Re: [PATCH v5 23/36] arm/build: Explicitly keep .ARM.attributes sections

Nick Desaulniers
2020-08-03T19:02:21Z

On Fri, Jul 31, 2020 at 4:18 PM Kees Cook <keescook@chromium.org> wrote:
>
> In preparation for adding --orphan-handling=warn, explicitly keep the
> .ARM.attributes section by expanding the existing ELF_DETAILS macro into
> ARM_DETAILS.
>
> Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
> Link: https://lore.kernel.org/lkml/CAKwvOdk-racgq5pxsoGS6Vtifbtrk5fmkmnoLxrQMaOvV0nPWw@mail.gmail.com/
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> arch/arm/include/asm/vmlinux.lds.h | 4 ++++
> arch/arm/kernel/vmlinux-xip.lds.S | 2 +-
> arch/arm/kernel/vmlinux.lds.S | 2 +-
> 3 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/include/asm/vmlinux.lds.h b/arch/arm/include/asm/vmlinux.lds.h
> index a08f4301b718..c4af5182ab48 100644
> --- a/arch/arm/include/asm/vmlinux.lds.h
> +++ b/arch/arm/include/asm/vmlinux.lds.h
> @@ -52,6 +52,10 @@
> ARM_MMU_DISCARD(*(__ex_table)) \
> COMMON_DISCARDS
>
> +#define ARM_DETAILS \
> + ELF_DETAILS \
> + .ARM.attributes 0 : { *(.ARM.attributes) }

I had to look up what the `0` meant:
https://sourceware.org/binutils/docs/ld/Output-Section-Attributes.html#Output-Section-Attributes
mentions it's an "address" and
https://ftp.gnu.org/old-gnu/Manuals/ld-2.9.1/html_chapter/ld_3.html#SEC21
mentions it as "start" (an address).
Unless we need those, can we drop them? (Sorry for the resulting churn
that would cause). I think the NO_LOAD stuff makes more sense, but
I'm curious if the kernel checks for that.

> +
> #define ARM_STUBS_TEXT \
> *(.gnu.warning) \
> *(.glue_7) \
> diff --git a/arch/arm/kernel/vmlinux-xip.lds.S b/arch/arm/kernel/vmlinux-xip.lds.S
> index 904c31fa20ed..57fcbf55f913 100644
> --- a/arch/arm/kernel/vmlinux-xip.lds.S
> +++ b/arch/arm/kernel/vmlinux-xip.lds.S
> @@ -150,7 +150,7 @@ SECTIONS
> _end = .;
>
> STABS_DEBUG
> - ELF_DETAILS
> + ARM_DETAILS
> }
>
> /*
> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> index bb950c896a67..1d3d3b599635 100644
> --- a/arch/arm/kernel/vmlinux.lds.S
> +++ b/arch/arm/kernel/vmlinux.lds.S
> @@ -149,7 +149,7 @@ SECTIONS
> _end = .;
>
> STABS_DEBUG
> - ELF_DETAILS
> + ARM_DETAILS
> }
>
> #ifdef CONFIG_STRICT_KERNEL_RWX
> --
> 2.25.1
>

--
Thanks,
~Nick Desaulniers