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    Subject[PATCH v5 07/36] x86/boot: Check that there are no run-time relocations
    Date
    From: Arvind Sankar <nivedita@alum.mit.edu>

    Add a linker script check that there are no run-time relocations, and
    remove the old one that tries to check via looking for specially-named
    sections in the object files.

    Drop the tests for -fPIE compiler option and -pie linker option, as they
    are available in all supported gcc and binutils versions (as well as
    clang and lld).

    Tested-by: Nick Desaulniers <ndesaulniers@google.com>
    Reviewed-by: Kees Cook <keescook@chromium.org>
    Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
    Reviewed-by: Fangrui Song <maskray@google.com>
    Reviewed-by: Sedat Dilek <sedat.dilek@gmail.com>
    Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
    Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
    Signed-off-by: Kees Cook <keescook@chromium.org>
    ---
    arch/x86/boot/compressed/Makefile | 28 +++-----------------------
    arch/x86/boot/compressed/vmlinux.lds.S | 8 ++++++++
    2 files changed, 11 insertions(+), 25 deletions(-)

    diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
    index 7db0102a573d..96d53e300ab6 100644
    --- a/arch/x86/boot/compressed/Makefile
    +++ b/arch/x86/boot/compressed/Makefile
    @@ -29,7 +29,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \
    vmlinux.bin.xz vmlinux.bin.lzo vmlinux.bin.lz4

    KBUILD_CFLAGS := -m$(BITS) -O2
    -KBUILD_CFLAGS += -fno-strict-aliasing $(call cc-option, -fPIE, -fPIC)
    +KBUILD_CFLAGS += -fno-strict-aliasing -fPIE
    KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
    cflags-$(CONFIG_X86_32) := -march=i386
    cflags-$(CONFIG_X86_64) := -mcmodel=small
    @@ -51,7 +51,7 @@ UBSAN_SANITIZE :=n
    KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
    # Compressed kernel should be built as PIE since it may be loaded at any
    # address by the bootloader.
    -LDFLAGS_vmlinux := $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker)
    +LDFLAGS_vmlinux := -pie $(call ld-option, --no-dynamic-linker)
    LDFLAGS_vmlinux += -T

    hostprogs := mkpiggy
    @@ -86,30 +86,8 @@ vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
    vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_thunk_$(BITS).o
    efi-obj-$(CONFIG_EFI_STUB) = $(objtree)/drivers/firmware/efi/libstub/lib.a

    -# The compressed kernel is built with -fPIC/-fPIE so that a boot loader
    -# can place it anywhere in memory and it will still run. However, since
    -# it is executed as-is without any ELF relocation processing performed
    -# (and has already had all relocation sections stripped from the binary),
    -# none of the code can use data relocations (e.g. static assignments of
    -# pointer values), since they will be meaningless at runtime. This check
    -# will refuse to link the vmlinux if any of these relocations are found.
    -quiet_cmd_check_data_rel = DATAREL $@
    -define cmd_check_data_rel
    - for obj in $(filter %.o,$^); do \
    - $(READELF) -S $$obj | grep -qF .rel.local && { \
    - echo "error: $$obj has data relocations!" >&2; \
    - exit 1; \
    - } || true; \
    - done
    -endef
    -
    -# We need to run two commands under "if_changed", so merge them into a
    -# single invocation.
    -quiet_cmd_check-and-link-vmlinux = LD $@
    - cmd_check-and-link-vmlinux = $(cmd_check_data_rel); $(cmd_ld)
    -
    $(obj)/vmlinux: $(vmlinux-objs-y) $(efi-obj-y) FORCE
    - $(call if_changed,check-and-link-vmlinux)
    + $(call if_changed,ld)

    OBJCOPYFLAGS_vmlinux.bin := -R .comment -S
    $(obj)/vmlinux.bin: vmlinux FORCE
    diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
    index a4a4a59a2628..29df99b6cc64 100644
    --- a/arch/x86/boot/compressed/vmlinux.lds.S
    +++ b/arch/x86/boot/compressed/vmlinux.lds.S
    @@ -42,6 +42,12 @@ SECTIONS
    *(.rodata.*)
    _erodata = . ;
    }
    + .rel.dyn : {
    + *(.rel.*)
    + }
    + .rela.dyn : {
    + *(.rela.*)
    + }
    .got : {
    *(.got)
    }
    @@ -85,3 +91,5 @@ ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, "Unexpected GOT/PLT en
    #else
    ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0xc, "Unexpected GOT/PLT entries detected!")
    #endif
    +
    +ASSERT(SIZEOF(.rel.dyn) == 0 && SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations detected!")
    --
    2.25.1
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