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b=CEIDyS2djknf3O5c/eBT+dmxNXdN/G/oUW1+HL7y7blsCddi9eA80g/V5XSEFEC5O GWzeYpQW/88FuFjd3od24xYlzw1Y8NFhRT9CRAKfOxPxHoEVcWcuhbBFbnYJe5uJ3x 7znzB02zi5HOAp15fi78ez0zS7Xj27yJ7kQw7ICRyVUz6rAYf/2YbkbPXYFvZUG8WV LWvF2aht/cNIhoVT90q3Y2joyaxE/0lsIxm3UEWmJFmwQuHxu7g3uFWJfcB8187xQc XUdN+wa8na43x1Uw/a/neuqh2m6zrpJVGHLRYmer9FcDzhG671aBEzU5eMqcXSG2cb uBUJ5qlFBvWig== Message-ID: Date: Thu, 5 Nov 2026 11:07:44 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/filemap: stop fault-around when the walk steps back To: "Jose Fernandez (Anthropic)" , "Matthew Wilcox (Oracle)" , Jan Kara , Andrew Morton Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Krystian Kaniewski , stable@vger.kernel.org References: <20261031-jf-mm-filemap-map-pages-lower-bound-v2-1-21029744e589@linux.dev> 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: <20261031-jf-mm-filemap-map-pages-lower-bound-v2-1-21029744e589@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 1teqnt3ec3c4smugkbuoftty4ey1ireo X-Rspamd-Queue-Id: CB636180002 X-Rspam-User: X-Rspamd-Server: rspam08 X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793873269-520475 X-HE-Meta: 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 cTL5GeHd HRwQMuMTeUMPNk2KGBhuJHSchA7UE06sRQr6913qanshIkx0vGiiYvRu8yQncLGCbMT/y6LNTEBuEEUJyb/8KTvIqSD9kRZTunX7yQPtyf89VDE1QcgZTDCK0rQRN9jSIOTDTaE1fzZ0fR7Dfis3g0r4YKuUeC/nGQpEAy5TcAsDGc8XiU2II+iFkFSAQXkPlihNR/i17lk8zHkIpgwGRjx9nNvTqow/BPNABAuZe379THva5fGSwchW4ZubgvXdSJTV6QDxm9hznD/ygECc8cmHYbjDp2SilAOQr/KcxcU3z5Vxk3Iui/TCAAxh94GCTJhcVd4g0cv0tttw2WRgKhhTwilpFjarZvzhQV52jAhDeGIgO9noBjGq/IufYRljLqdVq1i2JkO8Dfms= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/31/26 05:33, Jose Fernandez (Anthropic) wrote: > filemap_map_pages() can dereference a PTE pointer outside the page table > it locked. KASAN has reported this as a use-after-free read [1]. The > same path can also write out of bounds. When the stray entry reads as > none, the fault-around loop maps a page there with set_pte_range(). > > Its fault-around loop walks the page cache and moves vmf->pte by the > change in index. A lower index moves it back. xas_find() can step back > to a lower index when a multi-index entry is split during the walk. > > [1] fixes xas_find(), but the loop still relies on the walk never > stepping back. Stop the fault-around when the walk steps back. ->fault() > maps the faulting page if the loop did not. > > Link: https://lore.kernel.org/20260904121301.200049-1-krystianmkaniewski@gmail.com [1] > Fixes: 6b24ca4a1a8d ("mm: Use multi-index entries in the page cache") > Cc: stable@vger.kernel.org > Signed-off-by: Jose Fernandez (Anthropic) > --- > Changes in v2: > - Add Fixes: and Cc: stable tags, and say in the message that the loop > can also write out of bounds (David Hildenbrand). > https://patch.msgid.link/0a1ad7d2-ff0e-4248-8f03-2a64a9134aae@kernel.org > - Link to v1: https://patch.msgid.link/20261028-jf-mm-filemap-map-pages-lower-bound-v1-1-0bf126e876d4@linux.dev > --- > mm/filemap.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/mm/filemap.c b/mm/filemap.c > index b74bc1e5015c..1df776907140 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -3968,6 +3968,13 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, > unsigned long end; > vm_fault_t map_ret; > > + /* A lower index could move vmf->pte out of its page table. */ > + if (unlikely(xas.xa_index < last_pgoff)) { > + folio_unlock(folio); > + folio_put(folio); > + break; > + } > + > addr += (xas.xa_index - last_pgoff) << PAGE_SHIFT; > vmf->pte += xas.xa_index - last_pgoff; > last_pgoff = xas.xa_index; > > --- > base-commit: 65ba8f34ec886ec72b2c07ddc8cf3d815c32869d > change-id: 20261028-jf-mm-filemap-map-pages-lower-bound-a623ed8a81c9 > > Best regards, > -- > Jose Fernandez (Anthropic) > I'm trusting on Andrew to pick this up :) -- Cheers, David