From: Nick Desaulniers ndesaulniers@google.com
commit ffcf9c5700e49c0aee42dcba9a12ba21338e8136 upstream.
Users of GNU ld (BFD) from binutils 2.39+ will observe multiple instances of a new warning when linking kernels in the form:
ld: warning: arch/x86/boot/pmjump.o: missing .note.GNU-stack section implies executable stack ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker ld: warning: arch/x86/boot/compressed/vmlinux has a LOAD segment with RWX permissions
Generally, we would like to avoid the stack being executable. Because there could be a need for the stack to be executable, assembler sources have to opt-in to this security feature via explicit creation of the .note.GNU-stack feature (which compilers create by default) or command line flag --noexecstack. Or we can simply tell the linker the production of such sections is irrelevant and to link the stack as --noexecstack.
LLVM's LLD linker defaults to -z noexecstack, so this flag isn't strictly necessary when linking with LLD, only BFD, but it doesn't hurt to be explicit here for all linkers IMO. --no-warn-rwx-segments is currently BFD specific and only available in the current latest release, so it's wrapped in an ld-option check.
While the kernel makes extensive usage of ELF sections, it doesn't use permissions from ELF segments.
Link: https://lore.kernel.org/linux-block/3af4127a-f453-4cf7-f133-a181cce06f73@ker... Link: https://sourceware.org/git/?p=binutils-gdb.git%3Ba=commit%3Bh=ba951afb99912d... Link: https://github.com/llvm/llvm-project/issues/57009 Reported-and-tested-by: Jens Axboe axboe@kernel.dk Suggested-by: Fangrui Song maskray@google.com Signed-off-by: Nick Desaulniers ndesaulniers@google.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/boot/Makefile | 2 +- arch/x86/boot/compressed/Makefile | 4 ++++ arch/x86/entry/vdso/Makefile | 2 +- 3 files changed, 6 insertions(+), 2 deletions(-)
--- a/arch/x86/boot/Makefile +++ b/arch/x86/boot/Makefile @@ -100,7 +100,7 @@ $(obj)/zoffset.h: $(obj)/compressed/vmli AFLAGS_header.o += -I$(objtree)/$(obj) $(obj)/header.o: $(obj)/zoffset.h
-LDFLAGS_setup.elf := -m elf_i386 -T +LDFLAGS_setup.elf := -m elf_i386 -z noexecstack -T $(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE $(call if_changed,ld)
--- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -54,6 +54,10 @@ else LDFLAGS += $(shell $(LD) --help 2>&1 | grep -q "-z noreloc-overflow" \ && echo "-z noreloc-overflow -pie --no-dynamic-linker") endif + +LDFLAGS += -z noexecstack +LDFLAGS += $(call ld-option,--no-warn-rwx-segments) + LDFLAGS_vmlinux := -T
hostprogs-y := mkpiggy --- a/arch/x86/entry/vdso/Makefile +++ b/arch/x86/entry/vdso/Makefile @@ -168,7 +168,7 @@ quiet_cmd_vdso = VDSO $@
VDSO_LDFLAGS = -shared $(call ld-option, --hash-style=both) \ $(call ld-option, --build-id) $(call ld-option, --eh-frame-hdr) \ - -Bsymbolic + -Bsymbolic -z noexecstack GCOV_PROFILE := n
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