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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 89A54C352A4 for ; Wed, 12 Feb 2020 21:10:34 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3544C21739 for ; Wed, 12 Feb 2020 21:10:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3544C21739 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lwn.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 82D1C6B0496; Wed, 12 Feb 2020 16:10:33 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7B6376B0497; Wed, 12 Feb 2020 16:10:33 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6A5CE6B0498; Wed, 12 Feb 2020 16:10:33 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0179.hostedemail.com [216.40.44.179]) by kanga.kvack.org (Postfix) with ESMTP id 4B9616B0496 for ; Wed, 12 Feb 2020 16:10:33 -0500 (EST) Received: from smtpin26.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 073EA181AEF10 for ; Wed, 12 Feb 2020 21:10:33 +0000 (UTC) X-FDA: 76482718746.26.seed35_7928e9c7ea856 X-HE-Tag: seed35_7928e9c7ea856 X-Filterd-Recvd-Size: 2428 Received: from ms.lwn.net (ms.lwn.net [45.79.88.28]) by imf08.hostedemail.com (Postfix) with ESMTP for ; Wed, 12 Feb 2020 21:10:32 +0000 (UTC) Received: from lwn.net (localhost [127.0.0.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ms.lwn.net (Postfix) with ESMTPSA id 94C40740; Wed, 12 Feb 2020 21:10:30 +0000 (UTC) Date: Wed, 12 Feb 2020 14:10:29 -0700 From: Jonathan Corbet To: Mike Rapoport Cc: linux-kernel@vger.kernel.org, Alan Cox , Andrew Morton , Andy Lutomirski , Christopher Lameter , Dave Hansen , James Bottomley , "Kirill A. Shutemov" , Matthew Wilcox , Peter Zijlstra , "Reshetova, Elena" , Thomas Gleixner , Tycho Andersen , linux-api@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH] mm: extend memfd with ability to create "secret" memory areas Message-ID: <20200212141029.7b89acee@lwn.net> In-Reply-To: <20200130162340.GA14232@rapoport-lnx> References: <20200130162340.GA14232@rapoport-lnx> Organization: LWN.net MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, 30 Jan 2020 18:23:41 +0200 Mike Rapoport wrote: > Hi, >=20 > This is essentially a resend of my attempt to implement "secret" mappin= gs > using a file descriptor [1].=20 So one little thing I was curious about as I read through the patch... > +static int secretmem_check_limits(struct vm_fault *vmf) > +{ > + struct secretmem_state *state =3D vmf->vma->vm_file->private_data; > + struct inode *inode =3D file_inode(vmf->vma->vm_file); > + unsigned long limit; > + > + if (((loff_t)vmf->pgoff << PAGE_SHIFT) >=3D i_size_read(inode)) > + return -EINVAL; > + > + limit =3D rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT; > + if (state->nr_pages + 1 >=3D limit) > + return -EPERM; > + > + return 0; > +} If I'm not mistaken, this means each memfd can be RLIMIT_MEMLOCK in lengt= h, with no global limit on the number of locked pages. What's keeping me fr= om creating 1000 of these things and locking down lots of RAM? Thanks, jon