bpf: Unify dynptr handling in the verifier

Simplify dynptr checking for helper and kfunc by unifying it. Remember
the initialized dynptr (i.e.,g !(arg_type |= MEM_UNINIT)) pass to a
dynptr kfunc during process_dynptr_func() so that we can easily
retrieve the information for verification later. By saving it in
meta->dynptr, there is no need to call dynptr helpers such as
dynptr_id(), dynptr_ref_obj_id() and dynptr_type() in check_func_arg().

Remove and open code the helpers in process_dynptr_func() when
saving id, ref_obj_id, and type.

Besides, since dynptr ref_obj_id information is now pass around in
meta->bpf_dynptr_desc, drop the check in helper_multiple_ref_obj_use.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Mykyta Yatsenko <yatsenko@meta.com>
Signed-off-by: Amery Hung <ameryhung@gmail.com>
Link: https://lore.kernel.org/r/20260529014936.2811085-3-ameryhung@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: ameryhung

include/linux/bpf_verifier.h

@@ -1438,6 +1438,13 @@ struct bpf_map_desc {
 	int uid;
 };
 
+/* The last initialized dynptr; Populated by process_dynptr_func() */
+struct bpf_dynptr_desc {
+	enum bpf_dynptr_type type;
+	u32 id;
+	u32 ref_obj_id;
+};
+
 struct bpf_kfunc_call_arg_meta {
 	/* In parameters */
 	struct btf *btf;
@@ -1478,16 +1485,12 @@ struct bpf_kfunc_call_arg_meta {
 	struct {
 		struct btf_field *field;
 	} arg_rbtree_root;
-	struct {
-		enum bpf_dynptr_type type;
-		u32 id;
-		u32 ref_obj_id;
-	} initialized_dynptr;
 	struct {
 		u8 spi;
 		u8 frameno;
 	} iter;
 	struct bpf_map_desc map;
+	struct bpf_dynptr_desc dynptr;
 	u64 mem_size;
 };
 

kernel/bpf/verifier.c

@@ -233,6 +233,7 @@ static void bpf_map_key_store(struct bpf_insn_aux_data *aux, u64 state)
 
 struct bpf_call_arg_meta {
 	struct bpf_map_desc map;
+	struct bpf_dynptr_desc dynptr;
 	bool raw_mode;
 	bool pkt_access;
 	u8 release_regno;
@@ -241,7 +242,6 @@ struct bpf_call_arg_meta {
 	int mem_size;
 	u64 msize_max_value;
 	int ref_obj_id;
-	int dynptr_id;
 	int func_id;
 	struct btf *btf;
 	u32 btf_id;
@@ -470,11 +470,6 @@ static bool is_ptr_cast_function(enum bpf_func_id func_id)
 		func_id == BPF_FUNC_skc_to_tcp_request_sock;
 }
 
-static bool is_dynptr_ref_function(enum bpf_func_id func_id)
-{
-	return func_id == BPF_FUNC_dynptr_data;
-}
-
 static bool is_sync_callback_calling_kfunc(u32 btf_id);
 static bool is_async_callback_calling_kfunc(u32 btf_id);
 static bool is_callback_calling_kfunc(u32 btf_id);
@@ -542,8 +537,6 @@ static bool helper_multiple_ref_obj_use(enum bpf_func_id func_id,
 		ref_obj_uses++;
 	if (is_acquire_function(func_id, map))
 		ref_obj_uses++;
-	if (is_dynptr_ref_function(func_id))
-		ref_obj_uses++;
 
 	return ref_obj_uses > 1;
 }
@@ -7221,8 +7214,9 @@ static int process_kptr_func(struct bpf_verifier_env *env, int regno,
  * use case. The second level is tracked using the upper bit of bpf_dynptr->size
  * and checked dynamically during runtime.
  */
-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)
+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, struct bpf_dynptr_desc *dynptr)
 {
 	int spi, err = 0;
 
@@ -7287,6 +7281,8 @@ static int process_dynptr_func(struct bpf_verifier_env *env, struct bpf_reg_stat
 		}
 
 		if (reg->type != CONST_PTR_TO_DYNPTR) {
+			struct bpf_func_state *state = bpf_func(env, reg);
+
 			spi = dynptr_get_spi(env, reg);
 			if (spi < 0)
 				return spi;
@@ -7296,6 +7292,14 @@ static int process_dynptr_func(struct bpf_verifier_env *env, struct bpf_reg_stat
 			 * in check_helper_call and mark_btf_func_reg_size in check_kfunc_call.
 			 */
 			mark_stack_slots_scratched(env, spi, BPF_DYNPTR_NR_SLOTS);
+
+			reg = &state->stack[spi].spilled_ptr;
+		}
+
+		if (dynptr) {
+			dynptr->type = reg->dynptr.type;
+			dynptr->id = reg->id;
+			dynptr->ref_obj_id = reg->ref_obj_id;
 		}
 	}
 	return err;
@@ -8065,72 +8069,6 @@ static int check_func_arg_reg_off(struct bpf_verifier_env *env,
 	}
 }
 
