linux-kernel - [PATCH] x86/retpoline: change RETPOLINE into CONFIG

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Date:   Mon, 31 Dec 2018 15:42:53 -0800
From:   Nadav Amit <namit@...are.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Nadav Amit <namit@...are.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Zhenzhong Duan <zhenzhong.duan@...cle.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Andy Lutomirski <luto@...nel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        <stable@...r.kernel.org>
Subject: [PATCH] x86/retpoline: change RETPOLINE into CONFIG_RETPOLINE

A recent enhancement intentionally fails the kernel build if the
compiler does not support retpolines and CONFIG_RETPOLINE is set.

However, the patch that introduced it did not change RETPOLINE macro
references into CONFIG_RETPOLINE ones. As a result, indirect branches
that are used by init functions are not kept (i.e., they use
retpolines), and modules that do not use retpolines are marked as
retpoline-safe.

Fix it be changing RETPOLINE into CONFIG_RETPOLINE.

Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Zhenzhong Duan <zhenzhong.duan@...cle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: David Woodhouse <dwmw@...zon.co.uk>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc: stable@...r.kernel.org
Signed-off-by: Nadav Amit <namit@...are.com>
---
 arch/x86/kernel/cpu/bugs.c   | 2 +-
 include/linux/compiler-gcc.h | 2 +-
 include/linux/module.h       | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 8654b8b0c848..1de0f4170178 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -215,7 +215,7 @@ static enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init =
 static enum spectre_v2_user_mitigation spectre_v2_user __ro_after_init =
 	SPECTRE_V2_USER_NONE;
 
-#ifdef RETPOLINE
+#ifdef CONFIG_RETPOLINE
 static bool spectre_v2_bad_module;
 
 bool retpoline_module_ok(bool has_retpoline)
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 2010493e1040..977ddf2774f9 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -68,7 +68,7 @@
  */
 #define uninitialized_var(x) x = x
 
-#ifdef RETPOLINE
+#ifdef CONFIG_RETPOLINE
 #define __noretpoline __attribute__((__indirect_branch__("keep")))
 #endif
 
diff --git a/include/linux/module.h b/include/linux/module.h
index fce6b4335e36..0c575f51fe57 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -817,7 +817,7 @@ static inline void module_bug_finalize(const Elf_Ehdr *hdr,
 static inline void module_bug_cleanup(struct module *mod) {}
 #endif	/* CONFIG_GENERIC_BUG */
 
-#ifdef RETPOLINE
+#ifdef CONFIG_RETPOLINE
 extern bool retpoline_module_ok(bool has_retpoline);
 #else
 static inline bool retpoline_module_ok(bool has_retpoline)
-- 
2.17.1