linux-kernel - [tip: x86/build] vmlinux.lds: Discard .note.gnu.property sections in generic NOTES

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Message-ID: <158533004496.28353.6659866597938496589.tip-bot2@tip-bot2>
Date:   Fri, 27 Mar 2020 17:27:24 -0000
From:   "tip-bot2 for H.J. Lu" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "H.J. Lu" <hjl.tools@...il.com>, Borislav Petkov <bp@...e.de>,
        Kees Cook <keescook@...omium.org>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: x86/build] vmlinux.lds: Discard .note.gnu.property sections in
 generic NOTES

The following commit has been merged into the x86/build branch of tip:

Commit-ID:     72cb2113c1bbd82cf3e062a39ff2753ee9d3fae7
Gitweb:        https://git.kernel.org/tip/72cb2113c1bbd82cf3e062a39ff2753ee9d3fae7
Author:        H.J. Lu <hjl.tools@...il.com>
AuthorDate:    Fri, 27 Mar 2020 05:11:01 -07:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Fri, 27 Mar 2020 15:58:13 +01:00

vmlinux.lds: Discard .note.gnu.property sections in generic NOTES

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 the 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 the kernel linker script is aligned to
4 bytes. But .note.gnu.property section must be aligned to 8 bytes on
x86-64, resulting in:

  [hjl@...-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

Since note.gnu.property section in the kernel image is never used,
discard it.

 [ bp: Massage. ]

Signed-off-by: H.J. Lu <hjl.tools@...il.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Kees Cook <keescook@...omium.org>
Link: https://lkml.kernel.org/r/20200327121101.948934-1-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 2444336..998eafa 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.*))					\