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References: <20231213233605.661251-1-iii@linux.ibm.com> <20231213233605.661251-18-iii@linux.ibm.com>
In-Reply-To: <20231213233605.661251-18-iii@linux.ibm.com>
From: Alexander Potapenko <glider@google.com>
Date: Fri, 22 Dec 2023 12:35:27 +0100
Message-ID: <CAG_fn=UNdruNOkyQ8c5mdWQGC1-xP+86GX9Zsdg3VSc=5itNaA@mail.gmail.com>
Subject: Re: [PATCH v3 17/34] lib/zlib: Unpoison DFLTCC output buffers
To: Ilya Leoshkevich <iii@linux.ibm.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>
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On Thu, Dec 14, 2023 at 12:36=E2=80=AFAM Ilya Leoshkevich <iii@linux.ibm.co=
m> 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.
>
> Add the manual kmsan_unpoison_memory() calls for the output buffers.
> The logic is the same as in [1].
>
> [1] https://github.com/zlib-ng/zlib-ng/commit/1f5ddcc009ac3511e99fc88736a=
9e1a6381168c5
>
> Reported-by: Alexander Gordeev <agordeev@linux.ibm.com>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@google.com>


> @@ -34,6 +37,7 @@ static inline dfltcc_cc dfltcc(
>  )
>  {
>      Byte *t2 =3D op1 ? *op1 : NULL;
> +    unsigned char *orig_t2 =3D t2;
>      size_t t3 =3D len1 ? *len1 : 0;
>      const Byte *t4 =3D op2 ? *op2 : NULL;
>      size_t t5 =3D len2 ? *len2 : 0;
> @@ -59,6 +63,26 @@ static inline dfltcc_cc dfltcc(
>                       : "cc", "memory");
>      t2 =3D r2; t3 =3D r3; t4 =3D r4; t5 =3D r5;
>
> +    switch (fn & DFLTCC_FN_MASK) {

It might be a good idea to add a comment explaining what this block of
code does.
(And that it is no-op in non-KMSAN builds)