[RFC v2 PATCH 2/4] ebpf: Add sg_filter_run and sg helper

[Tushar Dave <tushar.n.dave@oracle.com>]

When sg_filter_run() is invoked it runs the attached eBPF
SOCKET_SG_FILTER program which deals with struct scatterlist.

In addition, this patch also adds bpf_sg_next helper function that
allows users to retrieve the next sg element from sg list.

Signed-off-by: Tushar Dave <tushar.n.dave@oracle.com>
Acked-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
---
 include/linux/filter.h                    |  2 +
 include/uapi/linux/bpf.h                  | 10 ++++-
 net/core/filter.c                         | 72 +++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h            | 10 ++++-
 tools/testing/selftests/bpf/bpf_helpers.h |  3 ++
 5 files changed, 95 insertions(+), 2 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 71618b1..d176402 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1072,4 +1072,6 @@ struct bpf_sock_ops_kern {
 					 */
 };
 
+int sg_filter_run(struct sock *sk, struct scatterlist *sg);
+
 #endif /* __LINUX_FILTER_H__ */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index ef0a7b6..036432b 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2076,6 +2076,13 @@ struct bpf_stack_build_id {
  * 	Return
  * 		A 64-bit integer containing the current cgroup id based
  * 		on the cgroup within which the current task is running.
+ *
+ * int bpf_sg_next(struct bpf_scatterlist *sg)
+ *	Description
+ *		This helper allows user to retrieve next sg element from
+ *		sg list.
+ *	Return
+ *		Returns 0 on success, or a negative error in case of failure.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -2158,7 +2165,8 @@ struct bpf_stack_build_id {
 	FN(rc_repeat),			\
 	FN(rc_keydown),			\
 	FN(skb_cgroup_id),		\
-	FN(get_current_cgroup_id),
+	FN(get_current_cgroup_id),	\
+	FN(sg_next),
 
 /* 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 8f67942..702ff5b 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -121,6 +121,53 @@ int sk_filter_trim_cap(struct sock *sk, struct sk_buff *skb, unsigned int cap)
 }
 EXPORT_SYMBOL(sk_filter_trim_cap);
 
+int sg_filter_run(struct sock *sk, struct scatterlist *sg)
+{
+	struct sk_filter *filter;
+	int err;
+
+	rcu_read_lock();
+	filter = rcu_dereference(sk->sk_filter);
+	if (filter) {
+		struct bpf_scatterlist bpfsg;
+		int num_sg;
+
+		if (!sg) {
+			err = -EINVAL;
+			goto out;
+		}
+
+		num_sg = sg_nents(sg);
+		if (num_sg <= 0) {
+			err = -EINVAL;
+			goto out;
+		}
+
+		/* We store a reference  to the sg list so it can later used by
+		 * eBPF helpers to retrieve the next sg element.
+		 */
+		bpfsg.num_sg = num_sg;
+		bpfsg.cur_sg = 0;
+		bpfsg.sg = sg;
+
+		/* For the first sg element, we store the pkt access pointers
+		 * into start and end so eBPF program can have pkt access using
+		 * data and data_end. The pkt access for subsequent element of
+		 * sg list is possible when eBPF program invokes bpf_sg_next
+		 * which takes care of setting start and end to the correct sg
+		 * element.
+		 */
+		bpfsg.start = sg_virt(sg);
+		bpfsg.end = bpfsg.start + sg->length;
+		BPF_PROG_RUN(filter->prog, &bpfsg);
+	}
+out:
+	rcu_read_unlock();
+
+	return err;
+}
+EXPORT_SYMBOL(sg_filter_run);
+
 BPF_CALL_1(bpf_skb_get_pay_offset, struct sk_buff *, skb)
 {
 	return skb_get_poff(skb);
@@ -3753,6 +3800,29 @@ static unsigned long bpf_xdp_copy(void *dst_buff, const void *src_buff,
 	.arg1_type      = ARG_PTR_TO_CTX,
 };
 
+BPF_CALL_1(bpf_sg_next, struct bpf_scatterlist *, bpfsg)
+{
+	struct scatterlist *sg = bpfsg->sg;
+	int cur_sg = bpfsg->cur_sg;
+
+	cur_sg++;
+	if (cur_sg >= bpfsg->num_sg)
+		return -ENODATA;
+
+	bpfsg->cur_sg = cur_sg;
+	bpfsg->start = sg_virt(&sg[cur_sg]);
+	bpfsg->end = bpfsg->start + sg[cur_sg].length;
+
+	return 0;
+}
+
+static const struct bpf_func_proto bpf_sg_next_proto = {
+	.func		= bpf_sg_next,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_CTX,
+};
+
 BPF_CALL_5(bpf_setsockopt, struct bpf_sock_ops_kern *, bpf_sock,
 	   int, level, int, optname, char *, optval, int, optlen)
 {
@@ -4720,6 +4790,8 @@ bool bpf_helper_changes_pkt_data(void *func)
 socksg_filter_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
 	switch (func_id) {
+	case BPF_FUNC_sg_next:
+		return &bpf_sg_next_proto;
 	default:
 		return bpf_base_func_proto(func_id);
 	}
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index c87ae16..a298498 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -2076,6 +2076,13 @@ struct bpf_stack_build_id {
  * 	Return
  * 		A 64-bit integer containing the current cgroup id based
  * 		on the cgroup within which the current task is running.
+ *
+ * int bpf_sg_next(struct bpf_scatterlist *sg)
+ *	Description
+ *		This helper allows user to retrieve next sg element from
+ *		sg list.
+ *	Return
+ *		Returns 0 on success, or a negative error in case of failure.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -2158,7 +2165,8 @@ struct bpf_stack_build_id {
 	FN(rc_repeat),			\
 	FN(rc_keydown),			\
 	FN(skb_cgroup_id),		\
-	FN(get_current_cgroup_id),
+	FN(get_current_cgroup_id),	\
+	FN(sg_next),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h
index f2f28b6..1997ba2 100644
--- a/tools/testing/selftests/bpf/bpf_helpers.h
+++ b/tools/testing/selftests/bpf/bpf_helpers.h
@@ -133,6 +133,9 @@ static int (*bpf_rc_keydown)(void *ctx, unsigned int protocol,
 	(void *) BPF_FUNC_rc_keydown;
 static unsigned long long (*bpf_get_current_cgroup_id)(void) =
 	(void *) BPF_FUNC_get_current_cgroup_id;
+static unsigned long long (*bpf_sg_next)(void *ctx) =
+	(void *) BPF_FUNC_sg_next;
+
 
 /* llvm builtin functions that eBPF C program may use to
  * emit BPF_LD_ABS and BPF_LD_IND instructions
-- 
1.8.3.1