linux-kernel - Re: [PATCH v13 4/7] arm64: mte: Enable TCO in functions that can read beyond buffer limits

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Message-ID: <bf45cf22-662b-e99c-4868-bfc64a0622b0@arm.com>
Date:   Tue, 23 Feb 2021 14:25:14 +0000
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: [PATCH v13 4/7] arm64: mte: Enable TCO in functions that can read
 beyond buffer limits

On 2/23/21 12:49 PM, Will Deacon wrote:
>>> I totally agree on this point. In the case of runtime switching we might need
>>> the rethink completely the strategy and depends a lot on what we want to allow
>>> and what not. For the kernel I imagine we will need to expose something in sysfs
>>> that affects all the cores and then maybe stop_machine() to propagate it to all
>>> the cores. Do you think having some of the cores running in sync mode and some
>>> in async is a viable solution?
>> stop_machine() is an option indeed. I think it's still possible to run
>> some cores in async while others in sync but the static key here would
>> only be toggled when no async CPUs are left.
> Just as a general point, but if we expose stop_machine() via sysfs we
> probably want to limit that to privileged users so you can't DoS the system
> by spamming into the file.

I agree, if we ever introduce the runtime switching and go for this option we
should make sure that we do it safely.

-- 
Regards,
Vincenzo