From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 728611A9FA7 for ; Mon, 2 Mar 2026 17:10:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772471412; cv=none; b=VsQiFcjCQWaWWls838dF1TvL6wo61SZF58tOhczmgefdiRwxhyS3yHkn1PzPVxmyKAyUXmkaSIaFT/tW53D1hKoXXgjgvFzuuD8MdvYF04M5SQcGf60HrcnQKY9eepzCosBPnmwfV2iSDEL4q0xrII/LMU5dA4jZ4yZwVh6bYVk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772471412; c=relaxed/simple; bh=jujI5PTVZLeukFg1F7/wlVAXbn5NpUo3sZPRb4/bT3w=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=NLJsWGg/Gljt/M5zbMDiAfnqyav1IjqDj3lL1THHJHQ4HxXzTn2b4FLsgE6ywStNl7OCz5PqdRTtzcE2v3BpqrjBw2OV27RTiTb3ajr+6V0AvnjCzHDqtbAei6qD7u6FauyoDrUpgmlC8Bso7uDnkDUroKlfzo/7eTNcHJW1Ypk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BQpd4BiR; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="BQpd4BiR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 51AF5C19423; Mon, 2 Mar 2026 17:10:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772471412; bh=jujI5PTVZLeukFg1F7/wlVAXbn5NpUo3sZPRb4/bT3w=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=BQpd4BiRMssnhKfl+1izhdifwWm0vZygYNim97Aj9I2ht5ckQFbx47TrTqL1IGtab 6iLtiiKM/fl7dK1ExJeh0nJhN9dnvSgSgGdcKluHnp94O5glAFXItZkfZqLJE58Oe3 NF3hjl1pcZ30D6eDNk+hz7oPHthBaiJc9uedYLB4OHlRQhDhcATwiGEjNdliBM+6IZ ZUPhBFMdLFkA3eU19Y5KQkA9Ebu7wBDFRDVB6DZHuvk/gHt8+y7NZkt1ODk5v63nBE JneS/GKyZVGPIGkylLJzyoUtDiEg9uAh0eyRhvhWCNm61I6S96HdYwOkYTXzOzMj2w KsHJOYODCyQ7w== Message-ID: <901fec30-c5c2-46c5-b48d-f9a8f5e5c928@kernel.org> Date: Mon, 2 Mar 2026 18:10:06 +0100 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-hotfixes] mm/huge_memory: fix memory corruption on huge zero page move To: Lorenzo Stoakes , Andrew Morton Cc: Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Matthew Wilcox , Chris Down , Suren Baghdasaryan , Mike Rapoport , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260302170619.867056-1-lorenzo.stoakes@oracle.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: <20260302170619.867056-1-lorenzo.stoakes@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/2/26 18:06, Lorenzo Stoakes wrote: > In commit eb1521dad8f3 ("userfaultfd: handle zeropage moves by > UFFDIO_MOVE"), handling was added to enable the moving of huge zero pages > in move_pages_huge_pmd(). > > This achieves this by setting src_folio to NULL, and adding subsequent > checks for src_folio being NULL to determine whether to perform the usual > move operations or to simply establish the huge zero page in the > destination. > > As part of this change, when installing the destination huge zero page it > invoked mk_huge_pmd() on src_page, correctly. > > However, commit e3981db444a0 ("mm: add folio_mk_pmd()") updated the code in > the huge zero page branch from mk_huge_pmd(src_page, ...) to > folio_mk_pmd(src_folio, ...), where src_folio is guaranteed to be NULL at > this point. > > This resulted in an invocation of folio_mk_pmd(NULL, ...) in effect, which > causes an invocation of page_to_pfn(0) and results in the installation of a > corrupted PMD entry and undefined behaviour. > > This patch fixes the issue by obtaining the zero folio via > page_folio(src_page) and feeding this into folio_mk_pmd(). This retains the > use of folio_mk_pmd() whilst avoiding the memory corruption. > > Additionally, this code path was not updated to reflect the changes > introduced by commit d82d09e48219 ("mm/huge_memory: mark PMD mappings of > the huge zero folio special"), meaning a zero huge folio was installed but > not marked special in this case. > > This patch additionally fixes that issue by invoking pmd_mkspecial(). > > With thanks to Chris Down who exposed this bug by adding an explicit test > for UFFDIO_MOVE in commit f07254dce67d ("selftests/mm: add UFFDIO_MOVE huge > zeropage PMD regression test"). > > Fixes: e3981db444a0 ("mm: add folio_mk_pmd()") > Cc: > Signed-off-by: Lorenzo Stoakes > --- > mm/huge_memory.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index c17965f5682f..de2a775590f1 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2796,8 +2796,12 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm > /* Follow mremap() behavior and treat the entry dirty after the move */ > _dst_pmd = pmd_mkwrite(pmd_mkdirty(_dst_pmd), dst_vma); > } else { > + struct folio *zero_folio = page_folio(src_page); > + > + VM_WARN_ON_ONCE_FOLIO(!is_huge_zero_folio(zero_folio), zero_folio); > src_pmdval = pmdp_huge_clear_flush(src_vma, src_addr, src_pmd); > - _dst_pmd = folio_mk_pmd(src_folio, dst_vma->vm_page_prot); > + _dst_pmd = folio_mk_pmd(zero_folio, dst_vma->vm_page_prot); > + _dst_pmd = pmd_mkspecial(_dst_pmd); > } > set_pmd_at(mm, dst_addr, dst_pmd, _dst_pmd); There are already patches in flight: https://lore.kernel.org/r/aaBVaHs8rIkNcwM0@chrisdown.name :) -- Cheers, David