linux-kernel - [PATCH] x86: Discard .note.gnu.property sections in vDSO

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Message-Id: <20200326174314.254662-1-hjl.tools@gmail.com>
Date:   Thu, 26 Mar 2020 10:43:14 -0700
From:   "H.J. Lu" <hjl.tools@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [PATCH] x86: Discard .note.gnu.property sections in vDSO

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@...-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@...-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@...il.com>
Reviewed-by: Kees Cook <keescook@...omium.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