Re: [PATCH v5 bpf-next 04/23] bpf: derive smin32/smax32 from umin32/umax32 bounds

Eduard Zingerman
2023-10-31T15:37:28Z

On Fri, 2023-10-27 at 11:13 -0700, Andrii Nakryiko wrote:
> > All the logic that applies to u64 vs s64, equally applies for u32 vs s32
> > relationships (just taken in a smaller 32-bit numeric space). So do the
> > same deduction of smin32/smax32 from umin32/umax32, if we can.
> >
> > Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
> > Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

> > ---
> > kernel/bpf/verifier.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index bf4193706744..0f66e9092c38 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -2324,6 +2324,13 @@ static void __update_reg_bounds(struct bpf_reg_state *reg)
> > /* Uses signed min/max values to inform unsigned, and vice-versa */
> > static void __reg32_deduce_bounds(struct bpf_reg_state *reg)
> > {
> > + /* if u32 range forms a valid s32 range (due to matching sign bit),
> > + * try to learn from that
> > + */
> > + if ((s32)reg->u32_min_value <= (s32)reg->u32_max_value) {
> > + reg->s32_min_value = max_t(s32, reg->s32_min_value, reg->u32_min_value);
> > + reg->s32_max_value = min_t(s32, reg->s32_max_value, reg->u32_max_value);
> > + }
> > /* Learn sign from signed bounds.
> > * If we cannot cross the sign boundary, then signed and unsigned bounds
> > * are the same, so combine. This works even in the negative case, e.g.