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Subject: Re: [PATCH v2 19/33] lib/zlib: Unpoison DFLTCC output buffers
From:   Ilya Leoshkevich <iii@linux.ibm.com>
To:     Alexander Potapenko <glider@google.com>
Cc:     Alexander Gordeev <agordeev@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Marco Elver <elver@google.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Pekka Enberg <penberg@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>,
        kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-s390@vger.kernel.org,
        linux-trace-kernel@vger.kernel.org,
        Mark Rutland <mark.rutland@arm.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Sven Schnelle <svens@linux.ibm.com>,
        Mikhail Zaslonko <zaslonko@linux.ibm.com>
Date:   Fri, 08 Dec 2023 15:14:01 +0100
In-Reply-To: <CAG_fn=WiT7C2QMCwq_nBg9FXZrJ2-mSyJuM1uVz_3Mag8xBHJg@mail.gmail.com>
References: <20231121220155.1217090-1-iii@linux.ibm.com>
         <20231121220155.1217090-20-iii@linux.ibm.com>
         <CAG_fn=WiT7C2QMCwq_nBg9FXZrJ2-mSyJuM1uVz_3Mag8xBHJg@mail.gmail.com>
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On Fri, 2023-12-08 at 14:32 +0100, Alexander Potapenko wrote:
> On Tue, Nov 21, 2023 at 11:07=E2=80=AFPM Ilya Leoshkevich <iii@linux.ibm.=
com>
> wrote:
> >=20
> > 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.
>=20
> 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.