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 D804C606A31A for ; Fri, 30 Oct 2026 03:42:09 +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=iZT1DzHM; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=FWAH9XrR DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Reply-To:List-Subscribe: List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id:Date: Content-Transfer-Encoding:Content-Type:References:In-Reply-To:Cc:To:Subject: From:Message-ID:MIME-Version:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Unsubscribe-Post:List-Owner; bh=8vt3r0dV4H78MyX5tyofuPfjl2FfIwvVkisCW8E4akc=; b=iZT1DzHMev5d6yRMbd9uliuKud EqCdxlXhyJ/HBZWPHSXzfKmbuaaFJ+Tbd27VXxsFXFUvy8s0PwCzwKKRjHxxYfz7Z7UwqsJxxYO+o 8AMRyAQGgLcf9Kh5IMORea065v/SckCkMgvR+lRc1vXEokPJ2JKueeLMuSLMF6IxG5BGhj+tns7LW Kn/pMVoIE/cHAB/rzdtfBL6wQRkqgCDrFqTcN/25EL3s+uLwBmdG4KEeLak5/xuBBCOKXs+f+NftE qmxp68K4WrVF6gbF1/Zj63DhVcdrSzk8CXPvIieTISNUxTY1szwIqX928wjD015o9ydGQuEkIk5yQ w1vViagQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xMdVJ-0000000AktV-1cjd; Fri, 30 Oct 2026 03:42:09 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xMdVI-0000000AksZ-1qWF for kexec@lists.infradead.org; Fri, 30 Oct 2026 03:42:08 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id DA112600DA; Fri, 30 Oct 2026 03:42:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 087E21F000C1; Fri, 30 Oct 2026 03:42:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793331727; bh=8vt3r0dV4H78MyX5tyofuPfjl2FfIwvVkisCW8E4akc=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=FWAH9XrRqNGdlVz48bcrq1+V5ulr2ptkvsIlZv5tR/SewdcA21FsGI0sfWCkvVI3w vlZOqqLr+j9nIeY+r0UDa3P2h7Q8UiJbj4R49KdyHvM8I8t5Bx8eIxo60ZNwaiXqFx Y3iBdeEohDmXI2JWsVCBX5AAC9biHBcL6LasvitQ7iZjN8Nhic1aDM46tk/4kVj0cI CFtbDbBIvz1de83W7IN6d+cT8ZDpS2FoXR0BjGFTOljQaxJMsf3nd40jpRiWL6JvJC rLwhFuy3EFpWb6KcaqEEIbuaDvsVdFJMGeAliDDa+yJCUdrw/xyg+N6MupITSmvtuj HPuLFoQNb0ivg== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH v2 35/47] mm/memory: reject remote COW faults on PFN mappings To: =?utf-8?b?RGF2aWQgSGlsZGVuYnJhbmQgKEFybSk=?= , "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" , "Pedro Falcato" , "Hugh Dickins" , "Pasha Tatashin" , "Pratyush Yadav" , =?utf-8?b?TWF0dGhldyBXaWxjb3ggKE9yYWNsZSk=?= , "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" Cc: kexec@lists.infradead.org, "Chris Mason" In-Reply-To: <20261029-fixes_core-v2-35-a64ce7f83abb@kernel.org> References: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> <20261029-fixes_core-v2-35-a64ce7f83abb@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Fri, 30 Oct 2026 03:42:04 +0000 X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: sashiko-reviews@lists.linux.dev Sender: "kexec" X-Spam-Status: No, score=-10.9 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 X-Archived-By: > From: Chris Mason >=20 > 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. >=20 > 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. >=20 > Reject these faults with VM_FAULT_SIGBUS when the target mm differs from > current->mm: remote faults. Ordinary (non-PFN) mappings are not affected. >=20 > 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. >=20 > Fix generated by an LLM and sent by Chris Mason in private. >=20 > 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 ] > Reviewed-by: Pedro Falcato > Signed-off-by: David Hildenbrand (Arm) Sashiko has reviewed this patch and found no issues. --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261029-fixes_core= -v2-0-a64ce7f83abb@kernel.org?part=3D35