linux-kernel - Re: [PATCH v2 19/33] lib/zlib: Unpoison DFLTCC output buffers

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Message-ID: <CAG_fn=XUSfppyVMZO5K2kaii+OSLxV_UbHcn3cuH3zBt9J3g1g@mail.gmail.com>
Date:   Fri, 8 Dec 2023 15:25:21 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     Ilya Leoshkevich <iii@...ux.ibm.com>
Cc:     Alexander Gordeev <agordeev@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Marco Elver <elver@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Pekka Enberg <penberg@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-s390@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Mikhail Zaslonko <zaslonko@...ux.ibm.com>
Subject: Re: [PATCH v2 19/33] lib/zlib: Unpoison DFLTCC output buffers

On Fri, Dec 8, 2023 at 3:14 PM Ilya Leoshkevich <iii@...ux.ibm.com> wrote:
>
> On Fri, 2023-12-08 at 14:32 +0100, Alexander Potapenko wrote:
> > On Tue, Nov 21, 2023 at 11:07 PM Ilya Leoshkevich <iii@...ux.ibm.com>
> > wrote:
> > >
> > > The constraints of the DFLTCC inline assembly are not precise: they
> > > do not communicate the size of the output buffers to the compiler,
> > > so
> > > it cannot automatically instrument it.
> >
> > KMSAN usually does a poor job instrumenting inline assembly.
> > Wouldn't be it better to switch to pure C ZLIB implementation, making
> > ZLIB_DFLTCC depend on !KMSAN?
>
> Normally I would agree, but the kernel DFLTCC code base is synced with
> the zlib-ng code base to the extent that it uses the zlib-ng code style
> instead of the kernel code style, and MSAN annotations are already a
> part of the zlib-ng code base. So I would prefer to keep them for
> consistency.

Hm, I didn't realize this code is being taken from elsewhere.
If so, maybe we should come up with an annotation that can be
contributed to zlib-ng, so that it doesn't cause merge conflicts every
time Mikhail is doing an update?
(leaving this up to you to decide).

If you decide to go with the current solution, please consider adding
an #include for kmsan-checks.h, which introduces
kmsan_unpoison_memory().