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imf08.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=Vuz79kYO; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf08.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793301998; b=hE025AukIuPnN5L0lxBz32SWQdgFl4MUMIbsHEgP+K80BbueXh7TxZqNaODpUknVHA4mm5 WKhkxMaMzS8YIb9KNROz9hsJQVn5voUDMc5BOKlDa7X7BGmMrKUw899yOCyw/GGC+HOd6o jl89hu9iN++FVN3oE6J4VoisPgKrAKk= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id EFD0743CE8; Thu, 29 Oct 2026 19:26:37 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0B31D1F01816; Thu, 29 Oct 2026 19:26:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793301997; bh=olq2oLw59YhnpeUJwxDmzWejxUeT+/sp90poHb2MYpE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Vuz79kYOC25Pp9Lahkn6JIoGjLKWZgFMbszt9wdYOSUiNklBr4qPAG+Z4n0nCZ1A0 eTnnRFm9Rw4IsBqS8OzDtTl17wf+e48vjls768zrm5h2RnQ9WeHLCsdOSWJIIaeEOb YML9LUIT7+G5zuOu3mOEaeFf/7OJ1Hauz1eLBtTE5Z/wfuS50OqrjJRgjI1JwBkGI+ kF1Ii/KT98x8jXIXfkV/UZVqCgi8xq9PU4qG3X67p4XghMEn7hf338VOMdjyjL/U8R ylDOaPrnvYV/ZL/kdu/Wn3yRVQ8rZ1F8Hz7yZiCTmDjZVn9p2Tb1lfA9FPtv+/Sj+Z orROyVbGDU/Kg== Message-ID: <0a1ad7d2-ff0e-4248-8f03-2a64a9134aae@kernel.org> Date: Thu, 29 Oct 2026 20:26:33 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/filemap: stop fault-around when the walk steps back To: "Jose Fernandez (Anthropic)" , "Matthew Wilcox (Oracle)" , Jan Kara , Andrew Morton Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Krystian Kaniewski References: <20261028-jf-mm-filemap-map-pages-lower-bound-v1-1-0bf126e876d4@linux.dev> 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: <20261028-jf-mm-filemap-map-pages-lower-bound-v1-1-0bf126e876d4@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: D022116000B X-Rspam-User: X-Stat-Signature: oo6fpdr1zrnykirruj7j1b6ket6u1cg9 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-Server: rspam03 X-HE-Tag: 1793301998-485248 X-HE-Meta: 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 0gVwwztz ys35yB632wBAmre3JXS8+eBzWI78r8fci3jKaGpN0CRWcgxNYeYmzZLMGs9SOp99Hvc7X0PrBsh6J0rhoGHy7aHewTL43e8Eh3Pbo0X1Ri7bu+kzd7T4Kb23fduelnxcUFxMRyIauuBVxNJcnaCitfJoRljPaOTTqsTrdfTarSezWcQMsjRqqJWFF8MsjjIPUlq/FXlQQo+xUdTsPQuYY3c76nzG3GROSKGBI0pckrONoS4GwNQJsnneiqzOebj+pY2Xs8Dcu0oir6cvx5ZV9Dxbv8t9ENqR0DIKqF1jbKr2P4rg= 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 10/29/26 16:50, Jose Fernandez (Anthropic) wrote: > filemap_map_pages() can dereference a PTE pointer outside the page table > it locked. KASAN has reported this as a use-after-free read [1]. Only read or also write? I assume only read. > > Its fault-around loop walks the page cache and moves vmf->pte by the > change in index. A lower index moves it back. xas_find() can step back > to a lower index when a multi-index entry is split during the walk. > > [1] fixes xas_find(), but the loop still relies on the walk never > stepping back. Stop the fault-around when the walk steps back. ->fault() > maps the faulting page if the loop did not. > > Link: https://lore.kernel.org/20260904121301.200049-1-krystianmkaniewski@gmail.com [1] > Signed-off-by: Jose Fernandez (Anthropic) > --- > mm/filemap.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/mm/filemap.c b/mm/filemap.c > index b74bc1e5015c..1df776907140 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -3968,6 +3968,13 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, > unsigned long end; > vm_fault_t map_ret; > > + /* A lower index could move vmf->pte out of its page table. */ > + if (unlikely(xas.xa_index < last_pgoff)) { > + folio_unlock(folio); > + folio_put(folio); > + break; > + } > + > addr += (xas.xa_index - last_pgoff) << PAGE_SHIFT; > vmf->pte += xas.xa_index - last_pgoff; > last_pgoff = xas.xa_index; Sounds like we want a Fixes: tag and Cc: stable? :) -- Cheers, David