linux-kernel - Re: [PATCH 3/4] KEYS: validate key trust only with selected owner key

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Message-ID: <CACE9dm8jdvU8YCiRzen66B9xEBX3qDs3tQjiZgb7+6P6zMaiCg@mail.gmail.com>
Date:	Thu, 12 Jun 2014 22:04:02 +0300
From:	Dmitry Kasatkin <dmitry.kasatkin@...il.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Dmitry Kasatkin <d.kasatkin@...sung.com>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Josh Boyer <jwboyer@...hat.com>,
	keyrings <keyrings@...ux-nfs.org>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>
Subject: Re: [PATCH 3/4] KEYS: validate key trust only with selected owner key

On 12 June 2014 22:01, Vivek Goyal <vgoyal@...hat.com> wrote:
> On Thu, Jun 12, 2014 at 09:36:46PM +0300, Dmitry Kasatkin wrote:
>> On 12 June 2014 20:32, Vivek Goyal <vgoyal@...hat.com> wrote:
>> > On Thu, Jun 12, 2014 at 08:23:57PM +0300, Dmitry Kasatkin wrote:
>> >> On 12/06/14 19:03, Vivek Goyal wrote:
>> >> > On Tue, Jun 10, 2014 at 11:48:17AM +0300, Dmitry Kasatkin wrote:
>> >> >> This patch provides kernel parameter to specify owner's key id which
>> >> >> must be used for trust validate of keys. Keys signed with other keys
>> >> >> are not trusted.
>> >> >>
>> >> >> Signed-off-by: Dmitry Kasatkin <d.kasatkin@...sung.com>
>> >> > Hi,
>> >> >
>> >> > I am continuing to work on verifying kernel signature for kexec/kdump. I
>> >> > am planning to take david howell's patches for pkcs7 signature
>> >> > verification and verify bzImage signature.
>> >> >
>> >> > Part of that process will boil down to verifying a certificate in
>> >> > pkcs7 x509 cert chain using a key in system_trusted_keyring.
>> >> >
>> >> > I think the OS vendor key which signs the kernel signing key propagates to
>> >> > system_trusted_keyring. (shim has that and I am not sure how shim makes
>> >> > it propogate all they way to system_trusted_keyring).
>> >> >
>> >> > So I was planning to use same functionality where I look for any key
>> >> > which can verify the signing cert of kernel. As OS vendor key will be
>> >> > in system_trusted_keyring, it should work.
>> >> >
>> >> > Now with this change where you will trust only one selected owner key.
>> >> > That means you will not even trust the OS vendor key which signs kernel
>> >> > signing key. I think this will stop working with  keys_ownerid=<....>
>> >> >
>> >> > As I am doing that work in parallel and I saw these patches, I thought
>> >> > I will bring it up.
>> >>
>> >> Hi Vivek,
>> >>
>> >> All keys stays in the keyring. Usage of owner_keyid is limited to
>> >> validate the trust of the loaded keys.
>> >
>> > Hi Dmitry,
>> >
>> > If owner_keyid scope is just limited to loading extra keys, then it
>> > should be fine as I don't want to load extra keys. I just want to
>> > verify already signed image whose key is supposed to be in
>> > system_trusted_keyring.
>> >
>> >>
>> >>
>> >> Do you really see OS verndor key (Fedora) on the system keyring?
>> >> shim is UEFI binary and can add it to the MOK database..
>> >
>> > I have been told that mechanism to propagate they key in shim which is
>> > used to verify kernel signature is in place and that key should show
>> > up in system_trusted_keyring. I have never verified it though. I will
>> > check it out.
>> >
>> > Thanks
>> > Vivek
>>
>>
>> Hi Vivek,
>>
>> The easiest way to get OS Vendor ker/certificate is just embed it into
>> the kernel along with
>> ephemeral (or not) module signing key... They all appears on .system keyring...
>
> I think it will be tricky as in current setup, signing happens on a different
> server and build server does not have access to keys.
>
> Thanks
> Vivek

It should not be tricky... Signing is done with private key...
Security measure has to be considered.

Certificate is public and is not a secret.. It can be on any build
machine in the world...

-- 
Thanks,
Dmitry
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