Re: Kdump with signed images

Mimi Zohar
2012-10-26T18:39:45Z

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