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

Add an out parameter to `propagate_precision()` to record whether any
new precision 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

@@ -4678,21 +4678,24 @@ static void mark_all_scalars_imprecise(struct bpf_verifier_env *env, struct bpf_
  * finalized states which help in short circuiting more future states.
  */
 static int __mark_chain_precision(struct bpf_verifier_env *env,
-				  struct bpf_verifier_state *starting_state, int regno)
+				  struct bpf_verifier_state *starting_state,
+				  int regno,
+				  bool *changed)
 {
 	struct bpf_verifier_state *st = starting_state;
 	struct backtrack_state *bt = &env->bt;
 	int first_idx = st->first_insn_idx;
 	int last_idx = starting_state->insn_idx;
 	int subseq_idx = -1;
 	struct bpf_func_state *func;
+	bool tmp, skip_first = true;
 	struct bpf_reg_state *reg;
-	bool skip_first = true;
 	int i, fr, err;
 
 	if (!env->bpf_capable)
 		return 0;
 
+	changed = changed ?: &tmp;
 	/* set frame number from which we are starting to backtrack */
 	bt_init(bt, starting_state->curframe);
 
@@ -4738,8 +4741,10 @@ static int __mark_chain_precision(struct bpf_verifier_env *env,
 				for_each_set_bit(i, mask, 32) {
 					reg = &st->frame[0]->regs[i];
 					bt_clear_reg(bt, i);
-					if (reg->type == SCALAR_VALUE)
+					if (reg->type == SCALAR_VALUE) {
 						reg->precise = true;
+						*changed = true;
+					}
 				}
 				return 0;
 			}
@@ -4798,10 +4803,12 @@ static int __mark_chain_precision(struct bpf_verifier_env *env,
 					bt_clear_frame_reg(bt, fr, i);
 					continue;
 				}
-				if (reg->precise)
+				if (reg->precise) {
 					bt_clear_frame_reg(bt, fr, i);
-				else
+				} else {
 					reg->precise = true;
+					*changed = true;
+				}
 			}
 
 			bitmap_from_u64(mask, bt_frame_stack_mask(bt, fr));
@@ -4816,10 +4823,12 @@ static int __mark_chain_precision(struct bpf_verifier_env *env,
 					continue;
 				}
 				reg = &func->stack[i].spilled_ptr;
-				if (reg->precise)
+				if (reg->precise) {
 					bt_clear_frame_slot(bt, fr, i);
-				else
+				} else {
 					reg->precise = true;
+					*changed = true;
+				}
 			}
 			if (env->log.level & BPF_LOG_LEVEL2) {
 				fmt_reg_mask(env->tmp_str_buf, TMP_STR_BUF_LEN,
@@ -4855,7 +4864,7 @@ static int __mark_chain_precision(struct bpf_verifier_env *env,
 
 int mark_chain_precision(struct bpf_verifier_env *env, int regno)
 {
-	return __mark_chain_precision(env, env->cur_state, regno);
+	return __mark_chain_precision(env, env->cur_state, regno, NULL);
 }
 
 /* mark_chain_precision_batch() assumes that env->bt is set in the caller to
@@ -4864,7 +4873,7 @@ int mark_chain_precision(struct bpf_verifier_env *env, int regno)
 static int mark_chain_precision_batch(struct bpf_verifier_env *env,
 				      struct bpf_verifier_state *starting_state)
 {
-	return __mark_chain_precision(env, starting_state, -1);
+	return __mark_chain_precision(env, starting_state, -1, NULL);
 }
 
 static bool is_spillable_regtype(enum bpf_reg_type type)
@@ -18893,7 +18902,9 @@ static int propagate_liveness(struct bpf_verifier_env *env,
  * propagate them into the current state
  */
 static int propagate_precision(struct bpf_verifier_env *env,
-			       const struct bpf_verifier_state *old)
+			       const struct bpf_verifier_state *old,
+			       struct bpf_verifier_state *cur,
+			       bool *changed)
 {
 	struct bpf_reg_state *state_reg;
 	struct bpf_func_state *state;
@@ -18941,7 +18952,7 @@ static int propagate_precision(struct bpf_verifier_env *env,
 			verbose(env, "\n");
 	}
 
-	err = mark_chain_precision_batch(env, env->cur_state);
+	err = __mark_chain_precision(env, cur, -1, changed);
 	if (err < 0)
 		return err;
 
@@ -19264,7 +19275,7 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 			 */
 			if (is_jmp_point(env, env->insn_idx))
 				err = err ? : push_jmp_history(env, cur, 0, 0);
-			err = err ? : propagate_precision(env, &sl->state);
+			err = err ? : propagate_precision(env, &sl->state, cur, NULL);
 			if (err)
 				return err;
 			return 1;