linux-kernel - Re: [PATCH 07/29] x86: Restore "text" Program Header with dummy section

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Date:   Thu, 10 Oct 2019 12:33:05 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Kees Cook <keescook@...omium.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-alpha@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-c6x-dev@...ux-c6x.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Michal Simek <monstr@...str.eu>, linux-parisc@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/29] x86: Restore "text" Program Header with dummy
 section

On Thu, Sep 26, 2019 at 10:55:40AM -0700, Kees Cook wrote:
> Instead of depending on markings in the section following NOTES to
> restore the associated Program Header, use a dummy section, as done
> in other architectures.

This is very laconic and after some staring at ld.info, I think you mean
this:

"   If you place a section in one or more segments using ':PHDR', then
the linker will place all subsequent allocatable sections which do not
specify ':PHDR' in the same segments."

but I could be way off. Yes, no?

IOW, please write in the commit messages first what the problem is
you're addressing.

> This is preparation for moving NOTES into the
> RO_DATA macro.
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  arch/x86/kernel/vmlinux.lds.S | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index e2feacf921a0..788e78978030 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -147,8 +147,9 @@ SECTIONS
>  	} :text = 0x9090
>  
>  	NOTES :text :note
> +	.dummy : { *(.dummy) } :text
>  
> -	EXCEPTION_TABLE(16) :text = 0x9090
> +	EXCEPTION_TABLE(16)

This is killing the filler byte but I have a suspicion that'll change
eventually to INT3... :)

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette