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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Thu, 18 Feb 2021 21:26:36 +0100
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Subject: Re: [PATCH] mm, kasan: don't poison boot memory
To:     David Hildenbrand <david@redhat.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        George Kennedy <george.kennedy@oracle.com>,
        Konrad Rzeszutek Wilk <konrad@darnok.org>,
        Will Deacon <will.deacon@arm.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>,
        Peter Collingbourne <pcc@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        Christoph Hellwig <hch@infradead.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, Feb 18, 2021 at 8:46 PM David Hildenbrand <david@redhat.com> wrote:
>
> > 1. For KASAN_GENERIC: leave everything as is to be able to detect
> > these boot-time bugs.
> >
> > 2. For KASAN_SW_TAGS: remove boot-time poisoning via
> > kasan_free_pages(), but use the "invalid" tag as the default shadow
> > value. The end result should be the same: bad accesses will be
> > detected. For unallocated memory as it has the default "invalid" tag,
> > and for allocated memory as it's poisoned properly when
> > allocated/freed.
> >
> > 3. For KASAN_HW_TAGS: just remove boot-time poisoning via
> > kasan_free_pages(). As the memory tags have a random unspecified
> > value, we'll still have a 15/16 chance to detect a memory corruption.
> >
> > This also makes sense from the performance perspective: KASAN_GENERIC
> > isn't meant to be running in production, so having a larger perf
> > impact is acceptable. The other two modes will be faster.
>
> Sounds in principle sane to me.

I'll post a v2 soon, thanks!

> Side note: I am not sure if anybody runs KASAN in production. Memory is
> expensive. Feel free to prove me wrong, I'd be very interest in actual
> users.

We run KASAN_SW_TAGS on some dogfood testing devices, and
KASAN_HW_TAGS is being developed with the goal to be running in
production.