linux-kernel - Re: RFC: sign the modules at install time

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Date:	Fri, 19 Oct 2012 11:46:04 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Josh Boyer <jwboyer@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Miller <davem@...emloft.net>,
	David Howells <dhowells@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: RFC: sign the modules at install time

Josh Boyer <jwboyer@...il.com> writes:
> On Thu, Oct 18, 2012 at 2:46 PM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>> On Wed, Oct 17, 2012 at 10:34 PM, Rusty Russell <rusty@...tcorp.com.au> wrote:
>>>
>>> Hacking the keyid and signer-name to be extracted every time by
>>> sign-file takes my modules_install time from 18.6 seconds to 19.1.  We'd
>>> get that back easily by making sign-file a perl script anyway; it calls
>>> out to perl 3 times already.
>>
>> Ok, that tiny slowdown seems worth the cleanup, especially if we'd get
>> it back from somebody re-writing it in perl.
>>
>> Want to sign off on the two patches, or put them in your git tree?
>
> I tested Rusty's version of the 'sign modules at module_install time'
> patch in a Fedora kernel build today.  It seems to work well enough,
> even if we wind up signing things twice.  A brief cleanup of my patch
> to add a modules_sign target on top of that is below.

I'm surprised.  Only the first signature (create on the unstripped
module) will be used by the kernel; this should fail to verify the
stripped module.  A quick and dirty check is:

grep -abo '~Module' /tmp/mod/lib/modules/3.7.0-rc1+/kernel/sound/pci/snd-intel8x0.ko
39828:~Module
40432:~Module

Perhaps eu-strip actually strips the appended signature?

> It might even be able to be moved entirely into scripts/Makefile.modinst
> but I haven't gotten that far yet.

I'll leave this for the moment.

Cheers,
Rusty.
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