From patchwork Sun Mar 22 01:22:26 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 228912 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=-3.8 required=3.0 tests=DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED autolearn=no 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 361B0C4332D for ; Sun, 22 Mar 2020 01:22:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0878120767 for ; Sun, 22 Mar 2020 01:22:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584840150; bh=GPIJXAU8IdYJRQY6I34QACgs/PHeLhjUhfPVGA19puk=; h=Date:From:To:Subject:In-Reply-To:List-ID:From; b=OrDMSlk9ZpU1mzhEtU8XdswPPqQvwci0Z49ko5xQFnNEgmOvm4nHTJjHGWjuCqCuB BvihOwoDc+4UsMzI+Pu8C/quMXhX8yMC8bPOBFnT1+dLWcD7jCTXl+O+wySiDCFYj0 xxEZ0oroglC2M30QezfrOzxyQraOxRTWg7/Lyq+4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728178AbgCVBW3 (ORCPT ); Sat, 21 Mar 2020 21:22:29 -0400 Received: from mail.kernel.org ([198.145.29.99]:41258 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726859AbgCVBW3 (ORCPT ); Sat, 21 Mar 2020 21:22:29 -0400 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0AB9E20757; Sun, 22 Mar 2020 01:22:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584840148; bh=GPIJXAU8IdYJRQY6I34QACgs/PHeLhjUhfPVGA19puk=; h=Date:From:To:Subject:In-Reply-To:From; b=sIgkxHmIyg5bf/bNSgO7qViDIKy9HuWF7IIlhuaPb1m8jG+rAtrzuBSJnD578Y6fJ Ejne412lZYBQF153iO3yl0FGXeUvusqkVOvSu1gkAdvPcKGsviMNEXKv0Xu8wPufd+ Fq6/xCgKkS6NxaT8yDMn+s4cOL/b+ksa+qgfpnQU= Date: Sat, 21 Mar 2020 18:22:26 -0700 From: Andrew Morton To: akpm@linux-foundation.org, dancol@google.com, dave.hansen@intel.com, jannh@google.com, joel@joelfernandes.org, linux-mm@kvack.org, mhocko@suse.com, minchan@kernel.org, mm-commits@vger.kernel.org, stable@vger.kernel.org, torvalds@linux-foundation.org, vbabka@suse.cz Subject: [patch 06/10] mm: do not allow MADV_PAGEOUT for CoW pages Message-ID: <20200322012226.yY5JKgG__%akpm@linux-foundation.org> In-Reply-To: <20200321181954.c0564dfd5514cd742b534884@linux-foundation.org> User-Agent: s-nail v14.8.16 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Michal Hocko Subject: mm: do not allow MADV_PAGEOUT for CoW pages Jann has brought up a very interesting point [1]. While shared pages are excluded from MADV_PAGEOUT normally, CoW pages can be easily reclaimed that way. This can lead to all sorts of hard to debug problems. E.g. performance problems outlined by Daniel [2]. There are runtime environments where there is a substantial memory shared among security domains via CoW memory and a easy to reclaim way of that memory, which MADV_{COLD,PAGEOUT} offers, can lead to either performance degradation in for the parent process which might be more privileged or even open side channel attacks. The feasibility of the latter is not really clear to me TBH but there is no real reason for exposure at this stage. It seems there is no real use case to depend on reclaiming CoW memory via madvise at this stage so it is much easier to simply disallow it and this is what this patch does. Put it simply MADV_{PAGEOUT,COLD} can operate only on the exclusively owned memory which is a straightforward semantic. [1] http://lkml.kernel.org/r/CAG48ez0G3JkMq61gUmyQAaCq=_TwHbi1XKzWRooxZkv08PQKuw@mail.gmail.com [2] http://lkml.kernel.org/r/CAKOZueua_v8jHCpmEtTB6f3i9e2YnmX4mqdYVWhV4E=Z-n+zRQ@mail.gmail.com Link: http://lkml.kernel.org/r/20200312082248.GS23944@dhcp22.suse.cz Fixes: 9c276cc65a58 ("mm: introduce MADV_COLD") Signed-off-by: Michal Hocko Reported-by: Jann Horn Acked-by: Vlastimil Babka Cc: Minchan Kim Cc: Daniel Colascione Cc: Dave Hansen Cc: "Joel Fernandes (Google)" Cc: Signed-off-by: Andrew Morton --- mm/madvise.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) --- a/mm/madvise.c~mm-do-not-allow-madv_pageout-for-cow-pages +++ a/mm/madvise.c @@ -335,12 +335,14 @@ static int madvise_cold_or_pageout_pte_r } page = pmd_page(orig_pmd); + + /* Do not interfere with other mappings of this page */ + if (page_mapcount(page) != 1) + goto huge_unlock; + if (next - addr != HPAGE_PMD_SIZE) { int err; - if (page_mapcount(page) != 1) - goto huge_unlock; - get_page(page); spin_unlock(ptl); lock_page(page); @@ -426,6 +428,10 @@ regular_page: continue; } + /* Do not interfere with other mappings of this page */ + if (page_mapcount(page) != 1) + continue; + VM_BUG_ON_PAGE(PageTransCompound(page), page); if (pte_young(ptent)) {