From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793873666; b=O6UWhVuvbf3yHiWpcwBFWWOoBakSZSvIQ1Z2CwjsKFBVeZWbuSXIZgiXEzur1r4rE+GA Xu3BtNARvKrfo/AMEQIp8+lB+uyrlwBLgIt7QDe5321mtNnIoQPZlFNoR0LnwtDaAZnUm fhdgNxSW2K3KvmMgQmDNZaZJvDHS+aKU8QOjQ2y7nY5tgK7RnKvjx3Hi64PgoILfDFb+u 814JqBs9XJek6GHVuUFnQVV040JjgXBTthN2JVi7puNkW3AbhPFb4h6nNGjwfYYK7Wvr3 tcINnCG/Pt451vdqkaFOPGaPHSPN9bUEKbqkTyIID5hhJedRroO5MgBLRSis3vQkl+w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793873666; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=cJgR5aeVC9lcVT/bd47FaWkr+JwpenNCqv7QqD2q5Bs=; b=DSNEKPPk6+yZxjG3Uvu5QbFtsrL0vZ3mbS/H/4mdI9PMZU5aTfx1DBKP+EPtq05SDQkq UGNQ5Lfyzvp/YXRjC/TPZmbqNMiteiDRk5oOOENjkl6ipmAUH+rHMlfmMcyEcqj8cVJjK +2aBppk+D30oct7/OlZ/MaaK/yiJg8llcM8zcyM/sOb/IanApj0vL6CdnXC1RPSGMC+FN UtjoVB0jkdQfkbVPEIishBTzuUJzwAaWML16McIg/YV5L2uIRGJaNKlhLsBfiyEiI+z4O grAiMkKneZrJfuGS623UA+favCDnfb/pcbcMWPK7VWJsSj+VwH7KZC0ZkAQ2BIs7Gug== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Op6BjMZv; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 85084606AA41; Thu, 5 Nov 2026 10:14:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Op6BjMZv Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0E1671F000C1; Thu, 5 Nov 2026 10:14:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793873666; bh=cJgR5aeVC9lcVT/bd47FaWkr+JwpenNCqv7QqD2q5Bs=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Op6BjMZvEwsjuxoAUkC8Ls8ldus0yPgt/yQbWwZwQRMcFlVeybfv/RTgIihY90P0o 6hwtujh/xZC3KmXw8CKUVrH9CgBmz87hYk08c0RXE0JnYvLXt0neFtGpI3S1z9ihsG tzfUumbxad+dX5WnRj5f9R1oN3EshlfEIH7griODZMkD0lhOWJTKO5QoQW3rbHExTi 7Y5Qe2uzFx4yjZmy+DYdTLx+ZWG1Hgk2KelHad79uAVveo8dALagy/j5GnNTUM+SKy 8J/nk4KICNKN3ZUxYzliP+GCsZaZ3nUW6vJ3vTG8JfWfH4DjMnnK3+i+QoLVHbSFz/ aWp+hd3ruMhdw== Message-ID: Date: Thu, 5 Nov 2026 11:14:19 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/2] mm/memfd: handle GUP references reliably when write-sealing To: Hugh Dickins , Baolin Wang , Andrew Morton , David Rheinsberg , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Shuah Khan , Randy Dunlap Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, stable@vger.kernel.org, Chris Mason References: <20261103-fixes_core_2-v1-0-f332954f1df4@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: <20261103-fixes_core_2-v1-0-f332954f1df4@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/3/26 19:31, David Hildenbrand (Arm) wrote: > I spent way too much time on this, looking for better options. I think > patch #1 fixes the most immediate issues but something like patch #2 is > needed. > > Long story short: someone can trigger a race such that we don't detect > GUP references when write-sealing, allowing to modify content later. > > Patch #1 handles pins reliably for folios with a pincount. Patch #2 > handles the remaining references, but can reject write-sealing with > populated file mappings. vm.memfd_write_seal_mapped allows restoring the > legacy behavior if needed. > > All alternatives to patch #2 I tried ended up too complicated and nasty > in corner cases. We should never have allowed write-sealing with > existing file mappings. > > Plenty of details in patch #2. > > Did some testing on x86-64 without any surprises. > > Signed-off-by: David Hildenbrand (Arm) > --- > David Hildenbrand (Arm) (2): > mm/memfd: handle GUP pins more reliably when write-sealing > mm/memfd: handle GUP references reliably when write-sealing > > Documentation/admin-guide/sysctl/vm.rst | 21 +++++++++++++++ > mm/memfd.c | 45 ++++++++++++++++++++++++++++++++- > 2 files changed, 65 insertions(+), 1 deletion(-) I think patch #1 is uncontroversial. It would be good to get some options on #2. With the current infrastructure we have, I don't really see a good way to tackle this differently. I'd assume CRIU+write-sealed-memfd+mlock is rather the corner case ... :) -- Cheers, David