[PATCH v2 0/2] link with -z noexecstack --no-warn-rwx-segments

[Nick Desaulniers]

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.

Broken up into 2 patches; one for the top level vmlinux, one x86
specific since a few places in the x86 build reset KBUILD_LDFLAGS.

Nick Desaulniers (2):
  Makefile: link with -z noexecstack --no-warn-rwx-segments
  x86: link vdso and boot with -z noexecstack --no-warn-rwx-segments

 Makefile                          | 5 +++++
 arch/x86/boot/Makefile            | 2 +-
 arch/x86/boot/compressed/Makefile | 4 ++++
 arch/x86/entry/vdso/Makefile      | 2 +-
 4 files changed, 11 insertions(+), 2 deletions(-)


base-commit: 15205c2829ca2cbb5ece5ceaafe1171a8470e62b
-- 
2.37.1.559.g78731f0fdb-goog