* [PATCH] Add RUNTIME_DISCARD_EXIT to generic DISCARDS
2020-01-30 20:06 ` H.J. Lu
@ 2020-01-30 20:47 ` H.J. Lu
2020-01-30 22:04 ` Kees Cook
0 siblings, 1 reply; 5+ messages in thread
From: H.J. Lu @ 2020-01-30 20:47 UTC (permalink / raw)
To: Kees Cook
Cc: LKML, Andy Lutomirski, Thomas Gleixner, Thomas Lendacky,
Sami Tolvanen, Heiko Carstens, Ingo Molnar, Borislav Petkov,
H . Peter Anvin, the arch/x86 maintainers, Yu-cheng Yu
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On Thu, Jan 30, 2020 at 12:06 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Thu, Jan 30, 2020 at 11:58 AM Kees Cook <keescook@chromium.org> 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 <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
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.
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From bde2821f5e01a5f49b227c6fb8ba6195c26381a9 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
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.
---
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
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] Add RUNTIME_DISCARD_EXIT to generic DISCARDS
2020-01-30 20:47 ` [PATCH] Add RUNTIME_DISCARD_EXIT to generic DISCARDS H.J. Lu
@ 2020-01-30 22:04 ` Kees Cook
0 siblings, 0 replies; 5+ messages in thread
From: Kees Cook @ 2020-01-30 22:04 UTC (permalink / raw)
To: H.J. Lu
Cc: LKML, Andy Lutomirski, Thomas Gleixner, Thomas Lendacky,
Sami Tolvanen, Heiko Carstens, Ingo Molnar, Borislav Petkov,
H . Peter Anvin, the arch/x86 maintainers, Yu-cheng Yu
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" <hjl.tools@gmail.com>
> 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 <keescook@chromium.org>
-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
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH] Add RUNTIME_DISCARD_EXIT to generic DISCARDS
@ 2020-01-30 22:43 H.J. Lu
2020-01-30 22:43 ` [PATCH] Discard .note.gnu.property sections in generic NOTES H.J. Lu
0 siblings, 1 reply; 5+ messages in thread
From: H.J. Lu @ 2020-01-30 22:43 UTC (permalink / raw)
To: linux-kernel
Cc: Andy Lutomirski, Thomas Gleixner, Kees Cook, Thomas Lendacky,
Sami Tolvanen, Heiko Carstens, Ingo Molnar, Borislav Petkov,
H . Peter Anvin, x86, Yu-cheng Yu
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.
Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
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
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH] Discard .note.gnu.property sections in generic NOTES
2020-01-30 22:43 [PATCH] Add RUNTIME_DISCARD_EXIT to generic DISCARDS H.J. Lu
@ 2020-01-30 22:43 ` H.J. Lu
2020-01-30 22:52 ` Kees Cook
0 siblings, 1 reply; 5+ messages in thread
From: H.J. Lu @ 2020-01-30 22:43 UTC (permalink / raw)
To: linux-kernel
Cc: Andy Lutomirski, Thomas Gleixner, Kees Cook, Thomas Lendacky,
Sami Tolvanen, Heiko Carstens, Ingo Molnar, Borislav Petkov,
H . Peter Anvin, x86, Yu-cheng Yu
With the command-line option, -mx86-used-note=yes, the x86 assembler
in binutils 2.32 and above generates a program property note in a note
section, .note.gnu.property, to encode used x86 ISAs and features. But
kernel linker script only contains a single NOTE segment:
PHDRS {
text PT_LOAD FLAGS(5);
data PT_LOAD FLAGS(6);
percpu PT_LOAD FLAGS(6);
init PT_LOAD FLAGS(7);
note PT_NOTE FLAGS(0);
}
SECTIONS
{
...
.notes : AT(ADDR(.notes) - 0xffffffff80000000) { __start_notes = .; KEEP(*(.not
e.*)) __stop_notes = .; } :text :note
...
}
The NOTE segment generated by kernel linker script is aligned to 4 bytes.
But .note.gnu.property section must be aligned to 8 bytes on x86-64 and
we get
[hjl@gnu-skx-1 linux]$ readelf -n vmlinux
Displaying notes found in: .notes
Owner Data size Description
Xen 0x00000006 Unknown note type: (0x00000006)
description data: 6c 69 6e 75 78 00
Xen 0x00000004 Unknown note type: (0x00000007)
description data: 32 2e 36 00
xen-3.0 0x00000005 Unknown note type: (0x006e6558)
description data: 08 00 00 00 03
readelf: Warning: note with invalid namesz and/or descsz found at offset 0x50
readelf: Warning: type: 0xffffffff, namesize: 0x006e6558, descsize:
0x80000000, alignment: 8
[hjl@gnu-skx-1 linux]$
Since note.gnu.property section in kernel image is never used, this patch
discards .note.gnu.property sections in kernel linker script by adding
/DISCARD/ : {
*(.note.gnu.property)
}
before kernel NOTE segment in generic NOTES.
Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
---
include/asm-generic/vmlinux.lds.h | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 6b943fb8c5fd..6659a7c07c84 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -818,7 +818,14 @@
#define TRACEDATA
#endif
+/*
+ * Discard .note.gnu.property sections which are unused and have
+ * different alignment requirement from kernel note sections.
+ */
#define NOTES \
+ /DISCARD/ : { \
+ *(.note.gnu.property) \
+ } \
.notes : AT(ADDR(.notes) - LOAD_OFFSET) { \
__start_notes = .; \
KEEP(*(.note.*)) \
--
2.24.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] Discard .note.gnu.property sections in generic NOTES
2020-01-30 22:43 ` [PATCH] Discard .note.gnu.property sections in generic NOTES H.J. Lu
@ 2020-01-30 22:52 ` Kees Cook
0 siblings, 0 replies; 5+ messages in thread
From: Kees Cook @ 2020-01-30 22:52 UTC (permalink / raw)
To: H.J. Lu
Cc: linux-kernel, Andy Lutomirski, Thomas Gleixner, Thomas Lendacky,
Sami Tolvanen, Heiko Carstens, Ingo Molnar, Borislav Petkov,
H . Peter Anvin, x86, Yu-cheng Yu
On Thu, Jan 30, 2020 at 02:43:37PM -0800, H.J. Lu wrote:
> With the command-line option, -mx86-used-note=yes, the x86 assembler
> in binutils 2.32 and above generates a program property note in a note
> section, .note.gnu.property, to encode used x86 ISAs and features. But
> kernel linker script only contains a single NOTE segment:
>
> PHDRS {
> text PT_LOAD FLAGS(5);
> data PT_LOAD FLAGS(6);
> percpu PT_LOAD FLAGS(6);
> init PT_LOAD FLAGS(7);
> note PT_NOTE FLAGS(0);
> }
> SECTIONS
> {
> ...
> .notes : AT(ADDR(.notes) - 0xffffffff80000000) { __start_notes = .; KEEP(*(.not
> e.*)) __stop_notes = .; } :text :note
> ...
> }
>
> The NOTE segment generated by kernel linker script is aligned to 4 bytes.
> But .note.gnu.property section must be aligned to 8 bytes on x86-64 and
> we get
>
> [hjl@gnu-skx-1 linux]$ readelf -n vmlinux
>
> Displaying notes found in: .notes
> Owner Data size Description
> Xen 0x00000006 Unknown note type: (0x00000006)
> description data: 6c 69 6e 75 78 00
> Xen 0x00000004 Unknown note type: (0x00000007)
> description data: 32 2e 36 00
> xen-3.0 0x00000005 Unknown note type: (0x006e6558)
> description data: 08 00 00 00 03
> readelf: Warning: note with invalid namesz and/or descsz found at offset 0x50
> readelf: Warning: type: 0xffffffff, namesize: 0x006e6558, descsize:
> 0x80000000, alignment: 8
> [hjl@gnu-skx-1 linux]$
>
> Since note.gnu.property section in kernel image is never used, this patch
> discards .note.gnu.property sections in kernel linker script by adding
>
> /DISCARD/ : {
> *(.note.gnu.property)
> }
>
> before kernel NOTE segment in generic NOTES.
>
> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Thanks!
Reviewed-by: Kees Cook <keescook@chromium.org>
-Kees
> ---
> include/asm-generic/vmlinux.lds.h | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 6b943fb8c5fd..6659a7c07c84 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -818,7 +818,14 @@
> #define TRACEDATA
> #endif
>
> +/*
> + * Discard .note.gnu.property sections which are unused and have
> + * different alignment requirement from kernel note sections.
> + */
> #define NOTES \
> + /DISCARD/ : { \
> + *(.note.gnu.property) \
> + } \
> .notes : AT(ADDR(.notes) - LOAD_OFFSET) { \
> __start_notes = .; \
> KEEP(*(.note.*)) \
> --
> 2.24.1
>
--
Kees Cook
^ permalink raw reply [flat|nested] 5+ messages in thread
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2020-01-30 22:43 [PATCH] Add RUNTIME_DISCARD_EXIT to generic DISCARDS H.J. Lu
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2020-01-30 22:52 ` Kees Cook
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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
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2020-01-30 19:58 ` Kees Cook
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2020-01-30 20:47 ` [PATCH] Add RUNTIME_DISCARD_EXIT to generic DISCARDS H.J. Lu
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