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

Will Deacon
2016-07-29T10:49:48Z

On Fri, Jul 29, 2016 at 12:46:49PM +0200, Ard Biesheuvel wrote:
> On 29 July 2016 at 11:30, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> > On 29 July 2016 at 11:06, Will Deacon <will.deacon@arm.com> wrote:
> >> 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?
> >>
> >
> > If you are ok with fixing up patches manually while applying, could we
> > just reorder them instead?
>
> Actually, this should go into v4.8-late not -stable

Then the fixes tag is pretty confusing, since that's a commit from v4.7.

Will