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AJvYcCVnfKKdjhTTsZvV/1lF4f287wZM62/z04StTNZX65TNxSJJ18MsVaaxfaRad+yPBg+FENTk1NUzY4mI3wdR3fv1n60= X-Gm-Message-State: AOJu0YwAIZx+hYbg3NVaR+3uBV8W1YlHe5qBr/6fVkCLI69R8QXgI5+t pA51mMccXXcaiD8FyjrBSCxNB6x9bWyQPoohlbUorsFh4iUcoYhsyYEWLN6PzBqbWUb2tcs5jj5 pxPjbmraatbWU7kY/Aqi48nSIqxT2sZkmDnQW X-Google-Smtp-Source: AGHT+IEdmrRM4Gbu+d4I3hoRKq+4aL4Fg6hfbxGg0ziYrJZB/rZ9bgxi2fl+hGtqtzvIL6W2TRHW+Qf+Zm5AY3puluQ= X-Received: by 2002:a05:6870:3a0f:b0:259:f03c:4e91 with SMTP id 586e51a60fabf-25c949cd968mr4093311fac.8.1718874075898; Thu, 20 Jun 2024 02:01:15 -0700 (PDT) MIME-Version: 1.0 References: <20240619154530.163232-1-iii@linux.ibm.com> <20240619154530.163232-18-iii@linux.ibm.com> In-Reply-To: <20240619154530.163232-18-iii@linux.ibm.com> From: Alexander Potapenko Date: Thu, 20 Jun 2024 11:00:39 +0200 Message-ID: Subject: Re: [PATCH v5 17/37] mm: slub: Disable KMSAN when checking the padding bytes 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-Queue-Id: 4E4B340028 X-Stat-Signature: or8f7inwtzow3o5jkjp96on4tiiesqf6 X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1718874077-21322 X-HE-Meta: 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 WkNrJB5/ NGG+DyCMy5iLOXGp1GxqLYZKbCBzMs+poSGNg9uiKabz4TbGmzyM/0p55UUhwOYOS0SQpH89MI2A2Q/ZcPnAe41v6n/irtcuLW3pPaJiSIrw/ZuuNLaIIUg/HdLphSXL+vHIgOrLz0QywpK9Ir02RaBqncaeiTLyaqilOe4lBwTRl/I9ChX6LzDvom0jUrZevi7HzxrADAxCx7GQvpEhgUov5AnGxAmzxYpp61bNv93hOHAq1sDxn8oHS3RBZQLhHRKJZe066Bv489uxd89OpA0jA0iwAeJBLUoZX X-Bogosity: Ham, tests=bogofilter, spamicity=0.099046, 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 Wed, Jun 19, 2024 at 5:45=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`. > > One possibility to fix this, since the intention behind guarding > memchr_inv() behind metadata_access_enable() is to touch poisoned > metadata without triggering KMSAN, is to unpoison its return value. > However, this approach is too fragile. So simply disable the KMSAN > checks in the respective functions. > > Signed-off-by: Ilya Leoshkevich Reviewed-by: Alexander Potapenko