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* [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; 6+ 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] 6+ messages in thread
* [PATCH] Discard .note.gnu.property sections in generic NOTES
@ 2020-03-27 12:11 H.J. Lu
  0 siblings, 0 replies; 6+ messages in thread
From: H.J. Lu @ 2020-03-27 12:11 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, Arnd Bergmann, linux-arch, Yu-cheng Yu

**"this patch depends on patch Add RUNTIME_DISCARD_EXIT to generic DISCARDS"**

With the command-line option, -mx86-used-note=yes, which can also be
enabled at binutils build time with

  --enable-x86-used-note  generate GNU x86 used ISA and feature properties

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, discard
.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>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 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.*))					\
-- 
2.25.1


^ permalink raw reply related	[flat|nested] 6+ messages in thread
* [PATCH 0/2] x86: Discard .note.gnu.property sections
@ 2020-01-24 18:18 H.J. Lu
  2020-01-24 18:18 ` [PATCH 2/2] x86: Discard .note.gnu.property sections in vmlinux H.J. Lu
  0 siblings, 1 reply; 6+ messages in thread
From: H.J. Lu @ 2020-01-24 18:18 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
x86 kernel vmlinux and vDSO linker scripts only contain a signle NOTE
segment which may not be incompatible with note.gnu.property sections.
Since note.gnu.property section from kernel are unused, they should be
discarded by adding

/DISCARD/ : {
 *(.note.gnu.property)
}

before .notes sections.

H.J. Lu (2):
  x86: Discard .note.gnu.property sections in vDSO
  x86: Discard .note.gnu.property sections in vmlinux

 arch/x86/entry/vdso/vdso-layout.lds.S |  4 ++++
 arch/x86/kernel/vmlinux.lds.S         | 11 +++++++++++
 2 files changed, 15 insertions(+)

-- 
2.24.1


^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2020-03-27 12:11 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2020-01-30 22:43 [PATCH] Add RUNTIME_DISCARD_EXIT to generic DISCARDS H.J. Lu
2020-01-30 22:43 ` [PATCH] Discard .note.gnu.property sections in generic NOTES H.J. Lu
2020-01-30 22:52   ` Kees Cook
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2020-03-27 12:11 H.J. Lu
2020-01-24 18:18 [PATCH 0/2] x86: Discard .note.gnu.property sections H.J. Lu
2020-01-24 18:18 ` [PATCH 2/2] x86: Discard .note.gnu.property sections in vmlinux H.J. Lu
2020-01-27 23:34   ` Kees Cook
2020-01-30 17:51     ` H.J. Lu
2020-01-30 19:51       ` Kees Cook
2020-01-30 20:04         ` H.J. Lu
2020-01-30 20:08           ` Kees Cook
2020-01-30 20:20             ` H.J. Lu
2020-01-30 20:48               ` [PATCH] Discard .note.gnu.property sections in generic NOTES H.J. Lu
2020-01-30 22:09                 ` Kees Cook

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