Re: [PATCH v4 05/15] tracepoint: Exclude tp_stub_func from CFI checking

Sami Tolvanen
2021-10-01T20:09:02Z

On Thu, Sep 30, 2021 at 11:51 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Thu, Sep 30, 2021 at 11:05 AM Sami Tolvanen <samitolvanen@google.com> wrote:
> >
> > If allocate_probes fails, func_remove replaces the old function
> > with a pointer to tp_stub_func, which is called using a mismatching
> > function pointer that will always trip indirect call checks with
> > CONFIG_CFI_CLANG. Use DEFINE_CFI_IMMEDATE_RETURN_STUB to define
> > tp_stub_func to allow it to pass CFI checking.
> >
> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> > ---
> > kernel/tracepoint.c | 5 +----
> > 1 file changed, 1 insertion(+), 4 deletions(-)
> >
> > diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> > index 64ea283f2f86..58acc7d86c3f 100644
> > --- a/kernel/tracepoint.c
> > +++ b/kernel/tracepoint.c
>
> looking at 4+5/15 together, I wonder if this TU should explicitly
> include linux/cfi.h?

Good point. Currently cfi.h is included in module.h, but including it
explicitly makes this less likely to break in future. I'll add an
explicit include in v5. Thanks for taking a look!

Sami