x86/retpoline: Avoid retpolines for built-in __init functions

[ Upstream commit 66f793099a636862a71c59d4a6ba91387b155e0c ]

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@amazon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: karahmed@amazon.de
Cc: peterz@infradead.org
Cc: bp@alien8.de
Link: https://lkml.kernel.org/r/1517484441-1420-2-git-send-email-dwmw@amazon.co.uk
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>

diff --git a/include/linux/init.h b/include/linux/init.h
index 21b6d768edd7a4e0f1aee98ed9f437000fa1b996..5f4d931095ce903ec49c180159dd1f03c305f25f 100644 (file)
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -4,6 +4,13 @@
 #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
@@ -39,7 +46,7 @@
 
 /* These are for everybody (although not all archs will actually
    discard it in modules) */
-#define __init         __section(.init.text) __cold notrace
+#define __init         __section(.init.text) __cold notrace __noretpoline
 #define __initdata     __section(.init.data)
 #define __initconst    __constsection(.init.rodata)
 #define __exitdata     __section(.exit.data)