Patch "x86/retpoline: Support retpoline builds with Clang" has been added to the 4.9-stable tree

Patch "x86/retpoline: Support retpoline builds with Clang" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    x86/retpoline: Support retpoline builds with Clang

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-retpoline-support-retpoline-builds-with-clang.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 87358710c1fb4f1bf96bbe2349975ff9953fc9b2 Mon Sep 17 00:00:00 2001
From: David Woodhouse <dwmw@amazon.co.uk>
Date: Mon, 19 Feb 2018 10:50:57 +0000
Subject: x86/retpoline: Support retpoline builds with Clang

From: David Woodhouse <dwmw@amazon.co.uk>

commit 87358710c1fb4f1bf96bbe2349975ff9953fc9b2 upstream.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: arjan.van.de.ven@intel.com
Cc: bp@alien8.de
Cc: dave.hansen@intel.com
Cc: jmattson@google.com
Cc: karahmed@amazon.de
Cc: kvm@vger.kernel.org
Cc: pbonzini@redhat.com
Cc: rkrcmar@redhat.com
Link: http://lkml.kernel.org/r/1519037457-7643-5-git-send-email-dwmw@amazon.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/Makefile              |    5 ++++-
 include/linux/compiler-clang.h |    5 +++++
 include/linux/compiler-gcc.h   |    4 ++++
 include/linux/init.h           |    8 ++++----
 4 files changed, 17 insertions(+), 5 deletions(-)

--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -184,7 +184,10 @@ KBUILD_AFLAGS += $(mflags-y)
 
 # Avoid indirect branches in kernel to deal with Spectre
 ifdef CONFIG_RETPOLINE
-    RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register)
+    RETPOLINE_CFLAGS_GCC := -mindirect-branch=thunk-extern -mindirect-branch-register
+    RETPOLINE_CFLAGS_CLANG := -mretpoline-external-thunk
+
+    RETPOLINE_CFLAGS += $(call cc-option,$(RETPOLINE_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_CFLAGS_CLANG)))
     ifneq ($(RETPOLINE_CFLAGS),)
         KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -DRETPOLINE
     endif
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -15,3 +15,8 @@
  * with any version that can compile the kernel
  */
 #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
+
+/* Clang doesn't have a way to turn it off per-function, yet. */
+#ifdef __noretpoline
+#undef __noretpoline
+#endif
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -88,6 +88,10 @@
 #define __weak		__attribute__((weak))
 #define __alias(symbol)	__attribute__((alias(#symbol)))
 
+#ifdef RETPOLINE
+#define __noretpoline __attribute__((indirect_branch("keep")))
+#endif
+
 /*
  * it doesn't make sense on ARM (currently the only user of __naked)
  * to trace naked functions because then mcount is called without
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -5,10 +5,10 @@
 #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")))
+#if defined(__noretpoline) && !defined(MODULE)
+#define __noinitretpoline __noretpoline
 #else
-#define __noretpoline
+#define __noinitretpoline
 #endif
 
 /* These macros are used to mark some functions or 
@@ -46,7 +46,7 @@
 
 /* These are for everybody (although not all archs will actually
    discard it in modules) */
-#define __init		__section(.init.text) __cold notrace __latent_entropy __noretpoline
+#define __init		__section(.init.text) __cold notrace __latent_entropy __noinitretpoline
 #define __initdata	__section(.init.data)
 #define __initconst	__section(.init.rodata)
 #define __exitdata	__section(.exit.data)


Patches currently in stable-queue which might be from dwmw@amazon.co.uk are

queue-4.9/x86-retpoline-support-retpoline-builds-with-clang.patch
queue-4.9/revert-x86-retpoline-simplify-vmexit_fill_rsb.patch
queue-4.9/x86-speculation-use-ibrs-if-available-before-calling-into-firmware.patch
queue-4.9/x86-speculation-objtool-annotate-indirect-calls-jumps-for-objtool.patch