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 ED7CA606A322 for ; Mon, 26 Oct 2026 23:28:33 +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=UHt+gVfd; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=IF7UNpYa 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:Cc:To:In-Reply-To:References :Message-Id:Content-Transfer-Encoding:Content-Type:MIME-Version:Subject:Date: From:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Unsubscribe-Post: List-Owner; bh=bKlj3iVdxa80tI8axGYbOkgCnYK7fspTKHlXYvaR2aI=; b=UHt+gVfduq0yox Av4NsAj+gOsX8EPuaIkKUBqadkfKgcr+IgDDooQVlMyfRmrMaLL3ka+b8eLhxL2V/aXiXrVNzI/6K jdVhx6I58+o31ZZJ9kzc4T07j5bINK0fFRqw7x7XT+9LowI6Ee6+QhjftHyy8Uvgaa36VXUpsiis1 Nvb3oHZ2f3X+vZ+5Sm7tgg0bYQwlErXcFG3XyLpCDMOZgNesHb4S7wODSjeYuZ6XRNn+zscxhwgiv UcqETd6loyjdSaFVKYzNMPql52Km4QRwxEPeaT3rE0RI4oPK3y9igvbffIzxJbOHwFszZvulsh8Fv F3SUY9OY4++bAXfjz4qA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xLU7F-00000003RIn-2r9a; Mon, 26 Oct 2026 23:28:33 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xLU7E-00000003RIh-46Zo for kexec@lists.infradead.org; Mon, 26 Oct 2026 23:28:33 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id B49E540DA6; Mon, 26 Oct 2026 23:28:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A3C3A1F01825; Mon, 26 Oct 2026 23:28:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793057312; bh=bKlj3iVdxa80tI8axGYbOkgCnYK7fspTKHlXYvaR2aI=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=IF7UNpYafd4KinbAs1yEkkzghUj/D3H6lcfEypHVdc8O5mJ/le53JbzB8PXIGDBZ2 92eHkhrsCMv3xbBPQgIrrR6h04i9Hzcb7uymxczaT3Bairn2RgNRTJslpdCGrtvOt2 gGGMSduqcmRf6l6ZEjkKV8KGvZk3TzPQSFa5cfL4jZ4rTy7EpdN8tAmItoI0jZfBeq mRsOTgGOGKevkd8l9Z5v6l2DRA7JHhLmeUEhDmQlcmfEOS6+6Xyh168s1+PpjNpW/Z Y5VwHZ1A7nLhFNOJ0TJlewJtDw/sGFXYMfvNX3bI+oOBUubWGSeZf9xih60jKvsFJg nWblBWTTYdPlw== From: "David Hildenbrand (Arm)" Date: Tue, 27 Oct 2026 00:17:54 +0100 Subject: [PATCH 34/46] mm/memory: reject remote COW faults on PFN mappings X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261027-fixes_core-v1-34-6f74bec9a5bb@kernel.org> References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> In-Reply-To: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> To: 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 , "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 Cc: 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, "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2202; i=david@kernel.org; h=from:subject:message-id; bh=iQuj7gPdQ9im9u/p2aFC5RRjFYSkqwBMiK+uc5Slg5w=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLLu35++9LPovWW5/yR/+Qn4LnnxaLHaroe2drv0FKZw2 L611nxR1lHKwiDGwSArpsgSFHzf4OXLdbXVbnzMMHNYmUCGMHBxCsBE/ikxMrS/ZVy+IDlP84+D 2u2XR0odt3OwqHyeEbtwitOb9ZcCnYoY/nvc/cDSJvRmm8HhzxaPd9hO0F/morJkqktsWscH5jN zbRgA X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A 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=-19.2 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,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 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) --- mm/memory.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/mm/memory.c b/mm/memory.c index 0f4db5080e371..ec7a1397ab833 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3761,6 +3761,13 @@ static inline int __wp_page_copy_user(struct page *dst, struct page *src, return 0; } + /* + * __copy_from_user_inatomic() only works as expected for local faults. + * Reject remote faults. + */ + if (unlikely(mm != current->mm)) + return -EFAULT; + /* * If the source page was a PFN mapping, we don't have * a "struct page" for it. We do a best-effort copy by @@ -4086,6 +4093,8 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf) folio_put(old_folio); delayacct_wpcopy_end(); + if (err == -EFAULT) + return VM_FAULT_SIGBUS; return err == -EHWPOISON ? VM_FAULT_HWPOISON : 0; } kmsan_copy_page_meta(&new_folio->page, vmf->page); -- 2.43.0