Re: [PATCH] x86/retpoline: change RETPOLINE into CONFIG_RETPOLINE

Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx> · Wed, 2 Jan 2019 09:17:01 +0800

On 2019/1/1 7:42, Nadav Amit wrote:
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@xxxxxxxxxxxxx>
Cc: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
---
  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)

Someone sent a similar patch last month, see below link,  you missed the 
change in scripts/mod/modpost.c

https://lkml.org/lkml/2018/12/10/540

But you patch description is more clear.

--
Thanks
Zhenzhong







