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=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, 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 85B65C433E0 for ; Tue, 26 Jan 2021 09:01:50 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3A386230FC for ; Tue, 26 Jan 2021 09:01:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3A386230FC Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=4nuGrLjLzaEnNg9/ZPfSAWMuE/oglFva6pXOSqqYC4A=; b=sZqbMA0KDBfCGMlz4eS66bYqw aTfKz2dw8imvXKO4qGkYrJJbGnuL3MuDkZYwaB1QupSGbL2lJCckNbTRtLiWN7Bs/q3Nrb2hSjEbl SAtHQFChFCsjWb7qEJI2DiltWs7+MyXRu7T1vviXCMmusqa4NXCAj/J8rpl/BvL9pi8ePDkLuqj/q qbmJ7N0iV6sWmzxw0v9BqOzGqADz0IvfctjIIgKEowRgOvD7TZQekCiHDjwlgwq6qLqbi04hbXLqV EsBKX5jefFliFo+Yqx6ycmk5HaLuOE+a3Jp746oYuaoPHrz1nDqsXaOS5nrcG8Brlo3JUB13H9TF9 wX/1sefDg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1l4KCx-0008RX-P9; Tue, 26 Jan 2021 09:00:19 +0000 Received: from mx2.suse.de ([195.135.220.15]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1l4KCt-0008Pt-Jk; Tue, 26 Jan 2021 09:00:16 +0000 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1611651614; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=zkv2AYFPAFtxWhWHYsYeaPluSGEX7L9fbE1dulH4ZuI=; b=GhOz2w0RXQwI2+PODq5b2aw0wmG2/sHAvfuOFXRfFu5hn6slnJT04Sf+X1LOm2o3qdxim/ JikKF5QkQLdr6WDSRfvS9d7btR4sMzkc9Aq9OiCszZ4qwYknWGfN3kTR7NPMMKuqkDIc/Q bxcYYnrayTxMggILhsJvpQJW45eKvt8= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 69D77AF4E; Tue, 26 Jan 2021 09:00:14 +0000 (UTC) Date: Tue, 26 Jan 2021 10:00:13 +0100 From: Michal Hocko To: Mike Rapoport Subject: Re: [PATCH v16 06/11] mm: introduce memfd_secret system call to create "secret" memory areas Message-ID: <20210126090013.GF827@dhcp22.suse.cz> References: <20210121122723.3446-1-rppt@kernel.org> <20210121122723.3446-7-rppt@kernel.org> <20210125170122.GU827@dhcp22.suse.cz> <20210125213618.GL6332@kernel.org> <20210126071614.GX827@dhcp22.suse.cz> <20210126083311.GN6332@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210126083311.GN6332@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210126_040015_877664_559A63AD X-CRM114-Status: GOOD ( 34.28 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , David Hildenbrand , Peter Zijlstra , Catalin Marinas , Dave Hansen , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, "H. Peter Anvin" , Christopher Lameter , Shuah Khan , Thomas Gleixner , Elena Reshetova , linux-arch@vger.kernel.org, Tycho Andersen , linux-nvdimm@lists.01.org, Will Deacon , x86@kernel.org, Matthew Wilcox , Mike Rapoport , Ingo Molnar , Michael Kerrisk , Palmer Dabbelt , Arnd Bergmann , James Bottomley , Hagen Paul Pfeifer , Borislav Petkov , Alexander Viro , Andy Lutomirski , Paul Walmsley , "Kirill A. Shutemov" , Dan Williams , linux-arm-kernel@lists.infradead.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Palmer Dabbelt , linux-fsdevel@vger.kernel.org, Shakeel Butt , Andrew Morton , Rick Edgecombe , Roman Gushchin Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue 26-01-21 10:33:11, Mike Rapoport wrote: > On Tue, Jan 26, 2021 at 08:16:14AM +0100, Michal Hocko wrote: > > On Mon 25-01-21 23:36:18, Mike Rapoport wrote: > > > On Mon, Jan 25, 2021 at 06:01:22PM +0100, Michal Hocko wrote: > > > > On Thu 21-01-21 14:27:18, Mike Rapoport wrote: > > > > > From: Mike Rapoport > > > > > > > > > > Introduce "memfd_secret" system call with the ability to create memory > > > > > areas visible only in the context of the owning process and not mapped not > > > > > only to other processes but in the kernel page tables as well. > > > > > > > > > > The user will create a file descriptor using the memfd_secret() system > > > > > call. The memory areas created by mmap() calls from this file descriptor > > > > > will be unmapped from the kernel direct map and they will be only mapped in > > > > > the page table of the owning mm. > > > > > > > > > > The secret memory remains accessible in the process context using uaccess > > > > > primitives, but it is not accessible using direct/linear map addresses. > > > > > > > > > > Functions in the follow_page()/get_user_page() family will refuse to return > > > > > a page that belongs to the secret memory area. > > > > > > > > > > A page that was a part of the secret memory area is cleared when it is > > > > > freed. > > > > > > > > > > The following example demonstrates creation of a secret mapping (error > > > > > handling is omitted): > > > > > > > > > > fd = memfd_secret(0); > > > > > ftruncate(fd, MAP_SIZE); > > > > > ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); > > > > > > > > I do not see any access control or permission model for this feature. > > > > Is this feature generally safe to anybody? > > > > > > The mappings obey memlock limit. Besides, this feature should be enabled > > > explicitly at boot with the kernel parameter that says what is the maximal > > > memory size secretmem can consume. > > > > Why is such a model sufficient and future proof? I mean even when it has > > to be enabled by an admin it is still all or nothing approach. Mlock > > limit is not really useful because it is per mm rather than per user. > > > > Is there any reason why this is allowed for non-privileged processes? > > Maybe this has been discussed in the past but is there any reason why > > this cannot be done by a special device which will allow to provide at > > least some permission policy? > > Why this should not be allowed for non-privileged processes? This behaves > similarly to mlocked memory, so I don't see a reason why secretmem should > have different permissions model. Because appart from the reclaim aspect it fragments the direct mapping IIUC. That might have an impact on all others, right? -- Michal Hocko SUSE Labs _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel