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

[Will Deacon]

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 at 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