linux-kernel - Re: [PATCH 0/3] KEXEC_SIG with appended signature

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Date:   Thu, 11 Nov 2021 17:23:31 -0500
From:   Nayna <nayna@...ux.vnet.ibm.com>
To:     Michal Suchánek <msuchanek@...e.de>
Cc:     keyrings@...r.kernel.org, Rob Herring <robh@...nel.org>,
        linux-s390@...r.kernel.org, Vasily Gorbik <gor@...ux.ibm.com>,
        Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Jessica Yu <jeyu@...nel.org>, linux-kernel@...r.kernel.org,
        David Howells <dhowells@...hat.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Paul Mackerras <paulus@...ba.org>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org,
        Frank van der Linden <fllinden@...zon.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Daniel Axtens <dja@...ens.net>
Subject: Re: [PATCH 0/3] KEXEC_SIG with appended signature


On 11/5/21 09:14, Michal Suchánek wrote:
> On Fri, Nov 05, 2021 at 09:55:52PM +1100, Daniel Axtens wrote:
>> Michal Suchanek <msuchanek@...e.de> writes:
>>
>>> S390 uses appended signature for kernel but implements the check
>>> separately from module loader.
>>>
>>> Support for secure boot on powerpc with appended signature is planned -
>>> grub patches submitted upstream but not yet merged.
>> Power Non-Virtualised / OpenPower already supports secure boot via kexec
>> with signature verification via IMA. I think you have now sent a
>> follow-up series that merges some of the IMA implementation, I just
>> wanted to make sure it was clear that we actually already have support
> So is IMA_KEXEC and KEXEC_SIG redundant?
>
> I see some architectures have both. I also see there is a lot of overlap
> between the IMA framework and the KEXEC_SIG and MODULE_SIg.

Originally, KEXEC_SIG was meant for PECOFF based signatures, while 
IMA_KEXEC mainly supported xattr based signatures.

Power (Non-virtualized/OpenPOWER) doesn't support PECOFF. Extended 
attributes based signature verification doesn't work with netboot. 
That's when appended signature support was added to IMA.

Using IMA_KEXEC has the benefit of being able to enable both signature 
verification and measurement of the kernel image.

Thanks & Regards,

      - Nayna