bpf: Add spis_*() helpers for 4-byte stack slot bitmasks

Add helper functions for manipulating u64[2] bitmasks that represent
4-byte stack slot liveness. The 512-byte BPF stack is divided into
128 4-byte slots, requiring 128 bits (two u64s) to track.

These will be used by the static stack liveness analysis in the
next commit.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260410-patch-set-v4-3-5d4eecb343db@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 67 insertions, 0 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index cec6054d6333..f34e7a074a20 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -224,6 +224,73 @@ enum bpf_stack_slot_type {
 
 #define BPF_REG_SIZE 8	/* size of eBPF register in bytes */
 
+/* 4-byte stack slot granularity for liveness analysis */
+#define BPF_HALF_REG_SIZE	4
+#define STACK_SLOTS		(MAX_BPF_STACK / BPF_HALF_REG_SIZE)	/* 128 */
+
+typedef struct {
+	u64 v[2];
+} spis_t;
+
+#define SPIS_ZERO	((spis_t){})
+#define SPIS_ALL	((spis_t){{ U64_MAX, U64_MAX }})
+
+static inline bool spis_is_zero(spis_t s)
+{
+	return s.v[0] == 0 && s.v[1] == 0;
+}
+
+static inline bool spis_equal(spis_t a, spis_t b)
+{
+	return a.v[0] == b.v[0] && a.v[1] == b.v[1];
+}
+
+static inline spis_t spis_or(spis_t a, spis_t b)
+{
+	return (spis_t){{ a.v[0] | b.v[0], a.v[1] | b.v[1] }};
+}
+
+static inline spis_t spis_and(spis_t a, spis_t b)
+{
+	return (spis_t){{ a.v[0] & b.v[0], a.v[1] & b.v[1] }};
+}
+
+static inline spis_t spis_xor(spis_t a, spis_t b)
+{
+	return (spis_t){{ a.v[0] ^ b.v[0], a.v[1] ^ b.v[1] }};
+}
+
+static inline spis_t spis_not(spis_t s)
+{
+	return (spis_t){{ ~s.v[0], ~s.v[1] }};
+}
+
+static inline bool spis_test_bit(spis_t s, u32 slot)
+{
+	return s.v[slot / 64] & BIT_ULL(slot % 64);
+}
+
+static inline void spis_or_range(spis_t *mask, u32 lo, u32 hi)
+{
+	u32 w;
+
+	for (w = lo; w <= hi && w < STACK_SLOTS; w++)
+		mask->v[w / 64] |= BIT_ULL(w % 64);
+}
+
+static inline spis_t spis_one_bit(u32 slot)
+{
+	if (slot < 64)
+		return (spis_t){{ BIT_ULL(slot), 0 }};
+	else
+		return (spis_t){{ 0, BIT_ULL(slot - 64) }};
+}
+
+static inline spis_t spis_single_slot(u32 spi)
+{
+	return spis_or(spis_one_bit(spi * 2), spis_one_bit(spi * 2 + 1));
+}
+
 #define BPF_REGMASK_ARGS ((1 << BPF_REG_1) | (1 << BPF_REG_2) | \
 			  (1 << BPF_REG_3) | (1 << BPF_REG_4) | \
 			  (1 << BPF_REG_5))