linux-kernel - Re: [PATCH v3 1/7] x86/boot/compressed: Move .got.plt entries out of the .got section

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Date:   Mon, 29 Jun 2020 17:51:00 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Fangrui Song <maskray@...gle.com>,
        Dmitry Golovin <dima@...ovin.in>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        "H . J . Lu" <hjl@...rceware.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/7] x86/boot/compressed: Move .got.plt entries out of
 the .got section

On Mon, 29 Jun 2020 at 17:50, Arvind Sankar <nivedita@...m.mit.edu> wrote:
>
> On Mon, Jun 29, 2020 at 08:48:05AM -0700, Kees Cook wrote:
> > On Mon, Jun 29, 2020 at 10:09:22AM -0400, Arvind Sankar wrote:
> >
> > This is also being done on arm64, and the section was specified slightly
> > differently (with INFO) which maybe should be done here too?
>
> I was actually just about to email you to ask what that INFO is for :)
> What does it do?
>

It makes the section non-allocatable, so it is dropped from the final image

> >
> >        .got.plt (INFO) : { *(.got.plt) }
> >        ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, ".got.plt not empty")
> >
> > Otherwise, yes, looks good.
> >
> > Reviewed-by: Kees Cook <keescook@...omium.org>
> >
> > > +
> > >     .data : {
> > >             _data = . ;
> > >             *(.data)
> > > @@ -77,3 +80,9 @@ SECTIONS
> > >
> > >     DISCARDS
> > >  }
> > > +
> > > +#ifdef CONFIG_X86_64
> > > +ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, "Unexpected GOT/PLT entries detected!")
> > > +#else
> > > +ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0xc, "Unexpected GOT/PLT entries detected!")
> > > +#endif
> > > --
> > > 2.26.2
> > >
> >
> > --
> > Kees Cook