-static struct bpf_reg_state *get_dynptr_arg_reg(struct bpf_verifier_env *env,
-						const struct bpf_func_proto *fn,
-						struct bpf_reg_state *regs)
-{
-	struct bpf_reg_state *state = NULL;
-	int i;
-
-	for (i = 0; i < MAX_BPF_FUNC_REG_ARGS; i++)
-		if (arg_type_is_dynptr(fn->arg_type[i])) {
-			if (state) {
-				verbose(env, "verifier internal error: multiple dynptr args\n");
-				return NULL;
-			}
-			state = &regs[BPF_REG_1 + i];
-		}
-
-	if (!state)
-		verbose(env, "verifier internal error: no dynptr arg found\n");
-
-	return state;
-}
-
-static int dynptr_id(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
-{
-	struct bpf_func_state *state = bpf_func(env, reg);
-	int spi;
-
-	if (reg->type == CONST_PTR_TO_DYNPTR)
-		return reg->id;
-	spi = dynptr_get_spi(env, reg);
-	if (spi < 0)
-		return spi;
-	return state->stack[spi].spilled_ptr.id;
-}
-
-static int dynptr_ref_obj_id(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
-{
-	struct bpf_func_state *state = bpf_func(env, reg);
-	int spi;
-
-	if (reg->type == CONST_PTR_TO_DYNPTR)
-		return reg->ref_obj_id;
-	spi = dynptr_get_spi(env, reg);
-	if (spi < 0)
-		return spi;
-	return state->stack[spi].spilled_ptr.ref_obj_id;
-}
-
-static enum bpf_dynptr_type dynptr_get_type(struct bpf_verifier_env *env,
-					    struct bpf_reg_state *reg)
-{
-	struct bpf_func_state *state = bpf_func(env, reg);
-	int spi;
-
-	if (reg->type == CONST_PTR_TO_DYNPTR)
-		return reg->dynptr.type;
-
-	spi = bpf_get_spi(reg->var_off.value);
-	if (spi < 0) {
-		verbose(env, "verifier internal error: invalid spi when querying dynptr type\n");
-		return BPF_DYNPTR_TYPE_INVALID;
-	}
-
-	return state->stack[spi].spilled_ptr.dynptr.type;
-}
-
 static int check_arg_const_str(struct bpf_verifier_env *env,
 			       struct bpf_reg_state *reg, argno_t argno)
 {
@@ -8488,7 +8426,8 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 					 true, meta);
 		break;
 	case ARG_PTR_TO_DYNPTR:
-		err = process_dynptr_func(env, reg, argno_from_reg(regno), insn_idx, arg_type, 0);
+		err = process_dynptr_func(env, reg, argno_from_reg(regno), insn_idx, arg_type, 0,
+					  &meta->dynptr);
 		if (err)
 			return err;
 		break;
@@ -9170,7 +9109,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
 			if (ret)
 				return ret;
 
-			ret = process_dynptr_func(env, reg, argno, -1, arg->arg_type, 0);
+			ret = process_dynptr_func(env, reg, argno, -1, arg->arg_type, 0, NULL);
 			if (ret)
 				return ret;
 		} else if (base_type(arg->arg_type) == ARG_PTR_TO_BTF_ID) {
@@ -10278,52 +10217,10 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
 			}
 		}
 		break;
-	case BPF_FUNC_dynptr_data:
-	{
-		struct bpf_reg_state *reg;
-		int id, ref_obj_id;
-
-		reg = get_dynptr_arg_reg(env, fn, regs);
-		if (!reg)
-			return -EFAULT;
-
-
-		if (meta.dynptr_id) {
-			verifier_bug(env, "meta.dynptr_id already set");
-			return -EFAULT;
-		}
-		if (meta.ref_obj_id) {
-			verifier_bug(env, "meta.ref_obj_id already set");
-			return -EFAULT;
-		}
-
-		id = dynptr_id(env, reg);
-		if (id < 0) {
-			verifier_bug(env, "failed to obtain dynptr id");
-			return id;
-		}
-
-		ref_obj_id = dynptr_ref_obj_id(env, reg);
-		if (ref_obj_id < 0) {
-			verifier_bug(env, "failed to obtain dynptr ref_obj_id");
-			return ref_obj_id;
-		}
-
-		meta.dynptr_id = id;
-		meta.ref_obj_id = ref_obj_id;
-
-		break;
-	}
 	case BPF_FUNC_dynptr_write:
 	{
-		enum bpf_dynptr_type dynptr_type;
-		struct bpf_reg_state *reg;
+		enum bpf_dynptr_type dynptr_type = meta.dynptr.type;
 
