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

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Message-ID: <4f0eb4b4d4f6830f39555dc8a35f6ff88d6f8e63.camel@linux.ibm.com>
Date:   Fri, 08 Dec 2023 15:14:01 +0100
From:   Ilya Leoshkevich <iii@...ux.ibm.com>
To:     Alexander Potapenko <glider@...gle.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, 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.

The code is also somewhat tricky in the are of buffer management, so I
find it beneficial to have it checked for uninitialized memory
accesses.