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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 D935CCA9ECB for ; Thu, 31 Oct 2019 19:17:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AC1E320873 for ; Thu, 31 Oct 2019 19:17:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572549424; bh=wE7q2TFyOsW+GR4H9tqVpVKZDMZJNtUPDUlnoXzCkSY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=JREtSHhcEJmwRbpt0mkLo/Wtkf/i+mmuwNHgRU7LyWxUZUBLVE3HUdHIAWAbjg2vP 7Ezc73BNTUZ5SpWU31RKUojncQiR+S6to/VbD4HygadRoHVJ9YngdZgA3rh1H0VHoX HD9OMORlRnWGQNJGMwowMDkvUzFr5C53phC5oG1w= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729619AbfJaTRD (ORCPT ); Thu, 31 Oct 2019 15:17:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:52034 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729296AbfJaTRD (ORCPT ); Thu, 31 Oct 2019 15:17:03 -0400 Received: from rapoport-lnx (190.228.71.37.rev.sfr.net [37.71.228.190]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 975612080F; Thu, 31 Oct 2019 19:16:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572549422; bh=wE7q2TFyOsW+GR4H9tqVpVKZDMZJNtUPDUlnoXzCkSY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=CLZKcquG9n6x6VVl3YkcRfjVak/Ke+VAkHJDVPRDmcyfYXMLx2kPJMW08r6S6G7ae d7WIsYWQMqrUZu0vaGvOXhLwKZTTuC2Bd06ITKDtAkbPLdjaKNIY8o4ddKuhvcOL8w L0y2V9iihbBeBFIRMQ2zjZrFAJF5TC73bCi1zhA8= Date: Thu, 31 Oct 2019 20:16:52 +0100 From: Mike Rapoport To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, Alexey Dobriyan , Andrew Morton , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Dave Hansen , James Bottomley , Peter Zijlstra , Steven Rostedt , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , linux-api@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, Mike Rapoport Subject: Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings Message-ID: <20191031191651.GA26165@rapoport-lnx> References: <1572171452-7958-1-git-send-email-rppt@kernel.org> <1572171452-7958-2-git-send-email-rppt@kernel.org> <085ed07e-e646-f7a4-0370-06f33a2a4e4a@redhat.com> <20191030081529.GB20624@rapoport-lnx> <9eae3941-64cf-4ea1-0287-0e64bab192c6@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9eae3941-64cf-4ea1-0287-0e64bab192c6@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 30, 2019 at 09:19:33AM +0100, David Hildenbrand wrote: > On 30.10.19 09:15, Mike Rapoport wrote: > >On Tue, Oct 29, 2019 at 12:02:34PM +0100, David Hildenbrand wrote: > >>On 27.10.19 11:17, Mike Rapoport wrote: > >>>From: Mike Rapoport > >>> > >>>The mappings created with MAP_EXCLUSIVE are visible only in the context of > >>>the owning process and can be used by applications to store secret > >>>information that will not be visible not only to other processes but to the > >>>kernel as well. > >>> > >>>The pages in these mappings are removed from the kernel direct map and > >>>marked with PG_user_exclusive flag. When the exclusive area is unmapped, > >>>the pages are mapped back into the direct map. > >>> > >> > >>Just a thought, the kernel is still able to indirectly read the contents of > >>these pages by doing a kdump from kexec environment, right? > > > >Right. > > > >>Also, I wonder > >>what would happen if you map such pages via /dev/mem into another user space > >>application and e.g., use them along with kvm [1]. > > > >Do you mean that one application creates MAP_EXCLUSIVE and another > >applications accesses the same physical pages via /dev/mem? > > Exactly. > > > > >With /dev/mem all physical memory is visible... > > Okay, so the statement "information that will not be visible not only to > other processes but to the kernel as well" is not correct. There are easy > ways to access that information if you really want to (might require root > permissions, though). Right, but /dev/mem is an easy way to extract any information in any environment if one has root permissions... > -- > > Thanks, > > David / dhildenb > -- Sincerely yours, Mike.