linux-kernel - [PATCH 4/5] x86/alternatives: Add an auxilary section

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Date:	Thu, 21 Jan 2016 19:34:45 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Brian Gerst <brgerst@...il.com>, X86 ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 4/5] x86/alternatives: Add an auxilary section

From: Borislav Petkov <bp@...e.de>

Add .altinstr_aux for additional instructions which will be used before
and/or during patching. All stuff which needs more sophisticated
patching should go there. See next patch.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/vmlinux.lds.S | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 74e4bf11f562..1335ff4854ae 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -244,6 +244,15 @@ SECTIONS
 	 */
 	.altinstr_replacement : AT(ADDR(.altinstr_replacement) - LOAD_OFFSET) {
 		*(.altinstr_replacement)
+		/*
+		 * Section for code used exclusively before alternatives are
+		 * run. All references to such code must be patched out by
+		 * alternatives, normally by using a patch with
+		 * X86_FEATURE_ALWAYS.
+		 *
+		 * See static_cpu_has() for an example.
+		 */
+		*(.altinstr_aux)
 	}
 
 	/*
-- 
2.3.5