linux-kernel - [PATCH] arm64: link with -z norelro regardless of CONFIG

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Message-Id: <20201016175339.2429280-1-ndesaulniers@google.com>
Date:   Fri, 16 Oct 2020 10:53:39 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Peter Smith <Peter.Smith@....com>,
        "Fāng-ruì Sòng" <maskray@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        stable@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] arm64: link with -z norelro regardless of CONFIG_RELOCATABLE

With CONFIG_EXPERT=y, CONFIG_KASAN=y, CONFIG_RANDOMIZE_BASE=n,
CONFIG_RELOCATABLE=n, we observe the following failure when trying to
link the kernel image with LD=ld.lld:

error: section: .exit.data is not contiguous with other relro sections

ld.lld defaults to -z relro while ld.bfd defaults to -z norelro. This
was previously fixed, but only for CONFIG_RELOCATABLE=y.

Cc: stable@...r.kernel.org
Fixes: commit 3bbd3db86470 ("arm64: relocatable: fix inconsistencies in linker script and options")
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
While upgrading our toolchains for Android, we started seeing the above
failure for a particular config that enabled KASAN but disabled KASLR.
This was on a 5.4 stable branch.  It looks like
commit dd4bc6076587 ("arm64: warn on incorrect placement of the kernel by the bootloader")
made RELOCATABLE=y the default and depend on EXPERT=y. With those two
enabled, we can then reproduce the same failure on mainline.


 arch/arm64/Makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index f4717facf31e..674241df91ab 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -10,13 +10,13 @@
 #
 # Copyright (C) 1995-2001 by Russell King
 
-LDFLAGS_vmlinux	:=--no-undefined -X
+LDFLAGS_vmlinux	:=--no-undefined -X -z norelro
 
 ifeq ($(CONFIG_RELOCATABLE), y)
 # Pass --no-apply-dynamic-relocs to restore pre-binutils-2.27 behaviour
 # for relative relocs, since this leads to better Image compression
 # with the relocation offsets always being zero.
-LDFLAGS_vmlinux		+= -shared -Bsymbolic -z notext -z norelro \
+LDFLAGS_vmlinux		+= -shared -Bsymbolic -z notext \
 			$(call ld-option, --no-apply-dynamic-relocs)
 endif
 
-- 
2.29.0.rc1.297.gfa9743e501-goog