From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1bPtlh-0006Ib-Iu for kexec@lists.infradead.org; Wed, 20 Jul 2016 15:50:42 +0000 Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.11/8.16.0.11) with SMTP id u6KFnKRV088978 for ; Wed, 20 Jul 2016 11:50:20 -0400 Received: from e24smtp01.br.ibm.com (e24smtp01.br.ibm.com [32.104.18.85]) by mx0a-001b2d01.pphosted.com with ESMTP id 24a8eya0uk-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 20 Jul 2016 11:50:20 -0400 Received: from localhost by e24smtp01.br.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 20 Jul 2016 12:50:17 -0300 From: Thiago Jung Bauermann Subject: Re: [RFC 0/3] extend kexec_file_load system call Date: Wed, 20 Jul 2016 12:50:11 -0300 In-Reply-To: <34243612.Gid3QHG1hd@wuerfel> References: <87twfunneg.fsf@linux.vnet.ibm.com> <20160720083530.GK1041@n2100.armlinux.org.uk> <34243612.Gid3QHG1hd@wuerfel> MIME-Version: 1.0 Message-Id: <2545578.SWp0m9VQX8@hactar> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Arnd Bergmann Cc: Stewart Smith , bhe@redhat.com, Michael Ellerman , Balbir Singh , linuxppc-dev@lists.ozlabs.org, kexec@lists.infradead.org, Russell King - ARM Linux , Petr Tesarik , linux-kernel@vger.kernel.org, AKASHI Takahiro , "Eric W. Biederman" , dyoung@redhat.com, Vivek Goyal , linux-arm-kernel@lists.infradead.org Am Mittwoch, 20 Juli 2016, 13:12:20 schrieb Arnd Bergmann: > On Wednesday, July 20, 2016 8:47:45 PM CEST Michael Ellerman wrote: > > At least for stdout-path, I can't really see how that would > > significantly help an attacker, but I'm all ears if anyone has ideas. > > That's actually an easy one that came up before: If an attacker controls > a tty device (e.g. network console) that can be used to enter a debugger > (kdb, kgdb, xmon, ...), enabling that to be the console device > gives you a direct attack vector. The same thing will happen if you > have a piece of software that intentially gives extra rights to the > owner of the console device by treating it as "physical presence". I think people are talking past each other a bit in these arguments about what is relevant to security or not. For the kexec maintainers, kexec_file_load has one very specific and narrow purpose: enable Secure Boot as defined by UEFI. And from what I understand of their arguments so far, there is one and only one security concern: when in Secure Boot mode, a system must not allow execution of unsigned code with kernel privileges. So even if one can specify a different root filesystem and do a lot of nasty things to the system with a rogue userspace in that root filesystem, as long as the kernel won't load unsigned modules that's not a problem as far as they're concerned. Also, AFAIK attacks requiring "physical presence" are out of scope for the UEFI Secure Boot security model. Thus an attack that involves control of a console of plugging an USB device is also not a concern. One thing I don't know is whether an attack involving a networked IPMI console or a USB device that can be "plugged" virtually by a managing system (BMC) is considered a physical attack or a remote attack in the context of UEFI Secure Boot. -- []'s Thiago Jung Bauermann IBM Linux Technology Center _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec