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Tue, 18 Jun 2024 07:39:08 -0700 (PDT) MIME-Version: 1.0 References: <20240613153924.961511-1-iii@linux.ibm.com> <20240613153924.961511-17-iii@linux.ibm.com> In-Reply-To: <20240613153924.961511-17-iii@linux.ibm.com> From: Alexander Potapenko Date: Tue, 18 Jun 2024 16:38:31 +0200 Message-ID: Subject: Re: [PATCH v4 16/35] mm: slub: Unpoison the memchr_inv() return value To: Ilya Leoshkevich 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: C6A9A140011 X-Stat-Signature: 1uwun9n31a6rgim79iowhizsaqmswxqe X-Rspam-User: X-HE-Tag: 1718721549-737209 X-HE-Meta: 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 rlGWfVQ/ Xrzs9ORi3iUgT2l0PA4Zw7Wxv48SD1e1/oH2X6z1wHSn/+wr22aSJyJlroGjuGPimJRWRnFxt7fCZDd34e3kOzG4HRoSVs23W478T8zzZnA2Z5vzcyaP8vRNyq14DLyCtrd454htY6xAYsa0PbE/3XMpMHLC99dzcVYQ087k638kAgzBcM4Vhahfxftn37z0umx0U5T/k0xV+cCk4syhPn5VRJ7TV58Z+Ix7L2rqi/IV3lF21bd9x6KK/Igj8YutQrr5nMGocxIPJZWekuz92fhI69Yk+SLRhqsDEAM3IAPwWluceP1Kvye8Hfw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.290000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jun 13, 2024 at 5:39=E2=80=AFPM Ilya Leoshkevich wrote: > > Even though the KMSAN warnings generated by memchr_inv() are suppressed > by metadata_access_enable(), its return value may still be poisoned. > > 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`. > > The intention behind guarding memchr_inv() behind > metadata_access_enable() is to touch poisoned metadata without > triggering KMSAN, so unpoison its return value. What do you think about applying __no_kmsan_checks to these functions inste= ad?