linux-kernel - Re: Should we automatically generate a module signing key at all?

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Message-ID: <20150623203756.GA30826@amd>
Date:	Tue, 23 Jun 2015 22:37:57 +0200
From:	Pavel Machek <pavel@....cz>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andy Lutomirski <luto@...nel.org>,
	David Howells <dhowells@...hat.com>,
	Michal Marek <mmarek@...e.cz>,
	David Woodhouse <dwmw2@...radead.org>,
	Abelardo Ricart III <aricart@...nix.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Sedat Dilek <sedat.dilek@...il.com>, keyrings@...ux-nfs.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	LSM List <linux-security-module@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>
Subject: Re: Should we automatically generate a module signing key at all?

On Tue 2015-05-19 10:44:47, Linus Torvalds wrote:
> On Mon, May 18, 2015 at 5:51 PM, Andy Lutomirski <luto@...nel.org> wrote:
> >
> > I think we should get rid of the idea of automatically generated signing
> > keys entirely.  Instead I think we should generate, at build time, a list of
> > all the module hashes and link that into vmlinux.
> 
> Ugh. I think that would be a mistake. It doesn't add any new security
> (it's 100% equivalent to just using a throw-away key), and it adds new
> complexity and a new ordering dependency.
> 
> Yes, yes, "throwing away the key" is a somewhat gray area, and just
> unlinking the key-file without any secure erase in theory makes it
> recoverable. In practice, though, it is fine. If you have an attacker
> that has raw access to your disk and almost infinite resources, they
> have easier ways to make your life miserable.

We should really implement secure erase, and it probably needs to be
at kernel level.

> Even a non-secure unlinking of the temporary key file is going to make
> things like rootkit authors give up on trying to recover it. Really.

Placing the key in some kind of ram filesystem where erase is easy to
do might be easy solution to this...
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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