[PATCH v12 bpf-next 07/10] bpf: Add skb dynptrs

Joanne Koong
2023-02-26T08:52:29Z

Add skb dynptrs, which are dynptrs whose underlying pointer points
to a skb. The dynptr acts on skb data. skb dynptrs have two main
benefits. One is that they allow operations on sizes that are not
statically known at compile-time (eg variable-sized accesses).
Another is that parsing the packet data through dynptrs (instead of
through direct access of skb->data and skb->data_end) can be more
ergonomic and less brittle (eg does not need manual if checking for
being within bounds of data_end).

For bpf prog types that don't support writes on skb data, the dynptr is
read-only (bpf_dynptr_write() will return an error)

For reads and writes through the bpf_dynptr_read() and bpf_dynptr_write()
interfaces, reading and writing from/to data in the head as well as from/to
non-linear paged buffers is supported. Data slices through the
bpf_dynptr_data API are not supported; instead bpf_dynptr_slice() and
bpf_dynptr_slice_rdwr() (added in subsequent commit) should be used.

For examples of how skb dynptrs can be used, please see the attached
selftests.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
include/linux/bpf.h | 14 ++++++-
include/linux/filter.h | 18 ++++++++
include/uapi/linux/bpf.h | 13 +++++-
kernel/bpf/btf.c | 18 ++++++++
kernel/bpf/helpers.c | 76 +++++++++++++++++++++++++++-------
kernel/bpf/verifier.c | 61 +++++++++++++++++++++++++++
net/core/filter.c | 67 ++++++++++++++++++++++++++++++
tools/include/uapi/linux/bpf.h | 13 +++++-
8 files changed, 261 insertions(+), 19 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 296841a31749..e7436d7615b0 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -607,11 +607,14 @@ enum bpf_type_flag {
*/
NON_OWN_REF = BIT(14 + BPF_BASE_TYPE_BITS),

+ /* DYNPTR points to sk_buff */
+ DYNPTR_TYPE_SKB = BIT(15 + BPF_BASE_TYPE_BITS),
+
__BPF_TYPE_FLAG_MAX,
__BPF_TYPE_LAST_FLAG = __BPF_TYPE_FLAG_MAX - 1,
};

-#define DYNPTR_TYPE_FLAG_MASK (DYNPTR_TYPE_LOCAL | DYNPTR_TYPE_RINGBUF)
+#define DYNPTR_TYPE_FLAG_MASK (DYNPTR_TYPE_LOCAL | DYNPTR_TYPE_RINGBUF | DYNPTR_TYPE_SKB)

/* Max number of base types. */
#define BPF_BASE_TYPE_LIMIT (1UL << BPF_BASE_TYPE_BITS)
@@ -1146,6 +1149,8 @@ enum bpf_dynptr_type {
BPF_DYNPTR_TYPE_LOCAL,
/* Underlying data is a ringbuf record */
BPF_DYNPTR_TYPE_RINGBUF,
+ /* Underlying data is a sk_buff */
+ BPF_DYNPTR_TYPE_SKB,
};

int bpf_dynptr_check_size(u32 size);
@@ -2846,6 +2851,8 @@ u32 bpf_sock_convert_ctx_access(enum bpf_access_type type,
struct bpf_insn *insn_buf,
struct bpf_prog *prog,
u32 *target_size);
+int bpf_dynptr_from_skb_rdonly(struct sk_buff *skb, u64 flags,
+ struct bpf_dynptr_kern *ptr);
#else
static inline bool bpf_sock_common_is_valid_access(int off, int size,
enum bpf_access_type type,
@@ -2867,6 +2874,11 @@ static inline u32 bpf_sock_convert_ctx_access(enum bpf_access_type type,
{
return 0;
}
+static inline int bpf_dynptr_from_skb_rdonly(struct sk_buff *skb, u64 flags,
+ struct bpf_dynptr_kern *ptr)
+{
+ return -EOPNOTSUPP;
+}
#endif

