From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754060AbcGLOCp (ORCPT ); Tue, 12 Jul 2016 10:02:45 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48070 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753444AbcGLOCn (ORCPT ); Tue, 12 Jul 2016 10:02:43 -0400 Date: Tue, 12 Jul 2016 10:02:42 -0400 From: Vivek Goyal To: Thiago Jung Bauermann Cc: "Eric W. Biederman" , AKASHI Takahiro , dyoung@redhat.com, bhe@redhat.com, arnd@arndb.de, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [RFC 0/3] extend kexec_file_load system call Message-ID: <20160712140242.GA30181@redhat.com> References: <20160712014201.11456-1-takahiro.akashi@linaro.org> <87furf7ztv.fsf@x220.int.ebiederm.org> <2675986.6AfrV5PCe0@hactar> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2675986.6AfrV5PCe0@hactar> User-Agent: Mutt/1.6.1 (2016-04-27) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Tue, 12 Jul 2016 14:02:43 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 12, 2016 at 10:58:09AM -0300, Thiago Jung Bauermann wrote: > Hello Eric, > > Am Dienstag, 12 Juli 2016, 08:25:48 schrieb Eric W. Biederman: > > AKASHI Takahiro writes: > > > Device tree blob must be passed to a second kernel on DTB-capable > > > archs, like powerpc and arm64, but the current kernel interface > > > lacks this support. > > > > > > This patch extends kexec_file_load system call by adding an extra > > > argument to this syscall so that an arbitrary number of file descriptors > > > can be handed out from user space to the kernel. > > > > > > See the background [1]. > > > > > > Please note that the new interface looks quite similar to the current > > > system call, but that it won't always mean that it provides the "binary > > > compatibility." > > > > > > [1] http://lists.infradead.org/pipermail/kexec/2016-June/016276.html > > > > So this design is wrong. The kernel already has the device tree blob, > > you should not be extracting it from the kernel munging it, and then > > reinserting it in the kernel if you want signatures and everything to > > pass. > > > > What x86 does is pass it's equivalent of the device tree blob from one > > kernel to another directly and behind the scenes. It does not go > > through userspace for this. > > > > Until a persuasive case can be made for going around the kernel and > > probably adding a feature (like code execution) that can be used to > > defeat the signature scheme I am going to nack this. > > There are situations where userspace needs to change things in the device > tree to be used by the next kernel. > > For example, Petitboot (the boot loader used in OpenPOWER machines) is a > userspace application running in an intermediary Linux instance and uses > kexec to load the target OS. It has to modify the device tree that will be > used by the next kernel so that the next kernel uses the same console that > petitboot was configured to use (i.e., set the /chosen/linux,stdout-path > property). It also modifies the device tree to allow the kernel to inherit > Petitboot's Openfirmware framebuffer. Can some of this be done with the help of kernel command line options for second kernel? Vivek