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

Ard Biesheuvel
2016-07-29T10:46:49Z

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