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

[Kees Cook]

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@xxxxxxxxxxxx>
> Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Reviewed-by: Fangrui Song <maskray@xxxxxxxxxx>
> ---
>  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@xxxxxxxxxxxx>

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