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

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Message-ID: <CANpmjNPvx4oozqSf9ZXN8FhZia03Y0Ar0twrogkfoxTekHx39A@mail.gmail.com>
Date:   Fri, 16 Oct 2020 15:31:28 +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>
Subject: Re: [PATCH RFC 0/8] kasan: hardware tag-based mode for production use
 on arm64

On Fri, 16 Oct 2020 at 15:17, 'Andrey Konovalov' via kasan-dev
<kasan-dev@...glegroups.com> wrote:
[...]
> > > The intention with this kind of a high level switch is to hide the
> > > implementation details. Arguably, we could add multiple switches that allow
> > > to separately control each KASAN or MTE feature, but I'm not sure there's
> > > much value in that.
> > >
> > > Does this make sense? Any preference regarding the name of the parameter
> > > and its values?
> >
> > KASAN itself used to be a debugging tool only. So introducing an "on"
> > mode which no longer follows this convention may be confusing.
>
> Yeah, perhaps "on" is not the best name here.
>
> > Instead, maybe the following might be less confusing:
> >
> > "full" - current "debug", normal KASAN, all debugging help available.
> > "opt" - current "on", optimized mode for production.
>
> How about "prod" here?

SGTM.

[...]
>
> > > Should we somehow control whether to panic the kernel on a tag fault?
> > > Another boot time parameter perhaps?
> >
> > It already respects panic_on_warn, correct?
>
> Yes, but Android is unlikely to enable panic_on_warn as they have
> warnings happening all over. AFAIR Pixel 3/4 kernels actually have a
> custom patch that enables kernel panic for KASAN crashes specifically
> (even though they don't obviously use KASAN in production), and I
> think it's better to provide a similar facility upstream. Maybe call
> it panic_on_kasan or something?

Best would be if kasan= can take another option, e.g.
"kasan=prod,panic". I think you can change the strcmp() to a
str_has_prefix() for the checks for full/prod/on/off, and then check
if what comes after it is ",panic".

Thanks,
-- Marco