Possible build time regression affecting stable kernels

[Luiz Capitulino <luizcap@amazon.com>]

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.

- Luiz