On Fri, 2012-10-26 at 13:06 -0400, Vivek Goyal wrote: > On Fri, Oct 26, 2012 at 03:39:16AM +0100, Matthew Garrett wrote: > > On Thu, Oct 25, 2012 at 09:15:58PM -0400, Mimi Zohar wrote: > > > > > On a running system, the package installer, after verifying the package > > > integrity, would install each file with the associated 'security.ima' > > > extended attribute. The 'security.evm' digital signature would be > > > installed with an HMAC, calculated using a system unique key. > > > > The idea isn't to prevent /sbin/kexec from being modified after > > installation - it's to prevent it from being possible to install a > > system that has a modified /sbin/kexec. Leaving any part of this up to > > the package installer means that it doesn't solve the problem we're > > trying to solve here. 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. > > I am kind of lost now so just trying to summarize whatever I have > learned so far from this thread. Thanks for summarizing. > - 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. > > So until and unless we have a good solution to verify application's > integrity/authneticity at the time of kexec_load() system call we > still have the problem. And I don't think we have come up with a > solution for that yet (until and unless I missed something). > > Thanks > Vivek > Agreed, you need a new LSM/integrity hook. thanks, Mimi
