[PATCH] arm64: vmlinux.lds: make __rela_offset and __dynsym_offset ABSOLUTE

Will Deacon
2016-07-29T09:06:35Z

Hi Ard,

On Thu, Jul 28, 2016 at 04:15:14PM +0200, Ard Biesheuvel wrote:
> Due to the untyped KIMAGE_VADDR constant, the linker may not notice
> that the __rela_offset and __dynsym_offset expressions are absolute
> values (i.e., are not subject to relocation). This does not matter for
> KASLR, but it does confuse kallsyms in relative mode, since it uses
> the lowest non-absolute symbol address as the anchor point, and expects
> all other symbol addresses to be within 4 GB of it.
>
> Fix this by qualifying these expressions as ABSOLUTE() explicitly.
>
> Fixes: 0cd3defe0af4 ("arm64: kernel: perform relocation processing from ID map")
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
> arch/arm64/kernel/vmlinux.lds.S | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index 89d6e177ecbd..d49492179967 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -184,9 +184,9 @@ SECTIONS
> *(.hash)
> }
>
> - __rela_offset = ADDR(.rela) - KIMAGE_VADDR;
> + __rela_offset = ABSOLUTE(ADDR(.rela) - KIMAGE_VADDR);
> __rela_size = SIZEOF(.rela);
> - __dynsym_offset = ADDR(.dynsym) - KIMAGE_VADDR;
> + __dynsym_offset = ABSOLUTE(ADDR(.dynsym) - KIMAGE_VADDR);

You removed the __dynsym_offset entry entirely in "arm64: relocatable:
suppress R_AARCH64_ABS64 relocations in vmlinux", so I'll drop this part
of the patch and assume you'll do a separate backport for stable. Ok?

Will