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

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Date:	Fri, 22 May 2015 15:19:01 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	David Howells <dhowells@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	George Spelvin <linux@...izon.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	LSM List <linux-security-module@...r.kernel.org>,
	petkan@...-labs.com, "Theodore Ts'o" <tytso@....edu>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Subject: Re: Should we automatically generate a module signing key at all?

On Fri, May 22, 2015 at 3:15 PM, David Howells <dhowells@...hat.com> wrote:
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>
>> I forget the exact details of the signature ..., but for the modules
>> themselves, it's just appended to the module contents.
>
> Yes.
>
>> And because the size of the certificate list is variable, you can't just
>> zero it out or anything like that to make things compare equal.
>
> Since it's discarded at the end of boot, it could be padded significantly.

If you use the hash tree approach, the size of the thing in bzImage is constant.

--Andy
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