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Wed, 19 Jun 2024 11:46:52 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 90CFD2004B; Wed, 19 Jun 2024 11:46:50 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2858220063; Wed, 19 Jun 2024 11:46:50 +0000 (GMT) Received: from [9.155.200.166] (unknown [9.155.200.166]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 19 Jun 2024 11:46:50 +0000 (GMT) Message-ID: Subject: Re: [PATCH v4 16/35] mm: slub: Unpoison the memchr_inv() return value From: Ilya Leoshkevich To: Alexander Potapenko Cc: Alexander Gordeev , Andrew Morton , Christoph Lameter , David Rientjes , Heiko Carstens , Joonsoo Kim , Marco Elver , Masami Hiramatsu , Pekka Enberg , Steven Rostedt , Vasily Gorbik , Vlastimil Babka , Christian Borntraeger , Dmitry Vyukov , 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 , Roman Gushchin , Sven Schnelle Date: Wed, 19 Jun 2024 13:46:50 +0200 In-Reply-To: References: <20240613153924.961511-1-iii@linux.ibm.com> <20240613153924.961511-17-iii@linux.ibm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.4 (3.50.4-1.fc39) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: tzqSr8HO345mo1Ia6Q97gqSzudRJArNH X-Proofpoint-GUID: ljUZ8zkZEQkiMouQPJQ5SsIz1Fy2T4Or X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.28.16 definitions=2024-06-19_02,2024-06-19_01,2024-05-17_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 lowpriorityscore=0 malwarescore=0 mlxlogscore=749 phishscore=0 impostorscore=0 adultscore=0 spamscore=0 priorityscore=1501 suspectscore=0 bulkscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2405170001 definitions=main-2406190084 On Tue, 2024-06-18 at 16:38 +0200, Alexander Potapenko wrote: > On Thu, Jun 13, 2024 at 5:39=E2=80=AFPM Ilya Leoshkevich > wrote: > >=20 > > Even though the KMSAN warnings generated by memchr_inv() are > > suppressed > > by metadata_access_enable(), its return value may still be > > poisoned. > >=20 > > The reason is that the last iteration of memchr_inv() returns > > `*start !=3D value ? start : NULL`, where *start is poisoned. Because > > of > > this, somewhat counterintuitively, the shadow value computed by > > visitSelectInst() is equal to `(uintptr_t)start`. > >=20 > > The intention behind guarding memchr_inv() behind > > metadata_access_enable() is to touch poisoned metadata without > > triggering KMSAN, so unpoison its return value. >=20 > What do you think about applying __no_kmsan_checks to these functions > instead? Ok, will do. The __no_kmsan_checks approach is already taken by "mm: kfence: Disable KMSAN when checking the canary", so we might as well be consistent in how we fix these issues.