Re: [PATCH bpf-next v5 03/11] bpf: Add write access to tcp_sock and sock fields

This patch adds a macro, SOCK_OPS_SET_FIELD, for writing to
struct tcp_sock or struct sock fields. This required adding a new
field "temp" to struct bpf_sock_ops_kern for temporary storage that
is used by sock_ops_convert_ctx_access. It is used to store and recover
the contents of a register, so the register can be used to store the
address of the sk. Since we cannot overwrite the dst_reg because it
contains the pointer to ctx, nor the src_reg since it contains the value
we want to store, we need an extra register to contain the address
of the sk.

Also adds the macro SOCK_OPS_GET_OR_SET_FIELD that calls one of the
GET or SET macros depending on the value of the TYPE field.

Signed-off-by: Lawrence Brakmo <redacted>
---
 include/linux/filter.h |  3 +++
 include/net/tcp.h      |  2 +-
 net/core/filter.c      | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 425056c..139a9a3 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h

@@ -1007,6 +1007,9 @@ struct bpf_sock_ops_kern {
 		u32 replylong[4];
 	};
 	u32	is_fullsock;
+	u64	temp;			/* Used by sock_ops_convert_ctx_access
+					 * as temporary storaage of a register

+					 */
 };
 
 #endif /* __LINUX_FILTER_H__ */

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 6939e69..108d16a 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h

@@ -2010,7 +2010,7 @@ static inline int tcp_call_bpf(struct sock *sk, int op)
 	struct bpf_sock_ops_kern sock_ops;
 	int ret;
 
-	memset(&sock_ops, 0, sizeof(sock_ops));
+	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));