#ifdef CONFIG_INET
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 1727898f1641..de18e844d15e 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1542,4 +1542,22 @@ static __always_inline int __bpf_xdp_redirect_map(struct bpf_map *map, u64 index
return XDP_REDIRECT;
}

+#ifdef CONFIG_NET
+int __bpf_skb_load_bytes(const struct sk_buff *skb, u32 offset, void *to, u32 len);
+int __bpf_skb_store_bytes(struct sk_buff *skb, u32 offset, const void *from,
+ u32 len, u64 flags);
+#else /* CONFIG_NET */
+static inline int __bpf_skb_load_bytes(const struct sk_buff *skb, u32 offset,
+ void *to, u32 len)
+{
+ return -EOPNOTSUPP;
+}
+
+static inline int __bpf_skb_store_bytes(struct sk_buff *skb, u32 offset,
+ const void *from, u32 len, u64 flags)
+{
+ return -EOPNOTSUPP;
+}
+#endif /* CONFIG_NET */
+
#endif /* __LINUX_FILTER_H__ */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 62ce1f5d1b1d..d0351d30e551 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5325,11 +5325,17 @@ union bpf_attr {
* Description
* Write *len* bytes from *src* into *dst*, starting from *offset*
* into *dst*.
- * *flags* is currently unused.
+ *
+ * *flags* must be 0 except for skb-type dynptrs.
+ *
+ * For skb-type dynptrs:
+ * * For *flags*, please see the flags accepted by
+ * **bpf_skb_store_bytes**\ ().
* Return
* 0 on success, -E2BIG if *offset* + *len* exceeds the length
* of *dst*'s data, -EINVAL if *dst* is an invalid dynptr or if *dst*
- * is a read-only dynptr or if *flags* is not 0.
+ * is a read-only dynptr or if *flags* is not correct. For skb-type dynptrs,
+ * other errors correspond to errors returned by **bpf_skb_store_bytes**\ ().
*
* void *bpf_dynptr_data(const struct bpf_dynptr *ptr, u32 offset, u32 len)
* Description
@@ -5337,6 +5343,9 @@ union bpf_attr {
*
* *len* must be a statically known value. The returned data slice
* is invalidated whenever the dynptr is invalidated.
+ *
+ * skb type dynptrs may not use bpf_dynptr_data. They should
+ * instead use bpf_dynptr_slice and bpf_dynptr_slice_rdwr.
* Return
* Pointer to the underlying dynptr data, NULL if the dynptr is
* read-only, if the dynptr is invalid, or if the offset and length
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 84cca8473873..ef2d8969ed1f 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -207,6 +207,11 @@ enum btf_kfunc_hook {
BTF_KFUNC_HOOK_TRACING,
BTF_KFUNC_HOOK_SYSCALL,
BTF_KFUNC_HOOK_FMODRET,
+ BTF_KFUNC_HOOK_CGROUP_SKB,
+ BTF_KFUNC_HOOK_SCHED_ACT,
+ BTF_KFUNC_HOOK_SK_SKB,
+ BTF_KFUNC_HOOK_SOCKET_FILTER,
+ BTF_KFUNC_HOOK_LWT,
BTF_KFUNC_HOOK_MAX,
};

@@ -7708,6 +7713,19 @@ static int bpf_prog_type_to_kfunc_hook(enum bpf_prog_type prog_type)
return BTF_KFUNC_HOOK_TRACING;
case BPF_PROG_TYPE_SYSCALL:
return BTF_KFUNC_HOOK_SYSCALL;
+ case BPF_PROG_TYPE_CGROUP_SKB:
+ return BTF_KFUNC_HOOK_CGROUP_SKB;
+ case BPF_PROG_TYPE_SCHED_ACT:
+ return BTF_KFUNC_HOOK_SCHED_ACT;
+ case BPF_PROG_TYPE_SK_SKB:
+ return BTF_KFUNC_HOOK_SK_SKB;
+ case BPF_PROG_TYPE_SOCKET_FILTER:
+ return BTF_KFUNC_HOOK_SOCKET_FILTER;
+ case BPF_PROG_TYPE_LWT_OUT:
+ case BPF_PROG_TYPE_LWT_IN:
+ case BPF_PROG_TYPE_LWT_XMIT:
+ case BPF_PROG_TYPE_LWT_SEG6LOCAL:
+ return BTF_KFUNC_HOOK_LWT;
default:
return BTF_KFUNC_HOOK_MAX;
}
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index a784be6f8bac..1863bea0a21f 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1420,11 +1420,21 @@ static bool bpf_dynptr_is_rdonly(const struct bpf_dynptr_kern *ptr)
return ptr->size & DYNPTR_RDONLY_BIT;
}

