bpf: Simplify mark_stack_slot_obj_read() and callers

Rename mark_stack_slot_obj_read() as mark_stack_slots_scratched() and
directly call it from functions processing iter, dynptr and irq_flag.
Commit 6762e3a ("bpf: simplify liveness to use (callsite, depth)
keyed func_instances") has removed the dynamic liveness component in
mark_stack_slot_obj_read(). The function effectively only marks stack
slots as scratched and always succeed. Therefore, return void, drop the
unused bpf_reg_state argument and rename it to
mark_stack_slots_scratched() to reflect what it does now.

In addition, to prepare for unifying dynptr handling, dynptr_get_spi()
will be moved out of mark_dynptr_read(). As mark_dynptr_read() would join
mark_iter_read() as a thin wrapper of mark_stack_slots_scratched(), just
open code these helpers.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Amery Hung <ameryhung@gmail.com>
Link: https://lore.kernel.org/r/20260529014936.2811085-2-ameryhung@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: ameryhung

kernel/bpf/verifier.c

@@ -3006,50 +3006,13 @@ static int sort_subprogs_topo(struct bpf_verifier_env *env)
 	return ret;
 }
 
-static int mark_stack_slot_obj_read(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
-				    int spi, int nr_slots)
+static void mark_stack_slots_scratched(struct bpf_verifier_env *env,
+				       int spi, int nr_slots)
 {
 	int i;
 
 	for (i = 0; i < nr_slots; i++)
 		mark_stack_slot_scratched(env, spi - i);
-	return 0;
-}
-
-static int mark_dynptr_read(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
-{
-	int spi;
-
-	/* For CONST_PTR_TO_DYNPTR, it must have already been done by
-	 * check_reg_arg in check_helper_call and mark_btf_func_reg_size in
-	 * check_kfunc_call.
-	 */
-	if (reg->type == CONST_PTR_TO_DYNPTR)
-		return 0;
-	spi = dynptr_get_spi(env, reg);
-	if (spi < 0)
-		return spi;
-	/* Caller ensures dynptr is valid and initialized, which means spi is in
-	 * bounds and spi is the first dynptr slot. Simply mark stack slot as
-	 * read.
-	 */
-	return mark_stack_slot_obj_read(env, reg, spi, BPF_DYNPTR_NR_SLOTS);
-}
-
-static int mark_iter_read(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
-			  int spi, int nr_slots)
-{
-	return mark_stack_slot_obj_read(env, reg, spi, nr_slots);
-}
-
-static int mark_irq_flag_read(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
-{
-	int spi;
-
-	spi = irq_flag_get_spi(env, reg);
-	if (spi < 0)
-		return spi;
-	return mark_stack_slot_obj_read(env, reg, spi, 1);
 }
 
 /* This function is supposed to be used by the following 32-bit optimization
@@ -7261,7 +7224,7 @@ static int process_kptr_func(struct bpf_verifier_env *env, int regno,
 static int process_dynptr_func(struct bpf_verifier_env *env, struct bpf_reg_state *reg, argno_t argno, int insn_idx,
 			       enum bpf_arg_type arg_type, int clone_ref_obj_id)
 {
-	int err;
+	int spi, err = 0;
 
 	if (reg->type != PTR_TO_STACK && reg->type != CONST_PTR_TO_DYNPTR) {
 		verbose(env,
@@ -7323,7 +7286,17 @@ static int process_dynptr_func(struct bpf_verifier_env *env, struct bpf_reg_stat
 			return -EINVAL;
 		}
 
-		err = mark_dynptr_read(env, reg);
+		if (reg->type != CONST_PTR_TO_DYNPTR) {
+			spi = dynptr_get_spi(env, reg);
+			if (spi < 0)
+				return spi;
+
+			/*
+			 * For CONST_PTR_TO_DYNPTR, reg is already scratched by check_reg_arg
+			 * in check_helper_call and mark_btf_func_reg_size in check_kfunc_call.
+			 */
+			mark_stack_slots_scratched(env, spi, BPF_DYNPTR_NR_SLOTS);
+		}
 	}
 	return err;
 }
@@ -7433,9 +7406,7 @@ static int process_iter_arg(struct bpf_verifier_env *env, struct bpf_reg_state *
 		if (spi < 0)
 			return spi;
 
-		err = mark_iter_read(env, reg, spi, nr_slots);
-		if (err)
-			return err;
+		mark_stack_slots_scratched(env, spi, nr_slots);
 
 		/* remember meta->iter info for process_iter_next_call() */
 		meta->iter.spi = spi;
@@ -11399,7 +11370,7 @@ static int process_kf_arg_ptr_to_btf_id(struct bpf_verifier_env *env,
 static int process_irq_flag(struct bpf_verifier_env *env, struct bpf_reg_state *reg, argno_t argno,
 			     struct bpf_kfunc_call_arg_meta *meta)
 {
-	int err, kfunc_class = IRQ_NATIVE_KFUNC;
+	int err, spi, kfunc_class = IRQ_NATIVE_KFUNC;
 	bool irq_save;
 
 	if (meta->func_id == special_kfunc_list[KF_bpf_local_irq_save] ||
@@ -11440,9 +11411,11 @@ static int process_irq_flag(struct bpf_verifier_env *env, struct bpf_reg_state *
 			return err;
 		}
 
-		err = mark_irq_flag_read(env, reg);
-		if (err)
-			return err;
+		spi = irq_flag_get_spi(env, reg);
+		if (spi < 0)
+			return spi;
+
+		mark_stack_slots_scratched(env, spi, 1);
 
 		err = unmark_stack_slot_irq_flag(env, reg, kfunc_class);
 		if (err)