From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id B09C0606AA4C for ; Thu, 5 Nov 2026 10:14:30 +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 kanga.kvack.org (Postfix) id B24A76B05B2; Thu, 5 Nov 2026 05:14:29 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id AFC826B05B6; Thu, 5 Nov 2026 05:14:29 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A13926B05BA; Thu, 5 Nov 2026 05:14:29 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 7719B6B05B2 for ; Thu, 5 Nov 2026 05:14:29 -0500 (EST) Received: from smtpin24.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id DC1011A09D5 for ; Thu, 5 Nov 2026 10:14:28 +0000 (UTC) X-FDA: 85400655816.24.8E05781 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf04.hostedemail.com (Postfix) with ESMTP id 1C91F40003 for ; Thu, 5 Nov 2026 10:14:26 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Op6BjMZv; spf=pass (imf04.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793873667; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=cJgR5aeVC9lcVT/bd47FaWkr+JwpenNCqv7QqD2q5Bs=; b=lDA3X3Fi8KPIC+NXkyv/viLAAdO+tk75+oJ46EWV8ykcwiFgi+7HOipFzj7N3eVCxMYZX2 rY+77QlNSgDnJ+yululsvacgzR15M7ujw4qj+vvmxLErz7telMl68QZMJpCnmmYipStdGP ZtkSc1QUrbSZLX638bXXVLnY72xdWbI= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Op6BjMZv; spf=pass (imf04.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793873667; b=8IDY01ULgszhspkYPbqCVNUL7zbdng9g+yJysXDMwjiyaD6OaXU7Bz9xGFRqEgw+Q3NbVf TvkXz0xXNLq8VqeRxHNkhvyUVz0hPg+/EoaPgDZ/k+PLVrCAs3FyEVgGKK9B4dunCe9LdH wYHPrbxxOml6J675iNt+esl0e/qd1dU= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 3D76643C6B; Thu, 5 Nov 2026 10:14:26 +0000 (UTC) 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-Archived-By: 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 X-Stat-Signature: cbx8ktdz4cxx18xuybxwxffniiwzsqnh X-Rspamd-Server: rspam01 X-Rspam-User: X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: 1C91F40003 X-HE-Tag: 1793873666-802021 X-HE-Meta: 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 pM4ORvi+ zr7jJmEAFEBfWetBEXHWqV7YYMGUwK9YsXNblZe7pWx4O2GB510l9YOvZgIWbM+zC14dv9TSzjr/HuzYjac7vderYf/vn/9lGYeBTpFFinbcmuAGUXm8BXtXMUPRDp7VbF/AyyEJxIt8CIyRGxazpr2uKrpokxVfHSluLJRc5l2o/q75eU9cziRtD0TiUbKepGRphS3fTW1nX/sV7rVnzvATvPw7o08eCX5myv7yS3h6ghzAvOFDy49K88y3zNLkIYGC+CPKIVjCmyWXqz6nyk5BsavMENbwxKY6E Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 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