Re: Possible build time regression affecting stable kernels

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, May 31, 2023 at 10:12:40PM -0400, Luiz Capitulino wrote:
> Hi Paul,
> 
> A number of stable kernels recently backported this upstream commit:
> 
> """
> commit 4ce1f694eb5d8ca607fed8542d32a33b4f1217a5
> Author: Paul Moore <paul@paul-moore.com>
> Date:   Wed Apr 12 13:29:11 2023 -0400
> 
>     selinux: ensure av_permissions.h is built when needed
> """
> 
> We're seeing a build issue with this commit where the "crash" tool will fail
> to start, it complains that the vmlinux image and /proc/version don't match.
> 
> A minimum reproducer would be having "make" version before 4.3 and building
> the kernel with:
> 
> $ make bzImages
> $ make modules
> 
> Then compare the version strings in the bzImage and vmlinux images,
> we can use "strings" for this. For example, in the 5.10.181 kernel I get:
> 
> $ strings vmlinux | egrep '^Linux version'
> Linux version 5.10.181 (ec2-user@ip-172-31-79-134.ec2.internal) (gcc (GCC) 7.3.1 20180712 (Red Hat 7.3.1-15), GNU ld version 2.29.1-31.amzn2) #2 SMP Thu Jun 1 01:26:38 UTC 2023
> 
> $ strings ./arch/x86_64/boot/bzImage | egrep 'ld version'
> 5.10.181 (ec2-user@ip-172-31-79-134.ec2.internal) (gcc (GCC) 7.3.1 20180712 (Red Hat 7.3.1-15), GNU ld version 2.29.1-31.amzn2) #1 SMP Thu Jun 1 01:23:59 UTC 2023
> 
> The version string in the bzImage doesn't have the "Linux version" part, but
> I think this is added by the kernel when printing. If you compare the strings,
> you'll see that they have a different build date and the "#1" and "#2" are
> different.
> 
> This only happens with commit 4ce1f694eb5 applied and older "make", in my case I
> have "make" version 3.82.
> 
> If I revert 4ce1f694eb5 or use "make" version 4.3 I get identical strings (except
> for the "Linux version" part):
> 
> $ strings vmlinux | egrep '^Linux version'
> Linux version 5.10.181+ (ec2-user@ip-172-31-79-134.ec2.internal) (gcc (GCC) 7.3.1 20180712 (Red Hat 7.3.1-15), GNU ld version 2.29.1-31.amzn2) #1 SMP Thu Jun 1 01:29:11 UTC 2023
> 
> $ strings ./arch/x86_64/boot/bzImage | egrep 'ld version'
> 5.10.181+ (ec2-user@ip-172-31-79-134.ec2.internal) (gcc (GCC) 7.3.1 20180712 (Red Hat 7.3.1-15), GNU ld version 2.29.1-31.amzn2) #1 SMP Thu Jun 1 01:29:11 UTC 2023
> 
> Maybe the grouped target usage in 4ce1f694eb5 with older "make" is causing a
> rebuild of the vmlinux image in "make modules"? If yes, is this expected?
> 
> I'm afraid this issue could be high impact for distros with older user-space.

Is this issue also in 6.4-rc1 where this change came from?  What about
the other stable releases?

thanks,

greg k-h