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

[Dann Frazier]

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

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
>
>
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