-		reg = get_dynptr_arg_reg(env, fn, regs);
-		if (!reg)
-			return -EFAULT;
-
-		dynptr_type = dynptr_get_type(env, reg);
 		if (dynptr_type == BPF_DYNPTR_TYPE_INVALID)
 			return -EFAULT;
 
@@ -10515,10 +10412,7 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
 		return -EFAULT;
 	}
 
-	if (is_dynptr_ref_function(func_id))
-		regs[BPF_REG_0].dynptr_id = meta.dynptr_id;
-
-	if (is_ptr_cast_function(func_id) || is_dynptr_ref_function(func_id)) {
+	if (is_ptr_cast_function(func_id)) {
 		/* For release_reference() */
 		regs[BPF_REG_0].ref_obj_id = meta.ref_obj_id;
 	} else if (is_acquire_function(func_id, meta.map.ptr)) {
@@ -10532,6 +10426,11 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
 		regs[BPF_REG_0].ref_obj_id = id;
 	}
 
+	if (func_id == BPF_FUNC_dynptr_data) {
+		regs[BPF_REG_0].dynptr_id = meta.dynptr.id;
+		regs[BPF_REG_0].ref_obj_id = meta.dynptr.ref_obj_id;
+	}
+
 	err = do_refine_retval_range(env, regs, fn->ret_type, func_id, &meta);
 	if (err)
 		return err;
@@ -12187,38 +12086,25 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 				meta->release_regno = regno;
 			} else if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_clone] &&
 				   (dynptr_arg_type & MEM_UNINIT)) {
-				enum bpf_dynptr_type parent_type = meta->initialized_dynptr.type;
+				enum bpf_dynptr_type parent_type = meta->dynptr.type;
 
 				if (parent_type == BPF_DYNPTR_TYPE_INVALID) {
 					verifier_bug(env, "no dynptr type for parent of clone");
 					return -EFAULT;
 				}
 
 				dynptr_arg_type |= (unsigned int)get_dynptr_type_flag(parent_type);
-				clone_ref_obj_id = meta->initialized_dynptr.ref_obj_id;
+				clone_ref_obj_id = meta->dynptr.ref_obj_id;
 				if (dynptr_type_refcounted(parent_type) && !clone_ref_obj_id) {
 					verifier_bug(env, "missing ref obj id for parent of clone");
 					return -EFAULT;
 				}
 			}
 
-			ret = process_dynptr_func(env, reg, argno, insn_idx,
-						  dynptr_arg_type, clone_ref_obj_id);
+			ret = process_dynptr_func(env, reg, argno, insn_idx, dynptr_arg_type,
+						  clone_ref_obj_id, &meta->dynptr);
 			if (ret < 0)
 				return ret;
-
-			if (!(dynptr_arg_type & MEM_UNINIT)) {
-				int id = dynptr_id(env, reg);
-
-				if (id < 0) {
-					verifier_bug(env, "failed to obtain dynptr id");
-					return id;
-				}
-				meta->initialized_dynptr.id = id;
-				meta->initialized_dynptr.type = dynptr_get_type(env, reg);
-				meta->initialized_dynptr.ref_obj_id = dynptr_ref_obj_id(env, reg);
-			}
-
 			break;
 		}
 		case KF_ARG_PTR_TO_ITER:
@@ -12849,7 +12735,7 @@ static int check_special_kfunc(struct bpf_verifier_env *env, struct bpf_kfunc_ca
 		}
 	} else if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_slice] ||
 		   meta->func_id == special_kfunc_list[KF_bpf_dynptr_slice_rdwr]) {
-		enum bpf_type_flag type_flag = get_dynptr_type_flag(meta->initialized_dynptr.type);
+		enum bpf_type_flag type_flag = get_dynptr_type_flag(meta->dynptr.type);
 
 		mark_reg_known_zero(env, regs, BPF_REG_0);
 
@@ -12873,11 +12759,11 @@ static int check_special_kfunc(struct bpf_verifier_env *env, struct bpf_kfunc_ca
 			}
 		}
 
-		if (!meta->initialized_dynptr.id) {
+		if (!meta->dynptr.id) {
 			verifier_bug(env, "no dynptr id");
 			return -EFAULT;
 		}
-		regs[BPF_REG_0].dynptr_id = meta->initialized_dynptr.id;
+		regs[BPF_REG_0].dynptr_id = meta->dynptr.id;
 
 		/* we don't need to set BPF_REG_0's ref obj id
 		 * because packet slices are not refcounted (see
@@ -13063,7 +12949,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 	if (meta.release_regno) {
 		struct bpf_reg_state *reg = &regs[meta.release_regno];
 
-		if (meta.initialized_dynptr.ref_obj_id) {
+		if (meta.dynptr.ref_obj_id) {
 			err = unmark_stack_slots_dynptr(env, reg);
 		} else {
 			err = release_reference(env, reg->ref_obj_id);