From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761494Ab2KANyN (ORCPT ); Thu, 1 Nov 2012 09:54:13 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56559 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758235Ab2KANyM (ORCPT ); Thu, 1 Nov 2012 09:54:12 -0400 Date: Thu, 1 Nov 2012 09:53:56 -0400 From: Vivek Goyal To: Mimi Zohar Cc: Matthew Garrett , "Eric W. Biederman" , Khalid Aziz , kexec@lists.infradead.org, horms@verge.net.au, Dave Young , "H. Peter Anvin" , linux kernel mailing list , Dmitry Kasatkin , Roberto Sassu , Kees Cook Subject: Re: Kdump with signed images Message-ID: <20121101135356.GA15659@redhat.com> References: <20121024173651.GE1821@redhat.com> <1351145401.18115.78.camel@falcor> <20121025141048.GD9377@redhat.com> <1351190421.18115.92.camel@falcor> <20121025185520.GA17995@redhat.com> <1351214158.18115.186.camel@falcor> <20121026023916.GA16762@srcf.ucam.org> <20121026170609.GB24687@redhat.com> <1351276649.18115.217.camel@falcor> <20121101131003.GA14573@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121101131003.GA14573@redhat.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 On Thu, Nov 01, 2012 at 09:10:03AM -0400, Vivek Goyal wrote: [..] > > > > > - So say we can sign /sbin/kexec at build time and distros can do that. > > > - Verify the signature at exec time using kernel keyring and if > > > verification happens successfully, say process gains extra capability. > > > - Use this new capability to determine whether kexec_load() will be > > > successful or not. > > > > > > Even if we can do all this, it still has the issue of being able to > > > stop the process in user space and replace the code at run time > > > and be able to launch unsigned kernel. > > Thinking more about it. Can we just keep track whether a process was > ptraced or not and disallow kexec_load() syscall if it was ptraced. > (I am assuming that ptrace is the only way to change process code/data). > > So binaries can be signed offline. Signature verification can take place > using kernel keyring at exec() time. And we can keep track of ptraced > processes and disallow calling kexec_load() for such processes. If this > is implementable, this should take care of following requirement raised > by matthew. > > ************************************************************************ > It must be impossible for the kernel to launch any /sbin/kexec that hasn't > been signed by a trusted key that's been built into the kernel, and it > must be impossible for anything other than /sbin/kexec to make the kexec > system call. > ************************************************************************* > > Thoughts? Eric responded but my mistake he responded to only me. So I will quickly put his idea here. [start quote] You can't ptrace a process that has a capability you don't. That should be enforced in security/commoncap/ [end quote] This looks like a good idea. Upon verification signed binaries will be assigned special capability and then no unsigned binary should be able to ptrace signed/verified processes Thanks Vivek