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@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200326174314.254662-1-hjl.tools@gmail.com

diff --git a/arch/x86/entry/vdso/vdso-layout.lds.S b/arch/x86/entry/vdso/vdso-layout.lds.S
index ea7e015..4d15293 100644 (file)
--- 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