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

Andrii Nakryiko
2023-10-27T18:16:55Z

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>
---
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.
--
2.34.1