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

From: Catalin Marinas <catalin.marinas@arm.com>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>,
	Arnd Bergmann <arnd@arndb.de>,
	linux-kbuild@vger.kernel.org, Ard Biesheuvel <ardb@kernel.org>,
	Abbott Liu <liuwenliang@huawei.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Russell King <linux@armlinux.org.uk>,
	Jian Cai <jiancai@google.com>,
	Michal Marek <michal.lkml@markovi.net>,
	linux-arm-kernel@lists.infradead.org,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Mike Rapoport <rppt@linux.ibm.com>, Will Deacon <will@kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kbuild: Always link with '-z norelro'
Date: Mon, 16 Nov 2020 12:31:58 +0000	[thread overview]
Message-ID: <X7JxPkmYnUA7nKfx@trantor> (raw)
In-Reply-To: <20201112183839.1009297-1-natechancellor@gmail.com>

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@google.com>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.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@arm.com>

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