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Donenfeld" , David Hildenbrand , Alexander Viro , Christian Brauner , Jan Kara , Andrea Arcangeli , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v2 1/4] userfaultfd: correctly prevent registering VM_DROPPABLE regions Message-Id: <20250607150438.4439e19f74693445212d93df@linux-foundation.org> In-Reply-To: <20250607-uffd-fixes-v2-1-339dafe9a2fe@columbia.edu> References: <20250607-uffd-fixes-v2-0-339dafe9a2fe@columbia.edu> <20250607-uffd-fixes-v2-1-339dafe9a2fe@columbia.edu> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: E765140004 X-Stat-Signature: gptt7cae7a36hby8kqqbyzttdfm7qxp5 X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1749333880-792773 X-HE-Meta: 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 +w/Qm3e8 qCO5OC3N2I6jcGhMR2IwogVLeKsadTnnqvtevNIT/AlBVawUhX970NH9BE6nujYS8/pixPV3kgH8w6rZE28b3Y03sFOMyGGOHzp70XV7WPRXtUfF5fnUzXo3E4Sy32hf2FsgVRL2OQ2daEYSSgF/anja9UJ1VXjQtkaodZJMlCqKql7RtSs5N9912pV1/UO1BSf/vFaMcBUkHy10F5PBMlKCiam46Wr6V3cLbJw+YVvER9L6VIoRfCVFaySPkWqbdyDnASIiOPHdagEvstMSDhdEqYqA13VT9NvBwyPfBwXdzaemuQG7LJATCNN/P+Zi8UnnO X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 Sat, 07 Jun 2025 02:40:00 -0400 Tal Zussman wrote: > vma_can_userfault() masks off non-userfaultfd VM flags from vm_flags. > The vm_flags & VM_DROPPABLE test will then always be false, incorrectly > allowing VM_DROPPABLE regions to be registered with userfaultfd. > > Additionally, vm_flags is not guaranteed to correspond to the actual > VMA's flags. Fix this test by checking the VMA's flags directly. Wondering if we should backport this. afaict we don't know the userspace impact of this because nobody has tried it!