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References: <20211214162050.660953-1-glider@google.com> <YbjIHa/1Qr/v8Q8J@kroah.com>
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From:   Alexander Potapenko <glider@google.com>
Date:   Thu, 16 Dec 2021 11:12:52 +0100
Message-ID: <CAG_fn=Ub57GfJwUuuKqfc0rhFOdRF9e=vgb4fwm_bXYziraFMA@mail.gmail.com>
Subject: Re: [PATCH 00/43] Add KernelMemorySanitizer infrastructure
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Christoph Hellwig <hch@lst.de>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ilya Leoshkevich <iii@linux.ibm.com>,
        Ingo Molnar <mingo@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Kees Cook <keescook@chromium.org>,
        Marco Elver <elver@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Pekka Enberg <penberg@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vegard Nossum <vegard.nossum@oracle.com>,
        Vlastimil Babka <vbabka@suse.cz>, linux-mm@kvack.org,
        linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
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On Tue, Dec 14, 2021 at 5:36 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Tue, Dec 14, 2021 at 05:20:07PM +0100, Alexander Potapenko wrote:
> > KernelMemorySanitizer (KMSAN) is a detector of errors related to uses o=
f
> > uninitialized memory. It relies on compile-time Clang instrumentation
> > (similar to MSan in the userspace [1]) and tracks the state of every bi=
t
> > of kernel memory, being able to report an error if uninitialized value =
is
> > used in a condition, dereferenced, or escapes to userspace, USB or DMA.
>
> Why is USB unique here?

syzkaller just happens to be good at fuzzing USB drivers, so it was
fairly easy to implement and test USB support for KMSAN.
This should give the maintainers of other buses an idea of how this
could be done :)

 What about serial data?  i2c?  spi?  w1?  We
> have a lot of different I/O bus types :)

We hope to cover those after KMSAN hits upstream.

>
> And how is DMA checked given that the kernel shouldn't be seeing dma
> memory?

Before writing a buffer to DMA, that buffer's contents are checked by
KMSAN. If there are uninitialized bytes, those will be reported.
After reading a buffer from DMA, it is marked as initialized to avoid
false positives.
We do not track DMA memory itself.

> thanks,
>
> greg k-h


--=20
Alexander Potapenko
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