[tip: x86/build] x86/vdso: Discard .note.gnu.property sections in vDSO

[tip-bot2 for H.J. Lu]

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

Commit-ID:     4caffe6a28d3157c11cae923a40456a053c520ea
Gitweb:        https://git.kernel.org/tip/4caffe6a28d3157c11cae923a40456a053c520ea
Author:        H.J. Lu <hjl.tools@xxxxxxxxx>
AuthorDate:    Thu, 26 Mar 2020 10:43:14 -07:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Fri, 27 Mar 2020 15:53:05 +01:00

x86/vdso: Discard .note.gnu.property sections in vDSO

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) FILEHDR PHDRS; /* PF_R|PF_X */
   dynamic PT_DYNAMIC FLAGS(4); /* PF_R */
   note PT_NOTE FLAGS(4); /* PF_R */
   eh_frame_hdr 0x6474e550;
  }

The NOTE segment generated by the vDSO linker script is aligned to 4 bytes.
But the .note.gnu.property section must be aligned to 8 bytes on x86-64:

  [hjl@gnu-skx-1 vdso]$ readelf -n vdso64.so

  Displaying notes found in: .note
    Owner                Data size 	Description
    Linux                0x00000004	Unknown note type: (0x00000000)
     description data: 06 00 00 00
  readelf: Warning: note with invalid namesz and/or descsz found at offset 0x20
  readelf: Warning:  type: 0x78, namesize: 0x00000100, descsize: 0x756e694c, alignment: 8

Since the note.gnu.property section in the vDSO is not checked by the
dynamic linker, discard the .note.gnu.property sections in the vDSO.

 [ bp: Massage. ]

Signed-off-by: H.J. Lu <hjl.tools@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200326174314.254662-1-hjl.tools@xxxxxxxxx
---
 arch/x86/entry/vdso/vdso-layout.lds.S | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/entry/vdso/vdso-layout.lds.S b/arch/x86/entry/vdso/vdso-layout.lds.S
index ea7e015..4d15293 100644
--- a/arch/x86/entry/vdso/vdso-layout.lds.S
+++ b/arch/x86/entry/vdso/vdso-layout.lds.S
@@ -57,6 +57,13 @@ SECTIONS
 		*(.gnu.linkonce.b.*)
 	}						:text
 
+	/*
+	 * Discard .note.gnu.property sections which are unused and have
+	 * different alignment requirement from vDSO note sections.
+	 */
+	/DISCARD/ : {
+		*(.note.gnu.property)
+	}
 	.note		: { *(.note.*) }		:text	:note
 
 	.eh_frame_hdr	: { *(.eh_frame_hdr) }		:text	:eh_frame_hdr