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

[Zhenzhong Duan]

On 2018/10/30 16:36, Peter Zijlstra wrote:
> On Mon, Oct 29, 2018 at 11:55:06PM -0700, Zhenzhong Duan wrote:
> > Since CONFIG_RETPOLINE hard depends on compiler support now, so
> > replacing indirect-jump check with the range check is safe in that case.
>
> Can we put kprobes on module init text before we run alternatives on it?

Forgive me I doesn't understand your question. Do you mean this patch 
impact kprobes on module init text?

> > @@ -240,20 +242,16 @@ static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
> >   
> >   static int insn_is_indirect_jump(struct insn *insn)
> >   {
> > -	int ret = __insn_is_indirect_jump(insn);
> > +	int ret;
> >   
> >   #ifdef CONFIG_RETPOLINE
> > -	/*
> > -	 * Jump to x86_indirect_thunk_* is treated as an indirect jump.
> > -	 * Note that even with CONFIG_RETPOLINE=y, the kernel compiled with
> > -	 * older gcc may use indirect jump. So we add this check instead of
> > -	 * replace indirect-jump check.
> > -	 */
> > -	if (!ret)
> > +	/* Jump to x86_indirect_thunk_* is treated as an indirect jump. */
> >   		ret = insn_jump_into_range(insn,
> >   				(unsigned long)__indirect_thunk_start,
> >   				(unsigned long)__indirect_thunk_end -
> >   				(unsigned long)__indirect_thunk_start);
> > +#else
> > +		ret = __insn_is_indirect_jump(insn);
> >   #endif
> >   	return ret;
> >   }
>
> The resulting code is indented wrong.

Oh, yes. Thanks for point out.

Zhenzhong