[CentOS] Kernel live patching on CentOS Stream 9

Fri Jan 14 14:42:47 UTC 2022
Johnny Hughes <johnny at centos.org>

On 1/14/22 08:30, Johnny Hughes wrote:
> On 1/14/22 07:57, Gionatan Danti wrote:
>> Il 2022-01-14 13:17 Josh Boyer ha scritto:
>>> RHEL's kernel live patching uses upstream open source kpatch.  The
>>> sources to the kpatches are delivered in customer facing CDN repos at
>>> the same time as the kpatch itself.  We do not use proprietary code to
>>> produce or apply the kpatches.
>>> I can only speculate on whether RHEL kpatches would work on a CentOS
>>> kernel, but my assumption is that they would not due to how they are
>>> signed.
>> Is (well, was) the CentOS kernel identical at binary level to the RHEL 
>> one?
>> If so, the same kpatch should be applicable to both RHEL and CentOS 
>> (the old one).
>> But I seem to understand that the two kernels are *not* bytewise 
>> identical, so a binary kpatch can not be applied the CentOS. Is this 
>> true?
>> Anyway, RH kpatches are surely not compatible with CentOS stream. So I 
>> asked if some project was started to provide live kernel patching to 
>> the new CentOS project. If I don't miss something, this is not the case.
>> Regards.
> No .. none of the CentOS Kernels were EVER binary compatible with any 
> RHEL kernel.
> CentOS Linux has always been (now also including CentOS Stream 8 and 9) 
> a completely separate 'closed' build system.
> We use the SAME source code to build things, modified to remove 
> branding.  But CentOS has NEVER been (nor is any other rebuild 
> distribution now) Binary Compatible.
> Want to see how .. just extract two rpms with the same name from two 
> different distributions into separate directories and run a sha256sum on 
> all the files in the different directories with find command.  Some 
> files may be identical (most text files that are copied), others will 
> not be.
> It is virtually impossible for all produced packages to be 'binary 
> compatible' UNLESS they are built with exact the same files (not files 
> BUILT fromt he same sources .. the exact same files) in the build root 
> AND with exactly the same software doing the building.  Any group that 
> claims 'binary compatibility' is either lying or they do not understand 
> compiling and linking.
> CentOS never had that.  Neither does any rebuild.
> This is why the CentOS Project 'CHANGED' our term from binary compatible 
> to 'Functionally Compatible' a long time ago.  (Using same source code, 
> we produce DIFFERENT software .. that works the same way but has 
> different SHASUM values.  Don't be fooled by key words like 'binary 
> compatible' .. check it out for yourself.
> If you build kpatches to kernels, to make them work you need to build 
> the kpatch for the specific kernel (CentOS would need to build against 
> CentOS kernels, etc).  Also, there are the certificate signing issues 
> and keys that you would need to take into account.  You need to have the 
> CA Trust to be able to create signatures that the system will allow.
> _______________________________________________

As a bit of a helper .. we used to use this script to find differences:


Way back in the CentOS Linux 4 days.