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b=EpTqdnrXGAyVH25ewafsDwTfyw4v5r3vzLPpP0AhIJWLIDfLzam8w+JzkDW9fqn46 +pDhBZ9NJraPzz0hE7SDRCovSPuVXT9e7GQbp9aLXo/pd/aEADmdDOELtTUdxtKDuA BIzRhM8h1PrA6RfZdNSDrs5hJ/Txy4dO3RhN08oI= Date: Fri, 27 Jun 2025 13:09:45 -0700 From: Andrew Morton To: Lance Yang Cc: david@redhat.com, 21cnbao@gmail.com, baolin.wang@linux.alibaba.com, chrisl@kernel.org, kasong@tencent.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, v-songbaohua@oppo.com, x86@kernel.org, huang.ying.caritas@gmail.com, zhengtangquan@oppo.com, riel@surriel.com, Liam.Howlett@oracle.com, vbabka@suse.cz, harry.yoo@oracle.com, mingzhe.yang@ly.com, stable@vger.kernel.org, Barry Song , Lance Yang Subject: Re: [PATCH v2 1/1] mm/rmap: fix potential out-of-bounds page table access during batched unmap Message-Id: <20250627130945.dd074c7ea076359ac754a029@linux-foundation.org> In-Reply-To: <20250627062319.84936-1-lance.yang@linux.dev> References: <20250627062319.84936-1-lance.yang@linux.dev> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: A32D3140002 X-Stat-Signature: k5eazcgp57tpccormdy4b4tmopqu66p6 X-HE-Tag: 1751054987-985566 X-HE-Meta: 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 WAM14sum 3fDZpItcz4yi7NmaV3REkKUiRfxDFTtcYJTeROQw6TYQTAp5HkPYVxUVElRUv3erFbmLWrpS+jvc42wPcHHIpxYimf4l8omsDe+mT13aAfEAGedSQz6jgy64NkLCehoOwCtoogvyyNgE7Q9FhHU1dAMsUQapyrF+y9u0MbeoQm12KPi2hkiIWISlT/ZzGEcWZF6AtTbN0jwAE0VPTOMY+xoQcSWFKMg8q+0Er4YbDP9r3qNTTN5pu8omMyBpE8n24LPN8tUEfkJ3WQ/tBpLr4ER+MgkUbKpBmk5KLQnsCO53O8PdXxRjLYyiSELRDBzWuQatRZKjnFMY0FNjbrUFGBLJZLQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 27 Jun 2025 14:23:19 +0800 Lance Yang wrote: > As pointed out by David[1], the batched unmap logic in try_to_unmap_one() > can read past the end of a PTE table if a large folio is mapped starting at > the last entry of that table. It would be quite rare in practice, as > MADV_FREE typically splits the large folio ;) > > So let's fix the potential out-of-bounds read by refactoring the logic into > a new helper, folio_unmap_pte_batch(). > > The new helper now correctly calculates the safe number of pages to scan by > limiting the operation to the boundaries of the current VMA and the PTE > table. > > In addition, the "all-or-nothing" batching restriction is removed to > support partial batches. The reference counting is also cleaned up to use > folio_put_refs(). I'll queue this for testing while the updated changelog is being prepared.