From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]) by merlin.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1UIhrz-0000DE-2Y for kexec@lists.infradead.org; Thu, 21 Mar 2013 15:57:35 +0000 Date: Thu, 21 Mar 2013 10:58:23 -0500 From: "Serge E. Hallyn" Subject: Re: [PATCH 01/12] Security: Add CAP_COMPROMISE_KERNEL Message-ID: <20130321155823.GA4438@austin.hallyn.com> References: <1363798166.2553.29.camel@x230.sbx07502.somerma.wayport.net> <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> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20130321155220.GL3934@redhat.com> 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: Vivek Goyal Cc: Matthew Garrett , "linux-efi@vger.kernel.org" , "linux-pci@vger.kernel.org" , "kexec@lists.infradead.org" , James Morris , "linux-kernel@vger.kernel.org" , "linux-security-module@vger.kernel.org" , Mimi Zohar , "Serge E. Hallyn" 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. -serge _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec