lkml.org 
[lkml]   [2018]   [Oct]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 3/3] kprobes/x86: Simplify indirect-jump check in retpoline
On Wed, Oct 31, 2018 at 02:53:20PM +0100, Peter Zijlstra wrote:
> On Wed, Oct 31, 2018 at 02:01:20PM +0800, Zhenzhong Duan wrote:
> > 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?
>
> In that case we would still see the indirect paravirt calls for example,
> and we'd still need that cascade you took out.
>
> Now, I'm not at all sure we're able to use kprobes at those times, so it
> might be a non-issue.

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.

Does that not need the __insn_is_indirect_jump() thing?

> > > > @@ -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

\
 
 \ /
  Last update: 2018-10-31 15:01    [W:0.088 / U:0.780 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site