bpf: Add bpf_dynptr_slice and bpf_dynptr_slice_rdwr

Two new kfuncs are added, bpf_dynptr_slice and bpf_dynptr_slice_rdwr.
The user must pass in a buffer to store the contents of the data slice
if a direct pointer to the data cannot be obtained.

For skb and xdp type dynptrs, these two APIs are the only way to obtain
a data slice. However, for other types of dynptrs, there is no
difference between bpf_dynptr_slice(_rdwr) and bpf_dynptr_data.

For skb type dynptrs, the data is copied into the user provided buffer
if any of the data is not in the linear portion of the skb. For xdp type
dynptrs, the data is copied into the user provided buffer if the data is
between xdp frags.

If the skb is cloned and a call to bpf_dynptr_data_rdwr is made, then
the skb will be uncloned (see bpf_unclone_prologue()).

Please note that any bpf_dynptr_write() automatically invalidates any prior
data slices of the skb dynptr. This is because the skb may be cloned or
may need to pull its paged buffer into the head. As such, any
bpf_dynptr_write() will automatically have its prior data slices
invalidated, even if the write is to data in the skb head of an uncloned
skb. Please note as well that any other helper calls that change the
underlying packet buffer (eg bpf_skb_pull_data()) invalidates any data
slices of the skb dynptr as well, for the same reasons.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Link: https://lore.kernel.org/r/20230301154953.641654-10-joannelkoong@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 3f6992261ec5..efa5d4a1677e 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1548,6 +1548,9 @@ int __bpf_skb_store_bytes(struct sk_buff *skb, u32 offset, const void *from,
 			  u32 len, u64 flags);
 int __bpf_xdp_load_bytes(struct xdp_buff *xdp, u32 offset, void *buf, u32 len);
 int __bpf_xdp_store_bytes(struct xdp_buff *xdp, u32 offset, void *buf, u32 len);
+void *bpf_xdp_pointer(struct xdp_buff *xdp, u32 offset, u32 len);
+void bpf_xdp_copy_buf(struct xdp_buff *xdp, unsigned long off,
+		      void *buf, unsigned long len, bool flush);
 #else /* CONFIG_NET */
 static inline int __bpf_skb_load_bytes(const struct sk_buff *skb, u32 offset,
 				       void *to, u32 len)
@@ -1572,6 +1575,17 @@ static inline int __bpf_xdp_store_bytes(struct xdp_buff *xdp, u32 offset,
 {
 	return -EOPNOTSUPP;
 }
+
+static inline void *bpf_xdp_pointer(struct xdp_buff *xdp, u32 offset, u32 len)
+{
+	return NULL;
+}
+
+static inline void *bpf_xdp_copy_buf(struct xdp_buff *xdp, unsigned long off, void *buf,
+				     unsigned long len, bool flush)
+{
+	return NULL;
+}
 #endif /* CONFIG_NET */
 
 #endif /* __LINUX_FILTER_H__ */