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    Subject[PATCH 4.9 025/101] Makefile: link with -z noexecstack --no-warn-rwx-segments
    Date
    From: Nick Desaulniers <ndesaulniers@google.com>

    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@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>
    ---
    Makefile | 3 +++
    1 file changed, 3 insertions(+)

    --- a/Makefile
    +++ b/Makefile
    @@ -870,6 +870,9 @@ ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATI
    LDFLAGS_vmlinux += $(call ld-option, --gc-sections,)
    endif

    +LDFLAGS += -z noexecstack
    +LDFLAGS += $(call ld-option,--no-warn-rwx-segments)
    +
    ifeq ($(CONFIG_STRIP_ASM_SYMS),y)
    LDFLAGS_vmlinux += $(call ld-option, -X,)
    endif

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