linux-kernel - Re: [PATCH 14/29] vmlinux.lds.h: Allow EXCEPTION_TABLE to live in RO

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Date:   Thu, 10 Oct 2019 17:25:16 +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 14/29] vmlinux.lds.h: Allow EXCEPTION_TABLE to live in
 RO_DATA

On Thu, Sep 26, 2019 at 10:55:47AM -0700, Kees Cook wrote:
> Many architectures have an EXCEPTION_TABLE that needs only to be
> read-only. As such, it should live in RO_DATA. This creates a macro to
> identify this case for the architectures that can move EXCEPTION_TABLE
> into RO_DATA.
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  include/asm-generic/vmlinux.lds.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index d57a28786bb8..35a6cba39d9f 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -69,6 +69,17 @@
>  #define NOTES_HEADERS_RESTORE
>  #endif
>  
> +/*
> + * Some architectures have non-executable read-only exception tables.
> + * They can be added to the RO_DATA segment by specifying their desired
> + * alignment.
> + */
> +#ifdef RO_DATA_EXCEPTION_TABLE_ALIGN
> +#define RO_DATA_EXCEPTION_TABLE	EXCEPTION_TABLE(RO_DATA_EXCEPTION_TABLE_ALIGN)
> +#else
> +#define RO_DATA_EXCEPTION_TABLE
> +#endif
> +
>  /* Align . to a 8 byte boundary equals to maximum function alignment. */
>  #define ALIGN_FUNCTION()  . = ALIGN(8)
>  
> @@ -508,6 +519,7 @@
>  		__stop___modver = .;					\
>  	}								\
>  									\
> +	RO_DATA_EXCEPTION_TABLE						\
>  	NOTES								\
>  									\
>  	. = ALIGN((align));						\
> -- 

I think you can drop the "DATA" from the names as it is kinda clear
where the exception table lands:

RO_EXCEPTION_TABLE_ALIGN
RO_EXCEPTION_TABLE

The "read-only" part is the important one.

-- 
Regards/Gruss,
    Boris.

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