Re: [PATCH 3/3] kprobes/x86: Simplify indirect-jump check in retpoline

[Zhenzhong Duan]

On 2018/11/1 16:56, Peter Zijlstra wrote:
> On Thu, Nov 01, 2018 at 10:02:14AM +0800, Zhenzhong Duan wrote:
> > > Hmm, what about the case where we have RETPOLINE runtime disabled? Then
> > > the CALL_NOSPEC alternative patches in an indirect call again, and the
> > > retpolines are gone.
> >
> > Is RETPOLINE runtime toggle supported in upstream? I don't see such code.
>
> arch/x86/kernel/cpu/bugs.c look for the "nospectre_v2" and related
> options. That will avoid X86_FEATURE_RETPOLINE from being set, and thus
> the JMP_NOSPEC and CALL_NOSPEC alternatives will not patch out the
> indirect jump / call.
Yes, in this case there are also indirect branches. I'll drop 3rd patch 
in v2.

Thanks
Zhenzhong