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

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Date:   Thu, 3 Jan 2019 10:07:18 +0800
From:   Zhenzhong Duan <zhenzhong.duan@...cle.com>
To:     Nadav Amit <namit@...are.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 2019/1/3 1:23, Nadav Amit wrote:
>> 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.


See https://lkml.org/lkml/2018/12/21/244

-- 
Thanks
Zhenzhong