linux-kernel - Re: [PATCH] Add RUNTIME_DISCARD

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Message-ID: <202001301402.7E23309E2C@keescook>
Date:   Thu, 30 Jan 2020 14:04:04 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "H.J. Lu" <hjl.tools@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Thomas Lendacky <Thomas.Lendacky@....com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH] Add RUNTIME_DISCARD_EXIT to generic DISCARDS

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@...il.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@...omium.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