Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934010Ab3CUQJz (ORCPT ); Thu, 21 Mar 2013 12:09:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:29918 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933907Ab3CUQJv (ORCPT ); Thu, 21 Mar 2013 12:09:51 -0400 Date: Thu, 21 Mar 2013 12:04:41 -0400 From: Vivek Goyal To: "Serge E. Hallyn" Cc: Matthew Garrett , Mimi Zohar , James Morris , "linux-kernel@vger.kernel.org" , "linux-security-module@vger.kernel.org" , "linux-efi@vger.kernel.org" , "kexec@lists.infradead.org" , "linux-pci@vger.kernel.org" Subject: Re: [PATCH 01/12] Security: Add CAP_COMPROMISE_KERNEL Message-ID: <20130321160441.GB6575@redhat.com> References: <1363802506.2580.55.camel@falcor1.watson.ibm.com> <1363803158.2553.33.camel@x230.sbx07502.somerma.wayport.net> <1363806968.2580.86.camel@falcor1.watson.ibm.com> <1363811856.2553.37.camel@x230.sbx07502.somerma.wayport.net> <1363813877.2580.120.camel@falcor1.watson.ibm.com> <1363814289.2553.41.camel@x230.sbx07502.somerma.wayport.net> <20130321134348.GA3934@redhat.com> <20130321153725.GA3656@austin.hallyn.com> <20130321155220.GL3934@redhat.com> <20130321155823.GA4438@austin.hallyn.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130321155823.GA4438@austin.hallyn.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2739 Lines: 60 On Thu, Mar 21, 2013 at 10:58:23AM -0500, Serge E. Hallyn wrote: > Quoting Vivek Goyal (vgoyal@redhat.com): > > On Thu, Mar 21, 2013 at 10:37:25AM -0500, Serge E. Hallyn wrote: > > > Quoting Vivek Goyal (vgoyal@redhat.com): > > > ... > > > > Giving CAP_MODIFY_KERNEL to processess upon signature verification > > > > will simplify things a bit. > > > > > > > > Only thing is that signature verification alone is not sufficient. We > > > > also need to make sure after signature verification executable can > > > > not be modified in memory in any way. So that means atleast couple of > > > > things. > > > > > > Also what about context? If I construct a mounts namespace a certain > > > way, can I trick this executable into loading an old singed bzImage that > > > I had laying around? > > > > We were thinking that /sbin/kexec will need to verify bzImage signature > > before loading it. > > > > Key for verification is in kernel so idea was to take kernel's help > > in verifying signature. > > > > Not sure how exactly the interface should look like. > > > > - I was thinking may be process can mmap() the bzImage with MAP_LOCKED. > > We can create additional flag say MAP_VERIFY_SIG_POST, which tries > > to verify signature/integrity of mapped region of file after mapping and > > locking pages and mmap() fails if signature verification fails. > > > > There have been suggestions about creating new system call altogether. > > > > > > > > ISTM the only sane thing to do, if you're going down this road, > > > is to have CAP_MODIFIY_KERNEL pulled from bounding set for everyone > > > except a getty started by init on ttyS0. Then log in on serial > > > to update. Or run a damon with CAP_MODIFIY_KERNEL which listens > > > to a init_net_ns netlink socket for very basic instructions, like > > > "find and install latest signed bzImage in /boot". Then you can > > > at least trust that /boot for that daemon is not faked. > > > > daemon does not have the key and can't verify signature of signed > > bzImage. Even if it had the key, it can't trust the crypto code for > > signature verification as none of that is signed. > > I'm not saying not to use the kernel to verify the signature. Ok. So why can't /sbin/kexec can do the verification of bzImage with kernel's help. Due to crafted /boot/ it might load old signed bzImage, but it can't load unsigned/untrusted code on secureboot system at ring 0. I am hoping I did not miss your point entirely. Thanks Vivek -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/