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

From: Nathan Chancellor <natechancellor@gmail.com>
To: 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>
Cc: 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>,
	Ard Biesheuvel <ardb@kernel.org>,
	linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Nathan Chancellor <natechancellor@gmail.com>,
	Nick Desaulniers <ndesaulniers@google.com>
Subject: [PATCH] kbuild: Always link with '-z norelro'
Date: Thu, 12 Nov 2020 11:38:40 -0700	[thread overview]
Message-ID: <20201112183839.1009297-1-natechancellor@gmail.com> (raw)

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.

Cheers,
Nathan

 Makefile            | 2 ++
 arch/arm64/Makefile | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 008aba5f1a20..648bfb486244 100644
--- a/Makefile
+++ b/Makefile
@@ -984,6 +984,8 @@ ifeq ($(CONFIG_RELR),y)
 LDFLAGS_vmlinux	+= --pack-dyn-relocs=relr
 endif
 
+LDFLAGS_vmlinux += -z norelro
+
 # Align the bit size of userspace programs with the kernel
 KBUILD_USERCFLAGS  += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS))
 KBUILD_USERLDFLAGS += $(filter -m32 -m64 --target=%, $(KBUILD_CFLAGS))
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 5789c2d18d43..85495ff8f0fd 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -10,7 +10,7 @@
 #
 # Copyright (C) 1995-2001 by Russell King
 
-LDFLAGS_vmlinux	:=--no-undefined -X -z norelro
+LDFLAGS_vmlinux	:=--no-undefined -X
 
 ifeq ($(CONFIG_RELOCATABLE), y)
 # Pass --no-apply-dynamic-relocs to restore pre-binutils-2.27 behaviour

base-commit: f8394f232b1eab649ce2df5c5f15b0e528c92091
-- 
2.29.2

