linux-kernel - Re: [PATCH] x86: Don't discard .exit.text and .exit.data at link-time

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Message-ID: <202001301139.F8859A4@keescook>
Date:   Thu, 30 Jan 2020 11:40:44 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "H.J. Lu" <hjl.tools@...il.com>
Cc:     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>, x86@...nel.org,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH] x86: Don't discard .exit.text and .exit.data at link-time

On Thu, Jan 30, 2020 at 10:00:48AM -0800, H.J. Lu wrote:
> Since .exit.text and .exit.data sections are discarded at runtime, we
> should undefine EXIT_TEXT and EXIT_DATA to exclude .exit.text and
> .exit.data sections from default discarded sections.

This is just a correctness fix, yes? The EXIT_TEXT and EXIT_DATA were
already included before the /DISCARD/ section here, so there's no
behavioral change with this patch, correct?

-Kees

> 
> Signed-off-by: H.J. Lu <hjl.tools@...il.com>
> ---
>  arch/x86/kernel/vmlinux.lds.S | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index d1b942365d27..fb2c45cb1d1f 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -416,6 +416,12 @@ SECTIONS
>  	STABS_DEBUG
>  	DWARF_DEBUG
>  
> +	/* Sections to be discarded.  EXIT_TEXT and EXIT_DATA discard at runtime.
> +	 * not link time.  */
> +#undef EXIT_TEXT
> +#define EXIT_TEXT
> +#undef EXIT_DATA
> +#define EXIT_DATA
>  	DISCARDS
>  	/DISCARD/ : {
>  		*(.eh_frame)
> -- 
> 2.24.1
> 

-- 
Kees Cook