+void bpf_dynptr_set_rdonly(struct bpf_dynptr_kern *ptr)
+{
+ ptr->size |= DYNPTR_RDONLY_BIT;
+}
+
static void bpf_dynptr_set_type(struct bpf_dynptr_kern *ptr, enum bpf_dynptr_type type)
{
ptr->size |= type << DYNPTR_TYPE_SHIFT;
}

+static enum bpf_dynptr_type bpf_dynptr_get_type(const struct bpf_dynptr_kern *ptr)
+{
+ return (ptr->size & ~(DYNPTR_RDONLY_BIT)) >> DYNPTR_TYPE_SHIFT;
+}
+
u32 bpf_dynptr_get_size(const struct bpf_dynptr_kern *ptr)
{
return ptr->size & DYNPTR_SIZE_MASK;
@@ -1497,6 +1507,7 @@ static const struct bpf_func_proto bpf_dynptr_from_mem_proto = {
BPF_CALL_5(bpf_dynptr_read, void *, dst, u32, len, const struct bpf_dynptr_kern *, src,
u32, offset, u64, flags)
{
+ enum bpf_dynptr_type type;
int err;

if (!src->data || flags)
@@ -1506,13 +1517,23 @@ BPF_CALL_5(bpf_dynptr_read, void *, dst, u32, len, const struct bpf_dynptr_kern
if (err)
return err;

- /* Source and destination may possibly overlap, hence use memmove to
- * copy the data. E.g. bpf_dynptr_from_mem may create two dynptr
- * pointing to overlapping PTR_TO_MAP_VALUE regions.
- */
- memmove(dst, src->data + src->offset + offset, len);
+ type = bpf_dynptr_get_type(src);

- return 0;
+ switch (type) {
+ case BPF_DYNPTR_TYPE_LOCAL:
+ case BPF_DYNPTR_TYPE_RINGBUF:
+ /* Source and destination may possibly overlap, hence use memmove to
+ * copy the data. E.g. bpf_dynptr_from_mem may create two dynptr
+ * pointing to overlapping PTR_TO_MAP_VALUE regions.
+ */
+ memmove(dst, src->data + src->offset + offset, len);
+ return 0;
+ case BPF_DYNPTR_TYPE_SKB:
+ return __bpf_skb_load_bytes(src->data, src->offset + offset, dst, len);
+ default:
+ WARN_ONCE(true, "bpf_dynptr_read: unknown dynptr type %d\n", type);
+ return -EFAULT;
+ }
}

static const struct bpf_func_proto bpf_dynptr_read_proto = {
@@ -1529,22 +1550,36 @@ static const struct bpf_func_proto bpf_dynptr_read_proto = {
BPF_CALL_5(bpf_dynptr_write, const struct bpf_dynptr_kern *, dst, u32, offset, void *, src,
u32, len, u64, flags)
{
+ enum bpf_dynptr_type type;
int err;

- if (!dst->data || flags || bpf_dynptr_is_rdonly(dst))
+ if (!dst->data || bpf_dynptr_is_rdonly(dst))
return -EINVAL;

err = bpf_dynptr_check_off_len(dst, offset, len);
if (err)
return err;

- /* Source and destination may possibly overlap, hence use memmove to
- * copy the data. E.g. bpf_dynptr_from_mem may create two dynptr
- * pointing to overlapping PTR_TO_MAP_VALUE regions.
- */
- memmove(dst->data + dst->offset + offset, src, len);
+ type = bpf_dynptr_get_type(dst);

- return 0;
+ switch (type) {
+ case BPF_DYNPTR_TYPE_LOCAL:
+ case BPF_DYNPTR_TYPE_RINGBUF:
+ if (flags)
+ return -EINVAL;
+ /* Source and destination may possibly overlap, hence use memmove to
+ * copy the data. E.g. bpf_dynptr_from_mem may create two dynptr
+ * pointing to overlapping PTR_TO_MAP_VALUE regions.
+ */
+ memmove(dst->data + dst->offset + offset, src, len);
+ return 0;
+ case BPF_DYNPTR_TYPE_SKB:
+ return __bpf_skb_store_bytes(dst->data, dst->offset + offset, src, len,
+ flags);
+ default:
+ WARN_ONCE(true, "bpf_dynptr_write: unknown dynptr type %d\n", type);
+ return -EFAULT;
+ }
}

static const struct bpf_func_proto bpf_dynptr_write_proto = {
@@ -1560,6 +1595,7 @@ static const struct bpf_func_proto bpf_dynptr_write_proto = {

BPF_CALL_3(bpf_dynptr_data, const struct bpf_dynptr_kern *, ptr, u32, offset, u32, len)
{
+ enum bpf_dynptr_type type;
int err;

if (!ptr->data)
@@ -1572,7 +1608,19 @@ BPF_CALL_3(bpf_dynptr_data, const struct bpf_dynptr_kern *, ptr, u32, offset, u3
if (bpf_dynptr_is_rdonly(ptr))
return 0;

- return (unsigned long)(ptr->data + ptr->offset + offset);
+ type = bpf_dynptr_get_type(ptr);
+
+ switch (type) {
+ case BPF_DYNPTR_TYPE_LOCAL:
+ case BPF_DYNPTR_TYPE_RINGBUF:
+ return (unsigned long)(ptr->data + ptr->offset + offset);
+ case BPF_DYNPTR_TYPE_SKB:
+ /* skb dynptrs should use bpf_dynptr_slice / bpf_dynptr_slice_rdwr */
+ return 0;
+ default:
+ WARN_ONCE(true, "bpf_dynptr_data: unknown dynptr type %d\n", type);
+ return 0;
+ }
}

static const struct bpf_func_proto bpf_dynptr_data_proto = {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3a7f69b29053..ef38ec52569a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -750,6 +750,8 @@ static enum bpf_dynptr_type arg_to_dynptr_type(enum bpf_arg_type arg_type)
return BPF_DYNPTR_TYPE_LOCAL;
case DYNPTR_TYPE_RINGBUF:
return BPF_DYNPTR_TYPE_RINGBUF;
+ case DYNPTR_TYPE_SKB:
+ return BPF_DYNPTR_TYPE_SKB;
default:
return BPF_DYNPTR_TYPE_INVALID;
}
@@ -6295,6 +6297,9 @@ int process_dynptr_func(struct bpf_verifier_env *env, int regno, int insn_idx,
case DYNPTR_TYPE_RINGBUF:
err_extra = "ringbuf";
break;
+ case DYNPTR_TYPE_SKB:
+ err_extra = "skb ";
+ break;
default:
err_extra = "<unknown>";
break;
@@ -6737,6 +6742,24 @@ static int dynptr_ref_obj_id(struct bpf_verifier_env *env, struct bpf_reg_state
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->off);
+ 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_func_arg(struct bpf_verifier_env *env, u32 arg,
struct bpf_call_arg_meta *meta,
const struct bpf_func_proto *fn,
@@ -8383,6 +8406,27 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn

