[PATCH] arm64: errata: add module build workaround for erratum #843419

Dann Frazier dann.frazier at canonical.com
Wed Oct 7 23:07:54 PDT 2015


On Tue, Oct 6, 2015 at 4:29 PM, Ard Biesheuvel
<ard.biesheuvel at linaro.org> wrote:
> On 6 October 2015 at 22:44, Dann Frazier <dann.frazier at canonical.com> wrote:
>> On Wed, Sep 16, 2015 at 5:16 AM, Will Deacon <will.deacon at arm.com> wrote:
>>> Cortex-A53 processors <= r0p4 are affected by erratum #843419 which can
>>> lead to a memory access using an incorrect address in certain sequences
>>> headed by an ADRP instruction.
>>
>> Just a heads up that we're seeing a regression in the Ubuntu 4.2 kernel on
>> X-Gene after this patch is applied and the CONFIG enabled.
>>
>> Modules loads fail with messages like:
>>
>> [ 2.192721] module gpio_xgene_sb: unsupported RELA relocation: 275
>> [ 2.193609] module xgene_enet: unsupported RELA relocation: 275
>> [ 2.249402] module libahci: unsupported RELA relocation: 275
>> [ 2.249628] module xgene_enet: unsupported RELA relocation: 275
>> [ 2.359451] module xgene_enet: unsupported RELA relocation: 275
>> [ 2.389444] module xgene_enet: unsupported RELA relocation: 275
>> [ 3.473766] module linear: unsupported RELA relocation: 275
>> [ 3.543252] module multipath: unsupported RELA relocation: 275
>> [ 3.593268] module raid0: unsupported RELA relocation: 275
>> [ 3.663695] module raid1: unsupported RELA relocation: 275
>> [ 3.713964] module raid6_pq: unsupported RELA relocation: 275
>> [ 3.763983] module raid6_pq: unsupported RELA relocation: 275
>> [ 3.803975] module raid6_pq: unsupported RELA relocation: 275
>> [ 3.853881] module raid10: unsupported RELA relocation: 275
>> [ 3.924962] module raid6_pq: unsupported RELA relocation: 275
>>
>
> RELA #275 is the relocation against ADRP instructions, which GCC
> should not emit anymore when -mcmodel=large is in effect.
>
> Can you confirm that the modules have been rebuilt with this config as
> well?

Yeah, it was.

> Can you double check the GCC command line (with V=1) when doing
> 'make modules' to ensure that '-mcmodel=large' is being passed?

I did, and I don't see -mcmodel at all. On a whim I changed
CFLAGS_MODULE in the patch to KBUILD_CFLAGS_MODULE, and V=1 now shows
-mcmodel=large. I haven't had time yet to figure out why the KBUILD
variant is important, nor time to boot test such a build (travel day).

> Can
> you check with 'readelf -r' which objects still contain
> R_AARCH64_ADR_PREL_PG_HI21 relocations?

My readelf seems to truncate the type field (even w/ -W). Let me know
if you still need the list of objects after the above and I can try
fixing it.

  -dann

>
>
>> I haven't attempted to reproduce with a pure upstream kernel yet.
>>
>> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1502946
>>
>>    -dann
>>
>>> There is a linker fix to generate veneers for ADRP instructions, but
>>> this doesn't work for kernel modules which are built as unlinked ELF
>>> objects.
>>>
>>> This patch adds a new config option for the erratum which, when enabled,
>>> builds kernel modules with the mcmodel=large flag. This uses absolute
>>> addressing for all kernel symbols, thereby removing the use of ADRP as
>>> a PC-relative form of addressing. The ADRP relocs are removed from the
>>> module loader so that we fail to load any potentially affected modules.
>>>
>>> Signed-off-by: Will Deacon <will.deacon at arm.com>
>>> ---
>>>  arch/arm64/Kconfig         | 16 ++++++++++++++++
>>>  arch/arm64/Makefile        |  4 ++++
>>>  arch/arm64/kernel/module.c |  2 ++
>>>  3 files changed, 22 insertions(+)
>>>
>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>>> index 7d95663c0160..11ff4d57c92a 100644
>>> --- a/arch/arm64/Kconfig
>>> +++ b/arch/arm64/Kconfig
>>> @@ -331,6 +331,22 @@ config ARM64_ERRATUM_845719
>>>
>>>           If unsure, say Y.
>>>
>>> +config ARM64_ERRATUM_843419
>>> +       bool "Cortex-A53: 843419: A load or store might access an incorrect address"
>>> +       depends on MODULES
>>> +       default y
>>> +       help
>>> +         This option builds kernel modules using the large memory model in
>>> +         order to avoid the use of the ADRP instruction, which can cause
>>> +         a subsequent memory access to use an incorrect address on Cortex-A53
>>> +         parts up to r0p4.
>>> +
>>> +         Note that the kernel itself must be linked with a version of ld
>>> +         which fixes potentially affected ADRP instructions through the
>>> +         use of veneers.
>>> +
>>> +         If unsure, say Y.
>>> +
>>>  endmenu
>>>
>>>
>>> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
>>> index 15ff5b4156fd..f9914d7c1bb0 100644
>>> --- a/arch/arm64/Makefile
>>> +++ b/arch/arm64/Makefile
>>> @@ -41,6 +41,10 @@ endif
>>>
>>>  CHECKFLAGS     += -D__aarch64__
>>>
>>> +ifeq ($(CONFIG_ARM64_ERRATUM_843419), y)
>>> +CFLAGS_MODULE  += -mcmodel=large
>>> +endif
>>> +
>>>  # Default value
>>>  head-y         := arch/arm64/kernel/head.o
>>>
>>> diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
>>> index 67bf4107f6ef..876eb8df50bf 100644
>>> --- a/arch/arm64/kernel/module.c
>>> +++ b/arch/arm64/kernel/module.c
>>> @@ -332,12 +332,14 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
>>>                         ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 0, 21,
>>>                                              AARCH64_INSN_IMM_ADR);
>>>                         break;
>>> +#ifndef CONFIG_ARM64_ERRATUM_843419
>>>                 case R_AARCH64_ADR_PREL_PG_HI21_NC:
>>>                         overflow_check = false;
>>>                 case R_AARCH64_ADR_PREL_PG_HI21:
>>>                         ovf = reloc_insn_imm(RELOC_OP_PAGE, loc, val, 12, 21,
>>>                                              AARCH64_INSN_IMM_ADR);
>>>                         break;
>>> +#endif
>>>                 case R_AARCH64_ADD_ABS_LO12_NC:
>>>                 case R_AARCH64_LDST8_ABS_LO12_NC:
>>>                         overflow_check = false;
>>> --
>>> 2.1.4
>>>
>>>
>>> _______________________________________________
>>> linux-arm-kernel mailing list
>>> linux-arm-kernel at lists.infradead.org
>>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>
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