This patch adds a helper function called bpf_get_skb_hash to calculate
the skb hash for a packet at the XDP layer. In the helper function,
a local skb is allocated and we populate the fields needed in the skb
before calling skb_get_hash. To avoid memory allocations for each packet,
we allocate an skb per CPU and use the same buffer for subsequent hash
calculations on the same CPU.
Signed-off-by: Harshitha Ramamurthy <harshitha.ramamurthy@xxxxxxxxx>
---
include/uapi/linux/bpf.h | 8 ++++++
net/core/filter.c | 50 ++++++++++++++++++++++++++++++++++
tools/include/uapi/linux/bpf.h | 8 ++++++
3 files changed, 66 insertions(+)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index b134e679e9db..25aa850c8a40 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3394,6 +3394,13 @@ union bpf_attr {
* A non-negative value equal to or less than *size* on success,
* or a negative error in case of failure.
*
+ * u32 bpf_get_skb_hash(struct xdp_buff *xdp_md)
+ * Description
+ * Return the skb hash for the xdp context passed. This function
+ * allocates a temporary skb and populates the fields needed. It
+ * then calls skb_get_hash to calculate the skb hash for the packet.
+ * Return
+ * The 32-bit hash.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3538,6 +3545,7 @@ union bpf_attr {
FN(skc_to_tcp_request_sock), \
FN(skc_to_udp6_sock), \
FN(get_task_stack), \
+ FN(get_skb_hash), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/net/core/filter.c b/net/core/filter.c
index 7124f0fe6974..9f6ad7209b44 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3765,6 +3765,54 @@ static const struct bpf_func_proto bpf_xdp_redirect_map_proto = {
.arg3_type = ARG_ANYTHING,
};
+static DEFINE_PER_CPU(struct sk_buff *, hash_skb);
+
+BPF_CALL_1(bpf_get_skb_hash, struct xdp_buff *, xdp)
+{
+ void *data_end = xdp->data_end;
+ struct ethhdr *eth = xdp->data;
+ void *data = xdp->data;
+ unsigned long flags;
+ struct sk_buff *skb;
+ int nh_off, len;
+ u32 ret = 0;
+
+ /* disable interrupts to get the correct skb pointer */
+ local_irq_save(flags);
+
+ len = data_end - data;
+ skb = this_cpu_read(hash_skb);
+ if (!skb) {
+ skb = alloc_skb(len, GFP_ATOMIC);
+ if (!skb)
+ goto out;
+ this_cpu_write(hash_skb, skb);
+ }
+
+ nh_off = sizeof(*eth);
+ if (data + nh_off > data_end)
+ goto out;
+
+ skb->data = data;
+ skb->head = data;
+ skb->network_header = nh_off;
+ skb->protocol = eth->h_proto;
+ skb->len = len;
+ skb->dev = xdp->rxq->dev;
+
+ ret = skb_get_hash(skb);
+out:
+ local_irq_restore(flags);
+ return ret;
+}
+
+const struct bpf_func_proto bpf_get_skb_hash_proto = {
+ .func = bpf_get_skb_hash,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_CTX,
+};
+
static unsigned long bpf_skb_copy(void *dst_buff, const void *skb,
unsigned long off, unsigned long len)
{
@@ -6503,6 +6551,8 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
return &bpf_xdp_adjust_tail_proto;
case BPF_FUNC_fib_lookup:
return &bpf_xdp_fib_lookup_proto;
+ case BPF_FUNC_get_skb_hash:
+ return &bpf_get_skb_hash_proto;
#ifdef CONFIG_INET
case BPF_FUNC_sk_lookup_udp:
return &bpf_xdp_sk_lookup_udp_proto;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index b134e679e9db..25aa850c8a40 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3394,6 +3394,13 @@ union bpf_attr {
* A non-negative value equal to or less than *size* on success,
* or a negative error in case of failure.
*
+ * u32 bpf_get_skb_hash(struct xdp_buff *xdp_md)
+ * Description
+ * Return the skb hash for the xdp context passed. This function
+ * allocates a temporary skb and populates the fields needed. It
+ * then calls skb_get_hash to calculate the skb hash for the packet.
+ * Return
+ * The 32-bit hash.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3538,6 +3545,7 @@ union bpf_attr {
FN(skc_to_tcp_request_sock), \
FN(skc_to_udp6_sock), \
FN(get_task_stack), \
+ FN(get_skb_hash), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
--
2.20.1
