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.
Signed-off-by: H.J. Lu <[email protected]>
---
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
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?
-Kees
>
> Signed-off-by: H.J. Lu <[email protected]>
> ---
> 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
On Thu, Jan 30, 2020 at 11:40 AM Kees Cook <[email protected]> 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 <[email protected]>
> > ---
> > 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.
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 <[email protected]> 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
On Thu, Jan 30, 2020 at 11:58 AM Kees Cook <[email protected]> wrote:
>
> 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 <[email protected]> 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).
>
It should work.
Thanks.
--
H.J.
On Thu, Jan 30, 2020 at 12:06 PM H.J. Lu <[email protected]> wrote:
>
> On Thu, Jan 30, 2020 at 11:58 AM Kees Cook <[email protected]> wrote:
> >
> > 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 <[email protected]> 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
We should keep EXIT_CALL in DISCARDS. Only .exit.text and .exit.data
sections are discarded at runtime.
> > +#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).
> >
>
> It should work.
Here is the patch to add RUNTIME_DISCARD_EXIT to generic DISCARDS.
--
H.J.
On Thu, Jan 30, 2020 at 12:47:07PM -0800, H.J. Lu wrote:
> From bde2821f5e01a5f49b227c6fb8ba6195c26381a9 Mon Sep 17 00:00:00 2001
> From: "H.J. Lu" <[email protected]>
> Date: Thu, 30 Jan 2020 12:31:22 -0800
> Subject: [PATCH] Add RUNTIME_DISCARD_EXIT to generic DISCARDS
>
> 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.
Thanks for doing this! :) (I wasn't sure about _CALL, thanks also for
checking that.)
(The patch is missing your SoB?)
Reviewed-by: Kees Cook <[email protected]>
-Kees
> ---
> 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
> #define DISCARDS \
> /DISCARD/ : { \
> - EXIT_TEXT \
> - EXIT_DATA \
> + EXIT_DISCARDS \
> EXIT_CALL \
> *(.discard) \
> *(.discard.*) \
> --
> 2.24.1
>
--
Kees Cook