From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.38 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794394278; b=ZGf9BKFPdjVm6sTsigtbVlaqV3Ln5aqzdBh4OKOy+0ARRAHkVyCenkkL+Ul04C/Xis9o mXwCABzcGRXb+CzzYAiS/X6v/LoMDuEG9Ombu9kvFFWgJgdZRvAbyGi0A2nEwxLxOJaiV mU9hxyhGkx2zWeBeq+qE1QBaB2BQMDesyzfMc89spFJYKN81yTiuk+5xIHPUdhFBdknic aZVYn/+TgLw7V05SM71x2M7cFpC6va6V7a+amuwOl79aXOyyg82gAkPv+4K74zQiarZt3 6M+D8D1ouhRPtEu7Zz3XbRyqpEjIkOnkra9ZNilTn/StftsCi7oUptf27HB4/dGmf1A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794394278; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:To:Cc:Subject:Date:Message-ID: X-Mailer:In-Reply-To:References:MIME-Version:Content-Type: Content-Transfer-Encoding; bh=zlaGDXenXs2WnOuYAO4yuwNGMasd1sp10+9WQn/o4CA=; b=LrWf+uoFt4EMjKKx13m/eifgC8Jk9kdblQ8A1xIbeJvWJQPDF0wKmewlxV8oOqkX6MS8 P/rJV/bcy8zOpxWiNw4mmpM9Heoz+KpQVzvrv+AbbM7Y0fD41M2Jkc/9g2CBnjP0cwHir KdkWAxrG2KJNi//kiFmhpQXT4p0RpLtI3gdXNwnAYvevLMvo0dh6oXV390Ks7n2qbjxFr +wPyqMrEW1YqK/2rgvilHQVE9yuOt1A6aKhjqy6cGXC8EIhXDhGBHG6+GgN0oUngnr94r htFObyNqCM7YlIBlqKOhL2bTBJetRj/bBXhsELTUD5KEvunRR5uwfoz3Bkshn0SW7vw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=mmo8Y1GX; arc=none smtp.remote-ip=91.218.175.38 Received: from mta0.migadu.com (out-38.mta0.migadu.com [91.218.175.38]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DC943606A324 for ; Wed, 11 Nov 2026 10:51:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org DC943606A324 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=mmo8Y1GX X-Envelope-To: stable@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=fJMpLHXJ3OMWwjsPOjW0na7I13zrAGAWG+nW9/yEEP4=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1794394275; v=1; x=1794999075; b=mmo8Y1GXusPnat7zHzGuHNTZRisJ8E9V7q1g1cUNks1AE+rkYpz+epFX1nb63bw9vTNJvVDP B6Q867ry6GAtOxaJptjrcLPPJVOwWB416R+bYaB/Q4n41lw25ux3Yr2Kpbw4mgE3c12WkcUoQ8n yG8JxAv1T6p5cGO3WhtNmJx8= X-Envelope-To: stable@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id c024eae9af748c53; Wed, 11 Nov 2026 10:51:10 +0000 X-Mizu-Trace-ID: c024eae9af748c53 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: stable@vger.kernel.org, sashal@kernel.org Cc: Samarth Narang , Lance Yang , Andrew Morton , "Lorenzo Stoakes (ARM)" , "Kiryl Shutsemau (Meta)" , "David Hildenbrand (Arm)" , Mel Gorman , Xu Xin , Chengming Zhou , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= , Andrea Arcangeli , Peter Xu , Bobby Powers , Brian Geffon , Denis Plotnikov , Doug Gilbert , Hugh Dickins , Johannes Weiner , Martin Cracauer , Marty McFadden , Maya Gokhale , Pavel Emelyanov , Rik van Riel , Shaohua Li , James Houghton , Jonathan Corbet , Paolo Bonzini , Sean Christopherson , SJ Park , Zi Yan , Mohammed EL Kadiri Subject: [PATCH 6.1.y 3/3] mm/ksm: fix userfaultfd protection during merge and unmerge Date: Wed, 11 Nov 2026 18:50:34 +0800 Message-ID: <20261111105034.51632-4-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261111105034.51632-1-lance.yang@linux.dev> References: <20261109201707-failed-6.1-990d6c2194a9@kernel.org> <20261111105034.51632-1-lance.yang@linux.dev> X-Mailing-List: stable@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: 8bit KSM