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Message-ID: <20121101135356.GA15659@redhat.com>
Date: Thu, 1 Nov 2012 09:53:56 -0400
From: Vivek Goyal <vgoyal@...hat.com>
To: Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc: Matthew Garrett <mjg@...hat.com>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Khalid Aziz <khalid@...ehiking.org>, kexec@...ts.infradead.org,
horms@...ge.net.au, Dave Young <dyoung@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>,
linux kernel mailing list <linux-kernel@...r.kernel.org>,
Dmitry Kasatkin <dmitry.kasatkin@...el.com>,
Roberto Sassu <roberto.sassu@...ito.it>,
Kees Cook <keescook@...omium.org>
Subject: Re: Kdump with signed images
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
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