linux-kernel - Re: [PATCH] x86: Don't discard .exit.text and .exit.data at link-time

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Date:   Thu, 30 Jan 2020 11:45:15 -0800
From:   "H.J. Lu" <hjl.tools@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     LKML <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>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH] x86: Don't discard .exit.text and .exit.data at link-time

On Thu, Jan 30, 2020 at 11:40 AM Kees Cook <keescook@...omium.org> wrote:
>
> On Thu, Jan 30, 2020 at 10:00:48AM -0800, H.J. Lu wrote:
> > Since .exit.text and .exit.data sections are discarded at runtime, we
> > should undefine EXIT_TEXT and EXIT_DATA to exclude .exit.text and
> > .exit.data sections from default discarded sections.
>
> This is just a correctness fix, yes? The EXIT_TEXT and EXIT_DATA were
> already included before the /DISCARD/ section here, so there's no
> behavioral change with this patch, correct?

That is correct.  I was confused by EXIT_TEXT and EXIT_DATA in generic
DISCARDS.   My patch just makes it more explicit.

> -Kees
>
> >
> > Signed-off-by: H.J. Lu <hjl.tools@...il.com>
> > ---
> >  arch/x86/kernel/vmlinux.lds.S | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> > index d1b942365d27..fb2c45cb1d1f 100644
> > --- a/arch/x86/kernel/vmlinux.lds.S
> > +++ b/arch/x86/kernel/vmlinux.lds.S
> > @@ -416,6 +416,12 @@ SECTIONS
> >       STABS_DEBUG
> >       DWARF_DEBUG
> >
> > +     /* Sections to be discarded.  EXIT_TEXT and EXIT_DATA discard at runtime.
> > +      * not link time.  */
> > +#undef EXIT_TEXT
> > +#define EXIT_TEXT
> > +#undef EXIT_DATA
> > +#define EXIT_DATA
> >       DISCARDS
> >       /DISCARD/ : {
> >               *(.eh_frame)
> > --
> > 2.24.1
> >
>
> --
> Kees Cook



-- 
H.J.