linux-kernel - Re: [PATCH RFC 0/8] kasan: hardware tag-based mode for production use on arm64

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Message-ID: <CANpmjNN3Ax2_CfxXixh8-NipXOx7s8vprg23ua-M_tvUKZGq0Q@mail.gmail.com>
Date:   Mon, 19 Oct 2020 14:23:20 +0200
From:   Marco Elver <elver@...gle.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Elena Petrova <lenaptr@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Serban Constantinescu <serbanc@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>
Subject: Re: [PATCH RFC 0/8] kasan: hardware tag-based mode for production use
 on arm64

On Wed, 14 Oct 2020 at 22:44, Andrey Konovalov <andreyknvl@...gle.com> wrote:
[...]
> A question to KASAN maintainers: what would be the best way to support the
> "off" mode? I see two potential approaches: add a check into each kasan
> callback (easier to implement, but we still call kasan callbacks, even
> though they immediately return), or add inline header wrappers that do the
> same.

This is tricky, because we don't know how bad the performance will be
if we keep them as calls. We'd have to understand the performance
impact of keeping them as calls, and if the performance impact is
acceptable or not.

Without understanding the performance impact, the only viable option I
see is to add __always_inline kasan_foo() wrappers, which use the
static branch to guard calls to __kasan_foo().

Thanks,
-- Marco