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

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Date:   Wed, 2 Jan 2019 17:23:19 +0000
From:   Nadav Amit <namit@...are.com>
To:     Zhenzhong Duan <zhenzhong.duan@...cle.com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <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" <stable@...r.kernel.org>
Subject: Re: [PATCH] x86/retpoline: change RETPOLINE into CONFIG_RETPOLINE

> On Jan 1, 2019, at 5:17 PM, Zhenzhong Duan <zhenzhong.duan@...cle.com> wrote:
> 
> 
> 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

Indeed. I missed this patch since it wasn’t on tip (and Google wasn’t
helpful either).

I wonder why it has still not been applied.