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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Thu, 12 Nov 2020 20:52:55 +0100
Message-ID: <CAAeHK+ycTa2nxg=vOVV_Sfn=w_883VRXYXE6Eb1gE=HXxSD8ow@mail.gmail.com>
Subject: Re: [PATCH v2 11/20] kasan: add and integrate kasan boot parameters
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     Marco Elver <elver@google.com>, Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        Will Deacon <will.deacon@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Thu, Nov 12, 2020 at 1:55 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> On Thu, Nov 12, 2020 at 12:53:58PM +0100, Marco Elver wrote:
> > On Thu, 12 Nov 2020 at 12:35, Catalin Marinas <catalin.marinas@arm.com> wrote:
> > >
> > > On Tue, Nov 10, 2020 at 11:20:15PM +0100, Andrey Konovalov wrote:
> > > > Hardware tag-based KASAN mode is intended to eventually be used in
> > > > production as a security mitigation. Therefore there's a need for finer
> > > > control over KASAN features and for an existence of a kill switch.
> > > >
> > > > This change adds a few boot parameters for hardware tag-based KASAN that
> > > > allow to disable or otherwise control particular KASAN features.
> > > >
> > > > The features that can be controlled are:
> > > >
> > > > 1. Whether KASAN is enabled at all.
> > > > 2. Whether KASAN collects and saves alloc/free stacks.
> > > > 3. Whether KASAN panics on a detected bug or not.
> > > >
> > > > With this change a new boot parameter kasan.mode allows to choose one of
> > > > three main modes:
> > > >
> > > > - kasan.mode=off - KASAN is disabled, no tag checks are performed
> > > > - kasan.mode=prod - only essential production features are enabled
> > > > - kasan.mode=full - all KASAN features are enabled
> > >
> > > Alternative naming if we want to avoid "production" (in case someone
> > > considers MTE to be expensive in a production system):
> > >
> > > - kasan.mode=off
> > > - kasan.mode=on
> > > - kasan.mode=debug
> >
> > I believe this was what it was in RFC, and we had a long discussion on
> > what might be the most intuitive options. Since KASAN is still a
> > debugging tool for the most part, an "on" mode might imply we get all
> > the debugging facilities of regular KASAN. However, this is not the
> > case and misleading. Hence, we decided to be more explicit and avoid
> > "on".
>
> Even better, kasan.mode=fast ;).

Well, it uses sync, so technically it's not as fast as it could be with async :)