linux-kernel - Re: [PATCH v2 08/18] arm64: don't disable ADR_PREL_PG_HI21* with ARM64_ERRATUM

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Date:   Wed, 15 Nov 2017 22:29:12 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Alex Matveev <alxmtvv@...il.com>, Andi Kleen <ak@...ux.intel.com>,
        Greg Hackmann <ghackmann@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-kbuild@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Yury Norov <ynorov@...iumnetworks.com>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: Re: [PATCH v2 08/18] arm64: don't disable ADR_PREL_PG_HI21* with ARM64_ERRATUM_843419

On 15 November 2017 at 21:34, Sami Tolvanen <samitolvanen@...gle.com> wrote:
> CONFIG_LTO_CLANG depends on GNU gold, which can generate ADR_PREL_PG_HI21*
> relocations even with --fix-cortex-a53-843419.
>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> ---
>  arch/arm64/kernel/module.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
> index f469e0435903..fec9a578f122 100644
> --- a/arch/arm64/kernel/module.c
> +++ b/arch/arm64/kernel/module.c
> @@ -336,14 +336,12 @@ 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;
> --
> 2.15.0.448.gf294e3d99a-goog
>

I think this change is reasonable in itself, but i do wonder how we
can ensure that the adrp instructions that GNU gold does generate are
not affected by the erratum, given that modules are partially linked
object files, not shared libraries.