Re: [PATCH v3 7/7] x86/boot: Check that there are no runtime relocations

Kees Cook
2020-06-29T18:38:07Z

On Mon, Jun 29, 2020 at 10:09:28AM -0400, Arvind Sankar wrote:
> Add a linker script check that there are no runtime 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).
>
> Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
> Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
> Reviewed-by: Fangrui Song <maskray@google.com>
> ---
> arch/x86/boot/compressed/Makefile | 28 +++-----------------------
> arch/x86/boot/compressed/vmlinux.lds.S | 8 ++++++++
> 2 files changed, 11 insertions(+), 25 deletions(-)

Reviewed-by: Kees Cook <keescook@chromium.org>

question below ...

> diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
> index a4a4a59a2628..a78510046eec 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)
> }

Should these be marked (INFO) as well?

> @@ -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 runtime relocations detected!")

I think I should be doing this same ASSERT style for other explicit
DISCARDS in my orphan series so we'll notice if they change, instead
of being silently dropped if they grow.

--
Kees Cook