linux-kernel - Re: [PATCH v3 1/1] mm/rmap: fix potential out-of-bounds page table access during batched unmap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <0a96ce38-163e-4566-b666-b074bd82c75a@linux.dev>
Date: Tue, 1 Jul 2025 22:15:27 +0800
From: Lance Yang <lance.yang@...ux.dev>
To: David Hildenbrand <david@...hat.com>, akpm@...ux-foundation.org,
 21cnbao@...il.com
Cc: baolin.wang@...ux.alibaba.com, chrisl@...nel.org, kasong@...cent.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, linux-riscv@...ts.infradead.org,
 lorenzo.stoakes@...cle.com, ryan.roberts@....com, v-songbaohua@...o.com,
 x86@...nel.org, huang.ying.caritas@...il.com, zhengtangquan@...o.com,
 riel@...riel.com, Liam.Howlett@...cle.com, vbabka@...e.cz,
 harry.yoo@...cle.com, mingzhe.yang@...com, stable@...r.kernel.org,
 Barry Song <baohua@...nel.org>, Lance Yang <ioworker0@...il.com>
Subject: Re: [PATCH v3 1/1] mm/rmap: fix potential out-of-bounds page table
 access during batched unmap



On 2025/7/1 22:03, David Hildenbrand wrote:
> On 30.06.25 03:13, Lance Yang wrote:
>> From: Lance Yang <lance.yang@...ux.dev>
>>
>> As pointed out by David[1], the batched unmap logic in try_to_unmap_one()
>> may read past the end of a PTE table when a large folio's PTE mappings
>> are not fully contained within a single page table.
>>
>> While this scenario might be rare, an issue triggerable from userspace 
>> must
>> be fixed regardless of its likelihood. This patch fixes the out-of-bounds
>> access by refactoring the logic into a new helper, 
>> folio_unmap_pte_batch().
>>
>> The new helper correctly calculates the safe batch size by capping the 
>> scan
>> at both the VMA and PMD boundaries. To simplify the code, it also 
>> supports
>> partial batching (i.e., any number of pages from 1 up to the calculated
>> safe maximum), as there is no strong reason to special-case for fully
>> mapped folios.
>>
>> [1] https://lore.kernel.org/linux-mm/ 
>> a694398c-9f03-4737-81b9-7e49c857fcbe@...hat.com
>>
>> Fixes: 354dffd29575 ("mm: support batched unmap for lazyfree large 
>> folios during reclamation")
>> Cc: <stable@...r.kernel.org>
>> Acked-by: Barry Song <baohua@...nel.org>
>> Suggested-by: David Hildenbrand <david@...hat.com>
> 
> Realized this now: This should probably be a "Reported-by:" with the 
> "Closes:" and and a link to my mail.

Got it. Both tags (Reported-by/Closes) will be in the next commit ;)