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Tue, 27 Oct 2026 16:34:44 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id sKFICKTS4GrQDgAAD6G6ig (envelope-from ); Tue, 27 Oct 2026 16:34:44 +0000 Date: Tue, 27 Oct 2026 16:34:42 +0000 From: Pedro Falcato To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, Chris Mason , stable@vger.kernel.org Subject: Re: [PATCH 34/46] mm/memory: reject remote COW faults on PFN mappings Message-ID: References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-34-6f74bec9a5bb@kernel.org> X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261027-fixes_core-v1-34-6f74bec9a5bb@kernel.org> X-Spamd-Result: default: False [-12.01 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RCVD_TLS_ALL(0.00)[]; FREEMAIL_CC(0.00)[linux-foundation.org,cmpxchg.org,kernel.org,linux.dev,tencent.com,google.com,linux.alibaba.com,infradead.org,suse.com,soleen.com,suse.cz,nvidia.com,surriel.com,arm.com,intel.com,redhat.com,gmail.com,suse.de,huaweicloud.com,lge.com,gourry.net,sk.com,ziepe.ca,kvack.org,vger.kernel.org,lists.infradead.org]; FROM_HAS_DN(0.00)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; ARC_NA(0.00)[]; DKIM_TRACE(0.00)[suse.de:+]; MISSING_XM_UA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:104:10:150:64:97:from,2a07:de40:b281:106:10:150:64:167:received]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; RCPT_COUNT_GT_50(0.00)[65]; TAGGED_RCPT(0.00)[]; TO_DN_SOME(0.00)[] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Flag: NO X-Spam-Score: -12.01 X-Spam-Level: X-Rspamd-Queue-Id: 8B6EF21E2F On Tue, Oct 27, 2026 at 12:17:54AM +0100, David Hildenbrand (Arm) wrote: > From: Chris Mason > > When handling a COW fault without a normal source page (PFN mappings), > __wp_page_copy_user() copies from the faulting user address. For remote > faults, this accesses the wrong address space, resulting in wrong data > getting copied. > > For example, user_events updates an enable bit in the registering > process's memory. If that memory needs to be faulted in, > user_event_enabler_fault_fixup() calls fixup_user_fault() from a work > item. Placing the enable bit in a private PFN mapping can trigger this > remote COW path. > > Reject these faults with VM_FAULT_SIGBUS when the target mm differs from > current->mm: remote faults. Ordinary (non-PFN) mappings are not affected. > > The user-address copy dates back to commit 6aab341e0a28 ("mm: re-architect > the VM_UNPAGED logic"); likely, actual ways to get remote faults in > there on COW PFN mappings appeared afterwards. But the fix is simple and > straight forward. > > Fix generated by an LLM and sent by Chris Mason in private. > > Fixes: 6aab341e0a28 ("mm: re-architect the VM_UNPAGED logic") > Cc: stable@vger.kernel.org > Signed-off-by: Chris Mason > Reviewed-by: Lorenzo Stoakes (ARM) > [ david: simplify comment and description ] > Signed-off-by: David Hildenbrand (Arm) Reviewed-by: Pedro Falcato -- Pedro