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Commit b73042b8 authored by Lawrence Brakmo's avatar Lawrence Brakmo Committed by Alexei Starovoitov
Browse files

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: default avatarLawrence Brakmo <brakmo@fb.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 34d367c5

include/linux/filter.h

+9 −0
Original line number Diff line number Diff line
@@ -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__ */

include/net/tcp.h

+1 −1
Original line number Diff line number Diff line
@@ -2011,7 +2011,7 @@ 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);

net/core/filter.c

+48 −0
Original line number Diff line number Diff line
@@ -4491,6 +4491,54 @@ 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;