From: Kees Cook <keescook@chromium.org>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Thomas Lendacky <Thomas.Lendacky@amd.com>,
Sami Tolvanen <samitolvanen@google.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H . Peter Anvin" <hpa@zytor.com>,
the arch/x86 maintainers <x86@kernel.org>,
Yu-cheng Yu <yu-cheng.yu@intel.com>
Subject: Re: [PATCH] x86: Don't discard .exit.text and .exit.data at link-time
Date: Thu, 30 Jan 2020 11:58:54 -0800 [thread overview]
Message-ID: <202001301152.DF108B6CC@keescook> (raw)
In-Reply-To: <CAMe9rOrrrZFWgVpsKAWjHKzVh3ZziFLs2ua0m0Ewymrjs-b+EA@mail.gmail.com>
On Thu, Jan 30, 2020 at 11:45:15AM -0800, H.J. Lu wrote:
> On Thu, Jan 30, 2020 at 11:40 AM Kees Cook <keescook@chromium.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.
Okay, so to that end and because this isn't arch-specific, I'd like to
see this be a behavioral flag, and then the generic DISCARDS macro can
be adjusted. This lets all architectures implement this without having
to scatter undef/define lines in each arch.
Something like this:
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index e00f41aa8ec4..f242d3b4814d 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -894,11 +894,17 @@
* section definitions so that such archs put those in earlier section
* definitions.
*/
-#define DISCARDS \
- /DISCARD/ : { \
+#ifdef RUNTIME_DISCARD_EXIT
+#define EXIT_DISCARDS
+#else
+#define EXIT_DISCARDS \
EXIT_TEXT \
EXIT_DATA \
- EXIT_CALL \
+ EXIT_CALL
+#endif
+#define DISCARDS \
+ /DISCARD/ : { \
+ EXIT_DISCARDS \
*(.discard) \
*(.discard.*) \
*(.modinfo) \
Then x86 and all other architectures that do this can just use
#define RUNTIME_DISCARD_EXIT
at the top (like EMITS_PT_NOTE, etc).
-Kees
> > > --- 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)
--
Kees Cook
next prev parent reply other threads:[~2020-01-30 19:58 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-30 18:00 [PATCH] x86: Don't discard .exit.text and .exit.data at link-time H.J. Lu
2020-01-30 19:40 ` Kees Cook
2020-01-30 19:45 ` H.J. Lu
2020-01-30 19:58 ` Kees Cook [this message]
2020-01-30 20:06 ` H.J. Lu
2020-01-30 20:47 ` [PATCH] Add RUNTIME_DISCARD_EXIT to generic DISCARDS H.J. Lu
2020-01-30 22:04 ` Kees Cook
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