From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761776Ab2KAOw2 (ORCPT ); Thu, 1 Nov 2012 10:52:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:16205 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761621Ab2KAOwZ (ORCPT ); Thu, 1 Nov 2012 10:52:25 -0400 Date: Thu, 1 Nov 2012 10:51:49 -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: <20121101145149.GB15821@redhat.com> References: <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> <20121101135356.GA15659@redhat.com> <1351780159.15708.17.camel@falcor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1351780159.15708.17.camel@falcor> 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 10:29:19AM -0400, Mimi Zohar wrote: > On Thu, 2012-11-01 at 09:53 -0400, Vivek Goyal wrote: > > 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 > > That's a good generic solution, which I'm all in favor of, but it > doesn't resolve the latter half of Matthrew's requirement "and it must > be impossible for anything other than /sbin/kexec to make the kexec > system call." I think what matthew might have meant that anything other than signed trusted executable should not be able to call kexec_load(). Matthew? And if one wants only /sbin/kexec to call it, then just sign that one so no other executable will be able to call kexec_load(). Though I don't think that's the requirement here. Requirement is that only trusted executables should be able to call kexec_load(). Thanks Vivek