Re: [PATCH 5.15 5.10 5.4 v2] kbuild: fix Build ID if CONFIG_MODVERSIONS

[Tom Saeger <tom.saeger@oracle.com>]

On Wed, Dec 21, 2022 at 05:31:51PM +0100, Greg Kroah-Hartman wrote:
> On Thu, Dec 15, 2022 at 04:18:18PM -0700, Tom Saeger wrote:
> > Backport of:
> > commit 0d362be5b142 ("Makefile: link with -z noexecstack --no-warn-rwx-segments")
> > breaks arm64 Build ID when CONFIG_MODVERSIONS=y for all kernels
> > from: commit e4484a495586 ("Merge tag 'kbuild-fixes-v5.0' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild")
> > until: commit df202b452fe6 ("Merge tag 'kbuild-v5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild")
> > 
> > Linus's tree doesn't have this issue since 0d362be5b142 was merged
> > after df202b452fe6 which included:
> > commit 7b4537199a4a ("kbuild: link symbol CRCs at final link, removing CONFIG_MODULE_REL_CRCS")
> 
> Why can't we add this one instead of a custom change?

I quickly abandoned that route - there are too many dependencies.
> 
> > 
> > This kernel's KBUILD CONFIG_MODVERSIONS tooling compiles and links .S targets
> > with relocatable (-r) and now (-z noexecstack)
> > which results in ld adding a .note.GNU-stack section to .o files.
> > Final linking of vmlinux should add a .NOTES segment containing the
> > Build ID, but does NOT (on some architectures like arm64) if a
> > .note.GNU-stack section is found in .o's supplied during link
> > of vmlinux.
> > 
> > DISCARD .note.GNU-stack sections of .S targets.  Final link of
> > vmlinux then properly adds .NOTES segment containing Build ID that can
> > be read using tools like 'readelf -n'.
> > 
> > Fixes: 0d362be5b142 ("Makefile: link with -z noexecstack --no-warn-rwx-segments")
> > Cc: <stable@vger.kernel.org> # 5.15, 5.10, 5.4
> > Cc: <linux-kbuild@vger.kernel.org>
> > Cc: Nick Desaulniers <ndesaulniers@google.com>
> > Cc: Masahiro Yamada <masahiroy@kernel.org>
> > Cc: Nicholas Piggin <npiggin@gmail.com>
> > Cc: Michal Marek <michal.lkml@markovi.net>
> > Cc: Nathan Chancellor <nathan@kernel.org>
> > Signed-off-by: Tom Saeger <tom.saeger@oracle.com>
> > ---
> > 
> > v2:
> >   - Changed approach to append DISCARD section to generated linker script.
> >     - ld no longer emits warning (which was intent of 0d362b35b142) this
> >       addresses Nick's v1 feedback.
> >     - this is applied to all arches, not just arm64
> >   - added commit refs and notes why this doesn't occur in Linus's tree
> >     to address Greg's v1 feedback.
> >   - added Fixes: 0d362b35b142 requested by Nick
> >   - added note to changelog for 7b4537199a4a requested by Nick
> >   - build tested on arm64 and x86
> >    
> >    version           works(vmlinux contains Build ID)
> >    v4.14.302         x86, arm64
> >    v4.14.302.patched x86, arm64
> >    v4.19.269         x86, arm64
> >    v4.19.269.patched x86, arm64
> >    v5.4.227          x86
> >    v5.4.227.patched  x86, arm64
> >    v5.10.159         x86
> >    v5.10.159.patched x86, arm64
> >    v5.15.83          x86
> >    v5.15.83.patched  x86, arm64
> > 
> > v1: https://lore.kernel.org/all/cover.1670358255.git.tom.saeger@oracle.com/
> > 
> > 
> >  scripts/Makefile.build | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> > index 17aa8ef2d52a..e3939676eeb5 100644
> > --- a/scripts/Makefile.build
> > +++ b/scripts/Makefile.build
> > @@ -379,6 +379,8 @@ cmd_modversions_S =								\
> >  	if $(OBJDUMP) -h $@ | grep -q __ksymtab; then				\
> >  		$(call cmd_gensymtypes_S,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))	\
> >  		    > $(@D)/.tmp_$(@F:.o=.ver);					\
> > +		echo "SECTIONS { /DISCARD/ : { *(.note.GNU-stack) } }"		\
> > +		>> $(@D)/.tmp_$(@F:.o=.ver); 					\
> >  										\
> >  		$(LD) $(KBUILD_LDFLAGS) -r -o $(@D)/.tmp_$(@F) $@ 		\
> >  			-T $(@D)/.tmp_$(@F:.o=.ver);				\
> > 
> > base-commit: fd6d66840b4269da4e90e1ea807ae3197433bc66
> > -- 
> > 2.38.1
> > 
> 
> 
> I need some acks from some developers/maintainers before I can take
> this... {hint}
> 
> thanks,
> 
> greg k-h