On Thu, Dec 08, 2022 at 09:34:40PM +0100, Greg Kroah-Hartman wrote:
> On Tue, Dec 06, 2022 at 01:43:08PM -0700, Tom Saeger wrote:
> > Backport of: 0d362be5b142 ("Makefile: link with -z noexecstack --no-warn-rwx-segments")
> > breaks arm64 Build ID when CONFIG_MODVERSIONS=y.
> >
> > CONFIG_MODVERSIONS adds extra tooling to calculate symbol versions.
> > This kernel's KBUILD tooling uses both
> > relocatable (-r) and (-z noexecstack) to link head.o
> > which results in ld adding a .note.GNU-stack section.
> > Final linking of vmlinux should add a .NOTES segment containing the
> > Build ID, but does NOT if head.o has a .note.GNU-stack section.
> >
> > Selectively remove -z noexecstack from head.o's KBUILD_LDFLAGS to
> > prevent .note.GNU-stack from being added to head.o. Final link of
> > vmlinux then properly adds .NOTES segment containing Build ID that can
> > be read using tools like 'readelf -n'.
> >
> > Cc: <stable@xxxxxxxxxxxxxxx> # 5.15, 5.10, 5.4
> > Signed-off-by: Tom Saeger <tom.saeger@xxxxxxxxxx>
> > ---
> > arch/arm64/kernel/Makefile | 5 +++++
> > 1 file changed, 5 insertions(+)
>
> Why isn't this needed in Linus's tree?
0d362be5b142 ("Makefile: link with -z noexecstack --no-warn-rwx-segments")
was merged after
7b4537199a4a ("kbuild: link symbol CRCs at final link, removing CONFIG_MODULE_REL_CRCS")
Linus's tree never had -z noexecstack with these same KBUILD rules.
>
> And why not cc: everyone involved in this, I would need acks from
> maintainers to be able to accept this...
Fair request.
Between ~5.3 and 5.19-rc1 cherry-picking
0d362be5b142 ("Makefile: link with -z noexecstack --no-warn-rwx-segments")
and building arm64 with CONFIG_MODVERSIONS=y
results in vmlinux missing Build ID
head.S is compiled to head.o
head.o is linked (ld) with -r and -z noexecstack which adds .note.GNU-stack section in head.o
head.o is then linked again with vmlinux (resulting vmlinux is missing .NOTE segment)
Can folks confirm/deny ld behavior is expected (arm64)?
And whether the above patch would be an acceptable fix for these kernel
versions?
repro test in cover letter: https://lore.kernel.org/all/cover.1670358255.git.tom.saeger@xxxxxxxxxx/#r
Regards,
--Tom
>
> thanks,
>
> greg k-h
