linux-kernel - Re: [RFC][PATCH 1/2] modsig: add support to sign kernel modules using ephemeral keys

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Date:	Tue, 04 Dec 2012 14:11:43 -0500
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	linux-security-module@...r.kernel.org,
	Dmitry Kasatkin <dmitry.kasatkin@...el.com>,
	linux-kernel@...r.kernel.org, Mimi Zohar <zohar@...ibm.com>
Subject: Re: [RFC][PATCH 1/2] modsig: add support to sign kernel modules
 using ephemeral keys

On Tue, 2012-12-04 at 18:14 +0000, David Howells wrote:
> Rusty Russell <rusty@...tcorp.com.au> wrote:
> 
> > > +PHONY += _newmodpubkey_
> > > +_newmodpubkey_: 
> > > +	@rm -f $(MODSECKEY) $(MODPUBKEY)
> > > +	$(Q)$(MAKE) -W kernel/modsign_pubkey.o
> 
> Please don't do this.  It can muck up the dependencies as make thinks it has
> already done this file at this point.  Also, rebuilding bzImage yet again
> wouldn't be the best.  We already do it a number of times.  Further, if
> vmlinux is already installed when you rebuild, you may confuse gdb if the
> debuginfo then no longer matches vmlinux.

> You have to expose the private key *anyway* - so how much does this actually
> gain you?  Especially with a one-shot transient key.

The issue is creating a new keypair is tied to modsign_pubkey.  This
patch forces the creation of a new keypair, by removing the existing
one, compiles modsign_pubkey.o, and rebuilds the bzImage, and only then
signs the kernel modules and removes the private key.  The benefits of
defining a separate target to generate a keypair are described in the
patch description.

Mimi

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