[PATCH 5.10 25/54] arch: um: Mark the stack non-executable to fix a binutils warning

Greg Kroah-Hartman
2022-10-13T18:12:07Z

From: David Gow <davidgow@google.com>

[ Upstream commit bd71558d585ac61cfd799db7f25e78dca404dd7a ]

Since binutils 2.39, ld will print a warning if any stack section is
executable, which is the default for stack sections on files without a
.note.GNU-stack section.

This was fixed for x86 in commit ffcf9c5700e4 ("x86: link vdso and boot with -z noexecstack --no-warn-rwx-segments"),
but remained broken for UML, resulting in several warnings:

/usr/bin/ld: warning: arch/x86/um/vdso/vdso.o: missing .note.GNU-stack section implies executable stack
/usr/bin/ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker
/usr/bin/ld: warning: .tmp_vmlinux.kallsyms1 has a LOAD segment with RWX permissions
/usr/bin/ld: warning: .tmp_vmlinux.kallsyms1.o: missing .note.GNU-stack section implies executable stack
/usr/bin/ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker
/usr/bin/ld: warning: .tmp_vmlinux.kallsyms2 has a LOAD segment with RWX permissions
/usr/bin/ld: warning: .tmp_vmlinux.kallsyms2.o: missing .note.GNU-stack section implies executable stack
/usr/bin/ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker
/usr/bin/ld: warning: vmlinux has a LOAD segment with RWX permissions

Link both the VDSO and vmlinux with -z noexecstack, fixing the warnings
about .note.GNU-stack sections. In addition, pass --no-warn-rwx-segments
to dodge the remaining warnings about LOAD segments with RWX permissions
in the kallsyms objects. (Note that this flag is apparently not
available on lld, so hide it behind a test for BFD, which is what the
x86 patch does.)

Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ffcf9c5700e49c0aee42dcba9a12ba21338e8136
Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=ba951afb99912da01a6e8434126b8fac7aa75107
Signed-off-by: David Gow <davidgow@google.com>
Reviewed-by: Lukas Straub <lukasstraub2@web.de>
Tested-by: Lukas Straub <lukasstraub2@web.de>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/um/Makefile | 8 ++++++++
arch/x86/um/vdso/Makefile | 2 +-
2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/um/Makefile b/arch/um/Makefile
index 1cea46ff9bb7..775615141339 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -131,10 +131,18 @@ export LDS_ELF_FORMAT := $(ELF_FORMAT)
# The wrappers will select whether using "malloc" or the kernel allocator.
LINK_WRAPS = -Wl,--wrap,malloc -Wl,--wrap,free -Wl,--wrap,calloc

+# Avoid binutils 2.39+ warnings by marking the stack non-executable and
+# ignorning warnings for the kallsyms sections.
+LDFLAGS_EXECSTACK = -z noexecstack
+ifeq ($(CONFIG_LD_IS_BFD),y)
+LDFLAGS_EXECSTACK += $(call ld-option,--no-warn-rwx-segments)
+endif
+
LD_FLAGS_CMDLINE = $(foreach opt,$(KBUILD_LDFLAGS),-Wl,$(opt))

# Used by link-vmlinux.sh which has special support for um link
export CFLAGS_vmlinux := $(LINK-y) $(LINK_WRAPS) $(LD_FLAGS_CMDLINE)
+export LDFLAGS_vmlinux := $(LDFLAGS_EXECSTACK)

# When cleaning we don't include .config, so we don't include
# TT or skas makefiles and don't clean skas_ptregs.h.
diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile
index 5943387e3f35..5ca366e15c76 100644
--- a/arch/x86/um/vdso/Makefile
+++ b/arch/x86/um/vdso/Makefile
@@ -62,7 +62,7 @@ quiet_cmd_vdso = VDSO $@
-Wl,-T,$(filter %.lds,$^) $(filter %.o,$^) && \
sh $(srctree)/$(src)/checkundef.sh '$(NM)' '$@'

-VDSO_LDFLAGS = -fPIC -shared -Wl,--hash-style=sysv
+VDSO_LDFLAGS = -fPIC -shared -Wl,--hash-style=sysv -z noexecstack
GCOV_PROFILE := n

#
--
2.35.1