linux-kernel - Re: [PATCH 1/2] Add RUNTIME_DISCARD

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Message-ID: <20200326201142.GJ11398@zn.tnic>
Date:   Thu, 26 Mar 2020 21:11:42 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Kees Cook <keescook@...omium.org>
Cc:     "H.J. Lu" <hjl.tools@...il.com>, 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>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH 1/2] Add RUNTIME_DISCARD_EXIT to generic DISCARDS

On Thu, Mar 26, 2020 at 12:30:20PM -0700, H.J. Lu wrote:
> 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.
> 
> Signed-off-by: H.J. Lu <hjl.tools@...il.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> ---
>  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

/me goes back and reads the old thread on this...

Kees, do you expect other arches to actually need this
RUNTIME_DISCARD_EXIT thing or was that a hypothetical thing?

/me searches more...

oh, there's a patchset from you

https://lkml.kernel.org/r/20200228002244.15240-1-keescook@chromium.org

which already contains this patch *and* an ARM64 patch which defines
RUNTIME_DISCARD_EXIT so I'm guessing ARM64 wants to discard at runtime
too.

Which leaves the question why is H.J. sending that patch separate and
you carry it in a patchset about orphan section warning? Seems like it
wants to be in your patchset?

Thx.

-- 
Regards/Gruss,
    Boris.

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