Subject: Re: [RFC PATCH bpf-next v2 03/11] bpf: Unify dynptr handling in the verifier

From: Mykyta Yatsenko <[email-masked]>
Date: Wed, 11 Mar 2026 16:03:45 +0000

Amery Hung <[email-masked]> writes:

> Simplify dynptr checking for helper and kfunc by unifying it. Remember
> initialized dynptr in process_dynptr_func() so that we can easily
> retrieve the information for verification later.
>
> Signed-off-by: Amery Hung <[email-masked]>
> ---
>  kernel/bpf/verifier.c | 179 +++++++++---------------------------------
>  1 file changed, 36 insertions(+), 143 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 0f77c4c5b510..d52780962adb 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -277,8 +277,15 @@ struct bpf_map_desc {
>  	int uid;
>  };
>  
> +struct bpf_dynptr_desc {
> +	enum bpf_dynptr_type type;
> +	u32 id;
> +	u32 ref_obj_id;
nit: let's add a comment here explaining what this field is for.
> +};
> +
>  struct bpf_call_arg_meta {
>  	struct bpf_map_desc map;
> +	struct bpf_dynptr_desc initialized_dynptr;
>  	bool raw_mode;
>  	bool pkt_access;
>  	u8 release_regno;
> @@ -287,7 +294,6 @@ 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;
> @@ -346,16 +352,12 @@ 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 initialized_dynptr;
>  	u64 mem_size;
>  };
>  
> @@ -511,11 +513,6 @@ 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);
> @@ -597,8 +594,6 @@ 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;
>  }
> @@ -8750,7 +8745,8 @@ static int process_kptr_func(struct bpf_verifier_env *env, int regno,
>   * type, and declare it as 'const struct bpf_dynptr *' in their prototype.
>   */
>  static int process_dynptr_func(struct bpf_verifier_env *env, int regno, int insn_idx,
> -			       enum bpf_arg_type arg_type, int clone_ref_obj_id)
> +			       enum bpf_arg_type arg_type, int clone_ref_obj_id,
> +			       struct bpf_dynptr_desc *initialized_dynptr)
>  {
>  	struct bpf_reg_state *reg = reg_state(env, regno);
>  	int err;
> @@ -8825,6 +8821,20 @@ static int process_dynptr_func(struct bpf_verifier_env *env, int regno, int insn
>  		}
>  
>  		err = mark_dynptr_read(env, reg);
> +
> +		if (initialized_dynptr) {
> +			struct bpf_func_state *state = func(env, reg);
state is only used if reg->type != CONST_PTR_TO_DYNPTR, does it make
sense to move state = func(env, reg); to the corresponding if block?
> +			int spi;
> +
> +			if (reg->type != CONST_PTR_TO_DYNPTR) {
> +				spi = dynptr_get_spi(env, reg);
looking at the deleted dynptr_id() and dynptr_ref_obj_id() spi can be
negative, what changed here that we no longer need this check?
> +				reg = &state->stack[spi].spilled_ptr;
> +			}
> +
> +			initialized_dynptr->id = reg->id;
> +			initialized_dynptr->type = reg->dynptr.type;
> +			initialized_dynptr->ref_obj_id = reg->ref_obj_id;
> +		}
>  	}
>  	return err;
>  }
> @@ -9587,72 +9597,6 @@ 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 = 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 = 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 = func(env, reg);
> -	int spi;
> -
> -	if (reg->type == CONST_PTR_TO_DYNPTR)
> -		return reg->dynptr.type;
> -
> -	spi = __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_reg_const_str(struct bpf_verifier_env *env,
>  			       struct bpf_reg_state *reg, u32 regno)
>  {
> @@ -10007,7 +9951,8 @@ 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, regno, insn_idx, arg_type, 0);
> +		err = process_dynptr_func(env, regno, insn_idx, arg_type, 0,
> +					  &meta->initialized_dynptr);
>  		if (err)
>  			return err;
>  		break;
> @@ -10666,7 +10611,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
>  			if (ret)
>  				return ret;
>  
> -			ret = process_dynptr_func(env, regno, -1, arg->arg_type, 0);
> +			ret = process_dynptr_func(env, regno, -1, arg->arg_type, 0, NULL);
>  			if (ret)
>  				return ret;
>  		} else if (base_type(arg->arg_type) == ARG_PTR_TO_BTF_ID) {
> @@ -11771,52 +11716,10 @@ 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;
> -
> -		reg = get_dynptr_arg_reg(env, fn, regs);
> -		if (!reg)
> -			return -EFAULT;
> +		enum bpf_dynptr_type dynptr_type = meta.initialized_dynptr.type;
>  
> -		dynptr_type = dynptr_get_type(env, reg);
>  		if (dynptr_type == BPF_DYNPTR_TYPE_INVALID)
>  			return -EFAULT;
>  
> @@ -12007,10 +11910,7 @@ 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)) {
> @@ -12024,6 +11924,11 @@ 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.initialized_dynptr.id;
> +		regs[BPF_REG_0].ref_obj_id = meta.initialized_dynptr.ref_obj_id;
> +	}
> +
>  	err = do_refine_retval_range(env, regs, fn->ret_type, func_id, &meta);
>  	if (err)
>  		return err;
> @@ -13559,22 +13464,10 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
>  				}
>  			}
>  
> -			ret = process_dynptr_func(env, regno, insn_idx, dynptr_arg_type, clone_ref_obj_id);
> +			ret = process_dynptr_func(env, regno, insn_idx, dynptr_arg_type, clone_ref_obj_id,
> +						  &meta->initialized_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:
> -- 
> 2.47.3