[PATCH bpf-next 01/10] [bpf]: adding bpf_xdp_adjust_tail helper

Nikita V. Shirokov
2018-04-17T06:51:49Z

Adding new bpf helper which would allow us to manipulate
xdp's data_end pointer, and allow us to reduce packet's size
indended use case: to generate ICMP messages from XDP context,
where such message would contain truncated original packet.

Signed-off-by: Nikita V. Shirokov <tehnerd@tehnerd.com>
---
include/uapi/linux/bpf.h | 10 +++++++++-
net/core/filter.c | 29 ++++++++++++++++++++++++++++-
2 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c5ec89732a8d..9a2d1a04eb24 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -755,6 +755,13 @@ union bpf_attr {
* @addr: pointer to struct sockaddr to bind socket to
* @addr_len: length of sockaddr structure
* Return: 0 on success or negative error code
+ *
+ * int bpf_xdp_adjust_tail(xdp_md, delta)
+ * Adjust the xdp_md.data_end by delta. Only shrinking of packet's
+ * size is supported.
+ * @xdp_md: pointer to xdp_md
+ * @delta: A negative integer to be added to xdp_md.data_end
+ * Return: 0 on success or negative on error
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -821,7 +828,8 @@ union bpf_attr {
FN(msg_apply_bytes), \
FN(msg_cork_bytes), \
FN(msg_pull_data), \
- FN(bind),
+ FN(bind), \
+ FN(xdp_adjust_tail),

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
diff --git a/net/core/filter.c b/net/core/filter.c
index d31aff93270d..6c8ac7b548d6 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2717,6 +2717,30 @@ static const struct bpf_func_proto bpf_xdp_adjust_head_proto = {
.arg2_type = ARG_ANYTHING,
};

+BPF_CALL_2(bpf_xdp_adjust_tail, struct xdp_buff *, xdp, int, offset)
+{
+ /* only shrinking is allowed for now. */
+ if (unlikely(offset > 0))
+ return -EINVAL;
+
+ void *data_end = xdp->data_end + offset;
+
+ if (unlikely(data_end < xdp->data + ETH_HLEN))
+ return -EINVAL;
+
+ xdp->data_end = data_end;
+
+ return 0;
+}
+
+static const struct bpf_func_proto bpf_xdp_adjust_tail_proto = {
+ .func = bpf_xdp_adjust_tail,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_CTX,
+ .arg2_type = ARG_ANYTHING,
+};
+
BPF_CALL_2(bpf_xdp_adjust_meta, struct xdp_buff *, xdp, int, offset)
{
void *meta = xdp->data_meta + offset;
@@ -3053,7 +3077,8 @@ bool bpf_helper_changes_pkt_data(void *func)
func == bpf_l4_csum_replace ||
func == bpf_xdp_adjust_head ||
func == bpf_xdp_adjust_meta ||
- func == bpf_msg_pull_data)
+ func == bpf_msg_pull_data ||
+ func == bpf_xdp_adjust_tail)
return true;

return false;
@@ -3867,6 +3892,8 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
return &bpf_xdp_redirect_proto;
case BPF_FUNC_redirect_map:
return &bpf_xdp_redirect_map_proto;
+ case BPF_FUNC_xdp_adjust_tail:
+ return &bpf_xdp_adjust_tail_proto;
default:
return bpf_base_func_proto(func_id);
}
--
2.15.1