[PATCH v3 bpf-next 04/15] net: Add BPF_XDP_EGRESS as a bpf_attach_type

[David Ahern <dsahern@kernel.org>]

From: David Ahern <dahern@digitalocean.com>

Add new bpf_attach_type, BPF_XDP_EGRESS, for BPF programs attached
at the XDP layer, but the egress path.

Since egress path will not have ingress_ifindex and rx_queue_index
set, update xdp_is_valid_access to block access to these entries in
the xdp context when a program is attached with expected_attach_type
set.

Update dev_change_xdp_fd to verify expected_attach_type for a program
is BPF_XDP_EGRESS if egress argument is set.

The next patch adds support for the egress ifindex.

Signed-off-by: Prashant Bhole <prashantbhole.linux@gmail.com>
Co-developed-by: David Ahern <dahern@digitalocean.com>
Signed-off-by: David Ahern <dahern@digitalocean.com>
---
 include/uapi/linux/bpf.h       |  1 +
 net/core/dev.c                 | 11 +++++++++++
 net/core/filter.c              | 11 +++++++++++
 tools/include/uapi/linux/bpf.h |  1 +
 4 files changed, 24 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 2e29a671d67e..a9d384998e8b 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -215,6 +215,7 @@ enum bpf_attach_type {
 	BPF_TRACE_FEXIT,
 	BPF_MODIFY_RETURN,
 	BPF_LSM_MAC,
+	BPF_XDP_EGRESS,
 	__MAX_BPF_ATTACH_TYPE
 };
 
diff --git a/net/core/dev.c b/net/core/dev.c
index 726a93a5cb25..2f6e18fc02ed 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8730,6 +8730,17 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
 		if (IS_ERR(prog))
 			return PTR_ERR(prog);
 
+		if (egress && prog->expected_attach_type != BPF_XDP_EGRESS) {
+			NL_SET_ERR_MSG(extack, "XDP program in Tx path must use BPF_XDP_EGRESS attach type");
+			bpf_prog_put(prog);
+			return -EINVAL;
+		}
+		if (!egress && prog->expected_attach_type == BPF_XDP_EGRESS) {
+			NL_SET_ERR_MSG(extack, "XDP program in Rx path can not use BPF_XDP_EGRESS attach type");
+			bpf_prog_put(prog);
+			return -EINVAL;
+		}
+
 		if (!offload && bpf_prog_is_dev_bound(prog->aux)) {
 			NL_SET_ERR_MSG(extack, "using device-bound program without HW_MODE flag is not supported");
 			bpf_prog_put(prog);
diff --git a/net/core/filter.c b/net/core/filter.c
index a943df3ad8b0..b4d064c7fdec 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -6935,6 +6935,17 @@ static bool xdp_is_valid_access(int off, int size,
 				const struct bpf_prog *prog,
 				struct bpf_insn_access_aux *info)
 {
+	/* Rx data is only accessible from original XDP where
+	 * expected_attach_type is not set
+	 */
+	if (prog->expected_attach_type) {
+		switch (off) {
+		case offsetof(struct xdp_md, ingress_ifindex):
+		case offsetof(struct xdp_md, rx_queue_index):
+			return false;
+		}
+	}
+
 	if (type == BPF_WRITE) {
 		if (bpf_prog_is_dev_bound(prog->aux)) {
 			switch (off) {
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 2e29a671d67e..a9d384998e8b 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -215,6 +215,7 @@ enum bpf_attach_type {
 	BPF_TRACE_FEXIT,
 	BPF_MODIFY_RETURN,
 	BPF_LSM_MAC,
+	BPF_XDP_EGRESS,
 	__MAX_BPF_ATTACH_TYPE
 };
 
-- 
2.21.1 (Apple Git-122.3)