From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752584AbcGMH4J (ORCPT ); Wed, 13 Jul 2016 03:56:09 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:3507 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752557AbcGMHzy (ORCPT ); Wed, 13 Jul 2016 03:55:54 -0400 X-IBM-Helo: d03dlp03.boulder.ibm.com X-IBM-MailFrom: stewart@linux.vnet.ibm.com From: Stewart Smith To: Russell King - ARM Linux Cc: Petr Tesarik , linux-arm-kernel@lists.infradead.org, bhe@redhat.com, arnd@arndb.de, linuxppc-dev@lists.ozlabs.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, AKASHI Takahiro , "Eric W. Biederman" , Thiago Jung Bauermann , dyoung@redhat.com, vgoyal@redhat.com Subject: Re: [RFC 0/3] extend kexec_file_load system call In-Reply-To: <20160713073657.GX1041@n2100.armlinux.org.uk> References: <20160712014201.11456-1-takahiro.akashi@linaro.org> <87furf7ztv.fsf@x220.int.ebiederm.org> <50662781.Utjsnse3nb@hactar> <20160712225805.0d27fe5d@hananiah.suse.cz> <20160712221804.GV1041@n2100.armlinux.org.uk> <87twfunneg.fsf@linux.vnet.ibm.com> <20160713073657.GX1041@n2100.armlinux.org.uk> User-Agent: Notmuch/0.21+24~gbceb651 (http://notmuchmail.org) Emacs/25.0.94.1 (x86_64-redhat-linux-gnu) Date: Wed, 13 Jul 2016 17:55:33 +1000 MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16071307-8235-0000-0000-000008C712D3 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16071307-8236-0000-0000-0000330D82A4 Message-Id: <87poqinf9m.fsf@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-07-13_02:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1607130089 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Russell King - ARM Linux writes: > On Wed, Jul 13, 2016 at 02:59:51PM +1000, Stewart Smith wrote: >> Russell King - ARM Linux writes: >> > On Tue, Jul 12, 2016 at 10:58:05PM +0200, Petr Tesarik wrote: >> >> I'm not an expert on DTB, so I can't provide an example of code >> >> execution, but you have already mentioned the /chosen/linux,stdout-path >> >> property. If an attacker redirects the bootloader to an insecure >> >> console, they may get access to the system that would otherwise be >> >> impossible. >> > >> > I fail to see how kexec connects with the boot loader - the DTB image >> > that's being talked about is one which is passed from the currently >> > running kernel to the to-be-kexec'd kernel. For ARM (and I suspect >> > also ARM64) that's a direct call chain which doesn't involve any >> > boot loader or firmware, and certainly none that would involve the >> > passed DTB image. >> >> For OpenPOWER machines, kexec is the bootloader. Our bootloader is a >> linux kernel and initramfs with a UI (petitboot) - this means we never >> have to write a device driver twice: write a kernel one and you're done >> (for booting from the device and using it in your OS). > > I think you misunderstood my point. > > On ARM, we do not go: > > kernel (kexec'd from) -> boot loader -> kernel (kexec'd to) > > but we go: > > kernel (kexec'd from) -> kernel (kexec'd to) > > There's no intermediate step involving any bootloader. > > Hence, my point is that the dtb loaded by kexec is _only_ used by the > kernel which is being kexec'd to, not by the bootloader, nor indeed > the kernel which it is loaded into. > > Moreover, if you read the bit that I quoted (which is what I was > replying to), you'll notice that it is talking about the DTB loaded > by kexec somehow causing the _bootloader_ to be redirected to an > alternative console. This point is wholely false on ARM. Ahh.. I missed the bootloader bit there. In which case, we're the same on OpenPOWER, there is no intermediate bootloader - in our case we have linux (with kexec) taking on what uboot or grub is typically used for on other platforms. -- Stewart Smith OPAL Architect, IBM.