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=-6.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 7609FC433E6 for ; Mon, 25 Jan 2021 21:41:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 22C8522510 for ; Mon, 25 Jan 2021 21:41:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733059AbhAYVk7 (ORCPT ); Mon, 25 Jan 2021 16:40:59 -0500 Received: from mail.kernel.org ([198.145.29.99]:35688 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732797AbhAYViG (ORCPT ); Mon, 25 Jan 2021 16:38:06 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 743FA208C7; Mon, 25 Jan 2021 21:36:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611610595; bh=ajaCsDQ6e4U1hUENrIDNUbcuSNalQWKY+iQc4S18YHs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=cfQR8nUEYwM75PG5OUFV5JcmnnumpQwkS1CnVqcT2d4p/kUpcS/2u20YYyJroZRCW Jbt8N0i9NWstZhVeQAoWuL0s1n+n5az5ZLRoklNtsiaP1TJWCjFUBgluHnK4qcx2vR E16vQW+kwJovzCui9zqUqcbslF/9K9Il+/0P40Td3raK5Q2WzGx+8y38H1+/m5CZ3T SSW4VXI/VuuQaVG+TxLnGPfGOo0qcOYMor1OjHyeeaSkuT9z8sM7rhBjawSDsbXbG4 xDuvORI7oTg4YIT62Z9kQe6ps0I6CSs8pq6QDrPQmTgAxuIU4vdgt6s4t3c2vLy5LL LDqeEHslmluVA== Date: Mon, 25 Jan 2021 23:36:18 +0200 From: Mike Rapoport To: Michal Hocko Cc: Andrew Morton , Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , David Hildenbrand , Elena Reshetova , "H. Peter Anvin" , Ingo Molnar , James Bottomley , "Kirill A. Shutemov" , Matthew Wilcox , Mark Rutland , Mike Rapoport , Michael Kerrisk , Palmer Dabbelt , Paul Walmsley , Peter Zijlstra , Rick Edgecombe , Roman Gushchin , Shakeel Butt , Shuah Khan , Thomas Gleixner , Tycho Andersen , Will Deacon , linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org, x86@kernel.org, Hagen Paul Pfeifer , Palmer Dabbelt Subject: Re: [PATCH v16 06/11] mm: introduce memfd_secret system call to create "secret" memory areas Message-ID: <20210125213618.GL6332@kernel.org> References: <20210121122723.3446-1-rppt@kernel.org> <20210121122723.3446-7-rppt@kernel.org> <20210125170122.GU827@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210125170122.GU827@dhcp22.suse.cz> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- Sincerely yours, Mike.