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    Subject[tip: x86/boot] x86/*/Makefile: Use -fno-asynchronous-unwind-tables to suppress .eh_frame sections
    The following commit has been merged into the x86/boot branch of tip:

    Commit-ID: 003602ad5516e59940de42e44c8d8033387bb363
    Gitweb: https://git.kernel.org/tip/003602ad5516e59940de42e44c8d8033387bb363
    Author: Arvind Sankar <nivedita@alum.mit.edu>
    AuthorDate: Mon, 24 Feb 2020 18:21:28 -05:00
    Committer: Borislav Petkov <bp@suse.de>
    CommitterDate: Tue, 25 Feb 2020 13:18:29 +01:00

    x86/*/Makefile: Use -fno-asynchronous-unwind-tables to suppress .eh_frame sections

    While discussing a patch to discard .eh_frame from the compressed
    vmlinux using the linker script, Fangrui Song pointed out [1] that these
    sections shouldn't exist in the first place because arch/x86/Makefile
    uses -fno-asynchronous-unwind-tables.

    It turns out this is because the Makefiles used to build the compressed
    kernel redefine KBUILD_CFLAGS, dropping this flag.

    Add the flag to the Makefile for the compressed kernel, as well as the
    EFI stub Makefile to fix this.

    Also add the flag to boot/Makefile and realmode/rm/Makefile so that the
    kernel's boot code (boot/setup.elf) and realmode trampoline
    (realmode/rm/realmode.elf) won't be compiled with .eh_frame sections,
    since their linker scripts also just discard them.

    [1] https://lore.kernel.org/lkml/20200222185806.ywnqhfqmy67akfsa@google.com/

    Suggested-by: Fangrui Song <maskray@google.com>
    Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
    Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
    Reviewed-by: Kees Cook <keescook@chromium.org>
    Tested-by: Nathan Chancellor <natechancellor@gmail.com>
    Link: https://lkml.kernel.org/r/20200224232129.597160-2-nivedita@alum.mit.edu
    ---
    arch/x86/boot/Makefile | 1 +
    arch/x86/boot/compressed/Makefile | 1 +
    arch/x86/realmode/rm/Makefile | 1 +
    drivers/firmware/efi/libstub/Makefile | 3 ++-
    4 files changed, 5 insertions(+), 1 deletion(-)

    diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
    index 012b82f..24f011e 100644
    --- a/arch/x86/boot/Makefile
    +++ b/arch/x86/boot/Makefile
    @@ -68,6 +68,7 @@ clean-files += cpustr.h
    KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP
    KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
    KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
    +KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
    GCOV_PROFILE := n
    UBSAN_SANITIZE := n

    diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
    index 26050ae..c331113 100644
    --- a/arch/x86/boot/compressed/Makefile
    +++ b/arch/x86/boot/compressed/Makefile
    @@ -39,6 +39,7 @@ KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
    KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
    KBUILD_CFLAGS += -Wno-pointer-sign
    KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
    +KBUILD_CFLAGS += -fno-asynchronous-unwind-tables

    KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
    GCOV_PROFILE := n
    diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile
    index 99b6332..b11ec5d 100644
    --- a/arch/x86/realmode/rm/Makefile
    +++ b/arch/x86/realmode/rm/Makefile
    @@ -71,5 +71,6 @@ $(obj)/realmode.relocs: $(obj)/realmode.elf FORCE
    KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP -D_WAKEUP \
    -I$(srctree)/arch/x86/boot
    KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
    +KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
    GCOV_PROFILE := n
    UBSAN_SANITIZE := n
    diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
    index 98a8157..a1140c4 100644
    --- a/drivers/firmware/efi/libstub/Makefile
    +++ b/drivers/firmware/efi/libstub/Makefile
    @@ -12,7 +12,8 @@ cflags-$(CONFIG_X86) += -m$(BITS) -D__KERNEL__ -O2 \
    -mno-mmx -mno-sse -fshort-wchar \
    -Wno-pointer-sign \
    $(call cc-disable-warning, address-of-packed-member) \
    - $(call cc-disable-warning, gnu)
    + $(call cc-disable-warning, gnu) \
    + -fno-asynchronous-unwind-tables

    # arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly
    # disable the stackleak plugin
    \
     
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