On Thu, Dec 17, 2020 at 04:24:32PM -0800, 'Nick Desaulniers' via Clang Built Linux wrote:
> 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@xxxxxxxxx>
> Cc: Fāng-ruì Sòng <maskray@xxxxxxxxxx>
> Fixes: 3b92fa7485eb ("arm64: link with -z norelro regardless of CONFIG_RELOCATABLE")
> Reported-by: kernelci.org bot <bot@xxxxxxxxxxxx>
> Reported-by: Quentin Perret <qperret@xxxxxxxxxx>
> Acked-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> ---
> 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.
Should probably have
Cc: stable@xxxxxxxxxxxxxxx
then.
> 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
>
