On Mon, Jun 22, 2020 at 01:58:15PM -0700, Kees Cook wrote:
> We don't want to depend on the linker's orphan section placement
> heuristics as these can vary between linkers, and may change between
> versions. All sections need to be explicitly named in the linker
> script.
>
> Explicitly include debug sections when they're present. Add .eh_frame*
> to discard as it seems that these are still generated even though
> -fno-asynchronous-unwind-tables is being specified. Add .plt and
> .data.rel.ro to discards as they are not actually used. Add .got.plt
> to the image as it does appear to be mapped near .data. Finally enable
> orphan section warnings.
Can you elaborate a bit on what .got.plt is being used for, please? I
wonder if there's an interaction with an erratum workaround in the linker
or something.
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index a0d94d063fa8..3e628983445a 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -29,6 +29,10 @@ LDFLAGS_vmlinux += --fix-cortex-a53-843419
> endif
> endif
>
> +# We never want expected sections to be placed heuristically by the
> +# linker. All sections should be explicitly named in the linker script.
> +LDFLAGS_vmlinux += --orphan-handling=warn
> +
> ifeq ($(CONFIG_ARM64_USE_LSE_ATOMICS), y)
> ifneq ($(CONFIG_ARM64_LSE_ATOMICS), y)
> $(warning LSE atomics not supported by binutils)
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index 5427f502c3a6..c9ecb3b2007d 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -94,7 +94,8 @@ SECTIONS
> /DISCARD/ : {
> *(.interp .dynamic)
> *(.dynsym .dynstr .hash .gnu.hash)
> - *(.eh_frame)
> + *(.plt) *(.data.rel.ro)
> + *(.eh_frame) *(.init.eh_frame)
Do we need to include .eh_frame_hdr here too?
> }
>
> . = KIMAGE_VADDR + TEXT_OFFSET;
> @@ -209,6 +210,7 @@ SECTIONS
> _data = .;
> _sdata = .;
> RW_DATA(L1_CACHE_BYTES, PAGE_SIZE, THREAD_ALIGN)
> + .got.plt : ALIGN(8) { *(.got.plt) }
>
> /*
> * Data written with the MMU off but read with the MMU on requires
> @@ -244,6 +246,7 @@ SECTIONS
> _end = .;
>
> STABS_DEBUG
> + DWARF_DEBUG
I know you didn't add it, but do we _really_ care about stabs debug? Who
generates that for arm64?
Will
