Re: [PATCH] Add RUNTIME_DISCARD_EXIT to generic DISCARDS

Kees Cook
2020-01-30T22:04:08Z

On Thu, Jan 30, 2020 at 12:47:07PM -0800, H.J. Lu wrote:
> From bde2821f5e01a5f49b227c6fb8ba6195c26381a9 Mon Sep 17 00:00:00 2001
> From: "H.J. Lu" <hjl.tools@gmail.com>
> Date: Thu, 30 Jan 2020 12:31:22 -0800
> Subject: [PATCH] Add RUNTIME_DISCARD_EXIT to generic DISCARDS
>
> In x86 kernel, .exit.text and .exit.data sections are discarded at
> runtime not by linker. Add RUNTIME_DISCARD_EXIT to generic DISCARDS
> and define it in x86 kernel linker script to keep them.

Thanks for doing this! :) (I wasn't sure about _CALL, thanks also for
checking that.)

(The patch is missing your SoB?)

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

-Kees

> ---
> arch/x86/kernel/vmlinux.lds.S | 1 +
> include/asm-generic/vmlinux.lds.h | 10 ++++++++--
> 2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index e3296aa028fe..7206e1ac23dd 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -21,6 +21,7 @@
> #define LOAD_OFFSET __START_KERNEL_map
> #endif
>
> +#define RUNTIME_DISCARD_EXIT
> #define EMITS_PT_NOTE
> #define RO_EXCEPTION_TABLE_ALIGN 16
>
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index e00f41aa8ec4..6b943fb8c5fd 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -894,10 +894,16 @@
> * section definitions so that such archs put those in earlier section
> * definitions.
> */
> +#ifdef RUNTIME_DISCARD_EXIT
> +#define EXIT_DISCARDS
> +#else
> +#define EXIT_DISCARDS \
> + EXIT_TEXT \
> + EXIT_DATA
> +#endif
> #define DISCARDS \
> /DISCARD/ : { \
> - EXIT_TEXT \
> - EXIT_DATA \
> + EXIT_DISCARDS \
> EXIT_CALL \
> *(.discard) \
> *(.discard.*) \
> --
> 2.24.1
>

--
Kees Cook