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    Subject[PATCH 5.15 002/779] x86: link vdso and boot with -z noexecstack --no-warn-rwx-segments
    Date
    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@kernel.dk/
    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@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
    @@ -103,7 +103,7 @@ $(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
    @@ -69,6 +69,10 @@ LDFLAGS_vmlinux := -pie $(call ld-option
    ifdef CONFIG_LD_ORPHAN_WARN
    LDFLAGS_vmlinux += --orphan-handling=warn
    endif
    +LDFLAGS_vmlinux += -z noexecstack
    +ifeq ($(CONFIG_LD_IS_BFD),y)
    +LDFLAGS_vmlinux += $(call ld-option,--no-warn-rwx-segments)
    +endif
    LDFLAGS_vmlinux += -T

    hostprogs := mkpiggy
    --- a/arch/x86/entry/vdso/Makefile
    +++ b/arch/x86/entry/vdso/Makefile
    @@ -179,7 +179,7 @@ quiet_cmd_vdso = VDSO $@
    sh $(srctree)/$(src)/checkundef.sh '$(NM)' '$@'

    VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 \
    - $(call ld-option, --eh-frame-hdr) -Bsymbolic
    + $(call ld-option, --eh-frame-hdr) -Bsymbolic -z noexecstack
    GCOV_PROFILE := n

    quiet_cmd_vdso_and_check = VDSO $@

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