loses userfaultfd protection when replace_page() builds a new PTE from vma->vm_page_prot. Dropping its uffd bit lets a subsequent write go through ordinary COW instead of userfaultfd write protection handling. For RWP, a merged page also becomes readable without faulting. Keeping the uffd bit and restoring PAGE_NONE fixes merging, but we also have to handle unmerging. An existing KSM page can be protected with RWP before MADV_UNMERGEABLE, so unmerging already needs fixing independently of preserving RWP during merging. Unsharing replaces a shared page with a private one and should leave userfaultfd protection in place, as do_wp_page() already does for write protection. Currently, an unshare fault reaches do_uffd_rwp() before it can proceed to do_wp_page(). - With synchronous RWP, handle_userfault() returns VM_FAULT_SIGBUS. break_ksm() then reports success with a KSM page still merged. - With asynchronous RWP, protection is cleared before unsharing. Preserve the uffd bit when merging, and restore PAGE_NONE for RWP. Let FAULT_FLAG_UNSHARE skip RWP fault handling and keep PAGE_NONE on each private copy as well. Unsharing can then complete with RWP still armed for a subsequent access. Link: https://lore.kernel.org/20261026130054.91461-1-lance.yang@linux.dev Link: https://lore.kernel.org/all/20261019010934.697895-1-samarth.colleges@gmail.com/ Link: https://lore.kernel.org/all/20261020055518.36087-1-lance.yang@linux.dev/ Fixes: 63b2d4174c4a ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl") Fixes: 2d427bb01639 ("mm/userfaultfd: add RWP fault delivery and expose UFFDIO_REGISTER_MODE_RWP") Signed-off-by: Samarth Narang Signed-off-by: Lance Yang Signed-off-by: Andrew Morton Co-developed-by: Samarth Narang Acked-by: Lorenzo Stoakes (ARM) Reviewed-by: Kiryl Shutsemau (Meta) Acked-by: David Hildenbrand (Arm) Cc: Mel Gorman Cc: Xu Xin " Cc: Chengming Zhou Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Michal Hocko Cc: Jérôme Glisse Cc: Andrea Arcangeli Cc: Peter Xu Cc: Bobby Powers Cc: Brian Geffon Cc: Denis Plotnikov Cc: Doug Gilbert Cc: Hugh Dickins Cc: Johannes Weiner Cc: Martin Cracauer Cc: Marty McFadden Cc: Maya Gokhale Cc: Pavel Emelyanov Cc: Rik van Riel Cc: Shaohua Li Cc: James Houghton Cc: Jonathan Corbet Cc: Paolo Bonzini Cc: Sean Christopherson Cc: SJ Park Cc: Zi Yan Cc: Mohammed EL Kadiri Cc: (cherry picked from commit 990d6c2194a938a19a8cf94c6cfd75171345089b) --- Depends on patches 1 and 2, which backport 58f595c66591 and 6cce3314b928. Backport to 6.1: - Use the older pte_uffd_wp()/pte_mkuffd_wp() helpers. - Omit the mm/memory.c changes, since 6.1 has no RWP support. mm/ksm.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/ksm.c b/mm/ksm.c index b052f6141b6e..65da88db632f 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -1176,6 +1176,10 @@ static int replace_page(struct vm_area_struct *vma, struct page *page, dec_mm_counter(mm, MM_ANONPAGES); } + /* Preserve uffd-wp when replacing the page. */ + if (pte_uffd_wp(orig_pte)) + newpte = pte_mkuffd_wp(newpte); + flush_cache_page(vma, addr, pte_pfn(*ptep)); /* * No need to notify as we are replacing a read only page with another -- 2.49.0