linux-kernel - [PATCH v2] arm64: link with -z norelro for LLD or aarch64-elf

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Message-Id: <20201218002432.788499-1-ndesaulniers@google.com>
Date:   Thu, 17 Dec 2020 16:24:32 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     kernel-team <kernel-team@...roid.com>,
        Peter Smith <Peter.Smith@....com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        stable <stable@...r.kernel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        "Fāng-ruì Sòng" <maskray@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Alan Modra <amodra@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "kernelci . org bot" <bot@...nelci.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] arm64: link with -z norelro for LLD or aarch64-elf

With GNU binutils 2.35+, linking with BFD produces warnings for vmlinux:
aarch64-linux-gnu-ld: warning: -z norelro ignored

BFD can produce this warning when the target emulation mode does not
support RELRO program headers, and -z relro or -z norelro is passed.

Alan Modra clarifies:
  The default linker emulation for an aarch64-linux ld.bfd is
  -maarch64linux, the default for an aarch64-elf linker is
  -maarch64elf.  They are not equivalent.  If you choose -maarch64elf
  you get an emulation that doesn't support -z relro.

The ARCH=arm64 kernel prefers -maarch64elf, but may fall back to
-maarch64linux based on the toolchain configuration.

LLD will always create RELRO program header regardless of target
emulation.

To avoid the above warning when linking with BFD, pass -z norelro only
when linking with LLD or with -maarch64linux.

Cc: Alan Modra <amodra@...il.com>
Cc: Fāng-ruì Sòng <maskray@...gle.com>
Fixes: 3b92fa7485eb ("arm64: link with -z norelro regardless of CONFIG_RELOCATABLE")
Reported-by: kernelci.org bot <bot@...nelci.org>
Reported-by: Quentin Perret <qperret@...gle.com>
Acked-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
Changes V1 -> V2:
* s/relocation types/program headers/
* s/newer GNU binutils/GNU binutils 2.35+/
* Pick up Ard's Ack.

Note: maintainers may want to pick up the following tag:

Fixes: 3bbd3db86470 ("arm64: relocatable: fix inconsistencies in linker script and options")

or drop the existing fixes tag (this patch is more so in response to
change to BFD to warn than fix a kernel regression, IMO, but I don't
care). Either way, it would be good to fix this for the newly minted
v5.10.y.

I'll probably be offline for the next two weeks for the holidays, so no
promises on quick replies. Happy holidays+new year!


 arch/arm64/Makefile | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 6be9b3750250..90309208bb28 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
@@ -115,16 +115,20 @@ KBUILD_CPPFLAGS	+= -mbig-endian
 CHECKFLAGS	+= -D__AARCH64EB__
 # Prefer the baremetal ELF build target, but not all toolchains include
 # it so fall back to the standard linux version if needed.
-KBUILD_LDFLAGS	+= -EB $(call ld-option, -maarch64elfb, -maarch64linuxb)
+KBUILD_LDFLAGS	+= -EB $(call ld-option, -maarch64elfb, -maarch64linuxb -z norelro)
 UTS_MACHINE	:= aarch64_be
 else
 KBUILD_CPPFLAGS	+= -mlittle-endian
 CHECKFLAGS	+= -D__AARCH64EL__
 # Same as above, prefer ELF but fall back to linux target if needed.
-KBUILD_LDFLAGS	+= -EL $(call ld-option, -maarch64elf, -maarch64linux)
+KBUILD_LDFLAGS	+= -EL $(call ld-option, -maarch64elf, -maarch64linux -z norelro)
 UTS_MACHINE	:= aarch64
 endif
 
+ifeq ($(CONFIG_LD_IS_LLD), y)
+KBUILD_LDFLAGS	+= -z norelro
+endif
+
 CHECKFLAGS	+= -D__aarch64__
 
 ifeq ($(CONFIG_DYNAMIC_FTRACE_WITH_REGS),y)
-- 
2.29.2.684.gfbc64c5ab5-goog