From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EF8C8248F73; Mon, 22 Jun 2026 14:20:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782138038; cv=none; b=H79Gh2OwajDs41jt99l8OHOaXAtiEVlramOFwebiY/GOUJaGqZzK2ErZJF7Zg17/7tMFT1bohEV1tZ2N22veDtPINVHBy0e6dWzXIyMXmOKcyFyYnhmuXXeT8EvPTAXQyM5tH2rh8V8x77Xw+BRYHFFXTA4uA1zPSA8lr+9baBc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782138038; c=relaxed/simple; bh=BhTHbidjT81SQxLkUG1b5TPpTZt/QW8Ig73w74Gt/G8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Q1hm7aFouKq4EVA/BCdAqeuziygJ8JBJ024OnsG18XYOvznPT6MFAHfmo68JHOYDWKh7OjSFErSJL4l708ekdfTVx+wx09zreWFNfwAVgNl1h2SVXZF05htRDzsr9PhQiELBLsa2ZOGQWFZ1s2QQd4tordNHBNJj8fhBmfgLRUc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=izEH+IML; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="izEH+IML" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 606EF1F000E9; Mon, 22 Jun 2026 14:20:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782138036; bh=o+Xb3taXT85TT7EwmxpsyqZV0XfoZmQOVxpqJeSH654=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=izEH+IMLy43MqEQDUiW/ddt1sXlIm6bygQ1FyUWsVv9rM9xwKCGswy4pzOhgv8BHH CdKj9uG7LcZO14MM077GtN6Si52AWmOtNc3A6LOCh8uGMMuRdwRhp/PsCRfmyqNw9a JFTv6QmITyZMnGO22xhG3Pvgnk4ykHN40fBflWJtbqMhNWoqVaWRbisSpzAYMfo63n fP2a9oYqnVkja77/ToK0Uh8A1A+OPrtnwwc/CentJDmXlyKQTn9lVJ37srGZXRdQ8a AqeG9rXV+9QN3j8sdm61lD8rFgR7TfUbU5TXvrE1jc+SU7ATiXLi/s4dpGAAjqo3VJ j8cR7Z+QatKzQ== Message-ID: <6621c832-b399-40f9-b4b6-4519d6c4e0de@kernel.org> Date: Mon, 22 Jun 2026 16:20:31 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: page_ext: add count limit to page_ext_iter_next to prevent invalid PFN access To: Ketan , Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Luiz Capitulino Cc: kernel@oss.qualcomm.com, stable@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Matthew Wilcox , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport References: <20260622-page_ext-v2-1-135d4cfbc42f@oss.qualcomm.com> 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: <20260622-page_ext-v2-1-135d4cfbc42f@oss.qualcomm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/22/26 16:14, Ketan wrote: > The page_ext iteration API does not validate if the PFN still > belongs to a valid section while advancing the iterator. When > dynamically adding memory in the hotplug path, it can lead to a > NULL pointer dereference during page_ext_lookup at the boundary > of the last valid section when iterator count equals __pgcount. > > The for_each_page_ext() macro calls page_ext_iter_next() as its > loop increment. for_each_page_ext() does a > "__page_ext = page_ext_iter_next(&__iter)" at the end. This > causes page_ext_iter_next() to increment iter->index past > __pgcount and call page_ext_lookup(start_pfn + __pgcount). > During memory hotplug (online), the PFN at start_pfn + __pgcount > may belong to a section that has not yet been initialized, > causing page_ext_lookup() to trigger a NULL pointer dereference. > > [ 14.555124][ T846] Call trace: > [ 14.555125][ T846] lookup_page_ext+0x6c/0x108 (P) > [ 14.555127][ T846] page_ext_lookup+0x30/0x3c > [ 14.555129][ T846] __reset_page_owner+0x11c/0x260 > [ 14.571201][ T846] __free_pages_ok+0x5e8/0x8e0 > [ 14.571204][ T846] __free_pages_core+0x78/0xf0 > [ 14.571206][ T846] generic_online_page+0x14/0x24 > [ 14.597782][ T846] online_pages+0x178/0x30c > [ 14.597784][ T846] memory_block_change_state+0x284/0x32c > [ 14.597787][ T846] memory_subsys_online+0x4c/0x64 > [ 14.597789][ T846] device_online+0x88/0xb0 > [ 14.597791][ T846] online_memory_block+0x30/0x40 > [ 14.597793][ T846] walk_memory_blocks+0xac/0xe8 > [ 14.597794][ T846] add_memory_resource+0x280/0x298 > [ 14.656161][ T846] add_memory+0x60/0x98 > > Move the iteration boundary enforcement inside the iterator > functions, so callers cannot inadvertently access beyond the > requested range. > > Fixes: 9039b9096ea2 ("mm: page_owner: use new iteration API") > Cc: stable@vger.kernel.org > Suggested-by: David Hildenbrand > Suggested-by: Matthew Wilcox > Signed-off-by: Ketan Kishore > --- > Changes in v2: > - Incorporated comments from David and Matthew to check for invalid PFN > in page_ext iterator rather than checking for NULL section in > page_ext_lookup. > - Minor improvement in commit description to include the issue with > page_ext_iter_next > - Link to v1: https://patch.msgid.link/20260617-page_ext-v1-1-37ad802b1a38@oss.qualcomm.com > > To: Andrew Morton > To: David Hildenbrand > To: Lorenzo Stoakes > To: "Liam R. Howlett" > To: Vlastimil Babka > To: Mike Rapoport > To: Suren Baghdasaryan > To: Michal Hocko > To: Luiz Capitulino > Cc: kernel@oss.qualcomm.com > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > --- > include/linux/page_ext.h | 19 +++++++++++++------ > 1 file changed, 13 insertions(+), 6 deletions(-) > > diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h > index 61e876e255e8..4f7d7a8709de 100644 > --- a/include/linux/page_ext.h > +++ b/include/linux/page_ext.h > @@ -120,14 +120,18 @@ struct page_ext_iter { > * page_ext_iter_begin() - Prepare for iterating through page extensions. > * @iter: page extension iterator. > * @pfn: PFN of the page we're interested in. > + * @count: maximum number of page extensions to return. > * > * Must be called with RCU read lock taken. > * > * Return: NULL if no page_ext exists for this page. > */ > static inline struct page_ext *page_ext_iter_begin(struct page_ext_iter *iter, > - unsigned long pfn) > + unsigned long pfn, unsigned long count) > { > + if (count == 0) Nit: !count, but we can keep it as is. Thanks! Acked-by: David Hildenbrand (Arm) -- Cheers, David