Re: [PATCH] objtool,x86: Verify poke_int3_handler() is self contained

peterz
2020-07-27T12:50:28Z

On Mon, Jul 27, 2020 at 01:21:44PM +0200, Ingo Molnar wrote:
>
> * peterz@infradead.org <peterz@infradead.org> wrote:
>
> >
> > Abuse the SMAP rules to ensure poke_int3_handler() doesn't call out to
> > anything.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> > tools/objtool/check.c | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > --- a/tools/objtool/check.c
> > +++ b/tools/objtool/check.c
> > @@ -551,6 +551,14 @@ static const char *uaccess_safe_builtin[
> > "__memcpy_mcsafe",
> > "mcsafe_handle_tail",
> > "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
> > + /*
> > + * Abuse alert!
> > + *
> > + * poke_int3_handler() is not in fact related to uaccess at all, we
> > + * abuse the uaccess rules to ensure poke_int3_handler() is self
> > + * contained and doesn't CALL out to other code.
> > + */
> > + "poke_int3_handler",
>
> So ->uaccess_safe makes sure that we don't CALL into non-uaccess-safe
> functions, but it still allows CALLs into *other* uaccess-safe
> functions, right?
>
> So unless I missed something in the logic, the comment should say
> something like "doesn't CALL out to other non-uaccess safe code" or
> so? Which is, arguably, like 99% of all functions - but still, a whole
> bunch are allowed, such as low level instrumentation and other utility
> functions.

Right, so poke_int3_handler() is also noinstr and by that isn't allowed
to call out into !noinstr code. The intersection should be small.

But yeah, perhaps this is a bad idea and I should add another annotation
for this,.. dunno.