[PATCH bpf-next] bpf: Allow setting SO_TIMESTAMPING* with bpf_setsockopt()

[Jörn-Thorben Hinz]

A BPF application, e.g., a TCP congestion control, might benefit from or
even require precise (=hardware) packet timestamps. These timestamps are
already available through __sk_buff.hwtstamp and
bpf_sock_ops.skb_hwtstamp, but could not be requested: BPF programs were
not allowed to set SO_TIMESTAMPING* on sockets.

Enable BPF programs to actively request the generation of timestamps
from a stream socket. The also required ioctl(SIOCSHWTSTAMP) on the
network device must still be done separately, in user space.

This patch had previously been submitted in a two-part series (first
link below). The second patch has been independently applied in commit
7f6ca95d16b9 ("net: Implement missing getsockopt(SO_TIMESTAMPING_NEW)")
(second link below).

On the earlier submission, there was the open question whether to only
allow, thus enforce, SO_TIMESTAMPING_NEW in this patch:

For a BPF program, this won't make a difference: A timestamp, when
accessed through the fields mentioned above, is directly read from
skb_shared_info.hwtstamps, independent of the places where NEW/OLD is
relevant. See bpf_convert_ctx_access() besides others.

I am unsure, though, when it comes to the interconnection of user space
and BPF "space", when both are interested in the timestamps. I think it
would cause an unsolvable conflict when user space is bound to use
SO_TIMESTAMPING_OLD with a BPF program only allowed to set
SO_TIMESTAMPING_NEW *on the same socket*? Please correct me if I'm
mistaken.

Link: https://lore.kernel.org/lkml/20230703175048.151683-1-jthinz@xxxxxxxxxxxxxxxxxxxx/
Link: https://lore.kernel.org/all/20231221231901.67003-1-jthinz@xxxxxxxxxxxxxxxxxxxx/
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Deepa Dinamani <deepa.kernel@xxxxxxxxx>
Cc: Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx>
Signed-off-by: Jörn-Thorben Hinz <j-t.hinz@xxxxxxxxxxxxxxxxxxx>
---
 include/uapi/linux/bpf.h                            | 3 ++-
 net/core/filter.c                                   | 2 ++
 tools/include/uapi/linux/bpf.h                      | 3 ++-
 tools/testing/selftests/bpf/progs/bpf_tracing_net.h | 2 ++
 tools/testing/selftests/bpf/progs/setget_sockopt.c  | 4 ++++
 5 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 754e68ca8744..8825d0648efe 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2734,7 +2734,8 @@ union bpf_attr {
  * 		  **SO_RCVBUF**, **SO_SNDBUF**, **SO_MAX_PACING_RATE**,
  * 		  **SO_PRIORITY**, **SO_RCVLOWAT**, **SO_MARK**,
  * 		  **SO_BINDTODEVICE**, **SO_KEEPALIVE**, **SO_REUSEADDR**,
- * 		  **SO_REUSEPORT**, **SO_BINDTOIFINDEX**, **SO_TXREHASH**.
+ * 		  **SO_REUSEPORT**, **SO_BINDTOIFINDEX**, **SO_TXREHASH**,
+ * 		  **SO_TIMESTAMPING_NEW**, **SO_TIMESTAMPING_OLD**.
  * 		* **IPPROTO_TCP**, which supports the following *optname*\ s:
  * 		  **TCP_CONGESTION**, **TCP_BPF_IW**,
  * 		  **TCP_BPF_SNDCWND_CLAMP**, **TCP_SAVE_SYN**,
diff --git a/net/core/filter.c b/net/core/filter.c
index 8c9f67c81e22..4f5280874fd8 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5144,6 +5144,8 @@ static int sol_socket_sockopt(struct sock *sk, int optname,
 	case SO_MAX_PACING_RATE:
 	case SO_BINDTOIFINDEX:
 	case SO_TXREHASH:
+	case SO_TIMESTAMPING_NEW:
+	case SO_TIMESTAMPING_OLD:
 		if (*optlen != sizeof(int))
 			return -EINVAL;
 		break;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 7f24d898efbb..09eaafa6ab43 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -2734,7 +2734,8 @@ union bpf_attr {
  * 		  **SO_RCVBUF**, **SO_SNDBUF**, **SO_MAX_PACING_RATE**,
  * 		  **SO_PRIORITY**, **SO_RCVLOWAT**, **SO_MARK**,
  * 		  **SO_BINDTODEVICE**, **SO_KEEPALIVE**, **SO_REUSEADDR**,
- * 		  **SO_REUSEPORT**, **SO_BINDTOIFINDEX**, **SO_TXREHASH**.
+ * 		  **SO_REUSEPORT**, **SO_BINDTOIFINDEX**, **SO_TXREHASH**,
+ * 		  **SO_TIMESTAMPING_NEW**, **SO_TIMESTAMPING_OLD**.
  * 		* **IPPROTO_TCP**, which supports the following *optname*\ s:
  * 		  **TCP_CONGESTION**, **TCP_BPF_IW**,
  * 		  **TCP_BPF_SNDCWND_CLAMP**, **TCP_SAVE_SYN**,
diff --git a/tools/testing/selftests/bpf/progs/bpf_tracing_net.h b/tools/testing/selftests/bpf/progs/bpf_tracing_net.h
index 1bdc680b0e0e..95f5f169819e 100644
--- a/tools/testing/selftests/bpf/progs/bpf_tracing_net.h
+++ b/tools/testing/selftests/bpf/progs/bpf_tracing_net.h
@@ -15,8 +15,10 @@
 #define SO_RCVLOWAT		18
 #define SO_BINDTODEVICE		25
 #define SO_MARK			36
+#define SO_TIMESTAMPING_OLD     37
 #define SO_MAX_PACING_RATE	47
 #define SO_BINDTOIFINDEX	62
+#define SO_TIMESTAMPING_NEW     65
 #define SO_TXREHASH		74
 #define __SO_ACCEPTCON		(1 << 16)
 
diff --git a/tools/testing/selftests/bpf/progs/setget_sockopt.c b/tools/testing/selftests/bpf/progs/setget_sockopt.c
index 7a438600ae98..54205d10793c 100644
--- a/tools/testing/selftests/bpf/progs/setget_sockopt.c
+++ b/tools/testing/selftests/bpf/progs/setget_sockopt.c
@@ -48,6 +48,10 @@ static const struct sockopt_test sol_socket_tests[] = {
 	{ .opt = SO_MARK, .new = 0xeb9f, .expected = 0xeb9f, },
 	{ .opt = SO_MAX_PACING_RATE, .new = 0xeb9f, .expected = 0xeb9f, },
 	{ .opt = SO_TXREHASH, .flip = 1, },
+	{ .opt = SO_TIMESTAMPING_NEW, .new = SOF_TIMESTAMPING_RX_HARDWARE,
+		.expected = SOF_TIMESTAMPING_RX_HARDWARE, },
+	{ .opt = SO_TIMESTAMPING_OLD, .new = SOF_TIMESTAMPING_RX_HARDWARE,
+		.expected = SOF_TIMESTAMPING_RX_HARDWARE, },
 	{ .opt = 0, },
 };
 
-- 
2.39.2