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.

Fixes: 3b92fa74 ("arm64: link with -z norelro regardless of CONFIG_RELOCATABLE")
Fixes: 3bbd3db8 ("arm64: relocatable: fix inconsistencies in linker script and options")
Cc: <stable@vger.kernel.org> # 5.0.x-
Reported-by: kernelci.org bot <bot@kernelci.org>
Reported-by: Quentin Perret <qperret@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Alan Modra <amodra@gmail.com>
Cc: Fāng-ruì Sòng <maskray@google.com>
Link: https://lore.kernel.org/r/20201218002432.788499-1-ndesaulniers@google.comSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

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)