linux-kernel - Re: [PATCH v2 1/2] arm/build: Warn on orphan section placement

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Message-ID: <202006241242.9A6E0E2387@keescook>
Date:   Wed, 24 Jun 2020 12:43:41 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Russell King <linux@...linux.org.uk>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eli Friedman <efriedma@...cinc.com>
Subject: Re: [PATCH v2 1/2] arm/build: Warn on orphan section placement

On Tue, Jun 23, 2020 at 05:03:46PM -0700, Nick Desaulniers wrote:
> On Mon, Jun 22, 2020 at 1:49 PM Kees Cook <keescook@...omium.org> wrote:
> > [...]
> > @@ -37,6 +38,13 @@
> >                 *(.idmap.text)                                          \
> >                 __idmap_text_end = .;                                   \
> >
> > +#define ARM_COMMON_DISCARD                                             \
> > +               *(.ARM.attributes)                                      \
> 
> I could have sworn that someone (Eli?) once told me that this section
> (.ARM.attributes) is used for disambiguating which ARM version or
> which optional extensions were used when compiling, and that without
> this section, one would not be able to disassemble 32b ARM precisely.
> If that's the case, we might not want to discard it?

Perhaps we want to treat it like .comment and include it in the ELF?

> > +#define ARM_STUBS_TEXT                                                 \
> > +               *(.gnu.warning)                                         \
> > +               *(.glue_7t)                                             \
> > +               *(.glue_7)                                              \
> 
> This changes the order of .glue_7t relative to .glue_7.  Maybe that
> doesn't matter.

Good point. I'll swap it just for consistency.

Thanks!

-- 
Kees Cook