linux-kernel - Re: [PATCH 22/35] arm64: mte: Enable in-kernel MTE

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Date:   Tue, 8 Sep 2020 16:39:35 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Elena Petrova <lenaptr@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH 22/35] arm64: mte: Enable in-kernel MTE

On Fri, Aug 14, 2020 at 7:28 PM Andrey Konovalov <andreyknvl@...gle.com> wrote:
>
> From: Vincenzo Frascino <vincenzo.frascino@....com>
>
> The Tag Checking operation causes a synchronous data abort as
> a consequence of a tag check fault when MTE is configured in
> synchronous mode.
>
> Enable MTE in Synchronous mode in EL1 to provide a more immediate
> way of tag check failure detection in the kernel.
>
> As part of this change enable match-all tag for EL1 to allow the
> kernel to access user pages without faulting. This is required because
> the kernel does not have knowledge of the tags set by the user in a
> page.
>
> Note: For MTE, the TCF bit field in SCTLR_EL1 affects only EL1 in a
> similar way as TCF0 affects EL0.
>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
> ---
>  arch/arm64/kernel/cpufeature.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 4d3abb51f7d4..4d94af19d8f6 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1670,6 +1670,9 @@ static void cpu_enable_mte(struct arm64_cpu_capabilities const *cap)
>         write_sysreg_s(0, SYS_TFSR_EL1);
>         write_sysreg_s(0, SYS_TFSRE0_EL1);
>
> +       /* Enable Match-All at EL1 */
> +       sysreg_clear_set(tcr_el1, 0, SYS_TCR_EL1_TCMA1);
> +
>         /*
>          * CnP must be enabled only after the MAIR_EL1 register has been set
>          * up. Inconsistent MAIR_EL1 between CPUs sharing the same TLB may
> @@ -1687,6 +1690,9 @@ static void cpu_enable_mte(struct arm64_cpu_capabilities const *cap)
>         mair &= ~MAIR_ATTRIDX(MAIR_ATTR_MASK, MT_NORMAL_TAGGED);
>         mair |= MAIR_ATTRIDX(MAIR_ATTR_NORMAL_TAGGED, MT_NORMAL_TAGGED);
>         write_sysreg_s(mair, SYS_MAIR_EL1);
> +
> +       /* Enable MTE Sync Mode for EL1 */
> +       sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
>         isb();
>
>         local_flush_tlb_all();
> --
> 2.28.0.220.ged08abb693-goog
>

Should we change this commit to enable in-kernel MTE only if
KASAN_HW_TAGS is enabled?