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

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Message-ID: <CAAeHK+yuUJFbQBCPyp7S+hVMzBM0m=tgrWLMCskELF6SXHXimw@mail.gmail.com>
Date:   Fri, 16 Oct 2020 17:52:42 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Kostya Serebryany <kcc@...gle.com>,
        Serban Constantinescu <serbanc@...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>,
        Marco Elver <elver@...gle.com>
Subject: Re: [PATCH RFC 0/8] kasan: hardware tag-based mode for production use
 on arm64

On Fri, Oct 16, 2020 at 3:31 PM Marco Elver <elver@...gle.com> wrote:
>
> 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

CC Kostya and Serban.