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 40447399361 for ; Tue, 11 Aug 2026 15:24:55 +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=1786461897; cv=none; b=dTmQctc5J7mUaWPvRTTazwOCVAyB3KuuVu55ethJAW3CGVq/iJizAhV9xeUxw5XFOxALJkrz/nljh5Ka2ZZ5blwsuMPscglIrHeWPp0D3MyUL7FZ+TJMDfi6rajHfflVbkGnpvVls9eqPqJwVirDBs215FhD7ic4ARKQ5gp0LKI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786461897; c=relaxed/simple; bh=/xy6OHhs1F7kCUIV5LfQO2pGPYpI4W0NPQJZ6QbQ8BQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GagpfPOFF0rPgd7Tn5L0q92vXuj9IMqiS5vSAbdGBkpq5UMoYsttsrylAA2ZVSEqc2VFFquzWM+0a2uVn6I0qOG08Vpl93rAlxtTgmCqmEsF5LF7vazuQs6CMuNx6Ff/ixNT/dALZfe9aRW3Xk+wviY4pbgfxLmfgSxVeikcwc4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Rl5uPyJT; 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="Rl5uPyJT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE4711F000E9; Tue, 11 Aug 2026 15:24:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786461895; bh=RcdR/udWOVWmDwaf36nf5yccvfO8UVnYIWMO6Q65BHQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Rl5uPyJTVmZrjRtJ6ApP9rvVM8HtNAOAmzIApVhofdCiWqyH3iRLBr1WEl/TV2T5w 45udCjYJrThhfYSKyg6kwsFWU44uMATst58mLb/HldI9G/mdfDVsfprKLD/cX6Myn8 tX+mNiejAt9N62fL8sm+p82cro//bQX/O88I/GFCnA8Cc8VwSLq4Ub58OC6Q9XmKxv oVIPCRDNdjawcVXYW5sLGBTcwEY/HliXy2E5jMs/IKaWcBckJav6VFGN3nAmNCDyMW +84LC+gHmbfx3hf5XdPZvJW7u6NPhNn4OOo/H+1sWZD6EjQXs1R0gRgUesc7cN9jAv frL6Oukda0l4g== Message-ID: <0a052bbb-4923-43c1-80dd-099ef4c1fb4a@kernel.org> Date: Tue, 11 Aug 2026 17:24:50 +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: [RFC v2 PATCH] mm/cma: don't release CMA pages still in use To: Rik van Riel , Andrew Morton Cc: Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Chris Mason , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260810122737.030f8452@fangorn> <50b1dadb-37f1-48a0-adf6-c6ff8b704582@kernel.org> <007c8bf2717346bdba791e1a5079f4d0abad41f5.camel@surriel.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: <007c8bf2717346bdba791e1a5079f4d0abad41f5.camel@surriel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 8/11/26 05:49, Rik van Riel wrote: > On Mon, 2026-08-10 at 20:53 +0200, David Hildenbrand (Arm) wrote: >> On 8/10/26 18:27, Rik van Riel wrote: >>> When a driver calls dma_free_contiguous() before quiescing DMA, the >>> page still has a reference from the device. put_page_testzero() >>> there >>> returns false, WARN fires, but the code proceeds to >>> free_contig_frozen_range() putting a live page onto buddy and >>> clearing >>> the bitmap. Later cma_alloc() hands the same PFN to a new owner >>> while >>> the original holder still references it. >> >> Hm, it rather sounds like it's really the drivers job to quiescing >> DMA. Are you >> aware of an in-tree driver that can trigger this, and if so, how? >> >> Freeing memory through CMA, while the memory is still in use is >> problematic for >> CMA as you discovered :) > > I agree the driver should not be doing that.  > > I do not know of any driver that currently does it, but > it has led to CVE-2025-37837 in the past, and there > appear to have been other cases of this issue happening. > >>> + WARN(skipped, "%lu pages are still in use!\n", skipped); >> >> >> We still issue a WARN, which itself is problematic. See "Do not WARN >> lightly" in >> Documentation/process/coding-style.rst. >> >> So it's either >> >> (a) This scenario is valid to be triggered. In that case, WARN is not >> appropriate. >> >> (b) This scenario is not valid to be triggered. In that case, this is >> not a fix. > > If a driver does it with the current code, it can  > cause free list corruption, with potential for > temporary data exposure, until the system crashes. > > If we get rid of the free list corruption, it > can continue to be a WARN, since it will no longer > kill the system. > > If we continue to corrupt the free list when this > happens, it should probably be a panic? > > A simpler fix may be to not free any of the memory, > or the CMA address space, if there are still pages > in use at cma_release() time. Yes, keep it as simple as possible and complain. This is really something that must not happen, and the CVE in that above case is not this code's fault but the driver's fault. -- Cheers, David