskray@google.com>,
        Dan Rue <dan.rue@linaro.org>, Mark Brown <broonie@kernel.org>
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On Fri, Nov 13, 2020 at 11:34 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Thu, Nov 12, 2020 at 10:06 PM Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > On Fri, 13 Nov 2020 at 01:53, Nathan Chancellor
> > <natechancellor@gmail.com> wrote:
> > >
> > > On Thu, Nov 12, 2020 at 04:44:46PM -0800, Nick Desaulniers wrote:
> > > > On Thu, Nov 12, 2020 at 10:41 AM Nathan Chancellor
> > > > <natechancellor@gmail.com> wrote:
> > > > >
> > > > > Commit 3bbd3db86470 ("arm64: relocatable: fix inconsistencies in linker
> > > > > script and options") added '-z norelro' to the arm64 Makefile when
> > > > > CONFIG_RELOCATABLE was set to help support ld.lld because ld.lld
> > > > > defaults to '-z relro' but the kernel does not use program headers or
> > > > > adhere to the section layout that is required for RELRO to work.
> > > > >
> > > > > Commit 3b92fa7485eb ("arm64: link with -z norelro regardless of
> > > > > CONFIG_RELOCATABLE") unconditionally added it to LDFLAGS_vmlinux because
> > > > > an error occurs with CONFIG_KASAN set even when CONFIG_RELOCATABLE is
> > > > > unset.
> > > > >
> > > > > As it turns out, ARM experiences the same error after CONFIG_KASAN was
> > > > > implemented, meaning that '-z norelro' needs to be added to that
> > > > > Makefile as well (multi_v7_defconfig + CONFIG_KASAN=y + LD=ld.lld):
> > > > >
> > > > > $ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- LLVM=1 zImage
> > > > > ld.lld: error: section: .exit.data is not contiguous with other relro sections
> > > > >
> > > > > To avoid playing whack-a-mole with different architectures over time,
> > > > > hoist '-z norelro' into the main Makefile. This does not affect ld.bfd
> > > > > because '-z norelro' is the default for it.

Fangrui pointed out off list that this might need an ld-option wrapper
for older versions of GNU binutils.  Dan was showing me some build
logs today, and I thought I spotted such warnings about `-z norelro
will be ignored`.
-- 
Thanks,
~Nick Desaulniers