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 <bra...@fb.com>
---
include/linux/filter.h | 9 +++++++++
include/net/tcp.h | 2 +-
net/core/filter.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 58 insertions(+), 1 deletion(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 425056c..daa5a67 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1007,6 +1007,15 @@ struct bpf_sock_ops_kern {
u32 replylong[4];
};
u32 is_fullsock;
+ u64 temp; /* temp and everything after is not
+ * initialized to 0 before calling
+ * the BPF program. New fields that
+ * should be initialized to 0 should
+ * be inserted before temp.
+ * temp is scratch storage used by
+ * sock_ops_convert_ctx_access
+ * as temporary storage 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));
if (sk_fullsock(sk)) {
sock_ops.is_fullsock = 1;
sock_owned_by_me(sk);
diff --git a/net/core/filter.c b/net/core/filter.c
index 292bda8..1ff36ca 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4486,6 +4486,54 @@ static u32 sock_ops_convert_ctx_access(enum
bpf_access_type type,
offsetof(OBJ, OBJ_FIELD)); \
} while (0)
+/* Helper macro for adding write access to tcp_sock or sock fields.
+ * The macro is called with two registers, dst_reg which contains a pointer
+ * to ctx (context) and src_reg which contains the value that should be
+ * stored. However, we need an additional register since we cannot overwrite
+ * dst_reg because it may be used later in the program.
+ * Instead we "borrow" one of the other register. We first save its value
+ * into a new (temp) field in bpf_sock_ops_kern, use it, and then restore
+ * it at the end of the macro.
+ */
+#define SOCK_OPS_SET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ) \
+ do { \
+ int reg = BPF_REG_9; \
+ BUILD_BUG_ON(FIELD_SIZEOF(OBJ, OBJ_FIELD) > \
+ FIELD_SIZEOF(struct bpf_sock_ops, BPF_FIELD)); \
+ if (si->dst_reg == reg || si->src_reg == reg) \
+ reg--; \
+ if (si->dst_reg == reg || si->src_reg == reg) \
+ reg--; \
+ *insn++ = BPF_STX_MEM(BPF_DW, si->dst_reg, reg, \
+ offsetof(struct bpf_sock_ops_kern, \
+ temp)); \
+ *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF( \
+ struct bpf_sock_ops_kern, \
+ is_fullsock), \
+ reg, si->dst_reg, \
+ offsetof(struct bpf_sock_ops_kern, \
+ is_fullsock)); \
+ *insn++ = BPF_JMP_IMM(BPF_JEQ, reg, 0, 2); \
+ *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF( \
+ struct bpf_sock_ops_kern, sk),\
+ reg, si->dst_reg, \
+ offsetof(struct bpf_sock_ops_kern, sk));\
+ *insn++ = BPF_STX_MEM(BPF_FIELD_SIZEOF(OBJ, OBJ_FIELD), \
+ reg, si->src_reg, \
+ offsetof(OBJ, OBJ_FIELD)); \
+ *insn++ = BPF_LDX_MEM(BPF_DW, reg, si->dst_reg, \
+ offsetof(struct bpf_sock_ops_kern, \
+ temp)); \
+ } while (0)
+
+#define SOCK_OPS_GET_OR_SET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ, TYPE) \
+ do { \
+ if (TYPE == BPF_WRITE) \
+ SOCK_OPS_SET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ); \
+ else \
+ SOCK_OPS_GET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ); \
+ } while (0)
+
case offsetof(struct bpf_sock_ops, snd_cwnd):
SOCK_OPS_GET_FIELD(snd_cwnd, snd_cwnd, struct tcp_sock);
break;
--
2.9.5
