linux-kernel - Re: [PATCH] kbuild: Always link with '-z norelro'

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Date:   Mon, 16 Nov 2020 12:31:58 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Will Deacon <will@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Florian Fainelli <f.fainelli@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Abbott Liu <liuwenliang@...wei.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jian Cai <jiancai@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Ard Biesheuvel <ardb@...nel.org>, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH] kbuild: Always link with '-z norelro'

On Thu, Nov 12, 2020 at 11:38:40AM -0700, Nathan Chancellor 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.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1189
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
> 
> Hi all,
> 
> This should probably go into Russell's tree with acks from the arm64 and
> kbuild maintainers.

So that's a fix for arch/arm going in the top Makefile.

For the arm64 part:

Acked-by: Catalin Marinas <catalin.marinas@....com>