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[79.224.245.239]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a5323c08fasm207200f8f.44.2025.06.05.14.06.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Jun 2025 14:06:40 -0700 (PDT) Message-ID: <0a1dab1c-80d2-436f-857f-734d95939aec@redhat.com> Date: Thu, 5 Jun 2025 23:06:38 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/3] userfaultfd: prevent unregistering VMAs through a different userfaultfd To: Peter Xu Cc: Tal Zussman , Andrew Morton , "Jason A. Donenfeld" , Alexander Viro , Christian Brauner , Jan Kara , Pavel Emelyanov , Andrea Arcangeli , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org References: <20250603-uffd-fixes-v1-0-9c638c73f047@columbia.edu> <20250603-uffd-fixes-v1-2-9c638c73f047@columbia.edu> <84cf5418-42e9-4ec5-bd87-17ba91995c47@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: tWMJ3FbTo4ILMIpigmPfdlE7YQbBoIAhjhzyi1nIfvE_1749157603 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 8958C1C0010 X-Stat-Signature: yodgy7pkawa8mggr357b69i9p1iizd6o X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1749157605-202502 X-HE-Meta: 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 qyTfOIpS 6YsBix6CKTAq2GK6XsU2cunBYNcQSa/eOSztGZ8R7II8cdTMVMUOe60CB24P50O1Hkdpy8kx4CvOZuZkXp549QWx5b3Z+CrLYHUv0eiTfqZ+6zL6J54TIBR8JXmS6Zt7EXj0cM8mG/Tew9w1owbke3nFRNYxtQ7pkSm5lDkJfo6woKdt5d0n4zB6EEQKx11klaAL25dax/wIrlHwzfwKukNEc+BUaObrtOZsE+WTbmKaZpGATeVSYCCA3sDMwFXjxqm2YuNcOjzEyVSA7m7LPd57mTxLrObVgl6d1bCtschmVGVesH22q2jgkzgk831bKHB7zg/e9G2v/TDBlZ1n1zoddkezXBxX3wHqG2kex8znGlxEaXzn8gT/sWHNq9CybrQz2feIwz0icAqTIGqoAlQ7WYOFoSYfBO5riGWFR7SybAFS8uxAHK5zdrHWkvjmc9LuX 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 04.06.25 17:09, Peter Xu wrote: > On Wed, Jun 04, 2025 at 03:23:38PM +0200, David Hildenbrand wrote: >> On 04.06.25 00:14, Tal Zussman wrote: >>> Currently, a VMA registered with a uffd can be unregistered through a >>> different uffd asssociated with the same mm_struct. >>> >>> Change this behavior to be stricter by requiring VMAs to be unregistered >>> through the same uffd they were registered with. >>> >>> While at it, correct the comment for the no userfaultfd case. This seems >>> to be a copy-paste artifact from the analagous userfaultfd_register() >>> check. >> >> I consider it a BUG that should be fixed. Hoping Peter can share his >> opinion. > > Agree it smells like unintentional, it's just that the man page indeed > didn't mention what would happen if the userfaultfd isn't the one got > registered but only requesting them to be "compatible". > > DESCRIPTION > Unregister a memory address range from userfaultfd. The pages in > the range must be “compatible” (see UFFDIO_REGISTER(2const)). > > So it sounds still possible if we have existing userapp creating multiple > userfaultfds (for example, for scalability reasons on using multiple > queues) to manage its own mm address space, one uffd in charge of a portion > of VMAs, then it can randomly take one userfaultfd to do unregistrations. > Such might break. Not sure if relevant, but consider the following: an app being controlled by another process using userfaultfd. The app itself can "escape" uffd control of the other process by simply creating a userfaultfd and unregistering VMAs. -- Cheers, David / dhildenb