Add handling of a bunch of possible cases which allows deducing extra
information about subregister bounds, both u32 and s32, from full register
u64/s64 bounds.
Also add smin32/smax32 bounds derivation from corresponding umin32/umax32
bounds, similar to what we did with smin/smax from umin/umax derivation in
previous patch.
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
kernel/bpf/verifier.c | 52 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 52 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ee9837463092..d5fd41fb3031 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2117,6 +2117,58 @@ 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 upper 32 bits of u64/s64 range don't change,
+ * we can use lower 32 bits to improve our u32/s32 boundaries
+ */
+ if ((reg->umin_value >> 32) == (reg->umax_value >> 32)) {
+ /* u64 to u32 casting preserves validity of low 32 bits as
+ * a range, if upper 32 bits are the same
+ */
+ reg->u32_min_value = max_t(u32, reg->u32_min_value, (u32)reg->umin_value);
+ reg->u32_max_value = min_t(u32, reg->u32_max_value, (u32)reg->umax_value);
+
+ if ((s32)reg->umin_value <= (s32)reg->umax_value) {
+ reg->s32_min_value = max_t(s32, reg->s32_min_value, (s32)reg->umin_value);
+ reg->s32_max_value = min_t(s32, reg->s32_max_value, (s32)reg->umax_value);
+ }
+ }
+ if ((reg->smin_value >> 32) == (reg->smax_value >> 32)) {
+ /* low 32 bits should form a proper u32 range */
+ if ((u32)reg->smin_value <= (u32)reg->smax_value) {
+ reg->u32_min_value = max_t(u32, reg->u32_min_value, (u32)reg->smin_value);
+ reg->u32_max_value = min_t(u32, reg->u32_max_value, (u32)reg->smax_value);
+ }
+ /* low 32 bits should form a proper s32 range */
+ if ((s32)reg->smin_value <= (s32)reg->smax_value) {
+ reg->s32_min_value = max_t(s32, reg->s32_min_value, (s32)reg->smin_value);
+ reg->s32_max_value = min_t(s32, reg->s32_max_value, (s32)reg->smax_value);
+ }
+ }
+ /* Special case where upper bits form a small sequence of two
+ * sequential numbers (in 32-bit unsigned space, so 0xffffffff to
+ * 0x00000000 is also valid), while lower bits form a proper s32 range
+ * going from negative numbers to positive numbers.
+ * E.g.: [0xfffffff0ffffff00; 0xfffffff100000010]. Iterating
+ * over full 64-bit numbers range will form a proper [-16, 16]
+ * ([0xffffff00; 0x00000010]) range in its lower 32 bits.
+ */
+ if ((u32)(reg->umin_value >> 32) + 1 == (u32)(reg->umax_value >> 32) &&
+ (s32)reg->umin_value < 0 && (s32)reg->umax_value >= 0) {
+ reg->s32_min_value = max_t(s32, reg->s32_min_value, (s32)reg->umin_value);
+ reg->s32_max_value = min_t(s32, reg->s32_max_value, (s32)reg->umax_value);
+ }
+ if ((u32)(reg->smin_value >> 32) + 1 == (u32)(reg->smax_value >> 32) &&
+ (s32)reg->smin_value < 0 && (s32)reg->smax_value >= 0) {
+ reg->s32_min_value = max_t(s32, reg->s32_min_value, (s32)reg->smin_value);
+ reg->s32_max_value = min_t(s32, reg->s32_max_value, (s32)reg->smax_value);
+ }
+ /* 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
