From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4CB34C43331 for ; Mon, 1 Mar 2021 17:18:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2AF56651DD for ; Mon, 1 Mar 2021 17:18:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237869AbhCARSE (ORCPT ); Mon, 1 Mar 2021 12:18:04 -0500 Received: from mail.kernel.org ([198.145.29.99]:60754 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233651AbhCAQYl (ORCPT ); Mon, 1 Mar 2021 11:24:41 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 884DD64EC6; Mon, 1 Mar 2021 16:20:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1614615650; bh=76pg7xbG8DWoXD649UkrvAPXyffMUB//uVU5LKz0qY8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=AXqBx3TXRlY21TV1wuTDB9iA4ontKHfRtINRmFYlBqJHNYbw/Uhu50VUjTIUWA9mE fRDwgE0bGgfcDXmxVw/8AsIz5/8lRicq73S6SkZWruS7OYUd3/JfUdsZ5TKAFcAFeD /DuHD6g7FQ+aeeV5Mb3UH72UOv/zjWS2IbGWk3v0= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nicolai Stange , Vlastimil Babka , Sasha Levin Subject: [PATCH 4.9 012/134] mm, thp: make do_huge_pmd_wp_page() lock page for testing mapcount Date: Mon, 1 Mar 2021 17:11:53 +0100 Message-Id: <20210301161014.184679660@linuxfoundation.org> X-Mailer: git-send-email 2.30.1 In-Reply-To: <20210301161013.585393984@linuxfoundation.org> References: <20210301161013.585393984@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Vlastimil Babka Jann reported [1] a race between __split_huge_pmd_locked() and page_trans_huge_map_swapcount() which can result in a page to be reused instead of COWed. This was later assigned CVE-2020-29368. This was fixed by commit c444eb564fb1 ("mm: thp: make the THP mapcount atomic against __split_huge_pmd_locked()") by doing the split under the page lock, while all users of page_trans_huge_map_swapcount() were already also under page lock. The fix was backported also to 4.9 stable series. When testing the backport on a 4.12 based kernel, Nicolai noticed the POC from [1] still reproduces after backporting c444eb564fb1 and identified a missing page lock in do_huge_pmd_wp_page() around the call to page_trans_huge_mapcount(). The page lock was only added in ba3c4ce6def4 ("mm, THP, swap: make reuse_swap_page() works for THP swapped out") in 4.14. The commit also wrapped page_trans_huge_mapcount() into page_trans_huge_map_swapcount() for the purposes of COW decisions. I have verified that 4.9.y indeed also reproduces with the POC. Backporting ba3c4ce6def4 alone however is not possible as it's part of a larger effort of optimizing THP swapping, which would be risky to backport fully. Therefore this 4.9-stable-only patch just wraps page_trans_huge_mapcount() in page_trans_huge_mapcount() under page lock the same way as ba3c4ce6def4 does, but without the page_trans_huge_map_swapcount() part. Other callers of page_trans_huge_mapcount() are all under page lock already. I have verified the POC no longer reproduces afterwards. [1] https://bugs.chromium.org/p/project-zero/issues/detail?id=2045 Reported-by: Nicolai Stange Signed-off-by: Vlastimil Babka Signed-off-by: Sasha Levin --- mm/huge_memory.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1022,6 +1022,19 @@ int do_huge_pmd_wp_page(struct fault_env * We can only reuse the page if nobody else maps the huge page or it's * part. */ + if (!trylock_page(page)) { + get_page(page); + spin_unlock(fe->ptl); + lock_page(page); + spin_lock(fe->ptl); + if (unlikely(!pmd_same(*fe->pmd, orig_pmd))) { + unlock_page(page); + put_page(page); + goto out_unlock; + } + put_page(page); + } + if (page_trans_huge_mapcount(page, NULL) == 1) { pmd_t entry; entry = pmd_mkyoung(orig_pmd); @@ -1029,8 +1042,10 @@ int do_huge_pmd_wp_page(struct fault_env if (pmdp_set_access_flags(vma, haddr, fe->pmd, entry, 1)) update_mmu_cache_pmd(vma, fe->address, fe->pmd); ret |= VM_FAULT_WRITE; + unlock_page(page); goto out_unlock; } + unlock_page(page); get_page(page); spin_unlock(fe->ptl); alloc: