From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793440162; b=DKQcckXNXR9/bE3q1q36yj0cRvhodSVAW/IymsLSexHxzsBcJ7HPCivPQn19C3+Ge7zy tdtKlGvSwOfJ1ad1vAcTNg4VvzWrod8k7hCfCAaL806Ih4Ke6j0sH5QA/n6O9yBHWjqlx MfOxi6sxQIaX8eD57q7fSFNmwhT9jZlkO5apYsoF6EOoiJ3j0pN7YNYBEESXaHhVgOvlT t0v3rLWt6WOK6rr9ERs7tNIYGbGgnInnhLYg3exTLazkVaw6HoO5bwPGj7H0K9oPvJaFe TgmSvMkke4Hb/WFiHDwz3u4/AKT8BZFcJ/kL5fN0nr1Bda8AvM0WBGI+t0dsCc0G2Iw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793440162; h=Received:DKIM-Signature:From:Date:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:Message-Id:References:In-Reply-To:To:Cc: X-Mailer:X-Developer-Signature:X-Developer-Key; bh=pzeRdDMVfEMNbkMdT/nRgGx9sjoVV/E/1Sv6j9DFArI=; b=naFQny7G2GrfrWElFV5o3F2zcuzfAz8FHni9/pUWGW8VvIlzEeo5zd1SxASchSBPpZLr EQ/nYSwhvV8/lbuaqGr2oo+ncK2F23ye433I3iTEGvQYrkGGr6/DmqELwGf7I6pOvcCNF UYN6SeOhf/61HKKaaW9Utk4qtNw2tOxXjPVDPT9K83MExNbqLgHGwQltsOotW+F0AmLnG iZeqv0AJQf93cdKBt1aCb3Afd1vLlVJup2IERrzTnt1hcNMdDmyAlIAzXAAvOE3pQeO96 NBsrmyaC6FcBueJj+aHl+/Pur19PqlNJvfoylRko/VyzzXoIbtirEo3ljLF7Sy2hnZQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Nk8DpZQP; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 43E35606A31D; Sat, 31 Oct 2026 09:49:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Nk8DpZQP Received: by smtp.kernel.org (Postfix) with ESMTPSA id 768741F000C1; Sat, 31 Oct 2026 09:49:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793440161; bh=pzeRdDMVfEMNbkMdT/nRgGx9sjoVV/E/1Sv6j9DFArI=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=Nk8DpZQP6BzD9OA8zt/17XY/95wwW4UIU2PZ2B9LYSCoMPTi2ddtIV6u99LHr+5Oe g4tDbV0A9eSd5emCxI8wukjjJ2YT2aWaeikxo/9ZsvfdGNzOUVTriMj7ENkyyLHSUr /AmyIiG8Vw/uXBjmX5bA/kDSRtXD7rVcvEJxXTMudlPtX62drHe3FsXcaMp69dcM9/ YwYGbDDS5YN7PQOQjxE/6H/9hJFXhZl2GVnrqXpy2NO/l62R63MYQrI/IpmBB0SIR1 0pQhFdr/sND4w08uekTBmbzVcrRzdHw2xwe/pl3C0l93a6hCf30nDvqDtr32D5+WyV NJm0qxt4y7qnw== From: "David Hildenbrand (Arm)" Date: Sat, 31 Oct 2026 10:40:04 +0100 Subject: [PATCH v3 35/47] mm/memory: reject remote COW faults on PFN mappings 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="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261031-fixes_core-v3-35-d6437171ecc3@kernel.org> References: <20261031-fixes_core-v3-0-d6437171ecc3@kernel.org> In-Reply-To: <20261031-fixes_core-v3-0-d6437171ecc3@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, Muhammad Usama Anjum , "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2304; i=david@kernel.org; h=from:subject:message-id; bh=vy3o0JKxTUrol+3XYhfqk0XP7HsGSqgA1eThmpFZJfQ=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLKebs/sadz7N7koN4X/1CmTNuOJDc28a4xv2m9VPWy6Q qSCb2NnRykLgxgHg6yYIktQ8H2Dly/X1Va78THDzGFlAhnCwMUpABPxes3IMDdGTmx1U9JkAxWO z0JHpPjtV/9wspB8sXV9S7o/z6MaV0aGG98XcfzwDPadESJ0P5rn4aVNSzjtP99zunv3xwmuytf uHAA= X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A 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 ] Reviewed-by: Pedro Falcato Tested-by: Muhammad Usama Anjum 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 5392bcb1d24d6..ae8d567bc6ba3 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