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Subject[PATCH] x86: Discard .note.gnu.property sections in vDSO
Date
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 vDSO 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 vDSO 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 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
[hjl@gnu-skx-1 vdso]$

Since note.gnu.property section in vDSO is not checked by dynamic linker,
this patch discards .note.gnu.property sections in vDSO by adding

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

before .notes sections in vDSO linker script.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
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 ea7e0155c604..4d152933547d 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
--
2.25.1
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