bpf: set 'changed' status if propagate_liveness() did any updates

Add an out parameter to `propagate_liveness()` to record whether any
new liveness bits were set during its execution.

Signed-off-by: Eduard Zingerman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: eddyz87

kernel/bpf/verifier.c

@@ -18856,12 +18856,15 @@ static int propagate_liveness_reg(struct bpf_verifier_env *env,
  */
 static int propagate_liveness(struct bpf_verifier_env *env,
 			      const struct bpf_verifier_state *vstate,
-			      struct bpf_verifier_state *vparent)
+			      struct bpf_verifier_state *vparent,
+			      bool *changed)
 {
 	struct bpf_reg_state *state_reg, *parent_reg;
 	struct bpf_func_state *state, *parent;
 	int i, frame, err = 0;
+	bool tmp;
 
+	changed = changed ?: &tmp;
 	if (vparent->curframe != vstate->curframe) {
 		WARN(1, "propagate_live: parent frame %d current frame %d\n",
 		     vparent->curframe, vstate->curframe);
@@ -18880,6 +18883,7 @@ static int propagate_liveness(struct bpf_verifier_env *env,
 						     &parent_reg[i]);
 			if (err < 0)
 				return err;
+			*changed |= err > 0;
 			if (err == REG_LIVE_READ64)
 				mark_insn_zext(env, &parent_reg[i]);
 		}
@@ -18891,6 +18895,7 @@ static int propagate_liveness(struct bpf_verifier_env *env,
 			state_reg = &state->stack[i].spilled_ptr;
 			err = propagate_liveness_reg(env, state_reg,
 						     parent_reg);
+			*changed |= err > 0;
 			if (err < 0)
 				return err;
 		}
@@ -19266,7 +19271,7 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 			 * they'll be immediately forgotten as we're pruning
 			 * this state and will pop a new one.
 			 */
-			err = propagate_liveness(env, &sl->state, cur);
+			err = propagate_liveness(env, &sl->state, cur, NULL);
 
 			/* if previous state reached the exit with precision and
 			 * current state is equivalent to it (except precision marks)