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

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Date:   Wed, 2 Jan 2019 09:17:01 +0800
From:   Zhenzhong Duan <zhenzhong.duan@...cle.com>
To:     Nadav Amit <namit@...are.com>, Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Andy Lutomirski <luto@...nel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] x86/retpoline: change RETPOLINE into CONFIG_RETPOLINE


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@...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)

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