On Fri, Aug 19, 2022 at 8:46 AM Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > From: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > commit 0d362be5b14200b77ecc2127936a5ff82fbffe41 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: vmlinux: 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: 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@xxxxxxxxx/ > Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=ba951afb99912da01a6e8434126b8fac7aa75107 > Link: https://github.com/llvm/llvm-project/issues/57009 > Reported-and-tested-by: Jens Axboe <axboe@xxxxxxxxx> > Suggested-by: Fangrui Song <maskray@xxxxxxxxxx> > Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > --- > Makefile | 5 +++++ > 1 file changed, 5 insertions(+) > > --- a/Makefile > +++ b/Makefile > @@ -983,6 +983,11 @@ KBUILD_CFLAGS += $(KCFLAGS) > KBUILD_LDFLAGS_MODULE += --build-id=sha1 > LDFLAGS_vmlinux += --build-id=sha1 > > +KBUILD_LDFLAGS += -z noexecstack > +ifeq ($(CONFIG_LD_IS_BFD),y) > +KBUILD_LDFLAGS += $(call ld-option,--no-warn-rwx-segments) > +endif 5.10.y is missing CONFIG_LD_IS_BFD. Specifically commit 02aff8592204 ("kbuild: check the minimum linker version in Kconfig") which first landed in v5.12-rc1. I'd recommend simply dropping the `ifeq` guards; the ld-option guard will still work. Otherwise GNU BFD 2.39 users will observe linker warnings related to rwx-segments. Greg, do you mind dropping this patch and I'll supply a v2, or is it too late and I should send a patch on top? > + > ifeq ($(CONFIG_STRIP_ASM_SYMS),y) > LDFLAGS_vmlinux += $(call ld-option, -X,) > endif > > -- Thanks, ~Nick Desaulniers
