[PATCH 2/2] x86: Discard .note.gnu.property sections in vmlinux

From: "H.J. Lu" <hjl.tools@gmail.com>
To: linux-kernel@vger.kernel.org
Cc: Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Kees Cook <keescook@chromium.org>,
	Thomas Lendacky <Thomas.Lendacky@amd.com>,
	Sami Tolvanen <samitolvanen@google.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H . Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, Yu-cheng Yu <yu-cheng.yu@intel.com>
Subject: [PATCH 2/2] x86: Discard .note.gnu.property sections in vmlinux
Date: Fri, 24 Jan 2020 10:18:19 -0800	[thread overview]
Message-ID: <20200124181819.4840-3-hjl.tools@gmail.com> (raw)
In-Reply-To: <20200124181819.4840-1-hjl.tools@gmail.com>

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 linker script only contains a signle 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
...
}

which may not be incompatible with note.gnu.property sections.  Since
note.gnu.property section in kernel image is unused, this patch discards
.note.gnu.property sections in kernel linker script by adding

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

before .notes sections.  Since .exit.text and .exit.data sections are
discarded at runtime, it undefines EXIT_TEXT and EXIT_DATA to exclude
.exit.text and .exit.data sections from default discarded sections.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
 arch/x86/kernel/vmlinux.lds.S | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 3a1a819da137..6c6cc26b0177 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -150,6 +150,11 @@ SECTIONS
 	_etext = .;
 	. = ALIGN(PAGE_SIZE);
 
+	/* .note.gnu.property sections should be discarded */
+	/DISCARD/ : {
+		*(.note.gnu.property)
+	}
+
 	X86_ALIGN_RODATA_BEGIN
 	RO_DATA(PAGE_SIZE)
 	X86_ALIGN_RODATA_END
@@ -413,6 +418,12 @@ SECTIONS
 	STABS_DEBUG
 	DWARF_DEBUG
 
+	/* Sections to be discarded.  EXIT_TEXT and EXIT_DATA discard at runtime.
+	 * not link time.  */
+#undef EXIT_TEXT
+#define EXIT_TEXT
+#undef EXIT_DATA
+#define EXIT_DATA
 	DISCARDS
 	/DISCARD/ : {
 		*(.eh_frame)
-- 
2.24.1

