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=1793057313; b=Zy7tVjl7Lq0C4JW+mySTZVkT9kHGi4mkBAD8CV9NyGGNHvpi2c2mrpoD+7VGtqSYP8nR oUCbNfsvTKYARlohPMfAyxw1+dsSId1D9d5/3jP7z0xI4/aO/x4dYFJFrB4p/4kaZDN4+ GIo9wBEEO66Lw3wu8Z86UCRRQRiq/0a50YOqAxWxaXVtsdXGfQohsEaistz8zUa4qL6Tr 6dZz+t9cdP/qep6FcBsE/rWDrYMSkv13rkR9Bz2hGF+DbmyTAlUdriIUslDGSyV1ms7jp npK+cdKu6roNP6g1QkmdrNu5OaLR/gwJMIGYeKcMn/+uu4W5tDLb3GC0fe9pOEoj7rA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793057313; 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=bKlj3iVdxa80tI8axGYbOkgCnYK7fspTKHlXYvaR2aI=; b=lska5IbmFL1jnIPgcT79bgtxig5pYaxsbYOboSF0oXFDCXOUjedhFnM0XRHi++sDry+J OsuLuCSg92NdjCyEfSAdAJadIW6/KW+ZFGxcSBwqTBfSd0pkl2bsPYDW4kZkFEfn7HzGu Xr4j6Dp4DOuUl7dkOFQ9aHHOYR6+QFQ8Gwiu5WLFUgvfC4pth5Vvk14+ZZByppDBIgwvA YpJcHFI6/iwd3ZonGpEk6oea+FoSeH8vnY3veWMIP4/p1vX+jM93GC6W72pCnAMszQ2K3 hAgLJhz58ZuoRu6/n2RXhMgMfGhkitoVfvZTQFkeVVpEQWlZNg9D0IgWfQj/kpMT8zg== 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=IF7UNpYa; 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 BEC92606A31D; Mon, 26 Oct 2026 23:28:32 +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=IF7UNpYa 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-Mailing-List: linux-kernel@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: <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 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