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imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=dbt7B8Ja; spf=pass (imf04.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1772026853; a=rsa-sha256; cv=none; b=HBZ3RFHPP4HKbg65n68JPjgf74R56hfQwUg5elfSTZMq4UKDsAFLQjn6eixCzydbk708Aj ptjCu5OELlf8fzB6j0VcqW71nBUTnMOUORvgAxRn6OpcLkMxDmQuQYnqvwlHzMIIqVhyQb zTdkfvOuTMdh3MvBmoIo6CMadZ0rP9I= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 8DB7043DB3; Wed, 25 Feb 2026 13:40:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B842EC19421; Wed, 25 Feb 2026 13:40:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772026852; bh=rrMpGqEeFB0d/dInF1INAwjXcTLK5Z1RFzio2aHu3aw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=dbt7B8JaWvul8aSZkLa32oQQtVMKNtV7dFqwAsSkisijHEbNw23kdpos/6fBtt4xj vGicHEdKPCFzRhYQi7oCzW+I0qMOICLuJqiWPe9w2o4vMr0hvRSszdZhZo5zQNXSTt PF+0MAeTZHCFGaXF05UJgQYIQ6Elbu/1ztzUpDIVK9kng0XA+Fm5b0Bfm9oviSOno3 PBXhYYPXUD0ZLj6mICapcfwcwz+AGvuIhCUEY0COForJFKsENhBONrba3JUhAgogLY aZ/sW7uDiKiGOrPLerKuj232coIHuieYfGosVdqQTlgDudfijQbtP4OQBf27SPhd6g t4wCJv/rsmKvQ== Message-ID: <81065dd1-c131-48db-9ef6-01c0ec0001da@kernel.org> Date: Wed, 25 Feb 2026 14:40:41 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: Avoid calling folio_page() with an out-of-bounds index To: Li Zhe , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, ankur.a.arora@oracle.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260225092628.11687-1-lizhe.67@bytedance.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: <20260225092628.11687-1-lizhe.67@bytedance.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: A4CB740003 X-Stat-Signature: a3izjp7jmtzjdcancg31u5ytecs9nprd X-Rspam-User: X-HE-Tag: 1772026853-558770 X-HE-Meta: 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 9lGtg68u sO2VeMMVhEyNY/XtKiu4Vq4hOMewUSOsOllKNpLf3z50Oz+KXXWs/DRNJiI/UQ4GF5Ey+x0qZquw7FGOWQGSM8GZiBuJdEaim3t8jF7ITliCLbKtT89DJLAs7zVUcQd7gaIsZyy3YrJsGWPm+oppqgEjg8ZUkk2MTYP/uq4nGGv/7Iy33h29Q4t5SvfGdA0KFviy59/VwClZoaR3miBeg5TDnWe+ErbzFDgGV3ULFFxA1DZHiS7C+2u4TfzFL7Ba0WRUv4CtJOTRLR3rdv+zMGNT3CKqF6gn6kRti Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/25/26 10:26, Li Zhe wrote: > In folio_zero_user(), the page pointer is calculated via folio_page() > before checking if the number of pages to be cleared is greater than zero. > Furthermore, folio_page() does not verify that the page number lies > within folio. > > When 'addr_hint' is near the end of a large folio, the range 'r[0]' > represents an empty interval. In this scenario, 'nr_pages' will be > calculated as 0 and 'r[0].start' can be an index that is out-of-bounds > for folio_page(). The code unconditionally calls folio_page() on a wrong > index, even though the subsequent clearing logic is correctly skipped. > > While this does not cause a functional bug today, calculating a page > pointer for an out-of-bounds index is logically unsound and fragile. It > could pose a risk for future refactoring or trigger warnings from static > analysis tools. > > To fix this, move the call to folio_page() inside the 'if (nr_pages > 0)' > block. This ensures that the page pointer is only calculated when it is > actually needed for a valid, non-empty range of pages, thus making the code > more robust and logically correct. > > Signed-off-by: Li Zhe > --- > mm/memory.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 07778814b4a8..6f8c55d604b5 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -7343,12 +7343,14 @@ void folio_zero_user(struct folio *folio, unsigned long addr_hint) > r[0] = DEFINE_RANGE(r[2].end + 1, pg.end); > > for (i = 0; i < ARRAY_SIZE(r); i++) { > - const unsigned long addr = base_addr + r[i].start * PAGE_SIZE; > const long nr_pages = (long)range_len(&r[i]); > - struct page *page = folio_page(folio, r[i].start); > > - if (nr_pages > 0) > + if (nr_pages > 0) { > + const unsigned long addr = base_addr + r[i].start * PAGE_SIZE; > + struct page *page = folio_page(folio, r[i].start); > + > clear_contig_highpages(page, addr, nr_pages); > + } > } > } > It's all just arithmetic operations. Just like Willy says, I'd assume that the compiler can just move them around as it pleases. No dependencies. So I don't see any real benefit with this patch. -- Cheers, David