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;
+
+ dynptr_type = dynptr_get_type(env, reg);
+ if (dynptr_type == BPF_DYNPTR_TYPE_INVALID)
+ return -EFAULT;
+
+ if (dynptr_type == BPF_DYNPTR_TYPE_SKB)
+ /* this will trigger clear_all_pkt_pointers(), which will
+ * invalidate all dynptr slices associated with the skb
+ */
+ changes_data = true;
+
+ break;
+ }
case BPF_FUNC_user_ringbuf_drain:
err = __check_func_call(env, insn, insn_idx_p, meta.subprogno,
set_user_ringbuf_callback_state);
@@ -8898,6 +8942,7 @@ enum special_kfunc_type {
KF_bpf_rbtree_remove,
KF_bpf_rbtree_add,
KF_bpf_rbtree_first,
+ KF_bpf_dynptr_from_skb,
};

BTF_SET_START(special_kfunc_set)
@@ -8912,6 +8957,7 @@ BTF_ID(func, bpf_rdonly_cast)
BTF_ID(func, bpf_rbtree_remove)
BTF_ID(func, bpf_rbtree_add)
BTF_ID(func, bpf_rbtree_first)
+BTF_ID(func, bpf_dynptr_from_skb)
BTF_SET_END(special_kfunc_set)

BTF_ID_LIST(special_kfunc_list)
@@ -8928,6 +8974,7 @@ BTF_ID(func, bpf_rcu_read_unlock)
BTF_ID(func, bpf_rbtree_remove)
BTF_ID(func, bpf_rbtree_add)
BTF_ID(func, bpf_rbtree_first)
+BTF_ID(func, bpf_dynptr_from_skb)

static bool is_kfunc_bpf_rcu_read_lock(struct bpf_kfunc_call_arg_meta *meta)
{
@@ -9682,6 +9729,9 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
if (is_kfunc_arg_uninit(btf, &args[i]))
dynptr_arg_type |= MEM_UNINIT;

+ if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_skb])
+ dynptr_arg_type |= DYNPTR_TYPE_SKB;
+
ret = process_dynptr_func(env, regno, insn_idx, dynptr_arg_type);
if (ret < 0)
return ret;
@@ -16356,6 +16406,17 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
desc->func_id == special_kfunc_list[KF_bpf_rdonly_cast]) {
insn_buf[0] = BPF_MOV64_REG(BPF_REG_0, BPF_REG_1);
*cnt = 1;
+ } else if (desc->func_id == special_kfunc_list[KF_bpf_dynptr_from_skb]) {
+ bool seen_direct_write = env->seen_direct_write;
+ bool is_rdonly = !may_access_direct_pkt_data(env, NULL, BPF_WRITE);
+
+ if (is_rdonly)
+ insn->imm = BPF_CALL_IMM(bpf_dynptr_from_skb_rdonly);
+
+ /* restore env->seen_direct_write to its original value, since
+ * may_access_direct_pkt_data mutates it
+ */
+ env->seen_direct_write = seen_direct_write;
}
return 0;
}
diff --git a/net/core/filter.c b/net/core/filter.c
index 1d6f165923bf..f3afa31a9b10 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1721,6 +1721,12 @@ static const struct bpf_func_proto bpf_skb_store_bytes_proto = {
.arg5_type = ARG_ANYTHING,
};

+int __bpf_skb_store_bytes(struct sk_buff *skb, u32 offset, const void *from,
+ u32 len, u64 flags)
+{
+ return ____bpf_skb_store_bytes(skb, offset, from, len, flags);
+}
+
BPF_CALL_4(bpf_skb_load_bytes, const struct sk_buff *, skb, u32, offset,
void *, to, u32, len)
{
@@ -1751,6 +1757,11 @@ static const struct bpf_func_proto bpf_skb_load_bytes_proto = {
.arg4_type = ARG_CONST_SIZE,
};

