linux-kernel - [PATCH 1/2] x86/retpoline: No retpolines for built-in _

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Message-Id: <1517484441-1420-2-git-send-email-dwmw@amazon.co.uk>
Date:   Thu,  1 Feb 2018 11:27:20 +0000
From:   David Woodhouse <dwmw@...zon.co.uk>
To:     tglx@...utronix.de, karahmed@...zon.de, x86@...nel.org,
        linux-kernel@...r.kernel.org, bp@...en8.de, peterz@...radead.org
Subject: [PATCH 1/2] x86/retpoline: No retpolines for built-in __init functions

There's no point in building init code with retpolines, since it runs before
any potentially hostile userspace does. And before the retpoline is actually
ALTERNATIVEd into place, for much of it.

Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
---
 include/linux/init.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/init.h b/include/linux/init.h
index ea1b311..506a981 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -5,6 +5,13 @@
 #include <linux/compiler.h>
 #include <linux/types.h>
 
+/* Built-in __init functions needn't be compiled with retpoline */
+#if defined(RETPOLINE) && !defined(MODULE)
+#define __noretpoline __attribute__((indirect_branch("keep")))
+#else
+#define __noretpoline
+#endif
+
 /* These macros are used to mark some functions or 
  * initialized data (doesn't apply to uninitialized data)
  * as `initialization' functions. The kernel can take this
@@ -40,7 +47,7 @@
 
 /* These are for everybody (although not all archs will actually
    discard it in modules) */
-#define __init		__section(.init.text) __cold  __latent_entropy
+#define __init		__section(.init.text) __cold  __latent_entropy __noretpoline
 #define __initdata	__section(.init.data)
 #define __initconst	__section(.init.rodata)
 #define __exitdata	__section(.exit.data)
-- 
2.7.4