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

[Zhenzhong Duan]

On 2019/1/3 1:23, Nadav Amit wrote:
> > On Jan 1, 2019, at 5:17 PM, Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx> 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@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
> Indeed. I missed this patch since it wasnât on tip (and Google wasnât
> helpful either).
>
> I wonder why it has still not been applied.


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

--
Thanks
Zhenzhong