Re: [PATCH V6 04/11] compiler_types.h: Add __noinstr_section() for noinstr

[Mark Rutland]

On Sat, Oct 08, 2022 at 09:54:39AM +0800, Guo Ren wrote:
> On Mon, Oct 3, 2022 at 7:39 PM Mark Rutland <mark.rutland@xxxxxxx> wrote:
> >
> > On Sat, Oct 01, 2022 at 09:24:44PM -0400, guoren@xxxxxxxxxx wrote:
> > > From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
> > >
> > > And it will be extended for C entry code.
> > >
> > > Cc: Borislav Petkov <bp@xxxxxxxxx>
> > > Reviewed-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
> > > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > > Suggested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> > > Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > > Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
> > > ---
> > >  include/linux/compiler_types.h | 8 +++++---
> > >  1 file changed, 5 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> > > index 4f2a819fd60a..e9ce11ea4d8b 100644
> > > --- a/include/linux/compiler_types.h
> > > +++ b/include/linux/compiler_types.h
> > > @@ -227,9 +227,11 @@ struct ftrace_likely_data {
> > >  #endif
> > >
> > >  /* Section for code which can't be instrumented at all */
> > > -#define noinstr                                                              \
> > > -     noinline notrace __attribute((__section__(".noinstr.text")))    \
> > > -     __no_kcsan __no_sanitize_address __no_profile __no_sanitize_coverage
> > > +#define __noinstr_section(section)                           \
> > > +     noinline notrace __section(section) __no_profile        \
> > > +     __no_kcsan __no_sanitize_address __no_sanitize_coverage
> > > +
> > > +#define noinstr __noinstr_section(".noinstr.text")
> >
> > One thing proably worth noting here is that while KPROBES will avoid
> > instrumenting `.noinstr.text`, that won't happen automatically for other
> > __noinstr_section() sections, and that will need to be inhibited through other
> > means (e.g. the kprobes blacklist, explicit NOKPROBE_SYMBOL() annotation, or
> > otherwise).
> 
> In riscv, "we select HAVE_KPROBES if !XIP_KERNEL", so don't worry
> about that. I don't think we could enable kprobe for XIP_KERNEL in the
> future.

Sure; but someone else might use __noinstr_section() elsewhere where this could
matter, and I was suggesting that we could add a comment as above.

Thanks,
Mark.