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b=fg7LIiJR7AX9Jn66wWOxFwFC1Ilz8tBNN130l9pe8+ski/iiRItU7Grqgq/n1pD3b a794jZ3egI+eNs+hsjI4MdhkR8FGxEytWyl1w7i6X/OCyHUeCqu6fuato879HTU0/g mGLdvtRPpJAoRQtm9YYitdXw8vvnoOA1CWdr3jth5lNTf0j/apFF1zhS0hvHD22QSf fBvryou88infm346UlwypugTjY6FwlgJSkiKVobm+r0QlbgAgMIQ/KduN+w2495mnd W5srq7C+k7qgdA45I30LwtGtgtnK1gcLK6+EPxaAcJIXZU9RycxyrvqEXwy4n0KCIz jaelC2pgNc9/w== Message-ID: Date: Thu, 18 Jun 2026 11:25:31 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] userfaultfd: prevent registration of special VMAs To: Mike Rapoport Cc: Andrew Morton , Linus Torvalds , Alexander Viro , Christian Brauner , Jan Kara , Oleg Nesterov , Peter Xu , vova tokarev , linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org References: <20260617194059.2529406-1-rppt@kernel.org> <5a993689-f730-406d-8515-8bb6025cc851@kernel.org> <41ef0dce-e973-4947-b5e3-150fdb07f1a6@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 67FA840002 X-Stat-Signature: xwyz4ztrzzno7m87n5tbyyo9su73jb63 X-HE-Tag: 1781774736-804345 X-HE-Meta: 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 Fxa23JKR HpZNrPwkKUNaZu8kThs1+JXEb3CWyyl1XuYvEdMc2sNgLJnMwF0yRYyJkbl2TiVzDE6a/cY50XT92Vrpx8au3DUufMhxvwEfEUWYqeHiye4EbG/I50ZNLHsTA8RDVrV3C4kEIVoPr+svqfXRWhbs+h1LNoz17iKMV8Vc/g7fD6MIBbqw4Mh1vj0EvQ+21oB4CpAIOwt0cufirNW0P2SbcyGMfz+7yxVJO++GMlqCbskPoXBcv7qz646R6ta//ROR+nYao Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/18/26 11:21, Mike Rapoport wrote: > On Thu, Jun 18, 2026 at 10:47:19AM +0200, David Hildenbrand (Arm) wrote: >> On 6/18/26 10:43, Mike Rapoport wrote: >>> >>> Ah, hugetlb sets VM_DONTEXPAND, so it must me excluded to allow uffd with >>> hugetlb. >> >> It would probably be cleaner to just allow hugetlb, and then check for >> VM_SPECIAL if not hugetlb. > > Cleaner in what sense? > Will be uglier for sure, just take a look at vma_can_userfault(). I was thinking of this: diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 180bad42fc79..8a6803618a91 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -2029,7 +2029,10 @@ bool vma_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags, { const struct vm_uffd_ops *ops = vma_uffd_ops(vma); - if (vma->vm_flags & VM_DROPPABLE) + if (vma->vm_flags & (VM_DROPPABLE | VM_SHADOW_STACK)) + return false; + + if (!is_vm_hugetlb_page(vma) && (vma->vm_flags & VM_SPECIAL)) return false; vm_flags &= __VM_UFFD_FLAGS; -- Cheers, David