[PATCH bpf-next v3 1/9] bpf: Unify dynptr handling in the verifier

Amery Hung
2026-04-21T22:10:20Z

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. It is okay to drop spi < 0 check as
is_dynptr_reg_valid_init() has made sure the dynptr is valid.

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>
Signed-off-by: Amery Hung <ameryhung@gmail.com>
---
include/linux/bpf_verifier.h | 12 ++-
kernel/bpf/verifier.c | 178 +++++++----------------------------
2 files changed, 41 insertions(+), 149 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index b148f816f25b..dc0cff59246d 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -1319,6 +1319,12 @@ struct bpf_map_desc {
int uid;
};

+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;
@@ -1359,16 +1365,12 @@ 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;
};

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 185210b73385..41e4ea41c72e 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -232,6 +232,7 @@ 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;
@@ -240,7 +241,6 @@ 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;
@@ -434,11 +434,6 @@ 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);
@@ -507,8 +502,6 @@ 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;
}
@@ -7433,7 +7426,8 @@ static int process_kptr_func(struct bpf_verifier_env *env, int regno,
* and checked dynamically during runtime.
*/
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 *dynptr)
{
struct bpf_reg_state *reg = reg_state(env, regno);
int err;
@@ -7499,6 +7493,20 @@ static int process_dynptr_func(struct bpf_verifier_env *env, int regno, int insn
}

err = mark_dynptr_read(env, reg);
+
+ if (dynptr) {
+ struct bpf_func_state *state = bpf_func(env, reg);
+ int spi;
+
+ if (reg->type != CONST_PTR_TO_DYNPTR) {
+ spi = dynptr_get_spi(env, reg);
+ reg = &state->stack[spi].spilled_ptr;
+ }
+
+ dynptr->id = reg->id;
+ dynptr->type = reg->dynptr.type;
+ dynptr->ref_obj_id = reg->ref_obj_id;
+ }
}
return err;
}
@@ -8263,72 +8271,6 @@ 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_reg_const_str(struct bpf_verifier_env *env,
struct bpf_reg_state *reg, u32 regno)
{
@@ -8683,7 +8625,7 @@ 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->dynptr);
if (err)
return err;
break;
@@ -9342,7 +9284,7 @@ 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) {
@@ -10429,52 +10371,10 @@ 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;

@@ -10665,10 +10565,7 @@ 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)) {
@@ -10682,6 +10579,11 @@ 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;
@@ -12260,7 +12162,7 @@ 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");
@@ -12268,29 +12170,17 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
}

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, 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->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:
@@ -12894,7 +12784,7 @@ 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);

@@ -12918,11 +12808,11 @@ 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
@@ -13110,7 +13000,7 @@ 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);
--
2.52.0