Re: Possible build time regression affecting stable kernels

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Jun 01, 2023 at 09:13:21AM -0400, Luiz Capitulino wrote:
> 
> 
> On 2023-06-01 02:06, Greg KH wrote:
> 
> > 
> > 
> > 
> > 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?
> 
> Yes. I'm reporting this here because I'm more concerned with -stable kernels since
> they're more likely to be running on older user-space.

Yeah, we are bug-compatible!  :)

When this gets fixed in Linus's tree, I'll be glad to backport the
changes to the other kernels.  Please work with the developers to get
that fixed there.

thanks,

greg k-h