From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BCA68606A31E for ; Tue, 27 Oct 2026 16:34:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=v6WmAg1Y; dkim=pass (1024-bit key, unprotected) header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=DYrZ/Jaz; dkim=pass header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=ASJUs0Y3; dkim=neutral header.d=suse.de header.i=@suse.de header.a=rsa-sha256 header.s=susede2_rsa header.b=DYrZ/Jaz; dkim=neutral header.d=suse.de header.i=@suse.de header.a=ed25519-sha256 header.s=susede2_ed25519 header.b=ASJUs0Y3 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Unsubscribe-Post:List-Owner; bh=NxOIucUiikYry+49/JZI01aFrFYOW8xThyuNV5vreJE=; b=v6WmAg1YBAmjXOuNR0m5xUa1yd mi89nLKmmOi2QCw8c6jLtbuu1re/GMh5ns1Zsrz9IDxajuBKhdVerm7OgVv7A3ReZIsCu2mt77GxG fig+02etTOmVuJ9xp9AMczw3ubkyZXHBquUAOtu3ZDBTlizRagP/EW2BEtt2ePQYcZguGhWURgEhI Trzru3CMeAVz/U92Mg2yXI4ZxkX8Ym8bdTRJm2m12S/DRZhQdbN/C5baxjhBgB+tpGYYM247KgKK7 I4Kzy5bMQx2ebW/8CJUeLysckdFg0b7MCBiMfjgNWtOlg4dN66j7dOLsiqtYbk6JBqohI0qoY25eU MEeCvuvA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xLk8T-00000005NQL-1RrO; Tue, 27 Oct 2026 16:34:53 +0000 Received: from smtp-out1.suse.de ([195.135.223.130]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xLk8Q-00000005NPW-0nE8 for kexec@lists.infradead.org; Tue, 27 Oct 2026 16:34:52 +0000 Received: from imap1.dmz-prg2.suse.org (unknown [10.150.64.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 5F9E221F43; Tue, 27 Oct 2026 16:34:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1793118888; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=NxOIucUiikYry+49/JZI01aFrFYOW8xThyuNV5vreJE=; b=DYrZ/JazN4nYdi+afHyqz8QV5Coqg055GKzpqSPZHPK8CUtAMJPoogfHO+ZLq+JWeK+4aI GbRLRg3FfRMsvhmw2GiL/SNfYDelEZ5GTXOL0Q9Cvnz2Yaj9HgGbR/w8KJJWJvi1XdsaAn V3Apwr7tPm+1Y7oNf5QxrQ74gC1jdOQ= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1793118888; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=NxOIucUiikYry+49/JZI01aFrFYOW8xThyuNV5vreJE=; b=ASJUs0Y3+GZw/WVpyH6+w6sCacPWKT2KRvHrSVqOuFQr9nDHznF5LtwoRppLqlRrEce+qh ZjyPSP7vgHzUuWCQ== Authentication-Results: smtp-out1.suse.de; none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1793118888; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=NxOIucUiikYry+49/JZI01aFrFYOW8xThyuNV5vreJE=; b=DYrZ/JazN4nYdi+afHyqz8QV5Coqg055GKzpqSPZHPK8CUtAMJPoogfHO+ZLq+JWeK+4aI GbRLRg3FfRMsvhmw2GiL/SNfYDelEZ5GTXOL0Q9Cvnz2Yaj9HgGbR/w8KJJWJvi1XdsaAn V3Apwr7tPm+1Y7oNf5QxrQ74gC1jdOQ= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1793118888; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=NxOIucUiikYry+49/JZI01aFrFYOW8xThyuNV5vreJE=; b=ASJUs0Y3+GZw/WVpyH6+w6sCacPWKT2KRvHrSVqOuFQr9nDHznF5LtwoRppLqlRrEce+qh ZjyPSP7vgHzUuWCQ== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 57B3713419; 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-Archived-By: 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 [-11.80 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; TAGGED_RCPT(0.00)[]; ARC_NA(0.00)[]; MISSING_XM_UA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; RCPT_COUNT_GT_50(0.00)[65]; FROM_HAS_DN(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]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; R_RATELIMIT(0.00)[to_ip_from(RL8d8xedm6iu8o66torxsk6bwd)] X-Spam-Score: -11.80 X-Spam-Level: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261027_093450_940969_D3A1D405 X-CRM114-Status: GOOD ( 15.11 ) X-Spam-Score: -4.4 (----) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" X-Spam-Status: No, score=-11.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 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