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 77CA93EFD0F for ; Mon, 6 Jul 2026 08:42:52 +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=1783327377; cv=none; b=u/GC3t4PuCoR8PGOGfkrVlO+u28NUiNhcNe5eS67v63HM+sEreSiKqgf3H8MRPWVR61EoPvVxYHzhTfXmRtvOO5Q3pTGZu3ZFgxy6vM1JY/P8DY/OeR9Cer7zXXISHspheAYzlwKv9G/HN4RmrVoX9Xp6u+kdXRhnNM+Ls7lF+k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783327377; c=relaxed/simple; bh=ABKbfuWP5lwjpDBZ3VRFvR7M3/Q/sCT/ftkyieZL1mw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cWDMSCPok7ftmm5UPP4RtArtLnMdej4zqU0WdZHeo+OMImP6VFpG5l9HsVjMSPSgtwMjVlu8XzFBryQzORlkiCBjiE54gWOVDQGpJA55aJA1LwcxBcD3G2rRL7ZhwGJ1Ap2y4lOo+DwOVqR7E+CTGwEMM2fGAp9OpYlvqiKDMM8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GIn7Iybc; 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="GIn7Iybc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E18FD1F000E9; Mon, 6 Jul 2026 08:42:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783327370; bh=4Q5OO705sqjVj6V3CrHEmc9+5Y9WaD9cC61NbPqoX2M=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=GIn7IybcH1uE5DRSJIA+De7ml6yEreHoYtoLylpcdr3GmdnCHE1BTfJt77E81gIrC Bu4bNtxk72Z215rCaWwi1riDyON8LcC30fP0JWQbX3ZDlEKm73Z4JVvyg/VS25Tu0F U9kFe4eN8/5l2LqnonCP5kQPI4hSRTA0MtQbYniBu1TAG/o8crimtVNxICa3IGfTQm 44vkMz7rqjToCBYZJ4aNovjI2sQ/eOAxpg1prfNueRtcxJoJ8C/gbEQ8WlLhIT5qVM kyHoUejLrtHyd8J44dK+2YFbFNgNWhLQeoS+kQDnIxdK/jEy7vo/AMVARDnMihBhHQ I4ZtnrgU/XBGw== Message-ID: <503aee9e-97fc-4889-a379-3c0a5d140554@kernel.org> Date: Mon, 6 Jul 2026 10:42:46 +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] mm/secretmem: disable under HIGHMEM To: Mike Rapoport , Brendan Jackman Cc: Andrew Morton , Brendan Jackman , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260703-secretmem-highmem-v1-1-30d5ff944664@google.com> <20260704192603.40aa80cf9242b77aa75e8d8d@linux-foundation.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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/5/26 13:34, Mike Rapoport wrote: > On Sun, Jul 05, 2026 at 10:46:19AM +0000, Brendan Jackman wrote: >> On Sun Jul 5, 2026 at 2:26 AM UTC, Andrew Morton wrote: >>> >>> Well OK, but the secretmem code is still wrong. The patch protects >>> people from hitting the bug but leaves the bug in place. Surely it would be >>> better to fix the bug? >> >> I don't think the code is wrong if highmem is disabled. Certainly >> there is an implicit coupling between the .c file and the Kconfig file, >> but we could always add a BUILD_BUG_ON(IS_ENABLED(CONFIG_SECRETMEM)) to >> the relevant bit of code to make it explicit. >> >>> Is that as simple as adding the folio_test_highmem() test? >> >> This would fix the WARN+SIGBUS but I don't think it resolves the fact >> that this configuration is completely untested - there are likely other >> functional bugs? But more importantly, I am not sure if secretmem >> actually does its security job if kmap_local_page() isn't a NOP. I >> think shipping a "security feature" that doesn't do what it says would >> be really terrible. (It might work totally fine, I dunno, but it would >> require some research and deep thinking that I don't really want to do >> for a configuration with no users). >> >>> Or switching to GFP_KERNEL? >> >> ... Oh, that's a nice idea though :) > > GFP_USER if anything :) Right. > > But still with kmap() and friends not being an NOP the promise "kernel does > not map this memory" does not hold. > > I think that keeping SECRETMEM and HIGHMEM mutually exclusive is > conceptually correct. We could even limit it to 64BIT ;) -- Cheers, David