On Wed, Nov 22, 2023 at 7:13 AM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote:
>
> On Tue, 2023-11-21 at 17:16 -0800, Andrii Nakryiko wrote:
> > BPF verifier expects callback subprogs to return values from specified
> > range (typically [0, 1]). This requires that r0 at exit is both precise
> > (because we rely on specific value range) and is marked as read
> > (otherwise state comparison will ignore such register as unimportant).
> >
> > Add a simple test that validates that all these conditions are enforced.
> >
> > Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> > ---
>
> Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
>
> [...]
>
> > +SEC("?raw_tp")
> > +__failure __log_level(2)
> > +__flag(BPF_F_TEST_STATE_FREQ)
>
> Nit: although it is redundant, but maybe also check precision log to
> check that r0 is indeed marked precise?
>
sure, I'll add another expected msg, no problem
> > +__msg("from 10 to 12: frame1: R0=scalar(umin=1001) R10=fp0 cb")
> > +__msg("At callback return the register R0 has unknown scalar value should have been in (0x0; 0x1)")
> > +__naked int callback_precise_return_fail(void)
>
> [...]
>
>
