Re: Kdump with signed images

Vivek Goyal
2012-11-01T13:54:08Z

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