+int __bpf_skb_load_bytes(const struct sk_buff *skb, u32 offset, void *to, u32 len)
+{
+ return ____bpf_skb_load_bytes(skb, offset, to, len);
+}
+
BPF_CALL_4(bpf_flow_dissector_load_bytes,
const struct bpf_flow_dissector *, ctx, u32, offset,
void *, to, u32, len)
@@ -11621,3 +11632,59 @@ bpf_sk_base_func_proto(enum bpf_func_id func_id)

return func;
}
+
+__diag_push();
+__diag_ignore_all("-Wmissing-prototypes",
+ "Global functions as their definitions will be in vmlinux BTF");
+__bpf_kfunc int bpf_dynptr_from_skb(struct sk_buff *skb, u64 flags,
+ struct bpf_dynptr_kern *ptr__uninit)
+{
+ if (flags) {
+ bpf_dynptr_set_null(ptr__uninit);
+ return -EINVAL;
+ }
+
+ bpf_dynptr_init(ptr__uninit, skb, BPF_DYNPTR_TYPE_SKB, 0, skb->len);
+
+ return 0;
+}
+__diag_pop();
+
+int bpf_dynptr_from_skb_rdonly(struct sk_buff *skb, u64 flags,
+ struct bpf_dynptr_kern *ptr__uninit)
+{
+ int err;
+
+ err = bpf_dynptr_from_skb(skb, flags, ptr__uninit);
+ if (err)
+ return err;
+
+ bpf_dynptr_set_rdonly(ptr__uninit);
+
+ return 0;
+}
+
+BTF_SET8_START(bpf_kfunc_check_set_skb)
+BTF_ID_FLAGS(func, bpf_dynptr_from_skb)
+BTF_SET8_END(bpf_kfunc_check_set_skb)
+
+static const struct btf_kfunc_id_set bpf_kfunc_set_skb = {
+ .owner = THIS_MODULE,
+ .set = &bpf_kfunc_check_set_skb,
+};
+
+static int __init bpf_kfunc_init(void)
+{
+ int ret;
+
+ ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &bpf_kfunc_set_skb);
+ ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_ACT, &bpf_kfunc_set_skb);
+ ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SK_SKB, &bpf_kfunc_set_skb);
+ ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SOCKET_FILTER, &bpf_kfunc_set_skb);
+ ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_CGROUP_SKB, &bpf_kfunc_set_skb);
+ ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_OUT, &bpf_kfunc_set_skb);
+ ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_IN, &bpf_kfunc_set_skb);
+ ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_XMIT, &bpf_kfunc_set_skb);
+ return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_SEG6LOCAL, &bpf_kfunc_set_skb);
+}
+late_initcall(bpf_kfunc_init);
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 62ce1f5d1b1d..d0351d30e551 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5325,11 +5325,17 @@ union bpf_attr {
* Description
* Write *len* bytes from *src* into *dst*, starting from *offset*
* into *dst*.
- * *flags* is currently unused.
+ *
+ * *flags* must be 0 except for skb-type dynptrs.
+ *
+ * For skb-type dynptrs:
+ * * For *flags*, please see the flags accepted by
+ * **bpf_skb_store_bytes**\ ().
* Return
* 0 on success, -E2BIG if *offset* + *len* exceeds the length
* of *dst*'s data, -EINVAL if *dst* is an invalid dynptr or if *dst*
- * is a read-only dynptr or if *flags* is not 0.
+ * is a read-only dynptr or if *flags* is not correct. For skb-type dynptrs,
+ * other errors correspond to errors returned by **bpf_skb_store_bytes**\ ().
*
* void *bpf_dynptr_data(const struct bpf_dynptr *ptr, u32 offset, u32 len)
* Description
@@ -5337,6 +5343,9 @@ union bpf_attr {
*
* *len* must be a statically known value. The returned data slice
* is invalidated whenever the dynptr is invalidated.
+ *
+ * skb type dynptrs may not use bpf_dynptr_data. They should
+ * instead use bpf_dynptr_slice and bpf_dynptr_slice_rdwr.
* Return
* Pointer to the underlying dynptr data, NULL if the dynptr is
* read-only, if the dynptr is invalid, or if the offset and length
--
2.34.1